Bailey's Industrial Oil & Fat Products

BAILEY’S INDUSTRIAL OIL AND FAT PRODUCTS Sixth Edition Volume 1 Edible Oil and Fat Products: Chemistry, Properties, and Health Effects Edited by

Fereidoon Shahidi Memorial University of Newfoundland

Bailey’s Industrial Oil and Fat Products is available online at http://www.mrw.interscience.wiley.com/biofp

A John Wiley & Sons, Inc., Publication

BAILEY’S INDUSTRIAL OIL AND FAT PRODUCTS Sixth Edition Volume 2 Edible Oil and Fat Products: Edible Oils Edited by

Fereidoon Shahidi Memorial University of Newfoundland

Bailey’s Industrial Oil and Fat Products is available online at http://www.mrw.interscience.wiley.com/biofp

A John Wiley & Sons, Inc., Publication

BAILEY’S INDUSTRIAL OIL AND FAT PRODUCTS Sixth Edition Volume 3 Edible Oil and Fat Products: Specialty Oils and Oil Products Edited by

Fereidoon Shahidi Memorial University of Newfoundland

Bailey’s Industrial Oil and Fat Products is available online at http://www.mrw.interscience.wiley.com/biofp

A John Wiley & Sons, Inc., Publication

BAILEY’S INDUSTRIAL OIL AND FAT PRODUCTS Sixth Edition Volume 4 Edible Oil and Fat Products: Products and Applications Edited by

Fereidoon Shahidi Memorial University of Newfoundland

Bailey’s Industrial Oil and Fat Products is available online at http://www.mrw.interscience.wiley.com/biofp

A John Wiley & Sons, Inc., Publication

BAILEY’S INDUSTRIAL OIL AND FAT PRODUCTS Sixth Edition Volume 5 Edible Oil and Fat Products: Processing Technologies Edited by

Fereidoon Shahidi Memorial University of Newfoundland

Bailey’s Industrial Oil and Fat Products is available online at http://www.mrw.interscience.wiley.com/biofp

A John Wiley & Sons, Inc., Publication

BAILEY’S INDUSTRIAL OIL AND FAT PRODUCTS Sixth Edition Volume 6 Industrial and Nonedible Products from Oils and Fats Edited by

Fereidoon Shahidi Memorial University of Newfoundland

Bailey’s Industrial Oil and Fat Products is available online at http://www.mrw.interscience.wiley.com/biofp

A John Wiley & Sons, Inc., Publication

Copyright # 2005 by John Wiley & Sons, Inc. All rights reserved. Published by John Wiley & Sons, Inc., Hoboken, New Jersey. Published simultaneously in Canada. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400, fax 978-646-8600, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008. Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. For general information on our other products and services please contact our Customer Care Department within the U.S. at 877-762-2974, outside the U.S. at 317-572-3993 or fax 317-572-4002. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print, however, may not be available in electronic format. Library of Congress Cataloging-in-Publication Data: Shahidi, Fereidoon. Bailey’s industrial oil & fats products.– 6th ed./edited by Fereidoon Shahidi. p. cm. ‘‘A Wiley-Interscience publication.’’ Includes bibliographical references and index. Contents: v. 1. Edible oil and fat products: chemistry, properties, and health effects – v. 2. Edible oil and fat products: edible oils – v.3. Edible oil and fat products: specially oils and oil products – v. 4. Edible oil and fat products: products and applications – v. 5. Edible oil and fat products: processing technologies – v. 6. Industrial and nonedible products from oils and fats. ISBN 0-471-38460-7 (set) – ISBN 0-471-38552-2 (v. 1) – ISBN 0-471-38551-4 (v. 2) – ISBN 0-471-38550-6 (v. 3) – ISBN 0-471-38549-2 (v. 4) – ISBN 0-471-38548-4 (v. 5) – ISBN 0-471-38546-8 (v. 6) 1. Oils and fats, I. Title: Industrial oil & fats products. II. Title: Bailey’s industrial oil and fats products. III. Bailey, Alton Edward, 1907-1953. IV. Title. TP670.S46 2004 665–dc22 Printed in the United States of America 10 9 8 7 6 5 4 3 2 1

2004043351

Contributors R. G. ACKMAN: Canadian Institute of Fisheries Technology, Dalhousie University, Halifax, Nova Scotia, Canada, Fish Oils. YVONNE T. V. AGUSTIN: Coconut Oil. KLAUS A. ALEXANDERSEN: Margarine Processing Plants and Equipment. DAN ANDERSON: A Primer on Oils Processing Technology. YUSOF BASIRON: Palm Oil. MARI´A LUZ J. BENDAN˜ O: Coconut Oil. ANTHONY P. BIMBO: International Fisheries, Kilmarnock, Virginia, Rendering. MICHAEL J. BOYER: AWT-Agribusiness and Water, Cumming, Georgia, Environmental Impact and Waste Management. D. D. BROOKS: Oil-Dri Corporation, Chicago, Illinois, Adsorptive Separation of Oils. MICHAEL R. BURKE: Soaps. ELIAS C. CANAPI: Coconut Oil. VANCE CAUDILL: Packaging. ARMAND B. CHRISTOPHE: Ghent University Hospital, Ghent, Belgium, Structural Effects on Absorption, Metabolism, and Health Effects of Lipids. MICHAEL M. CHRYSAN: Margarines and Spreads. W. DE GREYT: De Smet Technologies & Services, Brussels, Belgium, Deodorization. NURHAN TURGUT DUNFORD: Oklahoma State University, Stillwater, Oklahoma, Germ Oils from Different Sources. SEVIM Z. ERHAN: National Center for Agricultural Utilization Research, Peoria, Illinois, Vegetable Oils as Lubricants, Hydraulic Fluids, and Inks. N.A.M. ESKIN: University of Manitoba, Winnipeg, Manitoba, Canada, Canola Oil. S. ESWARANANDAM: University of Arkansas, Fayetteville, Arkansas, Edible Films and Coatings From Soybean and Other Protein Sources. v

vi

CONTRIBUTORS

WALTER E. FARR: Walter E. Farr & Associates, Olive Branch, Mississippi, Hydrogenation: Processing Technologies. DAVID FIRESTONE: United States Food and Drug Administration, Washington, DC, Olive Oil. BRENT D. FLICKINGER: Archer Daniels Midland Company, Decatur, Illinois, Diacylglycerols. GREGORIO C. GERVAJIO: Fatty Acids and Derivatives from Coconut Oil. MARIA A. GROMPONE: Sunflower Oil. FRANK D. GUNSTONE: Vegetable Oils. MONOJ K. GUPTA: MG Edible Oil Consulting International, Richardson, Texas, Frying of Foods and Snack Food Production; Frying Oils. ¨ ZLEM GU¨ C¸ LU¨ -U ¨ STU¨ NDAG˘ : University of Alberta, Edmonton, Alberta, Canada, O Supercritical Technologies for Further Processing of Edible Oils. MICHAEL J. HAAS: Eastern Regional Research Center, Agricultural Research Service, Wyndmoor, Pennsylvania, Animal Fats. EARL G. HAMMOND: Iowa State University, Ames, Iowa, Soybean Oil. RICHARD W. HARTEL: University of Wisconsin, Madison, Wisconsin, Crystallization of Fats and Oils. BERNHARD HENNIG: University of Kentucky, Lexington, Kentucky, Dietary Lipids and Health. ERNESTO HERNANDEZ: Texas A&M University, College Station, Texas, Pharmaceutical and Cosmetic Use of Lipids. P. B. HERTZ: Agriculture and Agri-Food Canada, Saskatoon, Saskatchewan, Canada, Vegetable Oils as Biodiesel. NAVAM S. HETTIARACHCHY: University of Arkansas, Fayetteville, Arkansas, Edible Films and Coatings From Soybean and Other Protein Sources. DAVID HETTINGA: Butter. STEVEN E. HILL: Cooking Oils, Salad Oils, and Dressings. CHI-TANG HO: Rutgers University, New Brunswick, New Jersey, Flavor Components of Fats and Oils. LUCY SUN HWANG: National Taiwan University, Taipei, Taiwan, Sesame Oil. LAWRENCE A. JOHNSON: Iowa State University, Ames, Iowa, Soybean Oil. LYNN A. JONES: Collierville, Tennessee, Cottonseed Oil. AFAF KAMAL-ELDIN: SLU, Uppsala, Sweden, Minor Components of Fats and Oils. Y.K. KAMATH: Leather and Textile Uses of Fats and Oils. RAKESH KAPOOR: Bioriginal Food and Science Corp., Saskatoon, Saskatchewan, Canada, Conjugated Linoleic Acid Oils; Gamma Linolenic Acid Oils. M. KELLENS: De Smet Technologies & Services, Brussels, Belgium, Deodorization. TIMOTHY G. KEMPER: Oil Extraction. C. CLAY KING: Texas Women’s University, Denton, Texas, Cottonseed Oil.

CONTRIBUTORS

vii

DAVID D. KITTS: University of British Columbia, Vanuouver, British Columbia, Canada, Toxicity and Safety of Fats and Oils. XIAOHUA KONG: Agri-Food Materials Science Centre, University of Alberta Edmonton, Alberta, Canada, Vegetable Oils in Production of Polymers and Plastics. S. SEFA KOSEOGLU: Extraction and Refining Program, A Division of Filtration and Membrane World LLC, College Station, Texas, Membrane Processing of Fats and Oils. R. G. KRISHNAMURTHY: Cooking Oils, Salad Oils, and Dressings. PAUL KRONICK: Leather and Textile Uses of Fats and Oils. YONG LI: Purdue University, West Lafayette, Indiana, Dietary Lipids and Health. K. F. LIN: Paints, Varnishes, and Related Products. LAN LIN: Extraction and Refining Program, A Division of Filtration and Membrane World LLC, College Station, Texas, Membrane Processing of Fats and Oils. GARY R. LIST: Iowa State University, Ames, Iowa, Storage, Handling, and Transport of Oils and Fats. JERROLD W. LITWINENKO: University of Guelph, Guelph, Ontario, Canada, Fat Crystal Networks. EDMUND E. LUSAS: Fats and Oils in Feedstuffs and Pet Foods. JESSE L. LYNN, JR.: Detergents and Detergency. T. MAG: University of Manitoba, Winnipeg, Manitoba, Canada, Canola Oil. LINDA J. MALCOLMSON: Canadian International Grains Institute, Winnipeg, Manitoba, Canada, Flavor and Sensory Aspects. ALEJANDRO G. MARANGONI: University of Guelph, Guelph, Ontario, Canada, Fat Crystal Networks. NOBORU MATSUO: Kao Corporation, Tochigi, Japan, Diacylglycerols. W. W. MCCALLEY: Agriculture and Agri-Food Canada, Saskatoon, Saskatchewan, Canada, Vegetable Oils as Biodiesel. D. JULIAN MCCLEMENTS: The University of Massachusetts, Amherst, Massachusetts, Lipid Emulsions. B.E. MCDONALD: University of Manitoba, Winnipeg, Manitoba, Canada, Canola Oil. THOMAS A. MCKeon, USDA-ARS Western Regional Research Center, Albany, California, Transgenic Oils. SERPIL METIN: Cargill Inc., Minneapolis, Minnesota, Crystallization of Fats and Oils. DOUGLAS J. METZROTH: Shortenings: Science and Technology. HOMAN MIRALIAKBARI: Memorial University of Newfoundland, St. John’s, Newfoundland, Canada, Tree Nut Oils. ROBERT A. MOREAU: United States Department of Agriculture, Agricultural Research Service, Corn Oil. EVANGEKUBE A. MORO: Coconut Oil.

viii

CONTRIBUTORS

HARIKUMAR NAIR: Bioriginal Food & Science Corp., Saskatoon, Saskatchewan, Canada, Gamma Linolenic Acid Oils. SURESH S. NARINE: Agri-Food Materials Science Centre, University of Alberta, Edmonton, Alberta, Canada, Vegetable Oils in Production of Polymers and Plastics. RICHARD D. O’BRIEN: Plano, Texas, Cottonseed Oil; Shortenings: Types and Formulations. FRANK T. ORTHOEFER: Rice Bran Oil. JOHN W PARRY: University of Maryland, College Park, Maryland, Oils from Herbs, Spices, and Fruit Seeds. HAROLD E. PATTEE: North Carolina State University, Raleigh, North Carolina, Peanut Oil. ECONOMICO PEDROSA, JR.: Coconut Oil. M. D. PICKARD: By-Product Utilization. A. PROCTOR: University of Arkansas, Fayetteville, Arkansas, Adsorptive Separation of Oils. ROMAN PRZYBYLSKI: University of Manitoba, Winnipeg, Manitoba, Canada, Canola Oil; Flax Oil and High Linolenic Oils. COLIN RATLEDGE: Lipid Research Centre, University of Hull, Hull, United Kingdom, Oils from Microorganisms. MARTIN REANEY: Bioriginal Food and Science Corp., Saskatoon, Saskatchewan, Canada, Conjugated Linoleic Acid Oils. M. J. T. REANEY: Agriculture and Agri-Food Canada, Saskatoon, Saskatchewan, Canada, Vegetable Oils as Biodiesel. MIAN N. RIAZ: Texas A&M University, College Station, Texas, Extrusion Processing of Oilseed Meals for Food and Feed Production. GEOFFREY G. RYE: University of Guelph, Guelph, Ontario, Canada, Fat Crystal Networks. KIYOTAKA SATO: Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Japan, Polymorphism in Fats and Oils. K. M. SCHAICH: Rutgers University, New Brunswick, New Jersey, Lipid Oxidation: Theoretical Aspects. KEITH SCHROEDER: CC Engineering Ltd., Glycerine. CHARLIE SCRIMGEOUR: Scottish Crop Research Institute Dundee, Scotland, Chemistry of Fatty Acids. S. P. J. NAMAL SENANAYAKE: Martek Biosciences Corporation, Winchester, Kentucky, Dietary Fat Substitutes; Modification of Fats and Oils via Chemical and Enzymatic Methods. FEREIDOON SHAHIDI: Memorial University of Newfoundland, St. John’s, Newfoundland, Canada, Antioxidants: Regulatory Status; Antioxidants: Science, Technology, and Applications; Citrus Oils and Essences; Dietary Fat Substitutes;

CONTRIBUTORS

ix

Flavor Components of Fats and Oils; Lipid Oxidation: Measurement Methods; Marine Mammal Oils; Modification of Fats and Oils via Chemical and Enzymatic Methods; Novel Separation Techniques for Isolation and Purification of Fatty Acids and Oil By-Products; Quality Assurance of Fats and Oils; Tree Nut Oils. JOSEPH SMITH: Safflower Oil. VIJAI K.S. SHUKLA: International Food Science Center, Lystrup, Denmark, Confectionery Lipids. VIJAI K.S. SHUKLA: Iowa State University, Ames, Iowa, Storage, Handling, and Transport of Oils and Fats. CLYDE E. STAUFFER: Emulsifiers for the Food Industry; Fats and Oils in Bakery Products. CAIPING SU: Iowa State University, Ames, Iowa, Soybean Oil. BERNARD F. SZUHAJ: Szuhaj & Associates LLC, Fort Wayne, Indiana, Lecithins. DENNIS R. TAYLOR: DR Taylor Consulting, Port Barrington, Illinois, Bleaching. FERAL TEMELLI: University of Alberta, Edmonton, Alberta, Canada, Supercritical Technologies for Further Processing of Edible Oils. MICHAL TOBOREK: University of Kentucky, Lexington, Kentucky, Dietary Lipids and Health. SATORU UENO: Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Japan, Polymorphism in Fats and Oils. PHILLIP J. WAKELYN: National Cotton Council, Washington, DC, Cottonseed Oil. PETER J. WAN: USDA, ARS, New Orleans, Lowsiana, Cottonseed Oil. P. K. J. P. D. WANASUNDARA: Agriculture and Agri-Food Canada, Saskatoon Research Center, Saskatoon, Saskatchewan, Canada, Antioxidants: Science, Technology, and Applications; Novel Separation Techniques for Isolation and Purification of Fatty Acids and Oil By-Products. UDAYA N. WANASUNDARA: POS Pilot Plant Corporation, Saskatoon, Saskatchewan, Canada, Novel Separation Techniques for Isolation and Purification of Fatty Acids and Oil By-Products. TONG WANG: Iowa State University, Ames, Iowa, Soybean Oil; Storage, Handling, and Transport of Oils and Fats. BRUCE A. WATKINS: Purdue University, West Lafayette, Indiana, Dietary Lipids and Health. JOCHEN WEISS: The University of Massachusetts, Amherst, Massachusetts, Lipid Emulsions. NEIL D. WESTCOTT: Bioriginal Food and Science Corp., Saskatoon, Saskatchewan, Canada, Conjugated Linoleic Acid Oils. PAMELA J. WHITE: Iowa State University, Ames, Iowa, Soybean Oil. MAURICE A. WILLIAMS: Anderson Corporation, Cleveland, Ohio, Recovery of Oils and Fats from Oilseeds and Fatty Materials.

x

CONTRIBUTORS

JAMES P. WYNN: Martek Biosciences Corporation, Columbia, Maryland, Oils from Microorganisms. LIANGLI (LUCY) YU: University of Maryland, College Park, Maryland, Oils from Herbs, Spices, and Fruit Seeds. YING ZHONG: Memorial University of Newfoundland, St. John’s, Newfoundland, Canada, Antioxidants: Regulatory Status; Citrus Oils and Essences; Lipid Oxidation: Measurement Methods; Marine Mammal Oils. KEQUAN ZHOU: University of Maryland, College Park, Maryland, Oils from Herbs, Spices, and Fruit Seeds.

Preface Oils and fats are important components of foods, and they, or their derivatives and products thereof, play an important role in non-food applications. In food, oils and fats provide a concentrated source of energy as well as a carrier of fat-soluble components. They also serve as a heat transfer medium for food processing and render desirable texture and flavor as well as mouthfeel to products. Oils and fats originate from plant and animal sources. Although plant sources include oilseeds, tropical fruits, and alga, the latter may originate from land-based animals, fish, marine mammals, and derived sources. The main components of food lipids are triacylglycerols, but minor components are also important for quality characteristics, stability, and application areas. Both the type of fatty acids and their degree of unsaturation as well as the type and content of minor components affect the keeping quality of the oil, and certain minor components such as phytosterols might also be used for fingerprinting and authentification of the source materials. The physical state of fats and oils and their crystal structures are important for application of such products. In addition, formulation of products for special applications such as bakery, confectionary, frying, salad dressing, margarines, and spreads requires special characteristics that make the products suitable for such purposes. Thus, each source material will be important for its physical and chemical characteristics and hence suitability as a food component. Recent developments in the area of oils and fats has led to the production of specialty lipids from novel sources such as fruit seeds, nuts, and other minor plant sources. In addition, preparation of structured lipids for a myriad of applications has been of interest. Minor components of oils and fats may be isolated during processing and used as nutraceutical and functional food ingredients. Examples are lecithin, phytosterols, tocopherols, and tocotrienols, among others. Obviously, the health-promoting potential of such products is also of interest. The processing technologies employed for production of fats and oils, and associated components, to make them shelf-stable with acceptable sensory characteristics and flavor as well as secondary processing technologies for production of specific products are important considerations in this area. Food commodities xi

xii

PREFACE

may be produced, and some components may also be used in animal feed and other applications. There are many areas where oils and fats are used for non-food purposes. Thus, detergents, soaps, glycerine and polymers, inks, lubricants, and biodiesel may be derived from fatty acids and their derivatives. Many applications would provide alternatives to the use of synthetic material or environmentally friendly substitutes in non-food applications. The sixth edition of Bailey provides a comprehensive description of topics relevant to the oils and fats industry in six volumes as compared with five volumes in the fifth edition. The additional volume (volume 3) is mainly on specialty oils and fats and their byproducts or minor components as well as on those of low-calorie fat substitutes and structured lipids. An article on fish oils and one on marine mammal oils are also included in this volume. However, the material covered in other volumes is often substantially different from the available in the fifth edition as new articles are introduced, and when the title appears the same, substantial updating of the references and introduction of new material has occurred; new authors in some cases have made these contributions. Thus, the first volume includes three new articles on crystallization and physical properties of oils and fats. There are also new articles on antioxidant theory and regulatory status as well as on mechanisms and measurements of lipid oxidation. A new article has been introduced on quality assurance of oils and fats. Meanwhile, the second volume presents the main sources of food lipids, and new articles on sesame oil and rice bran oil have been introduced. The fourth volume provides a description of application areas, and here again new articles on confectinary lipids as well as on frying oils and snack food production have been added. The fifth volume on processing technologies introduces new articles on supercritical, membrane, and extrusion technologies. Finally, the sixth volume on nonedible uses of fats and oils has new articles on biodiesel, hydrolic fluids, lubricants, inks, as well as pharmaceutical and cosmetic uses of lipids. An article on the use of soybean oil in edible film and adhesive production is also included. Thus, the sixth edition is substantially different from what was available in the fifth edition. I am indebted to many authors for their state-of-the-art contributions as well as to primary and secondary reviewers for different articles. The advisory committee members served an important role in providing invaluable comments. In addition, staff from John Wiley and Sons provided considerable help in different aspects related to production and assembly of the work. This series serves as a primary source of and as a compendium of information on oils and fats for the industry, academia and government scientists, and technical personnel, and as a reference for senior undergraduate and graduate students in food science, nutrition, dietetics, biochemistry, and related disciplines. An integrated table of contents allows better search of materials of interest, and the last volume has a cumulative index. Extensive bibliography throughout the series also provides the reader with the opportunity to consult primary references for additional information. FEREIDOON SHAHIDI

Contents

Contributors ........................................................................

v

Preface ...............................................................................

xi

Volume 1. Edible Oil and Fat Products: Chemistry, Properties, and Health Effects 1.1

1.2

Chemistry of Fatty Acids ......................................................

1:1

1.1.1

Introduction .....................................................

1:1

1.1.2

Composition and Structure ..............................

1:2

1.1.3

Hydrolysis, Esterification, and Ester Exchange ........................................................

1:10

1.1.4

Oxidation .........................................................

1:15

1.1.5

Reduction ........................................................

1:25

1.1.6

Production of Surface Active Compounds and Oleochemicals ..........................................

1:27

1.1.7

Modifying Fatty Acid Structure .........................

1:32

1.1.8

Novel Chemistry for Functionalizing the Alkyl Chain ...............................................................

1:36

References ....................................................................

1:39

Crystallization of Fats and Oils ............................................

1:45

1.2.1

Introduction .....................................................

1:45

1.2.2

Lipid Phase Behavior .......................................

1:46

1.2.3

Crystallization Behavior ...................................

1:57

1.2.4

Controlling Crystallization ................................

1:68

1.2.5

Summary .........................................................

1:73

References ....................................................................

1:73

This page has been reformatted by Knovel to provide easier navigation.

xiii

xiv

Contents

1.3

Polymorphism in Fats and Oils ............................................

1:77

1.3.1

Introduction .....................................................

1:77

1.3.2

Basic Concepts of Polymorphism of Fats ........

1:78

1.3.3

Polymorphism of Monoacid Triacylglycerols ....

1:85

1.3.4

Polymorphism of Mixed-acid Triacylglycerols ................................................

1:90

1.3.5

Fat Mixtures and Polymorphism ......................

1:100

1.3.6

Polymorphism of Natural Fats .........................

1:108

1.3.7

Summary .........................................................

1:115

References ....................................................................

1:116

Fat Crystal Networks ............................................................

1:121

1.4.1

Introduction .....................................................

1:121

1.4.2

Mechanical Properties of Milkfat ......................

1:122

1.4.3

Lipid Composition ............................................

1:123

1.4.4

Processing Conditions .....................................

1:125

1.4.5

Nucleation and Crystal Growth ........................

1:126

1.4.6

Mechanical Properties .....................................

1:148

1.4.7

Assessing the Validity of the Model: Correlating Experimentally Determined Parameters ......................................................

1:154

Acknowledgments ..........................................................

1:158

References ....................................................................

1:158

Animal Fats ...........................................................................

1:161

1.5.1

Introduction .....................................................

1:161

1.5.2

Sources, Fatty Acid Content, and Acylglycerol Structure ......................................

1:162

Acylglycerol Structure and Its Relationship to Functionality and Use ......................................

1:168

1.5.4

Quality Indicators for Edible Fats .....................

1:171

1.5.5

Regulatory and Commercial Classifications of Animal Fats .................................................

1:174

1.4

1.5

1.5.3

This page has been reformatted by Knovel to provide easier navigation.

Contents 1.5.6

Patterns and Trends in the Production and Use of Animal Fats ..........................................

1:179

1.5.7

Processing of Animal Fats ...............................

1:182

1.5.8

Antioxidants in Animal Fats .............................

1:194

1.5.9

Characteristics of Animal Fat-based Shortenings and Frying Fats ............................

1:195

Recent Developments .....................................

1:197

Acknowledgments ..........................................................

1:205

References ....................................................................

1:205

Vegetable Oils ......................................................................

1:213

1.6.1

Introduction .....................................................

1:213

1.6.2

Biosynthesis ....................................................

1:213

1.6.3

Minor Components ..........................................

1:217

1.6.4

Classification of Vegetable Oils .......................

1:219

1.6.5

The Major Vegetable Oils and Fats .................

1:224

1.6.6

Speciality and Minor Oils .................................

1:232

1.6.7

Modification of Oils and Fats ...........................

1:242

1.6.8

Technological Procedures Used for Lipid Modification .....................................................

1:244

1.6.9

Biological Methods of Lipid Modification ..........

1:251

1.6.10

Production and Trade Statistics .......................

1:258

1.6.11

Conclusion .......................................................

1:259

References ....................................................................

1:259

Lipid Oxidation: Theoretical Aspects ...................................

1:269

1.7.1

Introduction .....................................................

1:269

1.7.2

Initiation (LH → L˙ ) ........................................

1:273

1.7.3

Propagation .....................................................

1:304

1.7.4

Termination .....................................................

1:333

1.7.5

Expanded Integrated Reaction Scheme ..........

1:341

References ....................................................................

1:343

1.5.10

1.6

1.7

xv

This page has been reformatted by Knovel to provide easier navigation.

xvi

Contents

1.8

Lipid Oxidation: Measurement Methods ..............................

1:357

1.8.1

Introduction .....................................................

1:357

1.8.2

Methods for Measuring Lipid Oxidation ............

1:358

1.8.3

Measurement of Oxygen Absorption ................

1:359

1.8.4

Measurement of Reactant Change ..................

1:360

1.8.5

Measurement of Primary Products of Oxidation .........................................................

1:361

Measurement of Secondary Products of Oxidation .........................................................

1:366

1.8.7

Measurement of Free Radicals ........................

1:373

1.8.8

Other Methods .................................................

1:374

1.8.9

Measurement of Frying Fat Deterioration ........

1:377

1.8.10

Methods for Measuring Antioxidant Activity .....

1:378

1.8.11

Conclusions and Recommendations ................

1:380

References ....................................................................

1:380

Flavor Components of Fats and Oils ...................................

1:387

1.9.1

Free Radical Autoxidation of Lipids .................

1:387

1.9.2

Hydroperoxides of Fatty Acids or Their Esters ..............................................................

1:388

Major Volatile Compounds of Commercial Fats and Oils ...................................................

1:395

References ....................................................................

1:408

1.10 Flavor and Sensory Aspects ................................................

1:413

1.8.6

1.9

1.9.3

1.10.1

Introduction .....................................................

1:413

1.10.2

Sensory Methods .............................................

1:413

1.10.3

Factors Affecting Sensory Measurements .......

1:415

1.10.4

Experimental Design and Statistical Analysis ...........................................................

1:416

1.10.5

Sensory Testing Facility ..................................

1:416

1.10.6

Sample Preparation and Presentation .............

1:418

1.10.7

Reference Samples .........................................

1:420

This page has been reformatted by Knovel to provide easier navigation.

Contents

xvii

1.10.8

Selection and Training of Panelists ..................

1:422

1.10.9

Monitoring and Motivation of Panelists ............

1:423

1.10.10 Sensory Evaluation of Oils ...............................

1:423

1.10.11 Sensory Evaluation of Oil-containing Foods ....

1:426

1.10.12 Sensory Evaluation of Frying Oils/Room Odor ................................................................

1:426

1.10.13 Sensory Evaluation of Fried Foods ..................

1:426

1.10.14 Electronic Nose ...............................................

1:427

1.10.15 Gas Chromatography-olfactometery ................

1:427

1.10.16 Conclusions .....................................................

1:427

References ....................................................................

1:428

1.11 Antioxidants: Science, Technology, and Applications .........

1:431

1.11.1

An Antioxidant – Definition ...............................

1:431

1.11.2

History of Antioxidants and Their Use ..............

1:432

1.11.3

Scope of Using Antioxidants in Food ...............

1:433

1.11.4

Oxidation of Fats and Oils and Mechanism of Antioxidants .....................................................

1:434

1.11.5

Classification of Antioxidants ...........................

1:436

1.11.6

Evaluation of Antioxidant Activity .....................

1:445

1.11.7

Commonly Used Antioxidants in Foods ...........

1:455

1.11.8

Estimation and Analysis of Antioxidants in Foods ..............................................................

1:474

Technological Considerations in Using Antioxidants .....................................................

1:474

1.11.10 Regulatory Status and Safety Issues of Synthetic and Natural Antioxidants ..................

1:475

1.11.11 Safety Considerations of Antioxidants Used in Foods ..........................................................

1:476

References ....................................................................

1:483

1.12 Antioxidants: Regulatory Status ...........................................

1:491

1.11.9

1.12.1

Introduction .....................................................

1:491

1.12.2

Synthetic Antioxidants .....................................

1:492

This page has been reformatted by Knovel to provide easier navigation.

xviii

Contents 1.12.3

Natural Antioxidants ........................................

1:503

1.12.4

Conclusions .....................................................

1:508

References ....................................................................

1:509

1.13 Toxicity and Safety of Fats and Oils ....................................

1:513

1.13.1

Introduction .....................................................

1:513

1.13.2

Adverse Effects of Fats and Associated Constituents ....................................................

1:515

Adverse Effects of Some Natural Constituents in Fats and Oils ...........................

1:530

1.13.4

Bioactive Lipid-soluble Constituents ................

1:533

1.13.5

Chemical Reactions in Fats .............................

1:535

1.13.6

Adverse Products from Overheated Fats and Oils ..................................................................

1:543

Toxic Substances Produced during Smoking, Charbroiling, and Barbecuing of Foods ............

1:545

Potential Hazards from Government Approved Antioxidants .....................................

1:547

Manufacturing Hazards in Processing Crude Oils and Fats ...................................................

1:550

1.13.10 Conclusions .....................................................

1:552

References ....................................................................

1:552

1.14 Quality Assurance of Fats and Oils .....................................

1:565

1.13.3

1.13.7 1.13.8 1.13.9

1.14.1

Introduction .....................................................

1:565

1.14.2

Oil Composition ...............................................

1:568

1.14.3

Minor Components ..........................................

1:570

1.14.4

Unsaponfiables Matter .....................................

1:570

1.14.5

Characteristics of Fats and Oils .......................

1:571

1.14.6

Color and Appearance .....................................

1:571

1.14.7

Oxidative Quality and Stability Tests ...............

1:572

1.14.8

Carbonyl Compounds ......................................

1:573

1.14.9

Polymers and Polar Components ....................

1:573

1.14.10 Antioxidants .....................................................

1:574

This page has been reformatted by Knovel to provide easier navigation.

Contents

xix

1.14.11 Adulteration .....................................................

1:574

1.14.12 Pollutants ........................................................

1:574

References ....................................................................

1:574

1.15 Dietary Lipids and Health .....................................................

1:577

1.15.1

Introduction .....................................................

1:577

1.15.2

PUFA Biochemistry .........................................

1:582

1.15.3

Molecular Actions ............................................

1:583

1.15.4

Fat and Chronic Diseases ...............................

1:586

1.15.5

Role of Dietary Fat in Cardiovascular Disease and Atherosclerosis ...........................

1:589

References ....................................................................

1:600

Volume 2. Edible Oil and Fat Products: Edible Oils 2.1

2.2

Butter ....................................................................................

2:1

2.1.1

Introduction .....................................................

2:1

2.1.2

Chemical Composition .....................................

2:2

2.1.3

Modification of Milkfat ......................................

2:12

2.1.4

Quality Control .................................................

2:21

2.1.5

Butter Manufacture ..........................................

2:26

2.1.6

Butter Fat Products ..........................................

2:45

2.1.7

Economics .......................................................

2:52

References ....................................................................

2:55

Canola Oil .............................................................................

2:61

2.2.1

Introduction .....................................................

2:61

2.2.2

Origin ...............................................................

2:62

2.2.3

Development of Canola ...................................

2:62

2.2.4

Composition ....................................................

2:63

2.2.5

Physical Properties ..........................................

2:74

2.2.6

Canola Oil Extraction and Processing ..............

2:76

2.2.7

Nutritional Properties of Canola Oil ..................

2:93

2.2.8

Major Food Uses .............................................

2:99

This page has been reformatted by Knovel to provide easier navigation.

xx

2.3

2.4

2.5

Contents 2.2.9

Nonfood Uses of Standard Canola Oil .............

2:109

2.2.10

Production of Oilseeds and Oils .......................

2:113

References ....................................................................

2:116

Coconut Oil ...........................................................................

2:123

2.3.1

The Coconut Palm ...........................................

2:123

2.3.2

The Fruit ..........................................................

2:126

2.3.3

Copra ..............................................................

2:128

2.3.4

Oil Extraction ...................................................

2:129

2.3.5

Refining ...........................................................

2:132

2.3.6

Coconut Oil Composition .................................

2:135

2.3.7

Chemical and Physical Tests ...........................

2:137

2.3.8

Uses ................................................................

2:141

2.3.9

Storage ............................................................

2:142

2.3.10

Economics .......................................................

2:143

References ....................................................................

2:146

Corn Oil ................................................................................

2:149

2.4.1

Overview .........................................................

2:149

2.4.2

Extraction and Refining ...................................

2:151

2.4.3

Composition ....................................................

2:155

2.4.4

Properties of Corn Oil ......................................

2:165

2.4.5

Major Food Uses of Corn Oil ...........................

2:167

2.4.6

Nonfood Uses of Corn Oil ................................

2:168

2.4.7

Conclusions .....................................................

2:168

References ....................................................................

2:169

Cottonseed Oil ......................................................................

2:173

2.5.1

Introduction .....................................................

2:173

2.5.2

Cottonseed Oil Industry Development .............

2:174

2.5.3

Cottonseed Oil Properties ................................

2:185

2.5.4

Cottonseed Handling, Oil Extraction and Processing .......................................................

2:207

This page has been reformatted by Knovel to provide easier navigation.

Contents 2.5.5

Regulatory Considerations: Cottonseed Oil Extraction and Processing ...............................

2:235

Cottonseed Oil Products Finishing Treatment ........................................................

2:242

2.5.7

Cottonseed Oil Utilization ................................

2:246

2.5.8

Liquid Oils .......................................................

2:248

2.5.9

Shortenings .....................................................

2:256

2.5.10

Margarine and Spreads ...................................

2:267

2.5.11

Other Cottonseed Oil Uses ..............................

2:272

References ....................................................................

2:272

Flax Oil and High Linolenic Oils ...........................................

2:281

2.6.1

Introduction .....................................................

2:281

2.6.2

Flax .................................................................

2:282

2.6.3

Perilla Oil .........................................................

2:292

2.6.4

Camelina .........................................................

2:294

2.6.5

Chia .................................................................

2:298

References ....................................................................

2:298

Olive Oil ................................................................................

2:303

2.7.1

Introduction and History ...................................

2:303

2.7.2

Statistics and Definitions .................................

2:306

2.7.3

Extraction Technology .....................................

2:310

2.7.4

Refining of Olive Oils .......................................

2:314

2.7.5

Refining of Pomace Oil ....................................

2:316

2.7.6

Olive Oil Components ......................................

2:317

2.7.7

Analysis of Olive Oils .......................................

2:320

References ....................................................................

2:328

Palm Oil ................................................................................

2:333

2.8.1

Introduction .....................................................

2:333

2.8.2

Chemical and Physical Properties of Palm Oil ....................................................................

2:339

Production Process .........................................

2:351

2.5.6

2.6

2.7

2.8

xxi

2.8.3

This page has been reformatted by Knovel to provide easier navigation.

xxii

Contents 2.8.4

Refining and Fractionation ...............................

2:371

2.8.5

End Uses .........................................................

2:388

2.8.6

Potential Developments ...................................

2:410

2.8.7

Nutritional Effects of Palm Oil ..........................

2:411

2.8.8

Prospects of Palm Oil and Market Requirements ..................................................

2:417

References ....................................................................

2:423

Peanut Oil .............................................................................

2:431

2.9.1

Peanut Origin and History ................................

2:431

2.9.2

Global ..............................................................

2:432

2.9.3

Environmental and Genotype Effects on the Composition Peanuts ......................................

2:445

Modification of Oil Characteristics through Breeding ..........................................................

2:445

2.9.5

Oil Color ..........................................................

2:446

2.9.6

Peanut Oil Evaluation and Composition ...........

2:447

2.9.7

Uses ................................................................

2:453

2.9.8

Dietary Aspects ...............................................

2:454

2.9.9

Allergenicity .....................................................

2:455

References ....................................................................

2:455

2.10 Rice Bran Oil ........................................................................

2:465

2.9

2.9.4

2.10.1

Introduction .....................................................

2:465

2.10.2

Composition of Rice and Rice Bran Lipids .......

2:466

2.10.3

Milling of Rice ..................................................

2:470

2.10.4

Enzymes in Rice Bran .....................................

2:473

2.10.5

Stabilization of Rice Bran ................................

2:475

2.10.6

Rice Bran to Rice Bran Oil ...............................

2:477

2.10.7

Refining of the Oil ............................................

2:478

2.10.8

Dewaxing ........................................................

2:479

2.10.9

Degumming and Deacidification ......................

2:479

This page has been reformatted by Knovel to provide easier navigation.

Contents

xxiii

2.10.10 Bleaching, Hydrogenation and Deodorerization ...............................................

2:480

2.10.11 Winterization ....................................................

2:481

2.10.12 Co-products from Processing ..........................

2:481

2.10.13 Composition of Refined Rice Bran Oil ..............

2:482

2.10.14 Rice Bran Oil Nutrition .....................................

2:483

2.10.15 Rice Bran Oil Utilization ...................................

2:485

2.10.16 Rice Oil Production (Potential) .........................

2:486

2.10.17 Summary .........................................................

2:487

References ....................................................................

2:487

2.11 Safflower Oil .........................................................................

2:491

2.11.1

History and Botanical Description ....................

2:491

2.11.2

Physical and Chemical Properties ...................

2:505

2.11.3

Processing .......................................................

2:511

2.11.4

Economics and Marketing ...............................

2:514

2.11.5

Quality Assessment .........................................

2:522

2.11.6

Storage and Transportation .............................

2:525

2.11.7

Unique Uses ....................................................

2:527

References ....................................................................

2:530

2.12 Sesame Oil ...........................................................................

2:537

2.12.1

Introduction .....................................................

2:537

2.12.2

Botany of Sesame ...........................................

2:538

2.12.3

World Production .............................................

2:541

2.12.4

Chemical Composition .....................................

2:544

2.12.5

Sesame Lignans and Lignan Glycosides .........

2:549

2.12.6

Processing .......................................................

2:555

2.12.7

Nutritional Characteristics ................................

2:564

Reference ......................................................................

2:570

2.13 Soybean Oil ..........................................................................

2:577

2.13.1

Introduction .....................................................

2:577

2.13.2

Composition of Soybeans ................................

2:578

This page has been reformatted by Knovel to provide easier navigation.

xxiv

Contents 2.13.3

Physical Properties of Soybean Oil ..................

2:584

2.13.4

Grading ...........................................................

2:589

2.13.5

Recovery of Oil from Soybeans .......................

2:591

2.13.6

Qualities of Soybean Oils and Meals Extracted by Different Methods ........................

2:600

2.13.7

Soy Protein Ingredients ...................................

2:603

2.13.8

Basic Processing Operations ...........................

2:604

2.13.9

Alternative Refining Methods ...........................

2:611

2.13.10 Coproducts and Utilization ...............................

2:612

2.13.11 Food and Biobased Product Uses of Soybean Oil .....................................................

2:614

2.13.12 Oxidative Quality of Soybean Oil .....................

2:629

2.13.13 Dietary Fatty Acids and Their Health Effects ...

2:638

References ....................................................................

2:641

2.14 Sunflower Oil ........................................................................

2:655

2.14.1

Historical Review .............................................

2:655

2.14.2

Sunflower Crops ..............................................

2:658

2.14.3

Chemical and Physical Properties of Regular Sunflower Oil ...................................................

2:664

Sunflower Seed of Modified Fatty Acid Composition ....................................................

2:674

2.14.5

Extraction and Processing of Sunflower Oil .....

2:685

2.14.6

Hydrogenation of Regular Sunflower Oil ..........

2:700

2.14.7

Storage and Deterioration of Sunflower Oil ......

2:703

2.14.8

Uses of Sunflower Oil ......................................

2:707

2.14.9

World Production and Distribution of Sunflower Oil ...................................................

2:713

2.14.10 Sunflower Oil Extraction and Processing by-products ......................................................

2:719

References ....................................................................

2:725

2.14.4

This page has been reformatted by Knovel to provide easier navigation.

Contents

xxv

Volume 3. Edible Oil and Fat Products: Specialty Oils and Oil Products 3.1

3.2

3.3

3.4

Conjugated Linoleic Acid Oils ..............................................

3:1

3.1.1

Introduction .....................................................

3:1

3.1.2

Metabolism ......................................................

3:2

3.1.3

Physiological Actions of CLA ...........................

3:3

3.1.4

Strategies to Increase Dietary Intake of CLA ...

3:8

3.1.5

Commercial Production of CLA ........................

3:8

3.1.6

Analysis of Conjugated Linoleic Acids .............

3:21

3.1.7

Conclusions .....................................................

3:29

References ....................................................................

3:29

Diacylglycerols .....................................................................

3:37

3.2.1

Introduction .....................................................

3:37

3.2.2

Comparison of DAG Oil vs. TAG Oil ................

3:39

3.2.3

Summary .........................................................

3:44

References ....................................................................

3:46

Citrus Oils and Essences .....................................................

3:49

3.3.1

Introduction .....................................................

3:49

3.3.2

Oil Extraction ...................................................

3:50

3.3.3

Chemical Composition .....................................

3:52

3.3.4

Storage of Citrus Oils ......................................

3:58

3.3.5

Applications of Citrus Oils and Essences .........

3:61

3.3.6

Challenges ......................................................

3:62

3.3.7

Conclusions .....................................................

3:63

References ....................................................................

3:63

Gamma Linolenic Acid Oils ..................................................

3:67

3.4.1

Introduction .....................................................

3:67

3.4.2

Sources of GLA ...............................................

3:68

3.4.3

Extraction of Oil ...............................................

3:76

3.4.4

Metabolism of GLA ..........................................

3:80

3.4.5

Cardiovascular Effects .....................................

3:83

This page has been reformatted by Knovel to provide easier navigation.

xxvi

3.5

Contents 3.4.6

Cancer .............................................................

3:87

3.4.7

Immune Function and Autoimmune Diseases .........................................................

3:93

3.4.8

Skin Conditions ...............................................

3:99

3.4.9

Diabetes ..........................................................

3:103

3.4.10

Premenstrual Syndrome (PMS) .......................

3:106

3.4.11

Infant Nutrition and Development ....................

3:107

3.4.12

Drug/Nutrient Interactions ................................

3:108

3.4.13

Safety of GLA-containing Oils ..........................

3:109

3.4.14

Current Research Focus ..................................

3:110

References ....................................................................

3:111

Oils from Microorganisms ....................................................

3:121

3.5.1

General Introduction and Background Information ......................................................

3:121

3.5.2

Commercial Microbial Oils ...............................

3:130

3.5.3

SCOs in Current (2003) Production .................

3:137

3.5.4

Prospects for Production of Other PUFAs by Microorganisms ...............................................

3:145

The Future of Microbial Oils .............................

3:147

Acknowledgments ..........................................................

3:149

References ....................................................................

3:150

Transgenic Oils ....................................................................

3:155

3.6.1

Introduction .....................................................

3:155

3.6.2

Technology for Altering Fatty Acid Composition ....................................................

3:158

Canola from Traditional Breeding of Oilseed Crops ...............................................................

3:159

High-oleic Sunflower from Mutagenesis of Oilseed Crops ..................................................

3:160

3.6.5

Applications of High-oleate Oils .......................

3:160

3.6.6

Altered Polyunsaturate Content through Mutagenesis ....................................................

3:162

3.5.5

3.6

3.6.3 3.6.4

This page has been reformatted by Knovel to provide easier navigation.

Contents

xxvii

Improved Oil Composition of a Transgenic Soybean ..........................................................

3:162

Improved Industrial Use from Genetically Engineering Oilseed Crops ..............................

3:163

3.6.9

Future Directions for Transgenic Oilseeds .......

3:164

3.6.10

Potential New Oils for Food, Feed, and Industruial Use ................................................

3:165

Issues Related to Transgenic Oilseeds ............

3:167

References ....................................................................

3:172

Tree Nut Oils ........................................................................

3:175

3.7.1

Introduction .....................................................

3:175

3.7.2

Almond ............................................................

3:176

3.7.3

Hazelnut ..........................................................

3:179

3.7.4

Pecan ..............................................................

3:182

3.7.5

Walnut .............................................................

3:183

3.7.6

Pistachio ..........................................................

3:185

3.7.7

Brazil Nut .........................................................

3:186

3.7.8

Pine Nut ..........................................................

3:186

3.7.9

Macadamia Nut ...............................................

3:187

3.7.10

Cashew Nut .....................................................

3:188

3.7.11

Use of Defatted Tree Nut Meals and Other Byproducts as Protein Sources ........................

3:188

Concluding Remarks .......................................

3:190

References ....................................................................

3:190

Germ Oils from Different Sources ........................................

3:195

3.8.1

Introduction .....................................................

3:195

3.8.2

Wheat Germ ....................................................

3:196

3.8.3

Corn Germ Oil .................................................

3:207

3.8.4

Rice Bran Oil ...................................................

3:215

3.8.5

Oat and Barley Oil ...........................................

3:223

3.8.6

Conclusions .....................................................

3:227

3.6.7 3.6.8

3.6.11 3.7

3.7.12 3.8

This page has been reformatted by Knovel to provide easier navigation.

xxviii

Contents References ....................................................................

3:227

Oils from Herbs, Spices, and Fruit Seeds ...........................

3:233

3.9.1

Introduction .....................................................

3:233

3.9.2

Edible Seed Oils Rich in α-linolenic Acid (18:3n3) ...........................................................

3:234

Edible Seed Oils Rich in γ-linolenic Acid (18:3n6) ...........................................................

3:239

Edible Seed Oils Rich in Linoleic Acid (18:2n6) ...........................................................

3:241

Edible Seed Oils Rich in Oleic Acid (18:1n-9) ..........................................................

3:248

Other Special Seed Oils of Fruit, Spice, and Herb ................................................................

3:254

Summary .........................................................

3:255

References ....................................................................

3:256

3.10 Marine Mammal Oils ............................................................

3:259

3.9

3.9.3 3.9.4 3.9.5 3.9.6 3.9.7

3.10.1

Introduction .....................................................

3:259

3.10.2

Lipid Classes ...................................................

3:260

3.10.3

Fatty Acid Composition ....................................

3:262

3.10.4

Oxidative Stability ............................................

3:267

3.10.5

Processing .......................................................

3:268

3.10.6

Production of ω3 Fatty Acid Concentrates .......

3:269

3.10.7

Applications .....................................................

3:271

3.10.8

Health Benefits and Disease Prevention ..........

3:272

3.10.9

Health Effects of DPA ......................................

3:273

3.10.10 Comparison of Fish Oil and Marine Mammal Oil ....................................................................

3:274

Reference ......................................................................

3:275

3.11 Fish Oils ................................................................................

3:279

3.11.1

Introduction .....................................................

3:279

3.11.2

Why Do We Still Have Fish Oils? .....................

3:282

This page has been reformatted by Knovel to provide easier navigation.

Contents 3.11.3

xxix

Fish Oil Fatty Acids and Gas-liquid Chromatography ..............................................

3:284

Saturated, Isomeric Monoenoic, and Unusual Fatty Acids ......................................................

3:290

3.11.5

Polyunsaturated Fatty Acids ............................

3:293

3.11.6

Fish Oil Production and Quality .......................

3:296

3.11.7

Concentrates of Fish Oil Omega-3 Products ....

3:303

3.11.8

The Other Oils .................................................

3:309

3.11.9

Conclusion .......................................................

3:311

References ....................................................................

3:313

3.12 Minor Components of Fats and Oils ....................................

3:319

3.11.4

3.12.1

Introduction .....................................................

3:319

3.12.2

The Chemistry of Minor Lipid Components ......

3:321

3.12.3

Significance of Minor Lipid Components ..........

3:336

3.12.4

Analysis of Minor Lipid Components ................

3:346

References ....................................................................

3:347

3.13 Lecithins ...............................................................................

3:361

3.13.1

Introduction .....................................................

3:361

3.13.2

Sources of Phospholipids ................................

3:362

3.13.3

Nomenclature, Classification, Structure and Composition, and Chemical/Physical Properties ........................................................

3:372

Manufacture, Fractionation, and Purification of Lecithins ......................................................

3:384

3.13.5

Food-grade Lecithin Products, Uses ................

3:400

3.13.6

Animal Feeds, Uses ........................................

3:420

3.13.7

Nonfood and Industrial Uses ...........................

3:427

3.13.8

Availability and Economics ..............................

3:438

3.13.9

Regulatory Aspects .........................................

3:439

3.13.10 Future Prospects .............................................

3:440

Acknowledgments ..........................................................

3:440

3.13.4

This page has been reformatted by Knovel to provide easier navigation.

xxx

Contents References ....................................................................

3:440

3.14 Lipid Emulsions ....................................................................

3:457

3.14.1

Introduction .....................................................

3:457

3.14.2

Definitions .......................................................

3:458

3.14.3

Droplet Characteristics ....................................

3:460

3.14.4

Emulsion Preparation ......................................

3:468

3.14.5

Physicochemical Properties of Food Emulsions ........................................................

3:480

Conclusions .....................................................

3:496

References ....................................................................

3:497

3.15 Dietary Fat Substitutes .........................................................

3:503

3.14.6

3.15.1

Introduction .....................................................

3:503

3.15.2

Reduced-calorie Structured Lipids as Fat Substitutes ......................................................

3:510

3.15.3

Fat Substitutes Based on Esters and Ethers ....

3:516

3.15.4

Fat Mimetics Based on Carbohydrates ............

3:528

3.15.5

Fat Mimetics Based on Proteins ......................

3:530

References ....................................................................

3:532

3.16 Structural Effects on Absorption, Metabolism, and Health Effects of Lipids ........................................................

3:535

3.16.1

Introduction .....................................................

3:535

3.16.2

Stereospecific Effects of Fat Digestion and Related Phenomena ........................................

3:537

Differences in Metabolism between Esterified and Free Fatty Acids .......................................

3:543

3.16.4

Postprandial Effects .........................................

3:545

3.16.5

Effects of Stereospecific Structure of Dietary Acylglycerols on Chylomicron Clearing and Tissue Targeting ..............................................

3:547

Effects of Stereospecific Structure of Dietary Triacylglycerols on Their Health-related Nutritional Effects ...........................................

3:547

3.16.3

3.16.6

This page has been reformatted by Knovel to provide easier navigation.

Contents 3.16.7

xxxi

Effects Related to Triacylglycerol Hydrophobicity .................................................

3:548

Effect of Acylglycerol Structure on Nutritional Effects .............................................................

3:549

Semi-synthetic Food Fats without Acylglycerol Structure ......................................

3:550

3.16.10 Conclusion .......................................................

3:550

References ....................................................................

3:551

3.17 Modification of Fats and Oils via Chemical and Enzymatic Methods ..............................................................

3:555

3.16.8 3.16.9

3.17.1

Introduction .....................................................

3:555

3.17.2

Hydrogenation .................................................

3:556

3.17.3

Fractionation ....................................................

3:557

3.17.4

Blending ..........................................................

3:558

3.17.5

Interesterification .............................................

3:558

3.17.6

Hydrolysis and Esterification ............................

3:569

3.17.7

Lipases in Lipid Modification ............................

3:571

3.17.8

Modification of Fats and Oils to Produce Structured Lipids .............................................

3:579

References ....................................................................

3:582

3.18 Novel Separation Techniques for Isolation and Purification of Fatty Acids and Oil by-products ....................

3:585

3.18.1

Introduction .....................................................

3:585

3.18.2

Methods of Obtaining Fatty Acids ....................

3:586

3.18.3

Separation of Byproduct Components .............

3:607

References ....................................................................

3:614

Volume 4. Edible Oil and Fat Products: Products and Applications 4.1

Frying Oils ............................................................................

4:1

4.1.1

Introduction .....................................................

4:1

4.1.2

Role of Oil or Fat in Frying ...............................

4:3

This page has been reformatted by Knovel to provide easier navigation.

xxxii

Contents 4.1.3

Applications of Frying Oil .................................

4:3

4.1.4

Selection of Frying Oil .....................................

4:4

4.1.5

The Frying Process .........................................

4:5

4.1.6

Chemical Reactions Occurring in Oil during Frying ..............................................................

4:7

4.1.7

Sources of Free Radicals ................................

4:11

4.1.8

Polymerization .................................................

4:11

4.1.9

Complexity of Oil Reactions in Frying ..............

4:12

4.1.10

Analytical Requirements for Fresh Frying Oil ....................................................................

4:14

Impact of Tocopherols and Tocotrienols in Frying Oil .........................................................

4:16

4.1.12

Factors Affecting Frying Oil Quality .................

4:17

4.1.13

Quality Standards of Oils (Table 3) ..................

4:19

4.1.14

Comments on Palm Oil ....................................

4:20

4.1.15

Enhancement of Frying Oil Performance .........

4:21

4.1.16

Storage and Transportation of Frying Oil .........

4:22

4.1.17

Hydrogenation and Trans-fat ...........................

4:23

4.1.18

Alternatives to Trans-fats .................................

4:25

4.1.19

Frying Shortening versus Frying Oils ...............

4:27

4.1.20

Summary .........................................................

4:28

References ....................................................................

4:29

Margarines and Spreads ......................................................

4:33

4.2.1

Historical Development of Margarine (4–7) ......

4:35

4.2.2

U.S. Trends .....................................................

4:36

4.2.3

Regulatory Status in the United States ............

4:37

4.2.4

Product Characteristics ...................................

4:42

4.2.5

Oils Used in Vegetable Oil Margarines and Spreads ...........................................................

4:45

4.2.6

Other Common Ingredients .............................

4:58

4.2.7

Processing .......................................................

4:63

4.1.11

4.2

This page has been reformatted by Knovel to provide easier navigation.

4.3

4.4

4.5

Contents

xxxiii

4.2.8

Low-calorie Spreads ........................................

4:68

4.2.9

Balanced Spreads ...........................................

4:70

4.2.10

Deterioration and Shelf Life .............................

4:71

References ....................................................................

4:73

Shortenings: Science and Technology ................................

4:83

4.3.1

Introduction .....................................................

4:83

4.3.2

Plastic Theory ..................................................

4:88

4.3.3

Formulation .....................................................

4:89

4.3.4

Manufacturing Processes and Equipment ........

4:94

4.3.5

Shortening Production Systems .......................

4:106

4.3.6

Analytical Evaluation and Quality Control ........

4:114

4.3.7

Packaging and Storage ...................................

4:116

4.3.8

Innovations ......................................................

4:117

References ....................................................................

4:123

Shortenings: Types and Formulations .................................

4:125

4.4.1

Introduction .....................................................

4:125

4.4.2

Shortening Attributes .......................................

4:132

4.4.3

Base Stock System .........................................

4:137

4.4.4

Shortening Formulation ...................................

4:140

4.4.5

Shortening Crystallization ................................

4:147

4.4.6

Plasticized Shortening Consistency .................

4:149

4.4.7

Liquid Opaque Shortenings .............................

4:153

4.4.8

Shortening Chips and Flakes ...........................

4:155

References ....................................................................

4:156

Confectionery Lipids .............................................................

4:159

4.5.1

Introduction .....................................................

4:159

4.5.2

Chemistry of Chocolate ...................................

4:159

4.5.3

Characteristics of Cocoa Butter .......................

4:160

4.5.4

Confectionery Fats ..........................................

4:165

4.5.5

Hard Butters ....................................................

4:168

4.5.6

Lauric CBS ......................................................

4:168

This page has been reformatted by Knovel to provide easier navigation.

xxxiv

4.6

4.7

Contents 4.5.7

Non-lauric CBS ................................................

4:170

4.5.8

Cocoa Butter Equivalents (CBEs) ....................

4:170

4.5.9

Organic Chocolate and Confectionery .............

4:171

4.5.10

Recipe Engineering and Oil Processing ...........

4:172

4.5.11

Conclusions and Future Prospectives ..............

4:173

References ....................................................................

4:173

Cooking Oils, Salad Oils, and Dressings .............................

4:175

4.6.1

Introduction .....................................................

4:175

4.6.2

Natural and Processed Cooking and Salad Oils ..................................................................

4:176

4.6.3

Stability of Salad and Cooking Oils ..................

4:178

4.6.4

Quality Evaluation of Salad and Cooking Oils ..................................................................

4:180

4.6.5

Additives for Salad and Cooking Oils ...............

4:183

4.6.6

Nutrition-oriented Salad and Cooking Oils .......

4:184

4.6.7

New Salad and Cooking Oils ...........................

4:184

4.6.8

Oil-based Dressings ........................................

4:185

4.6.9

Viscous or Spoonable Dressings .....................

4:185

4.6.10

Pourable Dressings .........................................

4:191

4.6.11

Reduced-calorie Dressings ..............................

4:196

4.6.12

Fat-free Dressings ...........................................

4:198

4.6.13

Refrigerated Dressings ....................................

4:200

4.6.14

Heat-stable Dressings .....................................

4:200

References ....................................................................

4:201

Fats and Oils in Bakery Products ........................................

4:207

4.7.1

Introduction .....................................................

4:207

4.7.2

Bread and Rolls ...............................................

4:208

4.7.3

Layered Doughs ..............................................

4:210

4.7.4

Cakes ..............................................................

4:212

4.7.5

Cake Donuts ....................................................

4:215

4.7.6

Cookies ...........................................................

4:216

This page has been reformatted by Knovel to provide easier navigation.

4.8

4.9

Contents

xxxv

4.7.7

Pie Crust, Biscuits ...........................................

4:219

4.7.8

Specifications for Bakery Shortenings .............

4:219

References ....................................................................

4:227

Emulsifiers for the Food Industry .........................................

4:229

4.8.1

Emulsifiers as Amphiphiles ..............................

4:229

4.8.2

Surfaces and Interfaces in Foods ....................

4:231

4.8.3

Surface Activity ................................................

4:231

4.8.4

Emulsions ........................................................

4:236

4.8.5

Foams .............................................................

4:242

4.8.6

Wetting ............................................................

4:243

4.8.7

Physical State of Emulsifier Plus Water ...........

4:244

4.8.8

Emulsifiers for Food Applications .....................

4:248

4.8.9

Interactions with Other Food Components .......

4:256

4.8.10. Some Food Applications ..................................

4:261

References ....................................................................

4:266

Frying of Foods and Snack Food Production ......................

4:269

4.9.1

Introduction .....................................................

4:269

4.9.2

Frying Process ................................................

4:270

4.9.3

Types of Restaurant Fryers .............................

4:270

4.9.4

Safety Issues ...................................................

4:277

4.9.5

Improving Restaurant Fryer Operation .............

4:278

4.9.6

Measuring Oil Quality in the Fryer ...................

4:279

4.9.7

Physical Testing Devices .................................

4:280

4.9.8

Chemical Tests ................................................

4:282

4.9.9

Filtration and Treatment of Oil .........................

4:284

4.9.10

Industrial Frying ...............................................

4:285

4.9.11

The Purpose of Frying Foods ..........................

4:288

4.9.12

Difference between the Frying and Other Cooking Methods .............................................

4:289

4.9.13

What Happens during Frying? ..........................

4:289

4.9.14

Types of Industrial Fryers ................................

4:290

This page has been reformatted by Knovel to provide easier navigation.

xxxvi

Contents 4.9.15

Criteria for Fryer Selection ...............................

4:294

4.9.16

Components in an Industrial Frying System .....

4:295

4.9.17

Continuous Potato Chip Process .....................

4:296

4.9.18

Extruded Products ...........................................

4:299

4.9.19

Heat Wave Fryers ............................................

4:303

4.9.20

Evolution of the Frying Industry into Diverse Products ..........................................................

4:304

4.9.21

Low Oil Snacks ................................................

4:304

4.9.22

Generation of Fines and Their Removal ..........

4:305

4.9.23

Terminology Used in Industrial Frying .............

4:307

4.9.24

Fryer Capacity .................................................

4:307

4.9.25

Key Points in Determining the Fryer Size ........

4:308

4.9.26

Heat Load Requirement ...................................

4:310

4.9.27

Air Requirement (for Combustion) ...................

4:313

4.9.28

Product Bulk Density .......................................

4:313

4.9.29

Oil Quality Management ..................................

4:313

4.9.30

Fryer Sanitation ...............................................

4:314

4.9.31

Summary .........................................................

4:314

References ....................................................................

4:315

4.10 Fats and Oils in Feedstuffs and Pet Foods .........................

4:317

4.10.1

History .............................................................

4:319

4.10.2

Information Sources, Authorities, and Obligations ......................................................

4:320

Availability, Characteristics, and Composition ....................................................

4:323

Digestion Metabolism and Fats Feeding Requirements ..................................................

4:341

Fat Utilization Practices ...................................

4:367

References ....................................................................

4:386

4.11 By-product Utilization ...........................................................

4:391

4.10.3 4.10.4 4.10.5

4.11.1

By-products of Seed Processing ......................

This page has been reformatted by Knovel to provide easier navigation.

4:391

Contents

xxxvii

By-products of Oil Refining ..............................

4:405

References ....................................................................

4:413

4.12 Environmental Impact and Waste Management .................

4:417

4.11.2

4.12.1

Introduction .....................................................

4:417

4.12.2

Process Components and Major Wastewater Sources ...........................................................

4:418

Process Factors Affecting Wastewater Generation and Characteristics .......................

4:421

4.12.4

Air Emissions, Sources, and Controls ..............

4:423

4.12.5

Solid and Hazardous Wastes, Sources, and Controls ...........................................................

4:427

4.12.6

Current Issues .................................................

4:429

4.12.7

Wastewater Treatment Processes and Technologies ...................................................

4:431

References ....................................................................

4:440

4.12.3

Volume 5. Edible Oil and Fat Products: Processing Technologies 5.1

A Primer on Oils Processing Technology ............................

5:1

5.1.1

Introduction .....................................................

5:1

5.1.2

Storage ............................................................

5:2

5.1.3

Preparation ......................................................

5:5

5.1.4

Mechanical Extraction .....................................

5:9

5.1.5

Solvent Extraction ............................................

5:11

5.1.6

Degumming, Lecithin Processing, and Physical Refining Pretreatment ........................

5:16

5.1.7

Caustic Refining ..............................................

5:20

5.1.8

Bleaching ........................................................

5:25

5.1.9

Dewaxing ........................................................

5:29

5.1.10

Hydrogenation .................................................

5:33

5.1.11

Interesterification .............................................

5:37

5.1.12

Fractionation ....................................................

5:39

This page has been reformatted by Knovel to provide easier navigation.

xxxviii

5.2

5.3

5.4

Contents

5.1.13

Deodorization and Physical Refining ...............

5:42

5.1.14

Shortening and Margarine Manufacturing ........

5:48

5.1.15

Acidulation .......................................................

5:53

5.1.16

Summary .........................................................

5:54

References ....................................................................

5:55

General References .......................................................

5:56

Oil Extraction ........................................................................

5:57

5.2.1

Evolution of Oil Extraction ...............................

5:57

5.2.2

Seed Preparation .............................................

5:63

5.2.3

Mechanical Extraction .....................................

5:71

5.2.4

Solvent Extraction ............................................

5:75

5.2.5

Summary .........................................................

5:97

References ....................................................................

5:97

Recovery of Oils and Fats from Oilseeds and Fatty Materials ...............................................................................

5:99

5.3.1

Introduction .....................................................

5:99

5.3.2

Mechanical Pretreatment .................................

5:102

5.3.3

Heat Pretreatment ...........................................

5:109

5.3.4

Mechanical Expression of Oil ..........................

5:128

5.3.5

Solvent Extraction ............................................

5:142

5.3.6

Types of Extractors ..........................................

5:160

5.3.7

Recovery of Solvent ........................................

5:172

5.3.8

Obtaining Oil from Fruit Pulps ..........................

5:180

Acknowledgements ........................................................

5:182

References ....................................................................

5:182

Storage, Handling, and Transport of Oils and Fats .............

5:191

5.4.1

Introduction .....................................................

5:191

5.4.2

Storage and Handling ......................................

5:200

5.4.3

Deterioration Processes ..................................

5:220

5.4.4

Conclusions and Future Perspectives ..............

5:226

References ....................................................................

5:226

This page has been reformatted by Knovel to provide easier navigation.

5.5

Contents

xxxix

Packaging .............................................................................

5:231

5.5.1

5.6

5.7

5.8

Conceptual Design of Packaging Systems for Oil Products .....................................................

5:231

5.5.2

Preliminary Engineering ..................................

5:238

5.5.3

Final Engineering ............................................

5:241

5.5.4

Packaging Systems Components ....................

5:244

5.5.5

Edible Oil Operations .......................................

5:258

5.5.6

Bulk Packaging Operations .............................

5:262

5.5.7

Summary .........................................................

5:263

5.5.8

Future Considerations .....................................

5:264

References ....................................................................

5:264

Adsorptive Separation of Oils ..............................................

5:267

5.6.1

Definitions .......................................................

5:267

5.6.2

Mathematical Models .......................................

5:268

5.6.3

Mechanisms ....................................................

5:279

5.6.4

Mechanics .......................................................

5:280

References ....................................................................

5:282

Bleaching ..............................................................................

5:285

5.7.1

Introduction .....................................................

5:285

5.7.2

Background and Historical Perspective ...........

5:286

5.7.3

Adsorptive Purification Agents – Description/ Preparation/Properties .....................................

5:287

5.7.4

Trace Constituents in Lipid Oils and Fats ........

5:297

5.7.5

Adsorptive Purification Process: General Description ......................................................

5:314

References ....................................................................

5:335

Deodorization .......................................................................

5:341

5.8.1

Introduction .....................................................

5:341

5.8.2

Deodorization Principle ....................................

5:343

5.8.3

Refined Oil Quality ...........................................

5:349

5.8.4

Deodorizer Technology ....................................

5:363

This page has been reformatted by Knovel to provide easier navigation.

xl

Contents 5.8.5

Commercial Deodorizer Systems ....................

5:376

5.8.6

Future Challenges ...........................................

5:381

References ....................................................................

5:382

Hydrogenation: Processing Technologies ...........................

5:385

5.9.1

Introduction .....................................................

5:385

5.9.2

Is There a Future for Hydrogenation? ..............

5:390

5.9.3

Research on Trans-reduction by Hydrogenation .................................................

5:390

5.9.4

The Trans-fat Issue .........................................

5:391

5.9.5

Hydrogen Supply for Hydrogenation ................

5:394

References ....................................................................

5:395

5.10 Supercritical Technologies for Further Processing of Edible Oils ............................................................................

5:397

5.9

5.10.1

Introduction .....................................................

5:397

5.10.2

Definition and Properties of Supercritical Fluids ...............................................................

5:398

Historic Development and Commercial Applications .....................................................

5:399

5.10.4

Solubility Behavior of Lipid Components ..........

5:400

5.10.5

Supercritical Fluid Processing of Fats and Oils ..................................................................

5:408

Novel Process Development: an Integrated Approach .........................................................

5:423

References ....................................................................

5:424

5.11 Membrane Processing of Fats and Oils ..............................

5:433

5.10.3

5.10.6

5.11.1

Introduction .....................................................

5:433

5.11.2

Composition of Crude Vegetable Oils ..............

5:434

5.11.3

Crude Vegetable Oil Refining ..........................

5:434

5.11.4

Vegetable Oil Degumming ...............................

5:435

5.11.5

Membrane Processing of Oils and Fats ...........

5:437

5.11.6

Conclusions .....................................................

5:456

References ....................................................................

5:457

This page has been reformatted by Knovel to provide easier navigation.

Contents 5.12 Margarine Processing Plants and Equipment .....................

xli 5:459

5.12.1

Crystallization of Oil and Fat Products .............

5:460

5.12.2

Processing Equipment for Margarine and Related Fat Products .......................................

5:469

5.12.3

Refrigerants for the Future ...............................

5:498

5.12.4

Plant Layout and Process Flowsheet ...............

5:499

5.12.5

Processing of Low-fat Spreads, Puff Pastry Margarine, and Puff Pastry Butter ....................

5:511

Production Control, Quality Control, and Sanitation ........................................................

5:523

References ....................................................................

5:528

5.13 Extrusion Processing of Oilseed Meals for Food and Feed Production ...................................................................

5:533

5.12.6

5.13.1

Introduction .....................................................

5:533

5.13.2

Types of Extruders ..........................................

5:534

5.13.3

Why Process Oilseed with Extrusion? .............

5:538

5.13.4

Soybeans Can Be Converted into Full-fat Soy by Using Dry or Wet Extruders .................

5:546

5.13.5

Extrusion-expelling of Oilseeds .......................

5:554

5.13.6

Extrusion-expelling of Soybeans ......................

5:554

5.13.7

Nutritional Advantages of Extrusion-expelling of Oilseeds ......................................................

5:559

5.13.8

Mechanical Crushing with Expanders ..............

5:563

5.13.9

Extrusion of Oilseeds before Extraction ...........

5:564

5.13.10 Extrusion of High Oilseeds ..............................

5:567

References ....................................................................

5:569

Volume 6. Industrial and Nonedible Products from Oils and Fats 6.1

Fatty Acids and Derivatives from Coconut Oil .....................

6:1

6.1.1

6:1

The World’s Fats and Oils Output ....................

This page has been reformatted by Knovel to provide easier navigation.

xlii

Contents 6.1.2

The Role of Coconut Oil in the Oleochemical Industry Worldwide ..........................................

6:2

Types of Fatty Acids and Derivatives from Coconut Oil and Their General Applications ....

6:4

6.1.4

Fatty Acids ......................................................

6:7

6.1.5

Methyl Esters ...................................................

6:13

6.1.6

Fatty Alcohols ..................................................

6:21

6.1.7

Glycerine .........................................................

6:29

6.1.8

Monoalkyl Phosphates .....................................

6:36

6.1.9

Alkanolamides .................................................

6:39

6.1.10

Surfactants ......................................................

6:43

6.1.11

Tertiary Amines ...............................................

6:52

References ....................................................................

6:54

Rendering .............................................................................

6:57

6.2.1

Introduction .....................................................

6:57

6.2.2

Modern Day Rendering ....................................

6:58

6.2.3

Byproducts ......................................................

6:60

6.2.4

Processing .......................................................

6:66

6.2.5

Product Composition .......................................

6:75

6.2.6

Proteins ...........................................................

6:78

6.2.7

Fats .................................................................

6:79

6.2.8

Oleochemistry .................................................

6:82

6.2.9

Refining ...........................................................

6:85

6.2.10

Bleaching or Color Reduction ..........................

6:86

6.2.11

Uses of Refined and Bleached Fats ................

6:87

6.2.12

Hydrogenation and Hydrogenated Products ....

6:87

6.2.13

Trans-esterification and Fatty Acid Esters .......

6:89

6.2.14

Bio-fuel and Bio-diesel Products ......................

6:93

6.2.15

Governmental Regulations ..............................

6:95

6.2.16

Environmental Issues ......................................

6:98

6.2.17

Future Outlook .................................................

6:99

6.1.3

6.2

This page has been reformatted by Knovel to provide easier navigation.

Contents 6.3

6.4

xliii

References ....................................................................

6:100

Soaps ...................................................................................

6:103

6.3.1

Introduction .....................................................

6:103

6.3.2

Physical Properties of Surfactants ...................

6:104

6.3.3

Soap Raw Materials and Their Processing ......

6:105

6.3.4

Soap Solution-phase Properties ......................

6:108

6.3.5

Soap Solid-phase Properties and Crystallization ..................................................

6:111

6.3.6

Commercial Processing ...................................

6:113

6.3.7

Bar Soap Manufacturing ..................................

6:122

6.3.8

Formulation of Soaps ......................................

6:126

6.3.9

Economic Aspects ...........................................

6:132

6.3.10

Analytical Characterization of Soap .................

6:132

6.3.11

Health, Safety, and Toxicology ........................

6:133

6.3.12

Additional Uses of Soap ..................................

6:133

References ....................................................................

6:134

General References .......................................................

6:136

Detergents and Detergency .................................................

6:137

6.4.1

Introduction .....................................................

6:137

6.4.2

Components of Detersive Systems ..................

6:140

6.4.3

Formulation .....................................................

6:142

6.4.4

Surfactants ......................................................

6:142

6.4.5

Factors Influencing Detergency .......................

6:149

6.4.6

Mechanisms ....................................................

6:156

6.4.7

Solid-soil Detergency .......................................

6:158

6.4.8

Oily-soil Detergency ........................................

6:164

6.4.9

Measurement of Detergency ............................

6:168

6.4.10

Fabric Detergency ...........................................

6:169

6.4.11

Hard-surface Detergency .................................

6:170

6.4.12

Detergent Manufacture ....................................

6:173

6.4.13

Analysis ...........................................................

6:176

This page has been reformatted by Knovel to provide easier navigation.

xliv

6.5

6.6

6.7

Contents 6.4.14

Health and Safety Factors ...............................

6:176

6.4.15

Environmental Considerations .........................

6:179

References ....................................................................

6:181

General References .......................................................

6:187

Glycerine ..............................................................................

6:191

6.5.1

Introduction .....................................................

6:191

6.5.2

Processing Principals and Details ....................

6:194

6.5.3

Processing Plants ............................................

6:212

6.5.4

Properties of Glyceine .....................................

6:215

6.5.5

Quality and Testing ..........................................

6:216

6.5.6

Processing Losses ..........................................

6:218

6.5.7

Waste Management ........................................

6:219

6.5.8

Uses, Applications, and Economics .................

6:219

6.5.9

Future Considerations .....................................

6:221

References ....................................................................

6:221

Vegetable Oils as Biodiesel .................................................

6:223

6.6.1

Introduction .....................................................

6:223

6.6.2

Biodiesel Quality ..............................................

6:224

6.6.3

Biodiesel and Diesel Emissions .......................

6:230

6.6.4

Resources for Biodiesel Production .................

6:233

6.6.5

Production Technology ....................................

6:234

6.6.6

Utilization Technology .....................................

6:246

6.6.7

Coproduct Use ................................................

6:251

6.6.8

The Future .......................................................

6:252

References ....................................................................

6:252

Vegetable Oils as Lubricants, Hydraulic Fluids, and Inks .......................................................................................

6:259

6.7.1

Introduction .....................................................

6:259

6.7.2

Vegetable Oil Structure and Composition ........

6:260

6.7.3

Oxidative Stability ............................................

6:261

6.7.4

Low-temperature Properties ............................

6:269

This page has been reformatted by Knovel to provide easier navigation.

Contents 6.7.5

Viscosities, Pour Points, and Oxidative Degradation Tendencies of Major Lubricant Basestocks ......................................................

6:272

Effect of Diluent and Additives on Lowtemperature Properties ....................................

6:274

Conclusions .....................................................

6:275

References ....................................................................

6:276

Vegetable Oils in Production of Polymers and Plastics ......

6:279

6.8.1

Introduction .....................................................

6:279

6.8.2

Polymers from Renewable Resources .............

6:280

6.8.3

Exploitation of the Functional Groups on Triglycerol Molecules for the Production of Polymers .........................................................

6:289

Use of Naturally Functionalized Triacylglycerol Oils in Interpenetrating Polymer Networks ...........................................

6:299

Conclusions .....................................................

6:303

References ....................................................................

6:303

Paints, Varnishes, and Related Products ............................

6:307

6.7.6 6.7.7 6.8

6.8.4

6.8.5 6.9

xlv

6.9.1

Relationship of Fats and Oils to the Paintcoating Industry ...............................................

6:307

A Brief Overview of the Coatings Technology ......................................................

6:309

Film Drying Process of Oil-based Coating Materials ..........................................................

6:314

6.9.4

Oleoresinous Varnishes ...................................

6:318

6.9.5

Alkyd Resins ....................................................

6:319

6.9.6

Safety and Environmental Precautions ............

6:343

6.9.7

Modification of Alkyd Resins by Blending with Other Polymers ........................................

6:343

6.9.8

Economic Aspects ...........................................

6:348

6.9.9

Future Prospects .............................................

6:349

6.9.2 6.9.3

This page has been reformatted by Knovel to provide easier navigation.

xlvi

Contents References ....................................................................

6:349

6.10 Leather and Textile Uses of Fats and Oils ..........................

6:353

6.10.1

General Use of Fats and Oils in Leather ..........

6:353

6.10.2

Softening of Leather ........................................

6:354

6.10.3

Softening with Fatliquor ...................................

6:355

6.10.4

Other Softening Materials ................................

6:358

6.10.5

Evaluating Effects of Fat in Leather .................

6:359

6.10.6

General Use of Fats and Oil for Textiles ..........

6:359

6.10.7

Common Textile Fibers ....................................

6:360

6.10.8

Processing of Fibers ........................................

6:360

6.10.9

Physical Effects of Oils and Fats on Fibers and Yarns ........................................................

6:362

6.10.10 Oils and Fats in Textile Processing ..................

6:365

6.10.11 Concluding Remarks .......................................

6:367

References ....................................................................

6:367

6.11 Edible Films and Coatings from Soybean and Other Protein Sources ....................................................................

6:371

6.11.1

Edible Films and Coatings ...............................

6:371

6.11.2

Protein Films ...................................................

6:374

References ....................................................................

6:388

6.12 Pharmaceutical and Cosmetic Use of Lipids .......................

6:391

6.12.1

Introduction .....................................................

6:391

6.12.2

Lipids in Disease Prevention and Treatment ....

6:393

6.12.3

Lipids in Drug Delivery .....................................

6:396

6.12.4

Lipids in Cosmetic Applications .......................

6:400

6.12.5

Processing Oils for Pharmaceutical and Cosmetics Applications ...................................

6:404

References ....................................................................

6:408

Index ..................................................................................

I:1

This page has been reformatted by Knovel to provide easier navigation.

BAILEY’S INDUSTRIAL OIL AND FAT PRODUCTS Sixth Edition Volume 1 Edible Oil and Fat Products: Chemistry, Properties, and Health Effects Edited by

Fereidoon Shahidi Memorial University of Newfoundland

Bailey’s Industrial Oil and Fat Products is available online at http://www.mrw.interscience.wiley.com/biofp

A John Wiley & Sons, Inc., Publication

1 Chemistry of Fatty Acids Charlie Scrimgeour Scottish Crop Research Institute Dundee, Scotland

1. INTRODUCTION Fatty acids, esterified to glycerol, are the main constituents of oils and fats. The industrial exploitation of oils and fats, both for food and oleochemical products, is based on chemical modification of both the carboxyl and unsaturated groups present in fatty acids. Although the most reactive sites in fatty acids are the carboxyl group and double bonds, methylenes adjacent to them are activated, increasing their reactivity. Only rarely do saturated chains show reactivity. Carboxyl groups and unsaturated centers usually react independently, but when in close proximity, both may react through neighboring group participation. In enzymatic reactions, the reactivity of the carboxyl group can be influenced by the presence of a nearby double bond. The industrial chemistry of oils and fats is a mature technology, with decades of experience and refinement behind current practices. It is not, however, static. Environmental pressures demand cleaner processes, and there is a market for new products. Current developments are in three areas: ‘‘green’’ chemistry, using cleaner processes, less energy, and renewable resources; enzyme catalyzed reactions, used both as environmentally friendly processes and to produce tailor-made products; and novel chemistry to functionalize the carbon chain, leading to new

Bailey’s Industrial Oil and Fat Products, Sixth Edition, Six Volume Set. Edited by Fereidoon Shahidi. Copyright # 2005 John Wiley & Sons, Inc.

1

2

CHEMISTRY OF FATTY ACIDS

compounds. Changing perceptions of what is nutritionally desirable in fat-based products also drives changing technology; interesterification is more widely used and may replace partial hydrogenation in the formulation of some modified fats. The coverage in this chapter is necessarily selective, focusing on aspects of fatty acid and lipid chemistry relevant to the analysis and industrial exploitation of oils and fats. The emphasis is on fatty acids and acylglycerols found in commodity oils and the reactions used in the food and oleochemical industries. The practical application of this chemistry is dealt with in detail in other chapters. Current areas of research, either to improve existing processes or to develop new ones, are also covered, a common theme being the use of chemical and enzyme catalysts. Compounds of second-row transition metals rhodium and ruthenium and the oxides of rhenium and tungsten have attracted particular interest as catalysts for diverse reactions at double bonds. Recent interest in developing novel compounds by functionalizing the fatty acid chain is also mentioned. To date, few of these developments have found industrial use, but they suggest where future developments are likely. A number of recent reviews and books cover and expand on topics discussed here (1–10).

2. COMPOSITION AND STRUCTURE 2.1. Fatty Acids Fatty acids are almost entirely straight chain aliphatic carboxylic acids. The broadest definition includes all chain lengths, but most natural fatty acids are C4 to C22, with C18 most common. Naturally occurring fatty acids share a common biosynthesis. The chain is built from two carbon units, and cis double bonds are inserted by desaturase enzymes at specific positions relative to the carboxyl group. This results in even-chain-length fatty acids with a characteristic pattern of methylene interrupted cis double bonds. A large number of fatty acids varying in chain length and unsaturation result from this pathway. Systematic names for fatty acids are too cumbersome for general use, and shorter alternatives are widely used. Two numbers separated by a colon give, respectively, the chain length and number of double bonds: octadecenoic acid with 18 carbons and 1 double bond is therefore 18:1. The position of double bonds is indicated in a number of ways: explicitly, defining the position and configuration; or locating double bonds relative to the methyl or carboxyl ends of the chain. Double-bond position relative to the methyl end is shown as n-x or ox, where x is the number of carbons from the methyl end. The n-system is now preferred, but both are widely used. The position of the first double bond from the carboxyl end is designated
x. Common names (Table 1) may be historical, often conveying no structural information, or abbreviations of systematic names. Alternative repre-

COMPOSITION AND STRUCTURE

3

TABLE 1. Fatty Acids in Commodity Oils and Fats. (a) Nomenclature and Structure. Fatty acid

Common name

4:0 6:0 8:0 10:0 12:0 14:0 16:0 18:0 18:1 9c 18:2 9c12c 18:3 9c12c15c 22:1 13c 20:5 5c 8c11c14c17c 22:6 4c7c10c13c16c19c

butyric caproic caprylic capric lauric myristic palmitic stearic oleic linoleic a-linolenic erucic EPA DHA



Formula

Chain length

CH3(CH2)2CO2H CH3(CH2)4CO2H CH3(CH2)6CO2H CH3(CH2)8CO2H CH3(CH2)10CO2H CH3(CH2)12CO2H CH3(CH2)14CO2H CH3(CH2)16CO2H CH3(CH2)7CH
CH(CH2)7CO2H CH3(CH2)4(CH
CHCH2)2(CH2)6CO2H CH3CH2(CH
CHCH2)3(CH2)6CO2H CH3(CH2)7CH
CH(CH2)11CO2H CH3CH2(CH
CHCH2)5(CH2)2CO2H CH3CH2(CH
CHCH2)6CH2CO2H

short short short/medium medium medium medium

long long long

Abbreviations of the systematic names eicosapentaenoic acid and docosahexaenoic acid.

sentations of linoleic acid (1) are 9Z,12Z-octadecadienoic acid; 18:2 9c12c; 18:2
CHCH2CH

CH(CH2)7COOH. n-6; 18:2 o6; 18:2
9,12; or CH3(CH2)4CH
18 12

COOH 1

9 1

The terms cis and trans, abbreviated c and t, are used widely for double-bond geometry; as with only two substituents, there is no ambiguity that requires the systematic Z/E convention. An expansive discussion of fatty acid and lipid nomenclature and structure appears in Akoh and Min (1). TABLE 1. (b) Occurrence. Fatty Acid

Significant Sources

4:0 6:0 8:0 10:0 12:0 14:0 16:0 18:0 18:1 9c 18:2 9c12c 18:3 9c12c15c 20:1 13c 20:5 5c8c11c14c17c 22:6 4c7c10c13c16c19c

butter, dairy fats (coconut, palm kernel) (coconut, palm kernel) (coconut, palm kernel) coconut, palm kernel coconut, palm kernel cottonseed, palm cocoa butter, tallow cottonseed, olive, palm, rape corn, sesame, soybean, sunflower linseed high erucic rape fish and animal fats fish and animal fats

4

CHEMISTRY OF FATTY ACIDS

Over 1000 fatty acids are known, but 20 or less are encountered in significant amounts in the oils and fats of commercial importance (Table 1). The most common acids are C16 and C18. Below this range, they are characterized as short or medium chain and above it as long-chain acids. Fatty acids with trans or non-methylene-interrupted unsaturation occur naturally or are formed during processing; for example, vaccenic acid (18:1 11t) and the conjugated linoleic acid (CLA) rumenic acid (18:2 9t11c) are found in dairy fats. Hydroxy, epoxy, cyclopropane, cyclopropene acetylenic, and methyl branched fatty acids are known, but only ricinoleic acid (12(R)-hydroxy-9Z-octadecenoic acid) (2) from castor oil is used for oleochemical production. Oils containing vernolic acid (12(S),13(R)-epoxy-9Z-octadecenoic acid) (3) have potential for industrial use. OH COOH 2 H

O

H COOH 3

Typical fatty acid composition of the most widely traded commodity oils is shown in Table 2. TABLE 2. Fatty Acid Content of the Major Commodity Oils (wt%). 16:0 (wt%)

18:1 (wt%)

18:2 18:3 (wt%) (wt%)

butter

28

14

1

1

castor coconut corn cottonseed fish

1 9 13 24 14

3 6 31 19 22

4 2 52 53 1

1

groundnut (peanut) lard linseed olive palm palm kernel rape sesame soybean sunflower tallow

13

37

41

27 6 10 44 9 4 9 11 6 26

44 17 78 40 15 56 38 22 18 31

11 14 7 10 2 26 45 53 69 2

Other [Fatty Acid (wt%)] 4:0 (9); 6:0–12:0 (18); 14:0 (14) þ odd chain and trans 18:1(OH) (90) 8:0 (8); 10:0 (7); 12:0 (48); 14:0 (18)

16:1 n-7 (12); 20:1 n-9 (12); 22:1 n-11 (11); 20:5 n-3 (7); 22:6 n-3 (7) C20–C24 (7) 1 60

14:0 (2) 18:0 (11) þ long and odd chain

8:0 (3); 10:0 (4); 12:0 (49); 14:0 (16) 10 18:0 (6) 8 18:0 (6) 14:0 (6) 18:0 (31) þ long and odd chain

Typical midrange values shown; the balance are minor components. Data from (9).  Cod liver oil.  Low-erucic-acid rape, e.g., Canola.

COMPOSITION AND STRUCTURE

5

Most commodity oils contain fatty acids with chain lengths between C16 and C22, with C18 fatty acids dominating in most plant oils. Palm kernel and coconut, sources of medium-chain fatty acids, are referred to as lauric oils. Animal fats have a wider range of chain length, and high erucic varieties of rape are rich in this C22 monoene acid. Potential new oil crops with unusual unsaturation or additional functionality are under development. Compilations of the fatty acid composition of oils and fats (6, 9, 11, 12) and less-common fatty acids (13) are available. The basic structure, a hydrophobic hydrocarbon chain with a hydrophilic polar group at one end, endows fatty acids and their derivatives with distinctive properties, reflected in both their food and industrial use. Saturated fatty acids have a straight hydrocarbon chain. A trans-double bond is accommodated with little change in shape, but a cis bond introduces a pronounced bend in the chain (Fig. 1). In the solid phase, fatty acids and related compounds pack with the hydrocarbon chains aligned and, usually, the polar groups together. The details of the packing, such as the unit cell angles and head-to-tail or head-to-head arrangement depend on the fatty acid structure (Fig. 2). The melting point increases with chain length and decreases with increased unsaturation (Table 3). Among saturated acids, odd chain acids are lower melting than adjacent even chain acids. The presence of cis-double bonds markedly lowers the melting point, the bent chains packing less well. Trans-acids have melting points much closer to those of the corresponding saturates. Polymorphism results in two or more solid phases with different melting points. Methyl esters are lower melting than fatty acids but follow similar trends. Fatty acid salts and many polar derivatives of fatty acids are amphiphilic, possessing both hydrophobic and hydrophilic areas within the one molecule. These are surface-active compounds that form monolayers at water/air and water/surface interfaces and micelles in solution. Their surface-active properties are highly dependent on the nature of the polar head group and, to a lesser extent, on the length of the alkyl chain. Most oleochemical processes are modifications of the carboxyl group to produce specific surfactants.

TABLE 3. Melting Points of Some Fatty Acids and Methyl Esters Illustrating the Effect of Chain Length and Unsaturation. Fatty acid

Melting Point ( C)

16:0 17:0 18:0 18:1 9c 18:2 9c12c 19:0 20:0

62.9 (30.7) 61.3 (29.7) 70.1 (37.8) 16.3, 13.4
5 69.4 (38.5) 76.1 (46.4)

Values for methyl esters in parenthesis. Data from (8) and (9).

Fatty Acid

18:1 9t 18:2 9t12t

Melting Point ( C)

45 29

6

CHEMISTRY OF FATTY ACIDS

Figure 1. ‘‘Ball and stick’’ models of (a) stearic acid, 18:0; (b) elaidic acid, 18:1 9t; and (c) oleic acid 18:1 9c. All three lie flat in the plane of the paper. The cis double bond causes a distinct kink in the alkyl chain of oleic acid.

2.2. Acylglycerols Fatty acids in oils and fats are found esterified to glycerol. Glycerol (1,2,3-trihydroxypropane) is a prochiral molecule. It has a plane of symmetry, but if the primary hydroxyls are esterified to different groups, the resulting molecule is chiral and exists as two enantiomers. The stereospecific numbering system is used to

Figure 2. Simplified diagram shows packing patterns of fatty acids in the solid phase. (a) and (b): Hydrocarbon tails (straight lines) aligned at different angles to the line of the polar head groups (circles). (c): Head to tail packing. (d): Head to head packing.

COMPOSITION AND STRUCTURE

CH2OH sn-1 (α) HO

H

R′COO

sn-2 (β)

L O

triacylglycerol

CH2OOCR

CH2OH

H

RCOO

CH2OH

H CH2OH

1-monoacyl-sn-glycerol (1-MAG)

2-monoacyl-sn-glycerol (2-MAG)

CH2OOCR R′COO

H

e.g.

CH2OOCR′′

stereospecific numbering of glycerol backbone

HO

P

CH2OOCR

CH2OH sn-3 (α) or (α′)

7

CH2OOCR

H

HO

CH2OH

H CH2OOCR′

1,2-diacyl-sn-glycerol (1,2-DAG)

1,3-diacyl-sn-glycerol (1,3-DAG) CH2OOCR

R′COO

H

O

CH2O P OX O phosphatidylcholine X = CH2CH2N+(CH3)3 phosphatidylethanolamine X = CH2CH2N+H3 Figure 3. Structure and stereospecific numbering of acylglycerols.

distinguish between enantiomers. The Fischer projection of glycerol is drawn with the backbone bonds going into the paper and the hydroxyl on the middle carbon to the left. The carbons are then numbered 1 to 3 from the top (Figure 3). The prefix sn- (for stereospecific numbering) denotes a particular enantiomer, rac- an equal mixture of enantiomers, and x- an unknown stereochemistry. In an asymmetric environment such as an enzyme binding site, the sn-1 and sn-3 groups are not interchangeable and reaction will only occur at one position. Simplified structures are often used; e.g., 1-palmitoyl-2-linoleoyl-3-oleoyl-sn-glycerol is abbreviated to PLO or drawn as shown in Figure 3. Storage fats (seed oils and animal adipose tissue) consist chiefly (98%) of triacylglycerols, with the fatty acids distributed among different molecular species. With only two fatty acids, a total of eight triacylglycerol isomers are possible, including enantiomers (Table 4). A full analysis of triacylglycerol molecular species is a major undertaking, and for some oils, there are still technical difficulties to be resolved. More commonly, triacylglycerols are distinguished by carbon number (the sum of the fatty acid chain lengths) or unsaturation, using GC or HPLC for analysis. The number of isomers increases as the cube of the number of fatty acids;

8

CHEMISTRY OF FATTY ACIDS

TABLE 4. Molecular Species of Triacylglycerols Containing only Palmitic and Oleic Acid.

enantiomers carbon number double bonds

PPP

POP

PPO

OPP

POO

OOP

OPO

OOO

48 0

50 1

* 50 1

* 50 1

** 52 2

** 52 2

52 2

54 3

Different methods of analysis will give different and often incomplete information about such a mixture. GC analysis will separate molecular species by carbon number (sum of fatty acid chain lengths). Silver-ion HPLC will separate by number of double bonds. Stereospecific analysis measures the proportions of fatty acids at the sn-1, sn-2, and sn-3 positions, but it does not detect individual molecular species.

hence, even in oils with a simple fatty acid composition, many molecular species of triacylglycerol may be present. Most natural triacylglycerols do not have a random distribution of fatty acids on the glycerol backbone. In plant oils, unsaturated acids predominate at the sn-2 position, with more saturated acids at sn-1 and sn-3. The distribution of fatty acids at the sn-1 and sn-3 positions is often similar, although not identical. However, a random distribution between these two positions is often assumed as full stereospecific analysis is a time-consuming specialist procedure. In animal fats, the type of fatty acid predominating at the sn-2 position is more variable; for example, palmitate may be selectively incorporated as well as unsaturated acids (Table 5). Only oils that are rich in one fatty acid contain much monoacid triacylglycerol, for example, olive (Table 5), sunflower, and linseed oils containing OOO, LLL, and LnLnLn, respectively. Compilations of the triacylglycerol composition of commodity and other oils are available (8, 9). The melting behavior of triacylglycerols generally reflects that expected from the fatty acid composition; triacylglycerols rich in long-chain and saturated acids

TABLE 5. Contrasting Triacylglycerol Composition of Some Commodity Oils [Molecular Species (wt%)]. Cocoa butter

Coconut

POP (18-23) POSt (36-41) StOSt (23-31)

12,12,8 (12) 12,12,10 (6) 12,12,12 (11) 12,12,14 (11) 14,12,8 (9)

unsymmetrical e.g., SSO 70 PDI and preferably >90 PDI) is the preferred starting material in manufacturing soy protein isolates. Under some conditions, extruded-expelled meal can be used, but the yield of soy isolate is reduced. The meal is ground in water adjusted to pH 8.0 with sodium hydroxide and centrifuged to remove insoluble fiber. The soluble fraction is acidified to pH 4.5, and the protein precipitates. The precipitated protein curd is separated from the soluble sugars by centrifuging. The protein curd may be washed, neutralized, and spray-dried. High protein solubility is not needed for protein concentrates and heating to insolubilize the protein and facilitate extracting the solubles (mostly sugars) with water is one way that has been used to prepare soy protein concentrates. Concentrates today, however, are normally made by extracting the sugars with either acid (pH 4.5) or aqueous ethanol (60–80%). Aqueous ethanol is most frequently used because it produces the blandest product, but ethanol denatures the protein and leaves the protein with reduced functional properties unless the product is refunctionalized by jet cooking (154, 155) or by homogenizing under alkaline conditions (156). Soy protein concentrate must contain >65% protein on a dry basis. The soybean storage proteins glycinin and b-conglycinin, which often are recognized in the older literature as 11S and 7S proteins, respectively, based on their sedimentation during ultra centrifuging, comprise 65–80% of the protein. Methods have even been developed to separate soy protein into fractions rich in individual proteins (157, 158). Some believe b-conglycinin has greater health benefits than glycinin. Soy protein isolates are used in dairy analogs (milk replacers and beverage powders), meat-pumping solutions, luncheon meats, and infant formulas, whereas soy protein concentrates are used in dairy analogs (milk replacers, beverage powders, cheeses, coffee whiteners, frozen desserts, whipped toppings), baked goods, and meat products (156). These protein products are used for their functional properties such as solubility, water absorption and binding, viscosity control, gelation,

604

SOYBEAN OIL

cohesion-adhesion, elasticity, emulsification, fat absorption and binding, foaming, and color control. The solubility and thermal properties of these products were recently compared by Lee et al. (159). Some products have high solubility even though they were largely denatured. Many health benefits have been attributed to soy protein products, either because of the proteins or accompanying phytochemicals, such as isoflavones, saponins, etc. There is a growing body of evidence that soy protein products may impact hypertension and heart disease, osteoporosis and bone health, and certain cancers. The perception of such nutritional benefits is driving an increased interest by food companies in the incorporation of soy protein products. In October 1999, the U.S. Food and Drug Administration (FDA) authorized a health claim for soy protein in cardiovascular disease. U.S. food labeling laws now permit a statement on the label that ‘‘Diets low in saturated fat and cholesterol that include 25 grams of soy protein a day may reduce the risk of heart disease. One serving of (name of food) provides (list number) grams of soy protein.’’ The health claim allowance is reported in the Federal Register (160) and is posted on the FDA website (161).

8. BASIC PROCESSING OPERATIONS As discussed in the previous section on soybean oil composition and Table 11, crude soybean oil can contain phospholipids, free fatty acids, lipid oxidation products, and unsaponificable matter, which includes chlorophyll and carotenoid pigments, tocopherols, sterols, and hydrocarbons. Some of these components negatively affect oil quality, and some may play positive roles in nutrition and functionality. The goal of oil refining is to remove the undesirable components so that a bland, stable, and nutritious product can be obtained. The basic processing operations in oil refining are (1) degumming, (2) neutralization, (3) bleaching, (4) hydrogenation, (5) deodorization, and (6) winterization or crystallization. These steps are outlined in a flow chart as shown in Figure 9. 8.1. Degumming Crude soybean oil contains a relatively high concentration of phospholipids compared with other vegetable oils. Degumming is a process of removing these components from crude soybean oil to improve its physical stability and facilitate further refining. Phospholipids can lead to dark-colored oils and they can also serve as precursors of off-flavor (162) compounds. Free fatty acids, pigments, and other impurities are also partially removed by degumming. Soybean oil can also be neutralized directly without degumming if gum or lecithin recovery is not desired. Conventional belief holds that the loss of neutral oil in refining crude oil by direct neutralization is less than the combined losses of degumming and caustic refining of the degummed oil. The quality of crude soybean oil influences the efficacy of degumming. Phospholipids can exist in a hydratable form, which can be readily removed by addition

BASIC PROCESSING OPERATIONS

605

Crude Soybean Oil Water FILTERING

Foots GUMS HYDRATING

Alkali

NEUTRALIZING CENTRIFUGING

Water

VACUUM DRYING

GUMS DRYING

Moisture

Lecithin Wash-water (residual soapstock) Moisture

BLEACHING FILTERING

Steam

Soapstock (free fatty acids, phosphatides)

WASHING CENTRIFUGING

Bleaching Earth

CENTRIFUGING

DEODORIZING POLISH FILTERING

Spent Bleaching Earth (color, residual soapstock) DISTILLATE CONDENSING Deodorizer Distillate (off-flavor compounds, minor volatiles, free fatty acids)

Salad & Cooking Oils

Figure 9. Diagram of conventional soybean oil refining.

of water, or in a nonhydratable form, which cannot be easily hydrated and removed. The nonhydratable phospholipids are considered to be the calcium and magnesium salts of phosphatidic acids, which are formed by enzymatic hydrolysis of the original phospholipids. This degradation can result from seed damage during storage and improper handling. List et al. (53) studied the factors promoting the formation of nonhydratable phospholipids in soybeans and showed that they are promoted by four interrelated factors: (1) moisture content of beans or flakes, (2) phospholipase D activity, (3) heat applied to beans or flakes prior to and during extraction, and (4) disruption of the cellular structure by cracking or flaking. These results suggest that a nonhydratable-phosphatide formation can be minimized by control of the moisture of beans or flakes entering the extraction process, inactivation of phospholipase D, and optimizing the temperature during conditioning of cracked beans or flakes. Normal quality soybean oil from the conventional solvent extraction contains about 90% hydratable and 10% nonhydratable phospholipids. Phosphoric or citric acid can be used as a pretreatment to achieve more complete removal of nonhydratable phospholipids, but their presence in the gum will darken it and reduce its quality. The total phospholipid content in crude soybean oils ranges from 1.85% to 2.75% (19) and partially depends on the seed preparation and extraction methods employed. Use of an expander or the Alcon process to cook the flakes prior to extraction will increase total phospholipids content in the crude oil and the phosphatidylcholine percentage in the gum (163).

606

SOYBEAN OIL

Degumming can be achieved in a batch or continuous fashion. In batch degumming, soft water at the same percentage as total phospholipid is added to oil heated to 70 C and mixed thoroughly for 30–60 min, followed by settling or centrifuging. In continuous water degumming, heated oil is mixed with water by an in-line proportioning and mixing system and the mixture is held in a retention vessel for 15–30 min before centrifugation. The phosphorus content is typically lowered to 12–170 ppm (164). A well-degummed soybean oil should contain less than 50 ppm of phosphorus, which is well below the 200 ppm level specified in the National Oilseed Processors Association (165) trading rules for crude degummed soybean oil. Degumming for physical refining, as opposed to alkali refining of soybean oil, requires more complete removal of the phospholipids to prevent darkening during fatty acid distillation. For more complete phospholipid removal, several modified degumming methods can be employed (166, 167). Recently, polymeric ultrafiltration membranes were used for degumming crude soybean oil and removing phospholipids from the crude oil/hexane miscella (168). Crude soybean oil also can be de-acidified by methanol extraction of the free fatty acids and the extract separated into fatty acids and solvent by a membrane filter (169). A surfactant-aided membrane degumming also has been applied to crude soybean oil, and the degummed oil contained 20–58 ppm of phosphorus (170). Supercritical carbon dioxide extraction was shown to be an effective means of degumming (171). In this process, soybean oil countercurrently contacted supercritical carbon dioxide at 55 MPa and 75 C. The phosphorus content of the oil was reduced from 620 ppm to less than 5 ppm. Ultrasonic degumming was also successfully used to reduce the gum content of soybean oil (172). 8.2. Neutralization Neutralization is also referred to as de-acidification and alkali or caustic refining. Neutralization is achieved by treating the soybean oil with aqueous alkaline solution (most commonly, sodium hydroxide) to neutralize the free fatty acids in a batch or continuous system. The soap formed in the reaction also adsorbs natural pigments, the gum and mucilaginous substances not removed by degumming. Natural settling or centrifugation is used to remove the soap. Crude soybean oil also can be netralized directly without degumming. When this is practiced, the oil commonly is pretreated with 300–1000 ppm of 75% phosphoric acid to facilitate removal of phospholipids. The percentage of excess sodium hydroxide solution required for crude oil is higher than that for degummed oil (173). The quality changes, such as lipid oxidation and reduction of tocopherols and phytosteols during neutralization, are considerable compared with the other processing steps as shown by Wang and Johnson (174), and also as presented in Table 12. The further phospholipid removal (below 2 ppm phosphorus) also reduces the oxidative stability of soybean oil (175) due to the antioxidant property of these phospholipids. One of the new developments in neutralization is the use of silica-based adsorbent to remove the residual soap instead of using water washing. Water usage and

BASIC PROCESSING OPERATIONS

607

TABLE 12. Effect of processing on content of tocopherols, sterols, and squalene in soybean oil (25). Processing Step

Tocopherols —————————— ppm % Loss

Crude Degummed Neutralized Bleached Deodorized

1132 1116 997 863 726

— 1.4 11.9 23.8 35.9

Sterols —————————— Ppm % Loss 3870 3730 3010 3050 2620

— 3.6 22.2 21.2 32.3

Squalene ————————— ppm % Loss 143 142 140 137 89

— 0.7 2.1 4.2 37.8

waste generation is greatly reduced by this practice. Sodium silicate also was used as a mild neutralizing agent to refine specialty oils (176). Its agglomerating tendency allowed the removal of the soap by filtration, and its low alkalinity minimized saponification of neutral oil and loss of minor nutrients. Other adsorbents, such as magnesium silicate, also were shown to be effective in reducing free fatty acids, as well as reducing primary and secondary oxidation products in the treated oil (175, 177). Physical refining or steam refining is a process similar to steam deodorization. Steam distillation is typically used for oil with a high free-fatty acid content to reduce the refining loss, which would be significant if caustic refining was used. Acid-aided degumming produces soybean oil with very low phosphorus content and makes the distillation of free fatty acids possible. Nevertheless, the relatively difficult task of removing sufficient phospholipids from soybean oil has prevented extensive use of this technique in the United States. Physical refining, however, has virtually replaced caustic refining of palm oil in Malaysia. 8.3. Bleaching Bleaching is a process designed not only to remove the oxidation-inducing pigments such as chlorophylls, but more importantly to decompose the peroxides produced by oxidation into lower molecular weight carbonyl compounds that can be removed by subsequent deodorization. Bleaching also removes other impurities such as soap and metal ions. In soybean oil refining, color reduction occurs at each step, nevertheless, the most significant reduction of chlorophylls occurs in the bleaching step. Acid-activated bleaching clay is most effective in adsorbing chlorophylls and decomposing peroxides, and it is commonly used for soybean oil. The chlorophyll content in normal crude soybean oil (1–1.5 ppm) can be reduced by 25% by alkali refining, and bleaching with acid earth further reduced chlorophylls to 15 ppb (178) The subsequent hydrogenation and deodorization remove or degrade red and yellow pigments more than chlorophyll, so incomplete chlorophyll removal by bleaching will cause the refined oil to appear greenish. The refined and bleached oil is particularly susceptible to oxidation and is less stable than the crude, degummed, refined, or deodorized oils (178).

608

SOYBEAN OIL

The desired bleaching endpoint is typically zero peroxide, although a color specification is often used as an important measure. The amount of bleaching earth should be adjusted based on the quality of oil to be bleached, and it usually ranges from 0.3% to 0.6% for a typical soybean oil. Low contents of phosphorus (5–10 ppm P) and soap (10–30 ppm) in the neutralized oil are essential to maximize the bleaching effect. Successful bleaching can be achieved by atmospheric batch bleaching, vacuum batch bleaching, or continuous vacuum bleaching at temperatures between 100 C and 120 C for 20–30 min. More details of soybean oil bleaching are described by Erickson (179). Recently, silica-based synthetic materials have been used in bleaching. The natural bleaching earth, fuller’s earth, a hydrated aluminum silicate, mostly has been replaced by acid activated clays, which are sulfuric- or hydrochloric-acid-treated bentonites or montmorillonites. Manufacturers continuously improve the quality and develop new bleaching earths to meet the market’s needs. Higher activity and filterability are the main focuses of such development. 8.4. Hydrogenation The high degree of unsaturation, particularly the relatively high content of linolenate, of soybean oil significantly limits its food applications because of low oxidative stability. Hydrogenation is used to improve oxidative stability as well as to increase the melting temperature of soybean oil. A great proportion of soybean oil is hydrogenated to produce cooking oil, bakery/confectionery fats, and shortening. When oil is treated with hydrogen gas in the presence of a catalyst (typically nickel) and under appropriate agitation and temperature conditions, it becomes more saturated and forms a semisolid or plastic fat that is suitable for many food applications. Selectivity is a term used to describe the relative reaction rate of the fatty acids from the more unsaturated to the more saturated forms. Perfect selectivity would provide sequential elimination of linolenate, linoleate, and then oleate. To completely hydrogenate linolenate while minimizing changes in the other acyl groups, a high ratio of the reaction rates of linolenate to linoleate compared with linoleate to oleate is desirable. Generally, selectivity increases with temperature and catalyst concentration and with decreases in hydrogen pressure and agitation rate (180). The effect of pressure on hydrogenation selectivity of soybean oil was reported by List et al. (181), who found that the linoleate-containing triacylglycerols were reduced at a slower rates than the linolenate-containing triacylglycerols under selective condition. At higher pressures (500 psi), the reaction was truly nonselective; whereas at 50 psi, the reaction became selective. Impurities in soybean oil, such as phosphorus, oxidation products, carotene, and metal ions can poison the catalyst and cause slower hydrogenation (182). A particular limitation with nickel catalyst is its low selectivity for linolenate over linoleate, and copper-containing catalysts have greater selectivity for linolenate acid than the conventional nickel catalysts (183). The use of copper catalyst can produce soybean oil that has a low degree of hydrogenation (iodine value of 110–115) but has less than

BASIC PROCESSING OPERATIONS

609

1% linolenate. However, copper catalysts are not as active as nickel catalysts; they are also easily poisoned (184). Furthermore, any trace of residual copper in the fully processed oil will promote lipid oxidation. The most common tests for degree of hydrogenation are congeal point and the iodine value as determined by refractive index. Refractive index is a valuable tool for iodine values above 95, but when the oil is further hydrogenated, refractive index becomes an inadequate measurement for melting prediction because increased amount of trans-isomers results in harder oil than the refractive index would indicate (185). For margarine or shortening, the solid fat index (SFI), as determined by dilatometry, or solid fat content (SFC), determined by nuclear magnetic resonance, is the most appropriate method to measure the consistency of the hydrogenated oil. These indices predict the workability and creaming ability at a particular temperature. Double-bond isomerization or trans-fatty acid formation is the most important side-reaction that occurs during hydrogenation, and it has a strong impact on the physical and possibly the nutritional properties of the products. Trans-double bonds are thermodynamically a more favorable configuration than their cis-counterpart; so trans-bonds are produced in significant quantities if the hydrogenation does not go to completion. The trans-fatty acids have a much higher melting point than their cis-isomers, therefore a fat product with considerable trans-acyl groups will have an elevated melting point, which is desirable in shortening and margarine applications. A partially hydrogenated soybean oil can have at least 30 different one-, two-, and three-double-bond isomers that will result in more than 4000 different triacylglycerol molecules. This complexity allows the production of a great variety of oils, margarines, and shortenings that have a wide range of physical and functional properties. However, the established relationship between trans-fat consumption and health has prompted research to minimize trans-double formation in fats and oils. Hydrogenation of soybean oil may be carried out in a batch or a continuous system. In the United States, batch operations are typical. More comprehensive reviews on hydrogenation and formulation can be found in Erickson and Erickson (180), Hastert (186), and Kellens (187). 8.5. Deodorization Deodorization is usually the last step in conventional oil processing. It is a steamstripping process in which good quality steam (1–3% of oil) generated from de-aerated and properly treated feed water is injected into soybean oil under high temperature (252–266  C) and high vacuum (10 ppt-TEQ) is commonly detected in fish and fish products. The vapor pressure of PCB can vary within a wide range. The more volatile PCBs have a vapor pressure around 40–75 mbar, which is similar to the vapor pressure of some organo-chlorine pesticides. Our own lab deodorization trials showed that PCBs and dioxins can be stripped from fish oil without degradation of the o-3 fatty acids (eicosapentaenoic acid, EPA, and docosahexaenoic acid, DHA) provided that the deodorization pressure is very low (>2 mbar) (Table 10). Other studies showed that deodorization at 230
C and 5 mbar was insufficient to remove a PCB heat-transfer agent from contaminated rice bran oil (28).

3.5. Deodorizer Distillate Volatile components removed during deodorization are collected in the deodorizer distillate. The overall composition of the deodorizer distillate depends on the

TABLE 10. PCB and Dioxin Stripping from Fish Oil. Fish Oil ————————————– Crude Deodorizeda Dioxins (pptb) Non-ortho PCB (pptb) Mono-ortho PCB (pptb) Free fatty acids (%) EPAc (%) DHAd (%) a

5.3 17.9 7.2 0.66 8.7 12.7

1.8 5.5 1.3 0.11 8.6 12.6

Lab deodorization: 190
C-1 mbar-2% steam; bWHO-TEQ ppt; Eicosapentenoic acid; dDocosahexenoic acid.

c

TABLE 11. Detailed Composition of Deodorizer Distillate Obtained During Chemical or Physical Refining of Different Soft Oils [Concentrations Expressed as % (w/w)]. Soybean Corn Sunflower Seed Rapeseed —————————————————————————————————————————————————————— —— Chemical Physical Physical Chemical Physical Chemical Squalene d-Tocopherol b-Tocopherol g-Tocopherol a-Tocopherol Total tocopherols Brassicasterol Campesterol Stigmasterol b-Sitosterol Other sterols1 Steryl esters Total sterols2 Monoacylglycerols Diacylglycerols Triacylglycerols FFA (as C18:1) 1

1.3–2.1 4.4–5.6 0.4–0.5 10.7–11.3 0.8 16.3–18.2 n.d.3 5.1–5.7 4.1–4.8 7.9–8.3 n.d. 2.3–2.6 19.4–21.4 1.2–1.9 2.7–3.8 5.1–5.9 33

Sum of 5-avenasterol; 7-avenasterol and 5-stigmasterol. Sum of free and esterified sterols. 3 Not detectable. 2

0.6 2.0 n.d. 5.0 0.5 7.5 n.d. 1.9 1.4 3.0 n.d. 4.5 10.8 1.9 8.1 3.8 73.8

0.2–1.0 0.1 0.1 1.1–2.8 0.2–0.4 1.5–3.4 n.d. 0.8–1.7 0.2–0.4 1.7–3.4 n.d. 0.6 3.3–6.1 0.1 0.5–1.3 0.1–0.8 77–81

0.7 n.d. n.d. 0.3 4.8 5.1 n.d. 1.6 2.0 8.6 1.7 0.3 14.2 0.9 1.9 2.6 39.2

1.0 n.d. n.d. 0.1 1.2 1.3 n.d. 0.5 0.6 2.6 0.6 0.1 4.4 n.d. 0.7 2.7 70.8

0.1–0.4 0.2–0.3 0.1–0.2 2.3–2.5 0.9–1.4 3.5–4.4 1.6–2.8 2.9–4.4 n.d. 4.1–6.2 n.d. 1.4–5.3 10.0–18.7 1.4–2.1 3.8–3.9 3.0–7.5 39–42

360

DEODORIZATION

processed oil characteristics, the applied refining mode (chemical or physical refining), the operating conditions during deodorization, and the design of the scrubber. Aside from desired components (fatty acids, tocopherols, sterols, etc.), volatile contaminants (pesticides, light PAH, etc.) will also be concentrated in the deodorizer distillate. Deodorizer distillates from physical refining consist mainly of free fatty acids (>80%) (Table 11) (29). This byproduct can have some value for use in feed products provided that it contains (very) low levels of contaminants. Where a higher degree of contamination exists, it can only be sold as a source of technical-grade fatty acids. Deodorizer distillate flow in physical refining can be 5% or more of the oil flow to the deodorizer, depending on the initial FFA content of the oil. Consequently, the theoretical concentration factor of the volatile contaminants in the deodorizer distillate will be around 20. Knowing that the concentration of light PAH in crude coconut oil can be high, levels of up to 10 ppm can be expected in coconut oil deodorizer distillate (Table 12). Deodorizer distillates obtained during the deodorization of chemical refined soybean oil usually have a significantly higher added value as a result of the high concentration of valuable minor components such as tocopherols and sterols (Table 11). A complex downstream processing of these deodorizer distillates, consisting of a combination of chemical and physical separation processes, finally results in the production of purified tocopherols and sterols. Deodorizer distillate flow is much lower in the case of chemical refining (0.2– 0.5% of the oil flow to the deodorizer). Consequently, contaminant concentration in the distillate can theoretically become 200–500 times higher than in the crude oil. For pesticides, the observed concentration factor is significantly lower, mainly because of thermal decomposition of some pesticides and incomplete condensation of volatile pesticides in the vapor scrubber. The limited amount of data available in the literature, combined with our own research figures, indicate that pesticide concentration in soybean, sunflower seed, and rapeseed deodorizer distillate is usually

TABLE 12. Polycyclic Aromatic Hydrocarbon Content (PAH) of Refined Coconut Oil and the Corresponding Deodorizer Distillate (Data in ppb). PAH Naphtalene Phenantrene Pyrene Benzo(b)fluoranthene Dibenz(a,h)anthracene Benzo(a)pyrene Sum of light PAH Sum of heavy PAH

Refined Coconut Oil 3.3 62.9 48.5 1.5 0.1 0.7 168.9 3.8

Own research data; coconut oil from Southeast Asian origin.

Deodorizer Distillate 1670 10,968 8142 8.9 0.5 1.3 38,690 21.3

REFINED OIL QUALITY

361

below 1 ppm. Only in very exceptional cases, when the degree of contamination in the crude oil is unacceptably high (>1 ppm), the pesticide concentration in the corresponding deodorizer distillate can increase to 50 ppm. Although contaminants can be removed from the deodorizer distillate during the downstream processing, their presence is certainly unwanted and may affect the commercial value of the distillate in a negative way. For this reason, edible oil refiners are becoming more and more interested in (new) technologies that can either remove the contaminants from the deodorizer distillate prior to sales or avoid their presence in (part of) the distillate. The first option seems to be the most straightforward choice because known technology, either adsorption or stripping, can be used. The overall volatility of the contaminants will be higher in the deodorizer distillate as a result of the higher initial concentration (cfr. Law of Raoult). Therefore, contaminants can be removed to a certain extent from the deodorizer distillate by stripping under appropriate processing conditions. Process technology and conditions have to be optimized to maximize the amount of the low-contaminant distillate stream. On the other hand, this process will always result in a certain contaminated residue fraction that has to be considered as a waste stream with no value. Alternatively, improved design of the scrubber (e.g., dual condensation) offers the possibility of collecting two different distillate fractions, one enriched in FFA and the other in unsaponifiable components (sterols, tocopherols, etc.).

3.6. Oil Loss During Deodorization Aside from volatile components (e.g., free fatty acids, secondary oxidation products, tocopherols, sterols, etc.), the deodorizer distillate also contains some neutral oil (tri-, di-, and mono-acylglycerols). With the exception of the more volatile monoacylglycerols, this neutral oil is present mainly as a result of mechanical entrainment by the stripping steam and is therefore considered as a direct refining loss. Neutral oil loss (NOL) mainly depends on the deodorization conditions. In general, NOL increases with higher deodorization temperature, lower pressure, and a larger amount of stripping steam. At the same time, NOL during steam refining is higher than during deodorization. This is because mechanical entrainment causes NOL to be proportional to the distillate flow or the amount of stripping steam, which are both higher in the case of steam refining. Improvement of the deodorizer design by the installation of baffles and demisters in the vapor chimneys has significantly reduced entrainment losses to 0.1–0.2% in chemical refining. For steam refining, an additional loss directly proportional to the FFA content has to be taken into account. For most oils (soybean oil, palm oil, etc.), NOL is exclusively due to mechanical carry-over. However, in lauric oils, part of the NOL is a consequence of effective evaporation of volatile shortchain mono- and diacylglycerols (30). (Table 13). This distillation loss of NOL is inherently due to the deodorization conditions, but is not affected by the deodorizer design.

362

DEODORIZATION

TABLE 13. Melting and Boiling Points of Some Fatty Acids and Glyceridic Components. Component Chain Length

Fatty Acid 3.4 16.7 31.6 44.2 54.4 62.9 69.6 16.3

C6 C8 C10 C12 C14 C16 C18 C18:1 Component Chain Length

Fatty Acid

C6 C8 C10 C12 C14 C16 C18 C18:1

61.7 87.5 110.3 130.2 149.2 167.4 183.6 /

a

Monoacylglycerol Diacylglycerol Melting Point (
C) 19.4 / 53 63 70.5 77 81.5 35.2

25 8.3 31.5 46.4 57.0 63.5 73.1 5.5

/ / 44.5 57.8 66.8 76.3 79.4 21.5

Monoacylglycerol Diacylglycerol Boiling Point (
C) at 1 mm Hg / / 175 186 199 211 190a 186a

Triacylglycerol

Triacylglycerol 0.05 mm Hg

/ / / / / /

135 179 213 244 275 298 313 308b

At 0.2 mm Hg; bolive oil.

Expected NOL can be estimated from the initial and final FFA content of the oil and the FFA content of the deodorizer distillate (FAD) by the following formulas: NOLð%Þ ¼ FAD flow ð100-FFAFAD -UnsapsFAD Þ=100; FADð%Þ ¼ ðFFAOIL IN -FFAOIL OUT Þ=ðFFAFAD -FFAOIL OUT Þ 100:

ð12Þ ð13Þ

In practice, NOL can be slightly higher as a result of hydrolysis of the refined oil during deodorization. Our own research showed that short-chain oils (e.g., coconut oil) are more prone to hydrolysis than long-chain oils (e.g., soybean oil). Hydrolysis during deodorization of coconut oil resulted in the production of 0.01– 0.03% additional FFA (30). 3.7. Handling and Storage of Deodorized Oil Deodorized oils require particular handling and storage conditions to avoid oxidation or other degradation reactions that may affect the quality. Flavor deterioration, in particular, and color reversion, to a lesser extent, may occur if the oil is not properly protected. Saturation of the oil with nitrogen after deodorization and low-temperature storage in stainless steel tanks protect the oil against oxidation when stored in bulk for a longer time. Modern processing plants are usually equipped with an inert gas blanketing system through the different refining stages. All parts in contact

DEODORIZER TECHNOLOGY

363

with the oil are made best of stainless steel (minimum SS 304) to avoid migration of Fe ions into the oil. Furthermore, the storage temperature is best kept as low as possible as the autoxidation rate increases as the temperature rises. For example, the rate of oxidation doubles with each 10
C increase in temperature. It has become common practice to add a small amount of citric acid (20–50 ppm) to the oil after deodorization, because it improves the flavor stability and, at the same time, acts as a metal chelator. Some refiners even add natural antioxidants (e.g., tocopherols), although it seems more logical to prevent the oil from losing too many natural antioxidants during deodorization by using less-severe conditions. In a modern refining operation, end-product storage is minimized. Refined oil is shipped in bulk or bottled as soon as possible. Furthermore, there is an increasing tendency to integrate the refinery with the finishing lines in the crushing plant as this strongly reduces intermediate and final oil storage. Despite careful measures taken during bulk handlling and shipment to industrial customers, a large part of the refined oil is redeodorized prior to its final use. This ‘‘brush’’ deodorization serves to remove small amounts of off-flavors formed during transport and storage. Redeodorization normally requires less-severe process conditions.

4. DEODORIZER TECHNOLOGY Deodorization is a multi-step process comprising de-aeration, heating, deodorization-deacidification, and cooling of the oil (Figure 9).

Figure 9. General overview of the different stages in deodorization.

364

DEODORIZATION

4.1. De-Aeration As a first step, the oil is de-aerated prior to heating in order to avoid excessive oxidation and, hence, risk of polymerization. Information of solubility of gases in oils is rather limited. Vegetable oils readily dissolve between 4% and 10% of their own volume of air and other gases at ambient temperature. All gases, with exception of carbon dioxide, increase in solubility with increasing temperature. The relation between solubility (S) and temperature (t) can be expressed by following linear equations (30): For Nitrogen

SðN2 Þ ¼ ½0:0590 þ 0:000400  t  100;

ð14Þ

For Oxygen

SðO2 Þ ¼ ½0:1157 þ 0:000443  t  100:

ð15Þ

With S: Solubility, gas in oil (% v/v) at atmospheric pressure; t: Temperature (
C). To achieve a proper de-aeration, the bleached oil is sprayed into a vessel under reduced pressure, before entering the heating section. The lower the pressure applied, the lower the residual oxygen level in the oil. Usually, the oil is heated to at least 80
C and sprayed in a tank, which is kept at a pressure below 50 mbar. Some refiners even use the low pressure of the deodorizer or add some sparge steam in the spraying vessel to improve de-aeration. 4.2. Heating and Cooling The subsequent heating of the oil is usually accomplished in two stages. In the first stage, the incoming oil is heated countercurrently in an oil-oil heat exchanger (economizer), with the finished oil leaving the deodorizer. Finally, the oil is heated under reduced pressure to the final deodorization temperature with a high-temperature source. Nowadays, nearly all deodorizers operate with high-pressure steam boilers (Figure 10) (Table 14). Thermal oil heaters were quite commonly used in the past to

Figure 10. High-pressure steam boiler used in deodorization (Geka).

DEODORIZER TECHNOLOGY

365

TABLE 14. Correlation Among Steam Pressure, Temperature, Latent Heat, and Specific Volume Pressure (bar) 1 2 3 5 7 10 15 20 30 40 50

Steam Temperature (
C) 99.6 120.2 133.5 151.8 164.9 179.9 198.3 212.4 233.8 250.3 263.9

Latent Heat (kJ/kg) 2258 2202 2163 2108 2065 2014 1945 1889 1794 1713 1640

Specific Volume (m3/kg) 1.694 0.8853 0.6056 0.3747 0.2762 0.1943 0.1316 0.09952 0.06663 0.04975 0.03943

heat edible oils, but, due to the potential risk of contamination, the use of thermal heating fluids has mostly been abandoned. The use of diphenyl/diphenyloxide (e.g., Downtherm1 A from Dow Chemical Co.) is still allowed, but only in exceptional cases and if no other alternative is available. In that case, a control and loss-detection system has to be installed and the deodorized oil needs a certificate of noncontamination. The net heating energy required for a deodorization system can be calculated as: H ¼ ½O c ðT2  T1 Þ f L f R ;

ð16Þ

where O is the amount of oil (kg), T1/T2 is the incoming and final temperature of the oil (
C), c is the average specific heat capacity of vegetable oils (typically 2.2– 2.4 kJ/kg
C), fL is the heat loss factor from radiation (typically 1.05–1.15), and fR is the heat recovery factor [1-(%heat recovery/100)]. In industrial practice, heat recovery has become an important factor because it minimizes the cost of additional heating of the oil to the deodorization temperature. In recent years, there has been a very fast evolution in the manufacture of heat exchangers for heat recovery. Generally speaking, they can be divided into external and internal heat exchangers (Figure 11). External heat exchangers usually result in high recovery and provide easier access for cleaning. On the other hand, internal heat exchangers allow energy recovery under vacuum and ensure less cross-contamination and less risk of fouling. The final choice for a heat-exchange system is based not only on its thermal performance but also on other criteria such as easy maintenance, low risk of fouling, low level of cross-contamination, and an acceptable installation cost compared with the expected energy recovery. Heat recovery can be achieved directly by exchange of heat between two oil streams at different temperatures (e.g., bleached vs. deodorized oil), flowing in a countercurrent direction through the exchangers, or indirectly by steam production.

366

DEODORIZATION

oil-steam heat exchanger plate

spiral

Internal heat exchangers

shell & tube

oil-oil heat exchanger

External heat exchanger

Figure 11. Examples of external and internal heat exchangers used in edible oil deodorization (Alfa Laval, Ciat, De Smet).

Direct heat recovery is the most efficient, with up to 85% of the heat recoverable. It is usually applied in continuous deodorizers, whereas the indirect heat recovery system is used preferentially in semi-continuous deodorizers with frequent feedstock changes. The efficiency of the indirect heat recovery depends largely on the type and design of the system (Figure 12). A special indirect heat-recovery device is the themosiphon system. The steam produced in the oil cooling section is sent in a closed loop to the oil heating section. The steam will condense there, and the water is returned to the cooling section. Final cooling of the oil is usually conducted under reduced pressure to prevent the possible production of degradation byproducts. The necessity of conducting cooling under vacuum while maintaining steam injection has always been a matter of discussion. As a result of the technological complexity and for cost reasons, cooling under vacuum is usually applied only in a large capacity deodorizer. Small capacity plants often make use of external oil–oil heat-exchanging devices. 4.3. Steam Stripping The necessary amount of stripping agent is directly proportional to its molecular weight. Therefore, stripping agents with the lowest possible molecular weights are selected. For economic reasons, steam is generally used, but the use of nitrogen has been studied extensively. Nitrogen has the advantage of being an inert and

DEODORIZER TECHNOLOGY

367

L.P. Steam Heating H.P. Steam Heating

H.P. Steam Heating

H.P. Steam Heating

L.P. Steam Generation

Water Cooling

L.P. Steam Generation & Thermosyphon Heat Recovery 75%

Double Thermosyphon Heat Recovery 67%

Single Thermosyphon Heat Recovery 45%

Figure 12. Indirect heat recovery systems used in semicontinuous deodorizers (thermosiphon systems) (De Smet). LP: low-pressure steam ; HP: high-pressure steam.

noncondensable gas. Theoretically, its use will result in lower loss (no hydrolysis) and a more pure deodorizer distillate. Although it is possible to work with nitrogen under the commonly applied process conditions, experiments have shown that the profitability is very uncertain, depending on the existing installations in the factory and the nitrogen supply (31, 33). Further studies have indicated that color, residual FFA, oxidative stability, as well as the formation of trans-fatty acids and the stripping of tocopherols are not affected by the nature of the stripping agent (34, 35). In any case, the stripping agent must be ‘‘dry’’ and free of oxygen. Superheating will ensure that the stripping agent is ‘‘dry’’ and that no cooling of the oil occurs. Apart from the stripping agent, different deodorizer designs attempt to provide the best contact between the gas phase and the oil phase by creating a large contact surface, together with an optimal sparge steam distribution. In this way, a maximum vaporization efficiency can be reached. Deodorization only occurs at the vapor-liquid contact zone where the lowest operating pressure exists. It is therefore essential to expose all parts of the oil to surface conditions. In most deodorizers, the stripping agent is introduced into the oil through special sparge coils with very fine holes (with a diameter between 0.5 and 2.5 mm) or by steam lift pumps. However, the main function of steam lift pumps is to improve agitation and enhance overall deodorization efficiency by continuously refreshing the oil in the top layer (Figure 13). A minimum oil layer height (more than 0.8 m) is required to allow good operation of a steam lift pump.

368

DEODORIZATION

Figure 13. Sparge steam injection systems used in deodorizers (De Smet, Tirtiaux).

Another way to improve the stripping is to increase the contact surface between steam and oil. In edible oil deodorization, this is accomplished in so-called packed columns that can be filled with various types of surface-extending devices. Packed columns have already been applied in edible oil deodorization for decades. A very good contact between the vapor and the oil at low pressure is created by a continuous thin film of oil flowing over the packing material. Both random and structured packings are used, but the structured packing is most preferred for its lower pressure drop and higher vaporization efficiency. As a result of the fact

Figure 14. Principle of countercurrent and cross-flow stripping.

369

DEODORIZER TECHNOLOGY

TABLE 15. Calculation of the Residual Free Fatty Acid Content in a C-18 Oil Under Ideal Conditions (Efficiency E ¼ 1). Conditions Theoretical trays Steam (kg/ton) FFA-in (%) Temperature Pressure (mbar) FFA-out (%) Pressure (mbar) FFA-out (%) Pressure (mbar) FFA-out (%)

Cross Flow Deodorizer

Packed Column

5 6 0.3 230 245 260 3 0.14 0.08 0.032 ——————————————— 2 0.097 0.043 0.014 ——————————————— 1.5 0.07 0.026 0.008

5 6 0.3 245 3–4 0.023

230 0.09

260 0.003

that stripping steam is introduced into the column in a countercurrent way, packed columns require less steam than tray deodorizers, which work according to the cross- flow principle (4) (Figure 14). For chemically refined oils, for example, a stripping steam consumption of 0.5–0.7% is reported as being sufficient for packed columns, compared with 1.0–1.2% for tray deodorizers. However, modern tray deodorizers today operate with even less steam, as low as 0.7–0.9%. The stripping efficiency of a deodorizer can be improved either by incorporating a packed column or by reducing the operating pressure of the deodorizer (Table 15). The best solution, of course, is a combination of both, but this results in an expensive deodorization technology. A convenient way of controlling the stripping steam flow through the steam distributors is to maintain a fixed pressure upstream of an orifice plate of known size. As the pressure always falls to a low value beyond the orifice, the flow of steam will be proportional to the absolute pressure on the upstream side of the orifice and the orifice surface (Table 16). Orifice plates are usually on each steam sparge coil to allow an independent adjustment and control of the steam flow rates. Steam from the main low-pressure

TABLE 16. Steam Flow Rates for Orifices of Different Size at Different Steam Pressure. Pressure (bar) Orifice Size (mm)

0.5

0.7

0.9

1 1.5 2 2.5 3 4 5

0.15 0.34 0.61 0.95 1.36 2.42 2.78

0.21 0.48 0.86 1.32 1.90 3.38 5.29

0.27 0.61 1.09 1.70 2.45 4.35 6.80

1.1 1.3 1.5 Steam Flow Rate (kg/hr) 0.33 0.75 1.33 2.08 2.99 5.31 8.31

0.39 0.88 1.37 2.46 3.54 6.28 9.82

0.45 1.02 1.82 2.84 4.08 7.25 11.5

1.7

1.9

0.51 1.16 2.06 3.21 4.62 8.21 12.8

0.67 1.29 2.30 3.59 5.17 9.18 14.3

370

DEODORIZATION

sparge steam line (3–5 bar) is distributed to different deodorizer compartments. Before entering into the sparge steam coils, the steam pressure is reduced to the required pressure by means of a pressure reducing valve. Usually, there is one pressure reducer per compartment to allow different steam injection rates over different deodorizer trays. Aside from a higher stripping efficiency, a packed column is also characterized by a very short holdup time. This may be sufficient for the stripping of certain volatile components (e.g., FFA, tocopherols, etc.) but not enough for a complete deodorization. Therefore, a holding vessel is usually placed after a packed column to properly deodorize the oil. The steam introduced in the retention vessel can be reused as stripping vapor for the packed column, which reduces overall steam consumption. The reuse of this ‘‘dirty’’ steam, however, may have a negative effect on the final oil quality. 4.4. Vapor-Scrubbing Systems The volatile components, stripped during deodorization, are condensed and usually recovered in a direct condenser or vapor scrubber (Figure 15). The vapor from the deodorizer consists mainly of steam, volatile fatty substances, and some noncondensables (e.g., air). The volatile substances are condensed by creating an intimate contact between the vapor and the fatty acid distillate circulating in the scrubber. This is done either by a series of sprayers Deaerator

Deodorizer

Vapor scrubber

Vacuum unit

802 s

822 MS 1

2

Heating

3

841 D

D

W

Deodorizing

4

5

Cooling

6

D

823

814

W

D

FATTY ACIDS

M

D

7 D

P808AG

881 816

FEEDSTOCK

P801

881AG

P822

M

DEODORIZED OIL

DE SMET "MULTISTOCK" DEODORIZING

Figure 15. Flowsheet of a stock change deodorizer (De Smet).

DEODORIZER TECHNOLOGY

371

TABLE 17. Composition of Deodorizer Distillates from Single- and Dual-Temperature Condensation.

Vegetable Oil1 Soybean oil Sunflower oil Palm oil 1

Dual-Temperature Condensation Single Temperature ——————————————————————— Distillate 1 Distillate 2 Condensation ——————————————————————————————————FFA (%) Tocos (%) FFA (%) Tocos (%) FFA (%) Tocos (%) 84.0 86.0 93.0

1.10 0.65 0.25

62.0 61.0 40.0

7.4 5.3 1.7

76.0 77.0 84.5

3.5 2.4 0.8

Initial FFA:  1%.

mounted in the ducts or through a packed bed (random or structured packing) in the scrubber vessel. The distillate is usually circulated at the lowest possible temperature (just above the melting point) to obtain the best possible condensation of the fatty matter present in the vapor phase that leaves the deodorizer. A demister is sometimes installed at the top of the scrubber ahead of the vacuum unit, to reduce liquid carryover of small oil droplets, which would otherwise end up in the water from the barometric condenser or in the condensate from the cold (or dry) condensers. Apart from efficient cooling of the vapor and condensing of the fatty matters, the pressure drop in the scrubber should be kept as low as possible because it directly affects the operating pressure of the main deodorizer. The pressure drop should be below 1 mbar, and preferably below 0.5 mbar. The conventional vapor-scrubber design results in one single deodorizer distillate. The main factors determining the overall composition of the distillate have been discussed earlier in this chapter. Recently, improved scrubbers operating at two different temperatures (so-called dual condensation principle) have been introduced. Especially in case of physical refining, this design can result in higher valueadded distillates because it allows the collection of a first distillate enriched in FFA and a second distillate with a higher concentration of unsaponifiable components (sterols, tocopherols, etc.) (Table 17). 4.5. Vacuum Systems 4.5.1. Conventional Vacuum Systems The low absolute pressure required in a

deodorizer, usually between 2 and 4 mbar, is commonly generated by vacuum systems consisting of a combination of steam ejectors (boosters), vapor condensers, and mechanical (liquid ring) vacuum pumps (Figure 16). Liquid ring pumps are used in the final stage of the vacuum system to remove the noncondensable gases. As a result of the large volume of vapor to be removed, motive steam consumption in such steam ejectors is quite high and may account for up to 85% of the steam consumed in a deodorizer. A way to reduce motive steam consumption in a steam-ejector system with barometric condensers is to lower the temperature of the water recirculating in the

372

DEODORIZATION

motive steam A

C

A B C D E F

B 4

3

1

6 5

2

7 8

process vapour from column scrubber to ejector vacuum system hotwell plate heat exchanger cooling tower

1-3 boosters/ejector 4 stand by ejector 5-6 direct contact condensers 7 liquid ring vacuum pump 8 separator

D E

DIFFUSER DISCHARGE

STEAM INLET

COMBINED STEAM CHEST AND NOZZLE PRESSURE TAP

F

SUCTION

Figure 16. Vacuum steam ejector system with barometric condensers used in edible oil deodorization (Ko¨rting).

barometric condensers (Table 18). The benefit of the lower motive steam consumption, however, must be weighed against the extra chilling capacity required and, thus, the electrical energy needed to cool the barometric condenser water. Another benefit from using a lower barometric condenser water temperature is a better condensation of volatile odoriferous material, which, in turn, reduces the odor emission problem. Together with the condensed steam and highly volatile material, a small TABLE 18. Effect of Barometric Condenser Water Temperature on Motive Steam Consumption in Steam Ejector System. Pressure Booster

Deodorizer

2.5 1.5

3 mbar 2 mbar

kg Motive Steam per kg Strippng Steam 30
C (1) 10
C (2) 4.5 6.2

Note: (1) Barometric condenser water inlet temperature: 24
C; outlet temperature: 30
C. (2) Barometric condenser water inlet temperature: 5
C; outlet temperature: 10
C.

1.6 2.5

DEODORIZER TECHNOLOGY

373

amount of fatty matter is usually found in the condenser water, 1% of the stripping steam. This fatty matter may decant partially and separate from the water. The waste water is usually sent to a water effluent treatment plant where it is mixed with other effluent streams from the refinery. 4.5.2. Dry Condensing Systems Special vacuum production units have been

developed to obtain lower pressures and operating costs and, at the same time, to reduce emissions by more efficient condensation of the volatiles. The dry condensing system is becoming more and more standard in new refining plants. With this system, the sparge steam is condensed on surface condensers working alternately at a very low temperature (around 30
C). The remaining noncondensables are removed either by mechanical pumps or roots blowers in series with a liquid ring pump or by a vacuum steam-ejector system (booster). The dry condensing system reduces the motive steam consumption but requires extra electrical energy. As a result of the relatively high capital cost, the return on investment (ROI) for a dry condensing system may take several years and depends largely on the ratio between the cost of steam and electricity. In Europe, with higher fuel costs, the production cost of steam is higher, which improves the ROI of a dry condensing system compared with a classic vacuum system. As an additional benefit, much lower waste water quantities are produced by dry condensing, which significantly reduces the cost of effluent treatment, thereby also improving ROI. The pressure in the deodorizer is always slighlty higher (0.5–1.5 mbar) than on the suction side of the vacuum unit, because of pressure losses caused by the oil demisters, the fatty matter scrubbers, and other equipment. Consequently, to reach an effective deodorization pressure of 2 mbar, a pressure of not more than 1.5 mbar at the suction side is required. To obtain an efficient steam sublimation at this low pressure, special stripping steam condensers operating at extremely low temperatures (30
C) are required. (Table 19). The commercially available dry condensing systems consist of two or more freeze condensers with horizontally or vertically orientated straight tubes, a refrigeration plant for the generation of cold refrigerant, which is evaporated in the tubes, and a vessel with relatively warm water for defrosting and cleaning of the tubes after a certain period of freezing. TABLE 19. Effect of Suction Pressure on Sublimation Point of Stripping Steam. Pressure at Condenser Side (mbar) 0.5 1 2 3 5 10 20 30

Sublimation Point of Water (
C) 27.3 20.3 12.9 8.4 2.4 7.0 17.5 24.1

374

DEODORIZATION

Separator

Condenser

Cooling water

Compressor

From distillate scrubber

Freeze condenser To de-aeration

Valve, open Valve, closed Vapor (vacuum) Refrigerant (ammonia) Non-condensable gases

Melt vessel

Condensate

LP steam

Figure 17. Schematic diagram of a dry condensing system with horizontal freeze condensers (e.g., Niro-Gea, Ko¨rting).

Dry condensing equipment can be equipped with either with horizontal or vertical freeze condensers (Figures 17 and 18). Advantages of ‘‘horizontal’’ dry condensing systems are the relatively simple and compact construction of the freeze condensers. On the other hand, the mass of the refrigerant in the gravity system is typically high.

Separator

Condenser

Cooling water

Compressor

From distillate scrubber

Freeze condenser Valve, open Valve, closed Vapor (vacuum)

To de-aeration

Refrigerant (ammonia) Non-condensable gases

Melt vessel

Condensate

LP steam

Figure 18. Schematic diagram of a dry condensing system with vertical freeze condensers (e.g., Graham Corporation).

DEODORIZER TECHNOLOGY

375

Compared with horizontal systems, ‘‘vertical’’ freeze condensers have a more efficient removal of ice and fatty matter from the tubes, which can drain freely by gravity. A disadvantage of the vertical orientation is the static pressure of the refrigerant column in the vertical tubes, which causes higher evaporating temperatures at the bottom. In order to guarantee sufficient sublimation of sparge steam over the entire height of the tubes, this evaporating temperature increase should be compensated by a similar reduction of the refrigerant temperature in the separator, reducing the energy efficiency of the refrigeration plant. The most essential feature of the recently developed SUBLIMAX system is the vertical orientation of the freeze condensers, combined with individual refrigerant injection at the top of the tubes to produce a falling film (Figure 19). This design results in high-heat-transfer coefficients and constant evaporating temperatures along the entire tube length.

Figure 19. Schematic diagram of the SUBLIMAX Dry Condensing system (De SmetSolutherm).

376

DEODORIZATION

5. COMMERCIAL DEODORIZER SYSTEMS Deodorization can be performed in different ways (continuous, semicontinuous, or batch). The selection of most appropriate deodorizer technology depends on many factors, such as the number of feedstock changes, heat recovery, investment, and operating costs. 5.1. Batch Deodorization Batch deodorization is especially suitable for small capacities ( 18:0. In practical terms, this process reflects the selective removal of double bonds via hydrogen addition such that saturated fatty acid (stearic) formation is minimized (7). ‘‘Catalyst selectivity’’ is somewhat meaningless unless the term is defined. There also are selective catalysts that do not meet the technical or practical definition of hydrogen selectivity. Such catalysts are sulfur-poisoned catalyst. Sulfided nickel catalyst produces high trans-isomers, has lower activity than conventional nickel, exhibits longer reaction times, and is used for specialty applications (e.g., coating fats and hard butters). Most unsaturated bonds in vegetable oils naturally occur in the cis-form. During partial hydrogenation, part of the cis-isomers is changed to trans-isomers. Transisomers have a dramatically higher melting point (42 C) as compared with cisisomers (6 C). The creation of trans-isomers is desirable in margarine oil in that a higher melting point can be achieved without developing a higher level of nutritionally undesirable saturated compounds. Altering hydrogenation conditions to produce higher (or lower) trans-isomers is termed ‘‘trans-isomer selectivity.’’ Factors influencing cis-trans-isomerization are shown in Table 2. A typical hydrogenation converter is shown in Figure 1. The converter is the heart of the complete hydrogenation system. Proper design and maintenance of the hydrogen gas distributor, the agitator, and the heating cooling coils are mandatory for optimum productivity and consistency of basestocks produced. Most converters are 30,000-pound, 40,000-pound, or 60,000-pound batch sizes with some now as large as 90,000 pounds. The common agitator design provides approximately 100 rpm, and radial flow impellers are used. The lower impeller is positioned slightly above the hydrogen gas distributor; therefore, the diameter of the gas distributor and the tip-to-tip dimension of the lower impeller are critical. Originally, the middle and top impellers were of the radial flow type also. Some converters have now been operating for many years with an axial flow impeller at the top position. Although the lower and middle radial flow impellers are ideally suited for gas dispersion, the top impeller pumps the oil downward, and if positioned properly, hydrogen gas in the headspace re-enters the oil. This design has enhanced the success of dead-end hydrogenation, dramatically reducing the amount

388

HYDROGENATION: PROCESSING TECHNOLOGIES

Turbine Agitator

Baffle

Heating & Cooling Coil

Gas Distributor

Hydrogenation Converter Dead-End Design Figure 1. Hydrogenation converter.

of purge or vent gas. These improvements are demonstrated in Figure 2. Other special agitation and hydrogen distribution systems have been developed, such as the Buss reactor, and the AGR (Advanced Gas Reactor), but these systems are falling out of favor because the added maintenance offsets any advantages these systems were supposed to provide. Proper hydrogen gas distribution and agitator design is important. Stratification of reacted and unreacted areas in the converter, as a result of improper agitation or hydrogen distribution, will add to unpredictability in basestocks from batch to batch. A complete semicontinuous hydrogenation plant is depicted in Figure 3. The main features of this system are: (1) a preheating and measuring tank, (2) a reactor or converter, (3) a drop tank, (4) a heat-recovery system, (5) steam generation via reactor cooling, and (6) single-step filtration.

INTRODUCTION

389

Figure 2. Improved hydrogenation design.

By arranging all the vessels for gravity drop, very rapid turnover of batches in the reactor results. In this manner, the reactor is used for reaction only; all heating, cooling, and filtration is accomplished external to the reactor. For example, if the average iodine value (IV) drop for all basestocks produced can be achieved in one hour, then a single system can deliver 24 batches per day (a 24-hour period). This system also demonstrates the latest technologies in heat recovery by heat exchange of the hot oil in the drop tank with the incoming cold oil and by steam generation for reactor cooling. The hydrogenation department becomes a net exporter of steam, the ultimate form of energy conservation. The system depicts improved reactor agitator design and improved automation. The complete process is controlled by programmable logic controllers (PLCs), giving precise in-point control that leads to extreme consistency from batch to batch.

390

HYDROGENATION: PROCESSING TECHNOLOGIES

Measuring tank

Steam

Catalyst

Vacuum unit

Steam

steam H2 Steam PI

PI

Flash tank

Pt

Pc

Reaction heat recovery water

FT

Hydrogen dosing Oil

Reactor FT

R TT TT

Black filter

Oil-oil heat exchanger

Drop tank

Spend catalyst

Hydrogenated oil

to bleaching & refining

Figure 3. Semicontinuous hydrogenation processing plant.

2. IS THERE A FUTURE FOR HYDROGENATION? There will always be a need for hydrogenated fats to provide functionality and improved stability. Hydrogenation, as practiced today, is the only way to produce commodity-priced, hardened oils. Any alternatives are going to have higher capital and operating costs. Although trans-fat in hydrogenated products is a consumer concern, the magnitude of consumer concern is unknown. If consumers believe that trans-fat is bad for their health, then hydrogenation (increasing saturated fat) is bad also. Products such as household shortening and heavy-duty frying fats are so high in saturated fat that any concern about using these products will be based on concerns about saturated fat as much as concerns about trans-fat. In summary, there is a continued need for hydrogenation of many products, but the volume of oils hydrogenated is certain to decrease, even with a population increase. All consumers worldwide are going to develop more and more concern for improving their health and longevity. Thus, the consumption of hydrogenated oils, and oils naturally high in saturated fat, must decrease. The first step will be the elimination of trans-fat in food products, because we now have the technology to do that. Removal of trans-fat will allow us time to find ways to reduce saturated fat, and remove hydrogenation from many products.

3. RESEARCH ON TRANS-REDUCTION BY HYDROGENATION Over the past decade, trans-acid reduction via hydrogenation has been of interest to catalyst producers (8) and research workers (9–11). An early study (13) clearly

THE TRANS-FAT ISSUE

391

showed that, with other factors being equal, i.e., pressure, agitation, and catalyst concentration, temperature has a marked effect on trans-acid formation in stirred batch reactors. The lower the temperature, the lower the extent of trans-acid formation. Although the reasons for this effect is not clearly understood, it would appear that, once triacylglycerols are adsorbed onto the catalyst surface, lower temperature favors saturation of double bonds rather than isomerization of cis-double bonds to the trans-form. Bailey (13) stated that at higher temperatures, where hydrogen lean conditions on the catalyst surface exist, more competition for the more unsaturated triacylglycerol molecules occurs. However, at higher temperatures, desorption with isomerization from cis- to trans-is more likely to occur than at lower temperatures. Trans-suppression in hydrogenated oils is the subject of a paper published in 1995 in which conditions necessary for trans-acid reductions in soybean and canola oils are reported (8). Trans-suppression in hydrogenated soybean oil was observed at lower temperatures, higher pressures, and higher catalyst concentrations compared with conditions where trans-acid formation was maximized. For example, reactions carried out at a temperature of 204 C, a catalyst concentration of 0.02% and 15 psi hydrogen pressure, normally used for selective hydrogenation, produced a maximum trans-acid (44%) at an iodine value of about 70. By comparison, reducing the temperature to 77 C and increasing the catalyst concentration to 0.11% at a pressure of 250 psi resulted in a 50% reduction in trans-acids. The author concluded that the rate of the reaction under conditions where transacids are suppressed are sufficiently fast for large scale adaptation. However, our results suggest that, at high pressures and at a temperature of 120 C with normal catalysts concentrations, 0.02% nickel, the rate of hydrogenation is much slower than normally observed (9). Another approach to reducing trans-acids involves electrochemical hydrogenation with a palladium catalyst in a solid-state electrolyte reactor (10) where about 50% reduction in trans-was observed compared with nickel at iodine values of about 90.

4. THE TRANS-FAT ISSUE Most unsaturated fatty acids in naturally occurring edible oils and fats contain carbon chains with double bonds in the cis-configuration. The trans-geometric isomers in unsaturated oils, and the fats produced from them, are a result of industrial processing at elevated temperatures such as physical refining, deodorization, and, particularly partial hydrogenation of the unsaturated oils. The amount of trans-fatty acids (TFA) formed is influenced by the duration and the temperature of processing and the initial degree of unsaturation. As a result of the presence of double bonds, unsaturated oils are more chemically reactive than saturated fats, and the reactivity increases with the number of double bonds. Thus, unsaturated oils, and especially polyunsaturated oils, are extremely vulnerable to heat, oxygen, and light. Consequently, they are not suitable for deep-frying and for the preparation of foods that are stored, such as snack foods.

392

HYDROGENATION: PROCESSING TECHNOLOGIES

Catalyst Vacuum unit Steam Steam

NaOH

DryerReactor

Bleach filter Bleach earth

Oil

Polling stear

Citric acid Bleacher

Spent bleach earth

Interesterified oil

Cooling To refining

Figure 4. The chemical interesterification process.

When these oils are partially hydrogenated (i.e., when hydrogen atoms are added to some of the unsaturated sites on the carbon chain in the presence of heat and a metal catalyst), the number of double bonds is reduced. The melting point and oxidative stability increase and the liquid oil is converted to a semisolid or solid resistant to oxidation and rancidity. In addition, some of the double bonds that are normally in the cis-configuration change into the trans-configuration. The consumption of foods high in TFA has been shown to raise low-density lipoprotein cholesterol (LDL or ‘‘bad’’ cholesterol), which increases the risk of developing coronary heart disease (CHD). This prompted the Food and Drug Administration (FDA) to require mandatory labeling of the trans-fat content in foods. Food manufacturers have to comply by January 1, 2006. The FDA’s chemical definition of TFA or trans-fats (TF) is ‘‘unsaturated fatty acids that contain one or more isolated (i.e., nonconjugated) double bonds in the trans-configuration.’’ The one food product that may be influenced the most by trans-fat concerns is margarine. Obviously, margarine must be a solid product, and this product cannot be replaced by liquid oils with improved stability. The most probable replacement for hydrogenation for margarine oils is interesterification. A chemical interesterification system is depicted in Figure 4. Although the chemical interesterification process is over 50 years old, it is coming back into popularity to process low trans-solid products. A new technology, an alternative to chemical interesterification, namely enzymatic interesterification is emerging. The process was introduced in the United States in 2003. This process is patented by Novozymes. Figure 5 depicts this process in a simplified form. Again, an interesterification system will have higher capital and operating costs, and a lower productivity than the hydrogenation process. Will food processors pay

THE TRANS-FAT ISSUE

393

Product Tank

Feed Tank Small Reactors in series Figure 5. The enzymatic interesterification process.

the higher price for interesterified margarine oils? It remains to be seen, and again, it will be driven by consumer concerns. Another good alternative for making margarine oils will be by the use of highstearate (high stearic-acid) soybean oil (14, 15). High-stearate soybean oil is genetically altered to have a higher (approximately 22%) stearic acid content. With a small amount (approximately 3%) of near-zero-IV soybean oil (zero trans-) added, a good tub margarine can be made. To make a stick margarine, the high-stearate soybean oil can be fractionated, with a high percentage of the stearine portion going into the stick margarine formulation. The author is developing (mid-2004) zero trans-, no hydrogenation, no interesterification, no modification of any kind, tub and stick margarines. The formula will include specially processed soybean oil, corn oil, cottonseed oil, or mid-oleic sunflower seed oil, and double-fractionated palm oil, or double-fractionated cottonseed oil. The products are proprietary for now. The leading manufacturer of prepared poultry products is changing (mid-2004) to a blend of lightly hydrogenated soybean oil and corn or cottonseed oil. This offers good fry-life while being zero trans-per serving size. The hydrogenated soybean oil lowers the price of the blend as a result of the rising cost of the highly stable liquid oils. The genetically altered oils, 3% linolenic acid, and now 1% linolenic acid soybean oil, may become popular as zero trans-frying fats, as the size of the crop for these seeds advances. These oils would be zero trans- and no hydrogenation. As touted by the ‘‘Better Bean Initiative,’’ the 3% linolenic variety could become the mainstream variety, requiring no identity preservation. (Note: If 3% linolenic acid soybean oil is lightly hydrogenated, less trans-would be produced because of the lower initial linolenic acid content). One must understand that the interesterification process, chemical or enzymatic, is of no value in making heavy-duty frying fats. The high percentage of unsaturated oil, even with interesterification and addition of near-zero IV fat to provide plasticity, is still unstable under heavy-stress frying conditions. The most logical zero trans-frying fats are the naturally stable oils, such as cottonseed oil, corn oil, peanut oil, and mid-oleic sunflower seed oil. The use of these oils increased dramatically in 2003 and early 2004 for this purpose. Already in limited supply, this heavy demand will dramatically increase the price of these oils.

394

HYDROGENATION: PROCESSING TECHNOLOGIES

The leading manufacturer of household shortening (and frying fat) is introducing (mid-2004) a new formula made up of lightly hydrogenated soybean oil, high palmitic refractioned cottonseed oil (45% palmitic), and a low percentage of zero IV soybean or cottonseed oil (near-zero IV is zero trans-). This product provides zero trans-per serving size of a food product, and no interesterification is needed. A new zero trans-, no hydrogenation, no modification of any kind, rich in omega-3 fatty acids, RBD soybean oil frying fat has been developed (patented) by Carolina Soy Products (Warsaw, North Carolina). Extensive fry tests prove that this oil has a fry life equal to, and often better, than the heavy-duty hydrogenated (high trans-) frying fats. The secret to this process is in the processing, not modification. This soybean oil (regular variety) is extruded and expellerpressed, no solvents, no harsh chemicals, and is physically refined.

5. HYDROGEN SUPPLY FOR HYDROGENATION For laboratory and pilot plant hydrogenation, high-pressure hydrogen gas cylinders can be used. For large industrial hydrogenation systems, either liquid hydrogen is

Figure 6. Steam/Methane Reforming Plant HYDRO-CHEM Processing, Subsidiary of Linde AG. (This figure is available in full color at http://www.mrw.interscience.wiley.com/biofp.)

REFERENCES

Export Steam Product

Fuel

395

H2 Product

8 7 3 9

2

6

Feed

Demin Water

4 1

5

Figure 7.

stored on site, or there is an on-site hydrogen gas-generating plant. Justification on using liquid hydrogen is dependent on the proximity of the liquid hydrogen manufacturing facility, and on the contract the hydrogen manufacturer is willing to negotiate. Often, particularly for a new plant, installation of an on-site hydrogengenerating plant can be justified. A typical high-capacity hydrogen-generating plant is shown in Figure 6. Needless to say, there will continue to be a need for hydrogenation for some products, certainly for coating fats, cocoa butter substitutes, cake icing, and cookies and crackers. These products, often blended with sweeteners, will probably become indulgence foods, to be used sparingly. The main fats and oils in the diet must be low trans-, lower saturated fat, and with a minimization of hydrogenation. Although offering challenges to the fats and oils manufacturer and food processor/food service, these challenges should be welcomed and embraced to improve the health of mankind.

REFERENCES 1. D. R. Erickson and M. D. Erickson, in D. R. Erickson, E. H. Pryde, T. L. Mounts, O. L. Brekke, and R. A. Falb, eds., American Soybean Association Monograph, Handbook of Soy Oil Processing and Utilization, AOCS Press, Champaign, Illinois, 1980, pp. 218– 238.

396

HYDROGENATION: PROCESSING TECHNOLOGIES

2. G. R. List and T. L. Mounts, in D. R. Erickson, E. H. Pryde, T. L. Mounts, O. L. Brekke, and R. A. Falb, eds., American Soybean Association Monograph, Handbook of Soy Oil Processing and Utilization, AOCS Press, Champaign, Illinois, 1980, pp. 193–214. 3. G. E. Hammerstrand and G. R. List, in D. R. Erickson, E. H. Pryde, T. L. Mounts, O. L. Brekke, and R. A. Falb, eds., Handbook of Soy Oil Processing and Utilization, AOCS Press, Champaign, Illinois, 1980, pp. 214–216. 4. R. D. Obrien, in D. R. Erickson, E. H. Pryde, T. L. Mounts, O. L. Brekke, and R. A. Falb, eds., American Soybean Association Monograph, Practical Handbook of Soy Oil Processing and Utilization, AOCS Press, Champaign, Illinois, 1995, pp. 258–276. 5. H. B. W. Patterson, Hydrogenation of Fats and Oils: Theory and Practice, AOCS Press, Champaign, Illinois, 1994. 6. J. C. Cowan, Soybean Digest, 26(12); 48–53 (1966). 7. R. R. Allen, J. Amer. Oil Chem. Soc., 45; 312A (1968). 8. J. Hasman, Inform, 8; 1150–1158 (1995). 9. J. W. King, R. L. Holliday, G. R. List, and J. M. Snyder, J. Amer. Oil Chem. Soc., 78; 107– 113 (2001). 10. K. Warner, W. E. Neff, G. R. List, and P. Pintauro, J. Amer. Oil Chem. Soc., 77; 1113–1117 (2000). 11. F. Eller, J. Teel, K. R. Steidley, and G. R. List, Effects of Pressure and Temperature on Oil Properties, Abstracts, World Conference on Oilseeds, Istanbul, Turkey, 2002. 12. Stingley and R. J. Wrobel, J. Amer. Oil Chem. Soc., 38; 201–205 (1961). 13. A. E. Bailey, Industrial Oil and Fat Products, 2nd ed., Interscience Publishers, New York, 1951, pp. 690–708. 14. G. R. List, T. L. Mounts, F. Orthoefer, and W. E. Neff, J. Amer. Oil Chem. Soc., 73; 729– 732 (1996). 15. G. R. List, T. Pelloso, F. Orthoefer, K. Warner, and W. E. Neff, J. Amer. Oil Chem. Soc., 78; 103–104 (2001). 16. W. E. Farr, in R. F. Wilson, ed., Hydrogenation: Proceedings of the World Conference on Oilseed Processing/Utilization, AOCS Press, Champaign, Illinois, 2001. 17. W. E. Farr and G. R. List, in N. T. Dunford, ed., Hydrogenation Techniques, Nutritionally Enhanced Processing, AOCS Press, Champaign, Illinois.

10 Supercritical Technologies for Further Processing of Edible Oils ¨ zlem Gu¨c¸lu¨-U ¨ stu¨ndag˘ Feral Temelli and O University of Alberta Edmonton, Alberta, Canada

1. INTRODUCTION Supercritical CO2 (SCCO2) technology has been widely investigated for the processing of fats and oils because SCCO2 offers an environmentally friendly alternative compared with the conventional processes involving organic solvents, resulting in solvent-free extracts and residues obtained under moderate operating conditions. The ability to modify solvent properties by changing operating conditions (temperature and pressure) or by the addition of cosolvents makes the SCCO2 process versatile, giving a unique advantage. This operational flexibility enables the processor to fine tune solvent properties for the specific separation problem at hand. Health benefits of minor lipid components, such as tocopherols, sterols, and certain fatty acids (o-3 fatty acids [a-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA)], g-linolenic acid, and conjugated linoleic acid) have been widely investigated in recent years (1, 2). Increasing evidence of health benefits of these lipid components coupled with changing consumer attitudes (increased awareness of diet-health link and increased tendency to self-medicate), Bailey’s Industrial Oil and Fat Products, Sixth Edition, Six Volume Set. Edited by Fereidoon Shahidi. Copyright # 2005 John Wiley & Sons, Inc.

397

398

SUPERCRITICAL TECHNOLOGIES FOR FURTHER PROCESSING OF EDIBLE OILS

which is reflected in the considerable growth in the functional foods and nutraceutical market (3) have led to the re-evaluation of conventional fats and oils processing for the recovery/concentration of these bioactive components. Supercritical fluid (SCF) technology has been increasingly used for the processing of nutraceuticals, including bioactive lipids, on a commercial level as it provides a solvent-free, ‘‘natural’’ product, which has a wide consumer appeal. With such major developments in the field of SCF technology, the objective of this chapter is to provide a critical overview of the solubility behavior of lipid components in SCCO2, which is fundamental for optimal process design as well as the unit operations of extraction, fractionation, and reactions using SCCO2 as applied to fats and oils processing.

2. DEFINITION AND PROPERTIES OF SUPERCRITICAL FLUIDS A fluid is in its ‘‘supercritical state’’ at temperatures and pressures higher than its critical values (Figure 1). Critical temperatures and pressures (Tc and Pc, respectively) of selected solvents are listed in Table 1. The critical point defines the highest pressure and temperature at which gas and liquid phases can coexist. As the critical point is approached, the distinction between the gaseous and liquid phases diminishes such that their properties are identical at the critical point.

Supercritical fluid

Solid Pressure

Pc

Liquid Critical point

Gas

Tc

Temperature

Figure 1. A typical phase diagram.

HISTORIC DEVELOPMENT AND COMMERCIAL APPLICATIONS

399

TABLE 1. Critical Points of Selected Solvents (4). Solvent Carbon Dioxide Ethane Ethylene Propane Propylene Methanol Acetone Benzene Toluene Ammonia Water

Tc (K)

Pc (MPa)

304 305 282 370 365 513 508 562 592 406 647

7.38 4.88 5.03 4.24 4.62 8.09 4.70 4.89 4.11 11.3 22.0

TABLE 2. Properties of Gases, Liquids, and Supercritical Fluids (5). Density (g/mL) Gas, 101.3 kPa, 15–30
C Supercritical fluid, Tc, Pc Tc, 4Pc Liquid, 15–30
C a

(0.6–2) 103 0.2–0.5 0.4–0.9 0.6–1.6

Viscosity (g/cm.s) (1–3) 104 (1–3) 104 (3–9) 104 (0.2–3) 102

Diffusivitya (cm2/s) 0.1–0.4 0.7 103 0.2 103 (0.2–2) 105

Self-diffusion for gas and SCF, binary mixture for liquid.

Supercritical fluids are attractive solvents as they exhibit physicochemical properties intermediate between those of liquids and gases (Table 2). The density, thus the solvating power, of a SCF approaches that of a liquid, whereas the diffusivity and viscosity are intermediate between gas-like and liquid-like values, resulting in faster mass transport capacity (5). As a result of the large compressibility near their critical points, SCFs’ densities/solvent power can be varied by changing operating conditions (temperature and pressure), resulting in operational flexibility, which can be exploited to achieve the required separation. Carbon dioxide is the solvent of choice for food applications. It is an inert, nontoxic, nonflammable, environmentally friendly solvent with a moderate critical temperature (31
C) and pressure (7.4 MPa), which is readily available in high purity and low cost (6).

3. HISTORIC DEVELOPMENT AND COMMERCIAL APPLICATIONS The discovery of the critical point of substances dates back to the 1820s when Cagniard de la Tour observed the disappearance of the gas-liquid meniscus at temperatures higher than critical values under pressure (7). The solvent power of SCFs has

400

SUPERCRITICAL TECHNOLOGIES FOR FURTHER PROCESSING OF EDIBLE OILS

been reported as early as 1879 (8). Although potential applications of near-critical fluids (SCFs and liquefied gases) had been proposed since the 1930s for various extraction and separation processes, such as the separation of high-molecular-weight mixtures (9), de-asphalting of petroleum (10), and purification of fatty oils (11), it was the work of Zosel (12) at the Max-Planck Institute in Mannheim, Germany, that brought this technology into commercial focus in the 1960s, which eventually led to its commercialization for coffee decaffeination and hops extraction purposes in Germany in the late 70s and early 80s. Since then, a number of supercritical fluid extraction (SFE) plants have been built around the world in varying sizes (ranging from 4 L to 6,500 L) for the processing of natural products such as hops, tobacco, spices and herbs, aromas, and nutraceuticals (13–17). In addition to extraction processes, applications of SCF technology have widened in recent years to include fractionation, particle design, coating, aerosols, impregnation, cleaning, supercritical water oxidation, analytical extraction and chromatography, production scale chromatography, extrusion, nucleation, infiltration of materials into polymers, and chemical reactions (15, 17). Motivations for commercialization of SCF technology included concerns over the use of organic solvents, which was reflected in tightening government regulations (for example, prohibition of the use of methylene chloride for coffee decaffeination in Germany was the driving force behind the commercialization of supercritical coffee decaffeination technology), changing consumer attitudes, improved product quality, increased demands on product performance, and development of innovative products or processes (14, 16). SFE has been increasingly used in recent years around the world for the processing of nutraceuticals as a ‘‘natural’’ alternative to traditional solvent-extraction processes. The ability to claim ‘‘natural extracts’’ in marketing these products is a significant advantage in today’s marketplace. SFE also offers the advantage of mild operating conditions for heatsensitive compounds (compared with distillation), and a solvent-free extract and residue (compared with solvent extraction). In addition, it provides an oxygenfree environment and, thus, limits oxidative degradation of the product.

4. SOLUBILITY BEHAVIOR OF LIPID COMPONENTS Fats and oils are complex mixtures containing lipid components belonging to major lipid classes, such as fatty acids, acylglycerols, and esters of fatty acids, and minor lipid components, such as sterols, tocopherols, hydrocarbons (e.g., squalene), and pigments (b-carotene and others). Successful application of SCF technology to any process requires information on the solubility behavior of the solutes of interest as affected by operating conditions and solute properties. Totally predictive modeling of multicomponent phase behavior in SCFs has not been realized yet. Therefore, experimental solubility measurements play an essential role in both development of thermodynamic models and process design. The accuracy/reliability of the experimental data also determines the success of thermodynamic modeling studies. Although solubility behavior of binary systems of lipids and SCCO2 has been

SOLUBILITY BEHAVIOR OF LIPID COMPONENTS

401

widely investigated (18–20), data on ternary and multicomponent systems are quite scarce. Multicomponent data are available for a limited number of systems, such as fatty acid ester mixtures, deodorizer distillates, and vegetable oils (21–25). A systematic in-depth analysis of the available solubility data ranging from binary to ternary and multicomponent systems has been carried out by the authors to establish the general solubility trends of minor and major lipid components as affected by temperature, pressure, and mixture composition, to study the deviation from binary behavior and assess implications for process development targeting fractionation of complex lipid mixtures (26–29). 4.1. Binary Systems Available literature solubility data of pure lipids belonging to major (fatty acids, mono-, di- and triacylglycerols, and fatty acid esters) and minor lipid classes (pigments, sterols, vitamins, and hydrocarbons) in SCCO2 were compiled (26, 27). These references (26, 27) contain exhaustive bibliography on lipid þ SCCO2 binary systems. Literature data were correlated using Chrastil’s equation, which is an empirical model used quite commonly to correlate the solubility of lipid components (30). This model is based on the formation of a solute-solvent complex on association of the solute and solvent molecules and establishes a linear relationship between ln(solubility) and ln(density) as follows: ln c ¼ k ln d þ a=T þ b;

ð1Þ

where c is the solubility of the solute in the supercritical solvent (g/L), d is the density of the pure solvent (g/L), and k (association number) is the number of molecules in the solute-solvent complex. Parameter a is dependent on the total heat of the reaction (heat of solvation þ heat of vaporization), and b is dependent on the molecular weights of the solute and solvent and the association constant. Parameter k, which is the slope of the solubility isotherm, reflects the density dependence of solubility. Parameter a, which is the slope of ln(solubility) versus 1/T plot, is a measure of the temperature dependence of solubility at constant density. At constant temperature, Equation 1 simplifies to ln c ¼ k0 ln d þ b0 :

ð2Þ

Chrastil’s equation was adopted in the systematic study of binary solubility behavior because it is easy to use and it does not require information on the properties of lipid components. Its parameters can then be used to interpret the effect of operating conditions on solubility. Its value, however, is limited for predictive modeling of solubility data, which should involve in-depth thermodynamic models (e.g., using an Equation of State (EOS) approach), describing all the phases present at equilibrium. The study of the binary component solubility database revealed wide discrepancies between experimental data reported by different researchers, primarily due to

402

SUPERCRITICAL TECHNOLOGIES FOR FURTHER PROCESSING OF EDIBLE OILS

6 Ref. 31 Ref. 32 Ref. 33 Ref. 34 Ref. 35 Ref. 36 Ref. 37 Ref. 38

Solubility (mole fraction*107)

5

4

3

2

1

0 0

5

10

15

20 25 Pressure (MPa)

30

35

40

45

Figure 2. Solubility isotherms of b-carotene at 313 K.

limitations of the experimental methods used and purity of samples. Although discrepancies were observed for a number of solutes, they were most apparent for sensitive solutes of low solubility, such as b-carotene (Figure 2). Impurities present in the samples as well as those deriving from sample degradation and isomeric purity of the solutes contributed to this variation. This finding highlights the need to exercise extreme caution not only when making solubility measurements, but also when interpreting the data. Solute solubility behavior in SCCO2 is determined by solute vapor pressure and intermolecular interactions between the solute and SCCO2 and, hence, is affected by operating conditions and solute properties. In binary systems of a homologous series (such as fatty acids), where intermolecular interactions are similar, solute solubilities are determined by molecular weight/vapor pressure such that solubility increased with decreasing molecular weight of the solute (Figure 3). Unsaturation in a compound affected solubility mainly through its effect on the physical state of the solute, as the melting point of fatty acids decreases with the introduction of double bonds. For example, the solubility of liquid oleic acid was substantially higher than that of stearic acid, which is a solid under the temperature and pressure conditions examined (Figure 3). As the differences between solute properties such as polarity increase, their molecular weight does not correlate with solubility in SCCO2, hence, other factors, such as specific molecular interactions, should also be considered. For example, in the acylglycerol series of oleic acid, (Figure 4, solubility isotherms constructed using Equation 2), oleic acid was the most soluble solute followed by mono- and diolein (for which relative solubilities were density dependent, such that more polar but lower molecular weight mono-olein was more soluble at low fluid densities). Triolein was the least soluble solute in this series.

SOLUBILITY BEHAVIOR OF LIPID COMPONENTS

Solubility (mole fraction*103)

6

403

Myristic Palmitic Stearic Oleic

5

4

3

2

1

0

0

5

10

15

20

25

30

35

40

45

Pressure (MPa) Figure 3. Solubility isotherms of myristic, palmitic, stearic, and oleic acids in SCCO2 at 308 K (26).

When the solubility of various minor lipid components were compared with that of selected components of other major lipid classes, it was found that a-tocopherol, oleic acid (a liquid fatty acid), and squalene were the most soluble solutes and b-carotene had the lowest solubility in SCCO2 (Figure 5, solubility isotherms constructed using Equation 2). Although the physical state of the solute had a significant impact on lipid solubility behavior, information on melting behavior of lipids in SCCO2 (e.g., melting 4 Oleic acid Monoolein Diolein Triolein

ln (solubility (g/L))

3 2 1 0 −1 −2 −3 6.40

6.45

6.50

6.55 6.60 6.65 ln (density (g/L))

6.70

6.75

6.80

Figure 4. Solubility of isotherms for acylglycerol series of oleic acid in SCCO2 at 323 K. (Solid lines represent regression results obtained using Equation 2).

404

SUPERCRITICAL TECHNOLOGIES FOR FURTHER PROCESSING OF EDIBLE OILS

4

ln (solubility (g/L))

2 0 −2 −4 −6 −8 Oleic acid Squalene a-Tocopherol

−10

Triolein Stigmasterol b-Carotene

−12 6.1

6.2

6.3

6.4

6.5

6.6

6.7

6.8

6.9

ln (density (g/L)) Figure 5. Solubility isotherms of lipid components at 323 K plotted using model parameters estimated using Equation 2.

point depression in SCCO2) was rather limited. Further research is required to provide information on the melting behavior of lipids in binary and multicomponent systems. Melting behavior of solutes should be noted during solubility measurements directly (using a view cell) or indirectly by studying the solute after the measurements for any evidence of melting. Lipid solubility increased with pressure for all the studied solutes, whereas a solubility maximum was observed in the solubility isotherms of solid solutes such as stearic acid, b-carotene, and b-sitosterol at pressures higher than 30 MPa (26, 27). Although the investigated liquid systems did not exhibit similar behavior, solubility maxima have been well established for vegetable oils at high pressures. Increasing the temperature at constant CO2 density increases the solubility because of an exponential increase in the solute vapor pressure. A temperature effect at constant CO2 density on solubility was observed for all compounds, although the magnitude of the effect varied. An isobaric increase in temperature decreases the solvent density and increases the vapor pressure of the solute. The overall impact of these two opposing effects of temperature on solubility is dependent on the pressure, resulting in a crossover of solute solubility isotherms. Below the crossover pressure, the density effect predominates and the solubility decreases with increasing temperature, which is referred to as retrograde behavior. Above this crossover point, the solubility increases with temperature because of the vapor pressure effect. In general, solid solutes (such as stigmasterol, b-carotene, and solid fatty acids) had a low crossover pressure and, therefore, showed nonretrograde behavior in the range of operating conditions commonly employed. Although the presence of a crossover point in solid systems has been well established previously, liquid systems and the effect of melting on the crossover behavior have not been addressed

SOLUBILITY BEHAVIOR OF LIPID COMPONENTS

405

adequately. Although a crossover pressure was observed for some liquid lipid components, solubility of liquid solutes, such as fatty acid esters, decreased with temperature in the investigated experimental range. Binary data can be used to determine the optimum fractionation conditions in the design of fractionation processes for mixtures such as fatty acid esters. For more complex mixtures containing different lipid classes, such as deodorizer distillates, or for mixtures/mixture components that undergo melting, the effect of operating conditions on multicomponent solubility behavior can vary greatly, depending on mixture composition. Regardless, binary solubility data can still provide invaluable information for the fractionation of lipid components and estimation of the degree of separation. For example, fractionation of solutes with similar binary solubilities, such as fatty acids, tocopherols, and squalene, would be very difficult to achieve by varying the operating conditions and may warrant additional processing steps; whereas solutes with different solubilities, such as triacylglycerols/sterols and fatty acids, can be separated with ease in a fractionation column. 4.2. Cosolvent Systems It is well known that the phase behavior of solutes in SCCO2 can be modified by the addition of a small amount of cosolvent, such as ethanol. The main effect of a cosolvent is the solubility enhancement that results from an increase in the density of SCCO2 þ cosolvent mixture or intermolecular interactions between the cosolvent and particular solutes. Selectivity of a separation can be improved by cosolvent addition only if there are specific intermolecular interactions between the cosolvent and one or more of the mixture components, as solubility of all mixture components is enhanced due to the density effect. Literature equilibrium solubility data of ternary systems of major and minor lipid components, cosolvents, and SCCO2 have been compiled (28), and the effect of cosolvent addition on the solubility behavior of fatty acids (stearic, palmitic, and behenic acids), squalene, and b-carotene studied. Cosolvent effect is quantified as solubility enhancement, which is the ratio of solubility obtained with cosolvent addition to that without a cosolvent (28). This reference (28) contains an exhaustive bibliography on cosolvent þ SCCO2 þ lipid systems. Solubility enhancements observed for lipid components in SCCO2 þ ethanol are summarized in Table 3. The high solubility enhancement observed in the presence of ethanol for fatty acid systems were attributed to H-bonding interactions. Such specific intermolecular interactions between a solute and a cosolvent can be exploited for fractionation of lipid mixtures. In the literature, the thermodynamic advantages of cosolvent addition have been emphasized; however, the effect of cosolvents on other aspects of the process, such as mass transfer, overall cost, and product/residue properties, has not been considered in depth. Benefits of cosolvent addition must be balanced against its disadvantages for a specific application. Cosolvent introduction and solvent recovery (separation of the cosolvent from the extract, SCF, and solids residue) increase the complexity of process design. As well, an increase in solvent loading may result

406

SUPERCRITICAL TECHNOLOGIES FOR FURTHER PROCESSING OF EDIBLE OILS

TABLE 3. Cosolvent Effect (Solubility Enhancement) of Ethanol in Lipid Systems. Solute

Solubility Enhancementa

Ethanol Concentration

T (K)

P (MPa)

Data from ref.

308 308, 318 308, 318

9.9, 19.7 8–19.7 8–16

39 39–41 42

313–333 308 333

15–28 15.2 20–27.5

43 44 45

343 333

20 34.5

46 47

Fatty acids b

1.0–8.8e 0.5–8.8e 1.21–6.7e

palmitic acid stearic acid behenic acid

1.5–63.7 1.2–63.2b 2.0–29.2b

b-carotene stigmasterol squalene

2.2–9.8b 4.0b 1.8–5.9c

0.3–2.4f 3.5g 4.1–12.0f

palm oil pistachio oil

20d 4.8d

10f 10f

Minor lipid components

Vegetable oils

a

Solubility enhancement ¼ the ratio of solubility obtained with cosolvent addition to that without a cosolvent. Calculations based on solubility in mole fraction. Solubility in w/w. d Solubility in wt %. e mol % in the supercritical phase (solute inclusive). f wt % (solute free). g mol % (solute free). b c

in the coextraction of undesirable compounds. The effect of cosolvent addition on the sample matrix and solutes of interest, such as alteration of functional properties of extraction residue and degradation of the extract by the cosolvent, should also be considered. Cosolvents should be used with caution as one of the major advantages offered by SCCO2, namely the ability to produce ‘‘natural’’ products with no organic solvent residue, may be negated. Ethanol is the cosolvent of choice for food applications because of its GRAS (Generally Recognized As Safe) status; but the removal of ethanol from the extract and residue requires the application of heat via evaporation, which may be detrimental to the quality of the extract and residue. This step also undermines another advantage of SCCO2 extraction that it can be carried out at low temperatures. 4.3. Multicomponent Systems Literature phase equilibrium data of ternary and higher (quaternary and quinary) systems of lipids and SCCO2 have been compiled (29). This reference (29) contains exhaustive bibliography of multicomponent lipid þ SCCO2 systems. For systems where an adequate number of data points were available, partition coefficients and selectivities were calculated, and the data analyzed by plotting vapor phase concentration (solubility in SCCO2), liquid phase concentration, partition coefficients, and selectivities as a function of pressure to determine the effect of operating conditions and feed composition on solubility behavior (29). The ternary systems studied included SCCO2 and two triacylglycerols (trilaurin (LLL)/tripalmitin

SOLUBILITY BEHAVIOR OF LIPID COMPONENTS

407

(PPP), trimyristin (MMM)/PPP, LLL/MMM), two fatty acids (oleic acid (OA)/linoleic acid (LA)), two fatty acid methyl esters (methyl myristate (MeM)/methyl palmitate (MeP) and methyl oleate (MeO)/methyl linoleate (MeL)), fatty acid/ triacylglycerol (OA/triolein (OOO)), and fatty acid methyl ester/fatty acid (MeO/ OA). The quaternary and quinary systems analyzed contained three triacylglycerols (LLL/MMM/PPP), three acylglycerols (mono-olein (MO)/diolein (DO)/OOO), and four triacylglycerols (PPP/palmitoyl-dioleoylglycerol (POO)/oleoyl-dipalmitoylglycerol (PPO)/OOO), respectively, in SCCO2. Binary solubility data were also included in the analysis to determine any deviation from expected behavior based on binary data. The value of binary data was limited in predicting solubility behavior in ternary and higher lipid systems as multicomponent solubilities deviated from binary behavior. Although solubility of the less soluble component increased in ternary systems of solid triacylglycerols in SCCO2, that of the more soluble component stayed the same, or was not affected. Solubility diminution was observed for both solutes in some liquid mixtures, such as fatty acid (oleic acid/linoleic acid) and fatty acid ester (methyl oleate/methyl linoleate) mixtures. The extent of this diminution was dependent on the initial feed concentration of the solute. However, in other liquid mixtures, solubility enhancement for one of the mixture components was also observed (for example, for oleic acid in the presence of methyl oleate). These deviations, in turn, affected the separation efficiency (assessed in terms of partition coefficient and selectivity) of the solutes of interest. Separation efficiency was lower than that predicted by binary data when the solubility of the less soluble solute was enhanced, in the mixture. On the other hand, separation efficiency was improved if the solubility of the more soluble component was enhanced, as observed in the quaternary mixture of SCCO2 and acylglycerols (MO/DO/OOO). Figure 6 shows that 45 40

MO/DO -10:10:80

MO/OOO-10:10:80

DO/OOO-10:10:80

MO/DO-33:33:33

MO/OOO-33:33:33

DO/OOO-33:33:33

MO/DO-binary

MO/OOO-binary

DO/OOO-binary

Selectivity

35 30 25 20 15 10 5 0 15

17

19

21

23 25 27 Pressure (MPa)

29

31

33

Figure 6. Selectivities (MO/DO, DO/OOO, MO/OOO) in quaternary acylglycerol mixture (data from Ref. 20).

408

SUPERCRITICAL TECHNOLOGIES FOR FURTHER PROCESSING OF EDIBLE OILS

the presence of a less polar component in the mixture (OOO, 33% or 80% of feed mixture) leads to solubility enhancement of the polar mixture components (MO and DO). This ‘‘dilution’’ effect can have important implications for fractionation processes, as it may improve the separation efficiency significantly if the more polar components are more soluble than the diluting component.

5. SUPERCRITICAL FLUID PROCESSING OF FATS AND OILS The ability to fine tune solvent properties of SCFs through changes in operating conditions can be exploited in a wide range of applications, such as extraction, fractionation, and reaction processes, where flexibility in process implementation offers the researcher/processor a gamut of possibilities. Supercritical fluid processing of fats and oils has been widely investigated over the last three decades. Earlier work on SCF processing of fats and oils as reviewed by Brunner and Peter (48) included extraction of oil from oilseeds, extraction of fat from egg yolk and starch-containing vegetable matter, extraction of lanolin from wool grease, refining of natural oils, purification of monoacylglycerols, and fractionation of cod liver oil, using a variety of solvents such as propane, propylene, ethylene, CO2, and ethane. Although some of the earlier studies focused on the extraction of commodity oils, such as canola and soybean (49, 50), extraction of specialty oils (oils high in bioactive components) (51–55) and fractionation of fats and oil mixtures (56, 57) have been the subject of more recent studies.

5.1. Supercritical Fluid Extraction 5.1.1. Fundamentals

The SFE process consists of two basic steps: extraction and separation. During the extraction step, the soluble material is extracted under high pressure from the solid feed material and transported away by the SCF. Separation of the supercritical solvent from the extract (regeneration of the supercritical solvent and recovery of the solute) can be achieved by reducing the density/solvent power of the SCF solvent by decreasing the pressure or by elevating the temperature or both. The process must be adapted to the separation problem at hand, considering the target material (58). The process can be operated on batch, semicontinuous, or continuous mode (59). Batch processing (Figure 7) involves contacting a batch of solid feed material with a continuous solvent stream. However, the necessity to depressurize the vessel for the introduction of a new batch of material limits the efficiency of the process. Therefore, most production plants are operated semicontinuously, where three or four vessels are operated in a cyclic fashion, such that as one vessel is being extracted, another is being loaded, and a third vessel is being pressurized/depressurized (Figure 7). Continuous introduction of the solid feed material into the

5.1.1.1. Mode of Operation

SUPERCRITICAL FLUID PROCESSING OF FATS AND OILS

Batch

409

Semicontinuous E1

E2

E3 Separator

Separator Extractor

Figure 7. Typical supercritical fluid extraction systems.

extraction vessel under high pressure poses an equipment design challenge, especially for the handling of large volumes of oilseeds. Lock hopper vessels and screw conveyors are some alternatives that are in operation or under development for the continuous processing of solid feed material under high pressure (7, 60). 5.1.1.2. Extraction Kinetics As in any extraction process, SFE kinetics consists

of three periods; solubility-controlled or a period of constant extraction rate, a transition period of falling extraction rate, and diffusion-controlled or asymptotic period with respect to solute extraction rate (Figure 8). During the initial period, the solute’s accessibility results in an extraction rate that is constant. Hence, the slope of the extraction curve, weight of extract versus volume or weight of CO2, can be used to determine the loading of the solvent. This value corresponds to solubility only if equilibrium is attained during extraction by operating at low enough solvent flow rates. The extraction rate starts to decline in the transition period and the mechanism of extraction kinetics is switched to diffusion of the solvent and solute into and out of the sample matrix. Therefore, efficiency of SFE process is affected by operating conditions (i.e., temperature, pressure, flow rate, solvent-to-feed ratio) and feed material properties (i.e., particle size, particle density, and porosity) and these parameters should be optimized for an efficient process. Flaking has been shown to be the most efficient pretreatment for the SFE of many oilseeds (49, 61–63). Mass transfer modeling of SFE of oilseeds has been studied by various researchers (49, 64, 65). Supercritical CO2 extraction of oilseeds has been the focus of extensive research activity in the 1980s when a variety of oilseeds, such as soybean, cottonseed, corn germ, rapeseed, and sunflower, were extracted using SCCO2 (66). Although SCCO2 extracted oils were shown to have similar quality compared with hexane extracts, they also had lighter color and lower iron and phospholipid content, resulting in a lower refining loss and reduction of subsequent refining steps (67–70). However, the oxidative stability of

5.1.2. Applications in Fats and Oils Processing

410

SUPERCRITICAL TECHNOLOGIES FOR FURTHER PROCESSING OF EDIBLE OILS

% Extracted

Maximum % extracted

Solubility Controlled Phase

Diffusion Controlled Phase

Transition Phase

Volume of Fluid Time of Extraction Figure 8. A typical supercritical fluid extraction curve.

CO2 extracts was lower than that of hexane-extracted oils, which was attributed to the lower phospholipid content of the CO2 extracts (71, 72). Protein quality of the CO2-extracted meal was comparable with that of hexane-extracted meal (73). In spite of the high volume of research carried out on extraction of oilseeds, commercial-scale SCCO2 extraction of oilseeds was not readily accepted. Even though the overall process based on SCCO2 extraction would be simpler compared with conventional hexane extraction in terms of eliminating the need for hexane evaporators and meal desolventizer, the high equipment costs associated with the SCCO2 process and the inability to achieve continuous processing of high volumes of oilseeds under SCF conditions have been cited as the major impediments to commercialization of the SCCO2 process (60). However, recent developments in equipment design (i.e., the coupling of CO2 with expeller technology) and stricter government regulations on the use of hexane may make this a reality in the near future. In the case of specialty oils, the cost of SFE can be balanced by the high value of the product and the added advantage of ‘‘natural’’ processing. Rice bran (74–77) and corn fiber oils (78) are currently receiving attention because of their high sterol content. Cereals such as wheat germ (79, 80) and barley (81) in addition to plants such as Silybum marianum (milk thistle) (82) have also been investigated as sources for the production of oils rich in tocopherols. SCCO2 extraction of oils rich in carotenes from sources such as palm fruit and oil fibers (83, 84) have also been

SUPERCRITICAL FLUID PROCESSING OF FATS AND OILS

411

reported. In the case of highly unsaturated oils, such as evening primrose (51–53), flaxseed (54), and poppy seed oils (55), which are good sources of a- and g-linolenic and linoleic acids, the ability to extract at mild operating conditions and in an oxygen-free environment offers a significant advantage of SCCO2 processing for these labile oils. 5.2. Supercritical Fluid Fractionation 5.2.1. Fundamentals In SCF fractionation, separation is based on differences in

the solubility behavior of mixture components deriving from both the differences in component volatilities (as in distillation) and the differences in intermolecular interactions between the mixture components and the SCF solvent (as in solvent extraction), as noted previously (12). SCF fractionation of extracts can be achieved by fractional extraction or fractional separation. During SFE, fractionation occurs as a function of time, which is reflected in the compositional differences of the fractions collected throughout the process. Fractional extraction, thus, relies on compositional differences between fractions obtained throughout the extraction. It is largely governed by the differences in the solubility behavior of extract components, but may also be affected by the location of the solutes in the solid sample matrix. During the extraction of vegetable oils, fractionation of minor components, such as phospholipids, sterols, and tocopherols, occurs as evidenced by their higher concentrations in specific fractions (50). Concentration of free fatty acids (FFA) has also been observed during SCCO2 extraction of oilseeds (50, 85). Free fatty acids are usually concentrated in the earlier fractions as a result of their higher solubility compared with that of triacylglycerols (85); however, Friedrich et al. (50) observed increasing concentrations of FFA in the later fractions during soybean oil extraction. Eggers and Sievers (63) observed that a higher amount of water was extracted compared with oil toward the end of SCCO2 extraction for rapeseed press-cake, and they attributed this to the higher transport resistance of water relative to oil in the cake. The compositional differences between fractions can be accentuated by using a density gradient, which can be achieved by increasing the pressure or adding a cosolvent at certain time intervals during extraction. In fractional separation (Figure 9), where the differences in the solubility behavior of extract components are exploited, fractionation is achieved after the extraction step using a series of separators operated at conditions adjusted to yield a stepwise decrease in solvent power/density. Supercritical fractionation of a liquid lipid feed material is usually carried out in a packed column. Standard columns are not available commercially and have to be custom built either in-house or by manufacturers of extraction units. Lab-scale and pilot-scale supercritical columns, 0.6–13.6 m high with internal diameters of 14.3– 68 mm are available in research labs around the world and have been used for the processing of deodorizer distillates (56, 57, 86–90), vegetable and fish oils (91– 105), cocoa butter, and milkfat (106–109). A schematic diagram of a typical SCCO2 fractionation column (2.8 m, 2.54 cm o.d.), which was designed and built

412

SUPERCRITICAL TECHNOLOGIES FOR FURTHER PROCESSING OF EDIBLE OILS

Fractional separation

Extractor

Separator 1

Separator Separator 2 3

Figure 9. A typical supercritical fluid fractional separation system.

in our lab and others is shown in Figure 10. Packed columns can be operated in a continuous mode by introducing the liquid feed material into the column using a feed pump to achieve a cocurrent or countercurrent operation. A thermal gradient along the column can be applied to generate an internal reflux such that feed components are subjected to higher temperatures (i.e., lower solvent densities) as they move up the column, resulting in enhanced separation efficiency. In earlier fractionation column designs, the thermal gradient was achieved using a hot finger mounted at the top of the column (12, 110), whereas in recent designs, the thermal gradient is achieved by independent temperature control of column zones (96). An external reflux can also be generated by adding an external reflux pump (111). Supercritical CO2 fractionation of fats and oils has been investigated by various researchers for the refining (deacidification and degumming) of oils, for the concentration of bioactive components of fats and oils and byproducts and for the fractionation of milkfat. Supercritical CO2 processing has been investigated as an alternative to traditional oil refining processes for various oils, such as palm (93, 112), rice bran (75, 92, 96), olive (91, 103), black cumin seed (113), peanut (94), and soybean oils (114). Dunford and King (92) achieved deacidification of rice bran oil to a level of