Food Emulsifiers and Their Applications

Food Emulsifiers and Their Applications

Food Emulsifiers and Their Applications Edited by

Gerard L. Hasenhuettl Kraft Foods

Richard W. Hartel University of Wisconsin

SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.

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Contents

xiii

Contributors Preface

XV

ONE Overview of Food Emulsifiers

1

Gerard L. Hasenhuettl 1.1 1.2 1.3 1.4

Introduction Emulsifiers as Food Additives Emulsifier Structure Emulsifier Functionality References

1 2 5 7 9

TWO Synthesis and Composition of Food-Grade Emulsifiers

11

R. J. Zielinski 2.1 2.2 2.3 2.4 2.5

Introduction Mono- and Diglycerides Propylene Glycol Monoesters Lactylated Esters Polyglycerol Esters vii

11 13 15 18 23

viii

Food Emulsifiers and Their Applications

2.6 Sorbitan Esters 2. 7 Ethoxylated Esters 2.8 Succinylated Esters 2.9 Fruit Acid Esters 2.10 Acetylated Monoglycerides 2.11 Phosphated Esters 2.12 Sucrose Esters References

26 26 29 31 33 36 36 38

THREE Analysis of Food Emulsifiers

39

Gerard L. Hasenhuettl

3.1 3.2 3.3 3.4 3.5 3.6

Introduction Thin-Layer and Column Chromatography Wet Chemical Analysis Physical Methods Instrumental Methods Setting Specifications for Food Emulsifiers References

39 40 43

52 54 62 63

FOUR

Carbohydrate/Emulsifier Interactions

67

Lynn B. Deffenbaugh

4.1 Introduction 4.2 Inclusion Complexes of Starch 4.3 Effects of External Lipid Materials on Starch Properties 4.4 Factors Affecting Complex Formation 4.5 Physical Properties of Starch/Emulsifier Complexes 4.6 Summary References

67 68 69 81 85 90 90

Contents

ix

FIVE

Protein/Emulsifier Interactions

Martin Bos, Tommy Nylander, Thomas Arnebrant,

95

and David C. Clark 5.1 5.2 5.3 5.4 5.5

Introduction Protein Stability Protein/Surfactant Interactions Protein/Phospholipid Interactions Protein/Emulsifier Interactions-Food Applications References

95 97 98 120 132 137

SIX

Physicochemical Aspects of an Emulsifier Functionality 147 Bjorn Bergenstahl 6.1 6.2 6.3 6.4

Introduction Surface Activity Solution Properties of Emulfiers The Use of Phase Diagrams to Understand Emulsifier Properties 6.5 Examples of the Relation between Phase Diagrams and Emulsion Stability 6.6 Some Ways to Classify Emulsifiers 6.7 The Emulsifier Surface References

147 148 149 153 154 161 167 171

SEVEN

Emulsifiers in Dairy Products and Dairy Substitutes

173

Stephen R. Euston 7.1 Introduction 7.2 Ice Cream

173 174

X

Food Emulsifiers and Their Applications

7.3 Whipped Cream and Whipping Cream 7.4 Whipped Toppings 7.5 Cream Liqueurs 7.6 Creams and Coffee Whiteners 7. 7 Processed Cheese 7.8 Recombined, Concentrated and Evaporated Milks 7.9 Other Dairy Applications of Emulsifiers 7.10 Summary References

183 187 191 194 197 199 202 203 204

EIGHT

Applications of Emulsifiers in Baked Foods

211

Frank T. Orthoefer

8.1 8.2 8.3 8.4 8.5 8.6 8. 7 8.8

Introduction History of Emulsified Shortenings Emulsifier Function in Baked Goods Role of the Shortening Role of the Emulsifier Emulsifier Interaction with Bakery Components Applications in Baked Goods Summary References

211 211 213 215 216 221 225 233 234

NINE

Emulsifiers in Confectionery

235

Mark Weyland

9.1 Introduction 9.2 Emulsifiers in Chocolate and Compound Coatings 9.3 Antibloom Agents in Chocolate and Compound Coatings 9.4 Other Emulsifiers Used in Coatings 9.5 Emulsifiers in Nonchocolate Confectionery

235 236 244 248 249

Contents

xi 252 253

9.6 Processing Aids References

TEN Margarines and Spreads

255

Eric Flack

10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 10.10 10.11 10.12

Introduction Early Development Yellow-Fat Consumption Definitions and Descriptions Structure and Raw Materials Fat Crystallization Emulsifiers Processing Reduced- and Low-Fat Spreads Oil-in-Water Spreads Liquid Magarine Summary References

255 256 257 258 262 263 267 270 274 278 278 279 279

ELEVEN Emulsifier Trends for the Future

281

Gerard L. Hasenhuettl

Globalization in the Food Industry Nutritionally Driven Changes in Food Trends toward Safer Emulsifers Emulsifer Structure and Interactions with Other Ingredients 11.5 Enzymatic Synthesis of Food Emulsifiers References

11.1 11.2 11.3 11.4

Index

282 282 283 284 285 286 287

Contributors

Thomas Arnebrant Department of Pharmaceutical Analysis Ferring AB Box 30047 S-216 13 Malmo, Sweden Bjorn Bergenstahl Institute for Surface Chemistry P.O. Box 5607 S-114 86 Stockholm, Sweden Martin Bos TNO Nutrition & Food Research Institute P.O. Box 360 3700 AJ Zeist, The Netherlands David C. Clark DMV International NBC-Iaan 80 P.O. Box 13 5460 BA Veghal, The Netherlands

xiii

xiv

Contributors

Lynn B. Deffenbaugh Hill's Pet Nutrition Science & Technology Center P.O. Bo.c 1658 Topeka, KS 66601-1658 Stephen R. Euston New Zealand Dairy Research Institute Private Bag 11029 Palmerston North, New Zealand Eric Flack Danisco Ingredients, Ltd. North Way Bury St. Edmonds Suffolk, 1P32 6NP, United Kingdom Gerard L. Hasenhuettl Kraft Foods, Inc. 801 Waukegan Rd. Glenview, IL 60025 Tommy Nylander University of Lund, Chemical Center Department of Physical Chemistry P.O. Box 124 S-22100 Lund, Sweden Frank T. Orthoefer 2004 Me Cracken St. Stuttgart, AR 72160 Mark Weyland Quest International 5115 Sedge Blvd. Hoffman Estates, IL 60192 Richard J. Zielinski Quest International Joliet Technical Center 24708 Durke Dr. Joliet, IL 60410-5249

Preface

Food emulsions have existed since long before people began to process foods for distribution and consumption. Milk, for example, is a natural emulsion/colloid in which a nutritional fat is stabilized by a milk-fat-globule membrane. Early processed foods were developed when people began to explore the art of cuisine. Butter and gravies were early foods used to enhance flavors and aid in cooking. By contrast, food emulsifiers have only recently been recognized for their ability to stabilize foods during processing and distribution. As economies of scale emerged, pressures for higher quality and extension of shelf life prodded the development of food emulsifiers and their adjunct technologies. Natural emulsifiers, such as egg and milk proteins and phospholipids, were the first to be generally utilized. Development of technologies for processing oils, such as refining, bleaching, and hydrogenation, led to the design of synthetic food emulsifiers. Formulation of food emulsions has, until recently, been practiced more as an art than a science. The complexity offood systems has been the barrier to fundamental understanding. Scientists have long studied emulsions using pure water, hydrocarbon, and surfactant, but food systems, by contrast, are typically a complex mixture of carbohydrate, lipid, protein, salts, and acid. Other surface-active ingredients, such as proteins and phospholipids, can demonstrate either synerXV

xvi

Preface

gistic or deleterious functionality during processing or in the finished food. The formulator of food emulsions has therefore traditionally been an experienced individual who reasoned by analogy to obtain desired technical effects in the new food products. Recent impressive progress has been made in understanding the physical chemistry of food emulsions, dispersions, and foams by application of sophisticated instrumentation and computing power. An appreciation of ingredient interactions has also been developed, as many of the references in this book bear testimony. However, a coherent work focusing on the design of emulsifiers for food applications has been notably absent. In this volume, we have attempted to collect material that clarifies the process of designing a commercially viable emulsifier system for new products or improvement of existing foods. The process begins with an understanding of the role and possibilities of the emulsifier to not only stabilize emulsions but also to provide critical secondary functionalities. Manufacturing technology is described and analytical tests that ensure the quality of the emulsifier ingredient are presented. Interactions of food emulsifiers with carbohydrates, proteins, and water are significant in their use and are extensively discussed. Applications of emulsifiers in the dairy, bakery, confectionery, and margarine industries demonstrate the reasoning process used to develop emulsion-based products. It is our

hope that this effort will stimulate further innovation directed at increasing the quality and reducing the expense of processed food products.

Acknowledgments The editors express their apprec1atwn to Barbara Bagnuolo and Julie Hasenhuettl for typing and proofreading large portions of the manuscript.

Gerard L. Hasenhuettl Richard W. Hartel

Food Emulsifiers and Their Applications

ONE

Overview of Food Emulsifiers Gerard L. Hasenhuettl

1.1

Introduction

Food emulsions, colloids, and foams have their origins in the evolution of animal species. Milk has a naturally occurring membrane that allows the dispersion of fat droplets into an aqueous environment. Early food formulations to produce butter, whipped cream, cheese, and ice cream built upon the natural emulsifiers present in the system. The development of mayonnaise in France as a cold sauce utilized the natural egg phospholipids to disperse a liquid oil into an acidified aqueous phase. The emulsifying power is still very impressive by today's standards since it allowed up to 80% oil to be dispersed without inversion to an oil-continuous emulsion. The invention of margarine by the French chemist Hippolyte Mege-Mouries in 1889 utilized the solid fat of tallow to produce a stable oil-continuous emulsion to serve as a low-cost substitute for butter. In this case, the emulsion had to be stable temporarily only until the product was chilled. Synthetic emulsifiers have come into common use only in the latter half of the twentieth century. Their development was driven by the emergence of the processed food industry, which needed technology to produce and preserve quality products that could be distributed through mass market channels. A key technical hurdle was to maintain product stability over an extended shelf

1

2

Food Emulsifiers and Their Applications

life. With small amounts of emulsifier, for example, salad dressings can be stored on a shelf for more than a year without visible separation. Now, other factors such as the development of rancidity limit consumer acceptance of aging products. Detailed knowledge of the physical chemistry of emulsions is best obtained when pure oil, water, and surfactants are used. Food emulsions, by contrast, are extraordinarily complex systems. Commercial fats and oils are complex mixtures of triglycerides that also contain small amounts of highly surface-active materials (Friberg and Larsson, 1990). Salt content and pH in food emulsions vary widely enough to have significant effects on their stability. Natural and commercial emulsifiers are often complex mixtures that vary in composition between different manufacturers. Other food ingredients, such as proteins and particulates, contribute surface activity that may dramatically alter the character of the emulsion. Because of all these complex relationships, the formulation of food emulsions grew up as an art, dominated by individuals having a great deal of experience. The gradual development of sophisticated techniques such as electron microscopy, nuclear magnetic resonance, and chromatography/mass spectrometry has solidified the art with a scientific dimension. The subject of food emulsions has been extensively reviewed by Friberg and Larsson (1990), Krog et al. (1985), and Jaynes (1985). This book will be oriented to the design, manufacture, and use of food emulsifiers as ingredients to improve the quality and economy of processed foods.

1.2

Emulsifiers as Food Additives

Approximately 500,000 metric tons of emulsifiers are produced and sold worldwide. However, since the value/volume ratio of these products is low, very little truly global trade has yet developed. In the United States, food emulsifiers fall into two categories: substances affirmed as GRAS (21CFR184) and direct food additives (21CFR172). Substances that have been affirmed as GRAS (generally recognized as safe) usually have less stringent regulations attached to their use. However, Food and Drug Administration Standards of Identity may preclude their use in certain standardized foods. In comparison, direct food additives may be allowed only in certain specific foods at low maximum allowable levels. The method of manufacture and analytical constants may also be defined. The most commonly used food emulsifiers are listed in Tables 1.1 and 1.2.

Overview of Food Emulsifiers

3

Table 1.1 Emulsifiers affirmed as GRAS Emulsifier

2ICFR No.

Lecithin

Functionalities

Typical applications

184.1400

Coemulsifier, viscosity reducer

Margarines, chocolate products

Monoglycerides

184.1505

Emulsifier, aerator, crystal stabilizer

Margarines, whipped toppings, peanut butter stabilizers

Diacetyltartaric acid esters of monoglycerides

184.1101

Emulsifier, film former

Baked goods, confections, dairy product analogs

Monosodium salt of analogs, phosphated monoglycerides

184.1521

Emulsifier, lubricant, release agent

Dairy products, soft candy

The European Economic Community (EEC) has also developed regulations for food additives that may be utilized within the member nations. Substances are divided into four annexes that have some resemblance to United States regulations. Annex I is similar to the GRAS list (2ICFRI82). These additives may be used anywhere except in natural or standardized processed foods. Annexes 2 and 3 resemble direct food additive regulations. A separate listing for solvents and solubilizing agents is contained in Annex 4, which is not separated in FDA regulations. Although the additive regulations are similar, great care must be taken in trade between the United States and the EEC because some specific emulsifiers are defined differently. For example, emulsifiers derived from polyglycerols up to decaglycerol are permitted in the United States, but they are limited to tetraglycerol or lower in the EEC. Other parts of the world have not developed into trading blocks with defined regulations. Each country may have a unique perspective on which emulsifiers may be allowed in food products. The problem is compounded by the fact that regulations are written in the national language, requiring extensive and careful translation. Some major differences in technology may develop because of a country's unique specifications. For example, polysorbates have not been permitted as food additives in Japan. As a result, technology for production of higher cost polyglycerol and sucrose esters has been widely developed there.

4

Food Emulsifiers and Their Applications

Table 1.2 Emulsifiers classified as direct food additives Emulsifier

21CFR No.

Functionalities

Typical applications

Emulsifier, plasticizer, surface-active agent

whipped toppings

Lactylated monoglycerides

172.850

Acetylated monoglycerides

172.828

Film former, moisture barrier

Fruits, nuts, pizza

Succinylated monoglycerides

172.830

Emulsifier, dough strengthener

Shortenings, bread

Ethoxylated monoglycerides

172.834

Emulsifier, stabilizer

Cakes, whipped toppings, frozen desserts

Sorbitan monostearate

172.842

Emulsifier, rehydrating agent

Confectionery coatings, yeast, cakes, icings

Polysorbates

172.836 172.838 172.840

Emulsifier, opacifier, solubilizer, wetting agent

Salad dressings, coffee whiteners, gelatins, ice cream

Polyglycerol esters

172.854

Emulsifier, aerator, cloud inhibitor

Icings, salad oils, peanut butter, fillings

Sucrose esters of fatty acids

172.859

Emulsifier, texturizer, film former

Baked goods, fruit coatings, confectionery

Calcium and sodium Stearoyllactylates

172.844 172.846

Emulsifier, dough conditioner, whipping agent

Bread, coffee whiteners, icings, dehydrated

Baked products,

potatoes Propylene glycol esters

172.858

Emulsifier, aerator

Cake mixes, whipped toppings

Overview of Food Emulsifiers

5

As with any other totally new food additive, the need to prove safety of the product in foods at high levels of consumption requires extensive toxicity studies and enormous documentation. The consequent financial and time commitments make development of totally new emulsifiers unattractive for emulsifier manufacturers. A somewhat easier development approach is to petition for expanded use (new applications or higher permitted levels) of emulsifiers that are already approved. However, even this tactic may require several years of review. In addition to national regulations, many food processors require their ingredients, including food emulsifiers, to be kosher so that their products are acceptable to Jewish and many Islamic consumers. For emulsifiers to be kosher, they must be produced from kosher-certified raw materials. This requirement precludes the use of almost all animal fats. This is not much of a problem since emulsifiers are easily produced from vegetable fats that can be blended to give similar fatty acid compositions. The major concern in kosher certification is to determine in advance whether the customer's rabbinical council recognizes the Hekhsher (kosher symbol) of the producer's rabbi. Products labeled as "all natural" must contain ingredients that have not been chemically processed or modified. Only lecithin or other naturally occurring materials such as proteins would be acceptable for these products.

1.3

Emulsifier Structure

Surface-active compounds (surfactants) operate through a hydrophilic head group that is attracted to the aqueous phase, and an often larger lipophilic tail that prefers to be in the oil phase. The surfactant therefore positions itself at the air/water or oil/water interface where it can act to lower surface or interfacial tension, respectively. Figure l.l shows some typical hydrophilic and lipophilic groups. Lipophilic tails are composed of Cl6 (palmitic) or longer fatty acids. Shorter chains, such as Cl2 (lauric), even though they can be excellent emulsifiers, can hydrolyze to give soapy or other undesirable flavors. Unsaturated fatty acids are Cl8 molecules having one (oleic) or two (linoleic) double bonds. Linoleic acid is usually avoided since it is easily oxidized and may produce an oxidized rancid off-flavor in the finished food. Fats may be hydrogenated to produce a mixture of saturated and unsaturated fatty acids. Emulsifiers produced from these fatty acids may have an intermediate consistency (often referred to as "plastic") between liquid and solid. These products

6

Food Emulsifiers and Their Applications

Lipophilic end

Hydrophilic end -OH

Saturated; palmitate or stearate

H

H

Unsaturated; oleate

Unsaturated; linoleate

Figure 1.1

Typical hydrophilic and lipophilic groups.

also contain measurable concentrations of trans (E) fatty acids that have higher melting points than the cis (Z) fatty acids. Polar head groups may be present in a variety of functional groups. They may be incorporated to produce anionic, cationic, amphoteric, or nonionic surfactants. Mono- and diglycerides, which contain an -OH functional group, are the most widely used nonionic emulsifiers. Lecithin, whose head group is a mixture of phosphatides, may be visualized as amphoteric or cationic, depending on the pH of the product. Proteins may also be surface active due to the occurrence of lipophilic amino acids such as phenylalanine, leucine, and isoleucine. lnterfacially active proteins will fold so that lipophilic groups penetrate into the oil droplet while hydrophilic portions of the chain extend into the aqueous phase. Proteins in this configuration may produce a looped structure that provides steric hindrance to oil-droplet flocculation and coalescence. Charged proteins may also stabilize emulsions due to repulsion of like charged droplets. Proteins may also destabilize water-in-oil emulsions, such as reduced fat margarines, by causing the emulsion to invert. Food emulsifiers may be thought of as designer molecules because the structure and number of heads and tails may be independently varied. A very useful conceptual tool is hydrophile/lipophile balance (HLB). The topic has been extensively reviewed by Becher, so only a brief description will be presented here. The number and relative polarity of polar groups in a surface-ac-

Overview of Food Emulsifiers

1

tive molecule determine whether the molecule will be water- or oil-soluble (or -dispersible). This concept has been quantitated by calculation of an HLB value to describe a given emulsifier. High-HLB values are associated with easy water dispersibility. Since conventional practice is to disperse the surfactant into the continuous phase, high-HLB emulsifiers are useful for preparing and stabilizing oil-in-water (0/W) emulsions. Low-HLB emulsifiers are useful for formulation of water-in-oil (W/0) emulsions, such as margarine. Extreme high or low values are not functional as emulsifiers since almost all of the molecule will be solubilized in the continuous phase. They would, however, be very useful for full solubilization of another ingredient, such as a flavor oil or vitamin, in the continuous phase. At some intermediate values of HLB, the molecule may not be stable in either phase and will result in high concentration at the interface.

1.4 Emulsifier Functionality In addition to their major function of producing and stabilizing emulsions, food emulsifiers contribute to numerous other functional roles, as shown in Table 1.3. Some foods, notably chocolate and peanut butter, are actually dispersions

Table 1.3 Other functions offood emulsifiers Emulsifier frmction

Example(s)

Whipping (aerating) agent Dispersant Dough conditioner Defoamer Starch complexer Crystallization inhibitor Antistaling agent Antis ticking agent Antispattering agent Freeze-thaw stabilizer

Whipped toppings Flavors, vitamins Bread, buns, rolls Yeast and sugar manufacturing Macaroni, pasta Salad oil Yeast-raised baked goods Candy, chewing gum Margarines, frying shortenings Frozen toppings and coffee

Gloss enhancer Cloud formers Hydrating agents Encapsulating agents Dispersion stabilizers

Whiteners Confectionery coatings Beverages Powdered milk drinks Flavors, aromas Peanut butter

8

Food Emulsifiers and Their Applications

of solid particles in a continuous fat or oil phase. Chocolate viscosity is controlled by the addition of soy lecithin or polyglycerol ricinoleate (PGPR). Oil separation in peanut butter is prevented by use of a monoglyceride or highmelting fat. In some cases the secondary effect may be of greater concern than formation of the emulsion. Strengthening of dough and retardation of staling are vital considerations to processors who bake bread. A common practice in the food industry is to use two- or three-component emulsifier blends to achieve multiple functionalities. In a cake emulsion, for example, aeration to produce high volume, foam stabilization, softness, and moisture retention are achieved by using an emulsifier blend. One useful statistical method to optimize emulsifier blends is the full factorial experimental design using a zero or low level of each emulsifier and a higher level of each emulsifier. The major advantage of this design is that it will detect two- and three-factor interactions that are not uncommon in complex food systems. Small-molecule emulsifiers (e.g., monoglycerides) may exert their effect by partially or totally displacing proteins from an oil/water interface. This replacement is entropically favored because of the difference in size and mobility of the species. Direct interaction of emulsifiers and proteins may be visualized through electrostatic and hydrogen bonding, although it is difficult to observe in a system that contains appreciable amounts of oil. Chapter 5 on emulsifier/protein interactions will elaborate on these concepts. Emulsifier suppliers generally employ knowledgeable technical service professionals to support their customers product development efforts. Their experience in selecting emulsifiers for a functional response is a valuable initial source of information. However, food processors may want to develop unique products that have no close relationship to a product currently in commerce. In this case, the supplier may have some general ideas for emulsifier selection. However, it may be necessary for product developers to define their own criteria for emulsifiers based on critical functions required in the product. Statistical experimental design is a very useful tool to optimize food emulsifiers and their concentrations. For example, a full factorial design (Krog et al., 1985; Jaynes, 1985) may be used to determine the levels of three emulsifiers to obtain an optimum product. Response surface methodology (RSM) and fractional factorial designs are very useful techniques because they reduce the number of experiments necessary to obtain optimal concentrations. However, since synergistic and antisynergistic effects are often observed between emulsifiers, care should be taken to design the experiments so that two-factor inter-

Overview of Food Emulsifiers

9

actions are not confounded. Robust design is also highly recommended so that the food product has minimal sensitivity to uncontrolled noise factors. The objective of this book is to provide the food industry professional or interested technical professional with an overview of what emulsifiers are, how they are prepared, and how they are utilized in food products. Although in many senses food emulsifiers have become commodity ingredients, sophisticated understanding and application in processed foods is likely to continue to advance.

References Friberg, S., Larsson, K. (eds.) (1990). Food Emulsions, Marcel Dekker, New York. Jaynes, E. {1985). "Applications in the food industry, II," in Encyclopedia of Emulsion Technology {ed. P. Becher), Vol. 2, Marcel Dekker, New York, 1985, pp. 367--85. Krog, N., Rilson, T.H., Larsson, K. (1985). "Applications in the food industry, " in Encyclopedia of Emulsion Technology (ed. P. Becher), Vol. 2, Marcel Dekker, New York, pp. 321-66.

TWO Synthesis and Composition of Food-Grade Emulsifiers R.J. Zielinski

There are a number of families of food-grade emulsifiers, which may be classified as Mono- and diglycerides Propylene glycol monoesters Lactylated esters Polyglycerol esters Sorbitan esters Ethoxylated esters Succinylated esters Fruit acid esters Acetylated mono- and diglycerides Phosphated mono- and diglycerides Sucrose esters In this chapter the general methods of preparing these food-grade emulsifiers and some of the characteristics of each group of esters will be discussed.

2.1

Introduction

The food-grade emulsifiers are generally esters composed of a hydrophilic (water-loving) end and a lipophilic (fat-loving) end. In general, the lipophilic end is composed of stearic, palmitic, oleic, or linoleic acid or combinations of these fatty acids. The hydrophilic end is generally composed of hydroxyl or carboxyl

11

12

Food Emulsifiers and Their Applications

groups. The melting point of the various esters within each family will be determined by the melting point of the fatty acids used to prepare the emulsifier. The melting points of the common fatty acids are given in Table 2.1. When stearic and palmitic acids dominate, the ester will be solid and relatively highTable 2.1 Melting points of fatty acids

C8:0 CIO:O Cl4:0 Cl6:0 Cl8:0 Cl8:1 Cl8:2

Acid

CMP

Caprylic acid Capric acid Lauric acid Myristic acid Palmitic acid Stearic acid Oleic acid Linoleic acid

16.3 31.5 44.2 56.4 62.9 69.6 14 -6

eC)

melting; when oleic and linoleic acids dominate, the ester will be low-melting and could be a liquid at room temperature. The fatty acids present in an emulsifier may be obtained from either a fat or oil or a fatty acid source. All fats and oils are triglycerides, and the fatty acids can be obtained from the triglycerides by a hydrolytic process followed by fractional distillation. Generally, either natural or fully hydrogenated fats and oils are split to obtain the fatty acids. This process is illustrated in Equation 1. 0

II

CH 2-0-C-R

I

CH 2-QH

0

II

CH-o--c-R1

I

CH 2-0-C-R

I

+

3H 20

I

CH-QH

I

CH 2-0H

+

R--cOOH

+

R1--cOOH

+

R2--cooH

0 Triglyceride

Glycerine

Fatty acids

(R = saturated or unsaturated alkyl chain) (1)

where R, R 1, and R2 are the alkyl portion of fatty acid groups.

13

Synthesis and Composition of Food-Grade Emulsifiers

Kosher oleic acid may be obtained from high-oleic safflower and high-oleic sunflower seed oils. It may also be obtained from a specially purified tall oil from pine trees. Commercial stearic acid may be of three types: (i) a mixture of about 90% stearic acid and 10% palmitic acid, (ii) a mixture of about 70% stearic acid, 30% palmitic acid, or (iii) a mixture of about 50% palmitic acid and 50% stearic acid; all are known as stearic acid. Generally, partially hydrogenated fats and oils are used to prepare plastic-type emulsifiers.

2.2

Mono- and Diglycerides

The mono- and diglycerides are the most widely used food-grade emulsifiers. They may be esters that are solid and high-melting, esters that are liquid at about room temperature, or a plastic-type ester. There are a variety of monoand diglycerides commercially available at the present time. These are commonly designated as (i) 40% a-monoglycerides, (ii) 50% a-monoglycerides, and (iii) 90% monoglycerides. Monoglycerides are commonly composed of a number of components, as indicated in Figure 2.1. These components are present in different amounts in the commercially available esters. The various types of commercial compositions are described in the following discussion. The mono- and diglycerides may be prepared by either an interesterification process with glycerine and triglycerides or a direct esterification process with fatty acids. These processes are illustrated in Equation 2. In the latter case, water of esterification is formed and removed during the process step.

0

0 CH 2-0H

I

CH-OH

I

I

CH-C-R

I

CH-OH

I

II

CH 2-0-C-R

I

0

II

CH-0-C-R

I

0

II

CH2-0-C-R

I

0

II

CH-0-C-R

I

0

II

CH 2-0H

CH-0-H

CH 2-0H

CH2-0-C-R

Glycerine

Monoglyceride

Diglyceride

Triglyceride

Figure 2.1

14

Food Emulsifiers and Their Applications

0

II

CH 2-0H

CH 2-0-c-R

I

I

+

CH-QH

I

0

II

I

heat

CH-0-C-R

I

0

CH-OH

CH 2-0H

CH-OH catalyst

+

I

I

II

I

CH-QH 0

II

CH 2-0H

CH 2-0-C-R

CH 2-0H

CH-Q-C-R

Glycerine

Triglyceride

Glycerine

Monoglyceride

0

I

CH-OH + R-cOOH

I Glycerine

II

CH 2-0H

CH 2-0H heat catalyst

I

CH 2-D-c-R

0

II

CH-O-c-R

I

0

II

+

I

0

II

CH-0-C-R

I

0

II

CH 2-0-C-R

CH 2-D-C-R

Diglyceride

Triglyceride

(2)

The catalysts commonly used in these processes are sodium hydroxide or hydrated lime (calcium hydroxide); the temperatures involved range from 200 to 250°C. The proportions of each of the products-free glycerine, monoglyceride, diglyceride, and triglyceride-are purely dependent on the molar ratio of glycerine and oil or glycerine and fatty acid used. The overall composition can be approximated using a random distribution of the free hydroxyl group and fatty acid groups (Feuge and Bailey, 1946). The various fatty acid groups from the oil or fatty acid are also assumed to he randomly distributed in the final product. Once the desired ratio of oil or fatty acid and glycerine has been chosen to yield the desired monoglyceride content, a number of different types of monoglyceride compositions are still potentially available. For example, if a 40% monoglyceride composition is desired, then (i) the catalyst may be neutralized,

Synthesis and Composition of Food-Grade Emulsifiers

15

generally by phosphoric acid; (ii) the catalyst may be not neutralized; (iii) the reaction mixture may be cooled to a determined temperature and the glycerine that is insoluble in the final composition removed by decantation type process; and (iv) the excess free glycerine may be removed from the reaction products by vacuum distillation. A 40% monoglyceride prepared by a decantation-type process (iii) may contain about 4% free glycerine, while a 40% monoglyceride prepared by a vacuum-stripping process will typically contain less than 1% free glycerine. A stripped 40% monoglyceride will typically be composed of about 46% monoglyceride, 43% diglyceride, 10% triglyceride, and 1% glycerine. Similarly, a 50% monoglyceride may be prepared by decantation from insoluble glycerine or by a vacuum-stripping process. A vacuum-stripped 50% monoglyceride will typically contain about 55% monoglyceride, 38% diglyceride, 5% triglyceride, and 2% free glycerine. Under the conditions of high temperature, very low pressure, and an extremely short path, monoglycerides may be distilled and thus concentrated and purified. This process is known as "molecular distillation." Typically, a 40% monoglyceride mixture is subjected to molecular distillation to yield monoglycerides of over 90% purity. The nondistilled portion is recycled for an additional interesterification process to yield another 40% monoglyceride-type composition for use as the feedstock. As previously mentioned, either nonhydrogenated or partially hydrogenated triglycerides, or saturated or unsaturated fatty acids, may be used to prepare solid, plastic, or liquid monoglyceride mixtures. The mono- and diglycerides have a generally recognized as safe (GRAS) FDA status.

2.3

Propylene Glycol Monoesters

Propylene glycol or 1,2-propanediol is a food-allowed, dihydroxy polyol that is used to prepare a variety of food-grade emulsifiers. The 1,3-propanediol is not allowed in preparing food-grade emulsifiers. There are two methods of preparing food-grade propylene glycol monoesters (PGME): (i) interesterification of propylene glycol with triglycerides and (ii) direct esterification with fatty acids. In contrast to the mono- and diglycerides, both procedures do not yield the same compositions. When an interesterification process is used, the final composition contains mono-, di-, and triglycerides in addition to propylene glycol mono and diesters. This is illustrated in Equation 3.

16

Food Emulsifiers and Their Applications

0

II

CH 2-QH

I

CH-OH

CH 2-0-c-R

+

I

~

I

0

heat

CH-O-C-R

I

catalyst

II

CH 3

CH 2-0-c-R

Propylene glycol

Triglyceride

0 CH 2-QH

I

CH-QH

0

II

II

CH 2-o-c-R

I

+

CH-OH

CH 2-0-c-R

+

I

I

~

I

CH-0-C-R

CH2-0H

+

I

I

+

CH-OH

I

CH 3

CH 3

CH 3

CH2-QH

Propylene glycol

Propylene glycol monoester

Propylene glycol diester

Glycerine

0

0

II

CH 2-0-c-R

CH 2-Q-C-R

I

I

CH-QH

I

0

II

+

I

CH 2-o-c-R

0

I

CH-0-C-R

I

+

I

0

II

CH-o-c-R

I

0

I

CH-QH

CH 2-QH

CH 2-o-c-R

Monoglyceride

Diglyceride

Triglyceride

(R =saturated or unsaturated alkyl chain) (3)

Synthesis and Composition of Food-Grade Emulsifiers

17

Basic catalysts such as sodium hydroxide or hydrated lime (calcium hydroxide) are used in the interesterification process. Generally, the excess propylene glycol and the glycerine formed during the reaction are removed by a vacuum distillation process. The basic catalyst is neutralized prior to the distillation process to prevent disproportionation of the products during the distillation process; the most commonly used acid is 85% phosphoric acid. The composition of the final product is controlled by the molar ratio of propylene glycol to triglyceride in the starting reaction mixture. The approximate final concentrations of propylene glycol monoester and monoglyceride may be determined by assuming that a random distribution occurs during the reaction process (Feuge and Bailey, 1946). By controlling the molar ratio of propylene glycol to triglyceride, propylene glycol monoester contents ranging from about 13 to 70% may be obtained. Generally, most commercial compositions contain 50 to 70% propylene glycol monoester. Commercial products containing propylene glycol monoesters of greater than 90% are produced by means of a molecular distillation process similar to that employed for the production of distilled monoglycerides. In the PGME case, an interesterification mixture containing a high concentration of PGME is used as a feedstock for the distillation process. Small amounts of distilled monoglycerides may co-distill with the propylene glycol monoester. The direct esterification of propylene glycol with fatty acids yields a mixture of free propylene glycol, propylene glycol monoester, and propylene glycol diester, as illustrated in Equation 4. The residual propylene glycol is generally removed by a vacuum steamstripping process. The amount of propylene glycol monoester ranges from 45 to 70% in commercially available compositions prepared by direct esterification of propylene glycol with fatty acids. The amount of monoester can be approximated by assuming a random distribution with various molar ratios of propylene glycol to fatty acid (Feuge and Bailey, 1946). A basic catalyst such as sodium hydroxide or hydrated lime is generally used during the esterification step to avoid the formation of dipropylene glycol esters. The basic catalyst is neutralized with an acid, usually 85% phosphoric acid, prior to the steam-stripping step to avoid a disproportionation of the monoester during the stripping step.

If a strong acid is used as a catalyst during the direct esterification step, then the distinct possibility of the self-condensation of propylene glycol to the dimer or trimer followed by esterification of the dimer or trimer exists. Thus, acid-catalyzed esterifications can contain dipropylene glycol monoesters and

18

Food Emulsifiers and Their Applications

0

I

CH 2--o-c-R

CH 2-0H

I

CH-OH

I

+

R-cOOH

I

heat

CH-OH

catalyst

CH 2

+

I

CH 3

0

II

CH 2-0-c-R

I

~

CH 2-0-C-R

I (4)

tripropylene glycol monoesters. These esters are not allowed by the FDA as direct food additives. The FDA regulations for propylene glycol monoesters allow the use of all edible oils and edible fatty acids. However, the majority of the propylene glycol monoesters commercially available contain very high percentages of palmitic acid and stearic acid that are saturated fatty acids. Few unsaturated propylene glycol monoesters are available at this time.

2.4

Lactylated Esters

Lactic acid, 2-hydroxypropanoic acid, is a bifunctional acid. As illustrated in Figure 2.2, fatty acid esters may be prepared by reaction with either the hydroxyl group or the fatty acid group. Lactic acid can also self-react to form polymeric (dimer, trimer, etc.) chains. These polymers can also react with fatty acid moieties. This is also illustrated in Figure 2.2. This self-condensation reaction cannot be avoided, and all lactic acid emulsifiers contain mixtures of monomer, dimer, and trimer esters.

Synthesis and Composition of Food-Grade Emulsifiers

19

/R-COOH OH f--- R-COOH

OH

I

I 0II

CH 3-c-COOH

f--- R-QH

I

CH 3-C-c-o-cOOH

f--- R-OH

I

I

H

H

Lactic acid

CH3

Dilactic acid

Figure2.2

2.4.1

Reaction at the Hydroxyl Group

Two broad categories of food-grade emulsifiers that are prepared by the reaction of the hydroxyl group of lactic acid with either fatty acids or fatty acid chlorides are commercially available: (i) the lactylic esters of fatty acids and (ii) partial metal salts of lactylic esters of fatty acids. Each will be discussed in tum. 2.4.1.1

Lactylic &ters of Fatty Acids.

Two types of lactylic esters of fatty acids

are commercially available. One composition contains approximately 60% monomer, 10% dimer and trimer, 30% free fatty acid, and 3% free polylactic acid. The second composition contains approximately 42% monomer, 16% dimer and trimer, 30% free fatty acid, and 12% polylactic acid. Three methods are available to prepare a lactylic ester with a 60% monomer content. The first is the reaction of lactic acid of known monomer content with a fatty acid chloride with or without the presence of a weak base to capture the hydrogen chloride generated (Thompson and Buddemeyer, 1956). This method uses a costly acid chloride and an extensive purification process. The second method involves the direct esterification of about a 1:1 molar ratio of sodium lactate and fatty acid, followed by acidification with mineral acid and isolation of the fatty lactylic ester (Eng, 1972). A third method of preparing a lactylic ester with a 60% monomer content is to react lactic acid with acetic anhydride to form the lactyl acetate. The lactyl acetate is then subjected to an acidolysis reaction with fatty acids in the presence of a sodium base under high-vacuum conditions. The mixture is then acidified with mineral acid and the fatty lactylic esters isolated. The lactylic ester with about 42% monomer and 16% dimer and trimer

20

Food Emulsifiers and Their Applications

acids most probably is prepared by the direct esterification of lactic acid with fatty acid in about a 1:1 molar ratio (Thompson et al., 1956). A high free polylactic acid content (see Chapter 3 for analytical procedure) indicates that the product has not been water-washed. There are no restrictions on the lactic acid content of the lactylic esters of fatty acids in the FDA regulations (21CFR172). There are no FDA restrictions on the edible fatty acids that may be used in the preparation of the lactylic esters of fatty acids; however, the stearate esters are most commonly produced. 2.4.1.2

Metallic Salts of Lactylic Esters of Fatty Acids. There are two metallic salts of lactylic esters of fatty acids that are used in the food industry: calcium salt and sodium salt. The calcium salt was commercialized first, as a dough conditioner for bread, and is known as calcium stearoyl-2-lactylate. The 2 indicates that 2 moles of lactic acid were used in its preparation. The sodium salt, which was commercialized later, is known as sodium stearoyl-2lactylate, sodium stearoyllactate, or simply "SSL." It is used extensively in many food applications. Both esters can be prepared by the same process, the direct esterification of the partial salt of lactic acid with a fatty acid in about a 2: l molar ratio of lactic acid to fatty acid (Thompson et al., 1956). Both esters have a monomer content of about 40%, a polymeric content of about 31%, and a polylactic acid content of about 6%. Care must be taken to use high-quality starting materials to avoid excessive darkening during the reaction process. The color of the final product can be reduced by the use of hydrogen peroxide as a bleaching agent. The amounts of lactic acid and metal ion content of both esters are regulated by the FDA and are about 34% and 4.5%, respectively. Only the use of specified grades of stearic acid is permitted by the FDA regulations for the products.

2.4.2 2.4.2.1

Reaction at the Carboxylic Acid Group Lactylated Monoglycerides.

The carboxylic acid group of lactic acid

can react with the hydroxyl group of other fatty acid-derived compositions to yield emulsifiers that are useful in many food products. One of the most common fatty acid compositions used is a reaction product with a monoglyceride to form a lactylated monoglyceride identified in the FDA regulations as glycerol-lacto esters of fatty acids. The overall simplified reaction is illustrated in Equation 5. As can be seen from Equation 5, the number of hydroxyl groups remain the

Synthesis and Composition of Food-Grade Emulsifiers

21

OH

I + CH -C-COOH 3 I H

____.

0

r,--o--c

OH

I I

-c-cH,

+ Hp

CH-OH

I Monoglyceride

Lactic acid

Lactylated monoglyceride

(5)

same in the reaction product as in the starting monoglyceride and a methyl group is introduced. This has the net effect of lowering the melting point and increasing the fat solubility of the lactylated monoglyceride compared to the starting monoglyceride. As previously discussed, lactic acid can homopolymerize; therefore, dilactate and trilactate esters of monoglycerides can and will be formed during the esterification reaction. A major variable in the formation of lactylated monoglycerides is the composition of the monoglyceride that is reacted with lactic acid. For example, Barsky (1950) disclosed the use of shortening compositions containing lactylated monoglyceride made by two different methods. The first lactylated monoglyceride was prepared by the reaction of l mole of oleic acid with l mole of glycerine; then the reaction product was reacted with 33% of 88% lactic acid. The second monoglyceride was prepared by the interesterification of 100 parts of partially hydrogenated oil with 25 parts of glycerine; then the reaction product was reacted with 29.5% of anhydrous lactic acid. In both cases, about a nominal 40% monoglyceride intermediate composition was made, and about 7% of free glycerine could be expected to be present in the monoglyceride mixture. The free glycerine can react with lactic acid to yield water-soluble, oil-insoluble, glycerol lactates.

22

Food Emulsifiers and Their Applications

These glycerol lactates can be removed by water-washing or can be steamstripped from the reaction mixture under reduced pressure. A distilled monoglyceride could also be used as a reacting monoglyceride composition. However, during the reaction with lactic acid, the distilled monoglyceride could totally or partially disproportionate to yield free glycerine and a mixture of mono-, di-, and triglycerides. Thus, the benefit of using a distilled monoglyceride could be lost. Other possibilities of starting monoglycerides are an unstripped intermediate monoglyceride with an a-mono content of 28 to 40%, a 40% U-monoglyceride that has been vacuum-stripped to remove the free glycerine, or a 50% monoglyceride type that has or has not been vacuum-stripped to remove the free glycerine before reaction with lactic acid. Of course, any diglycerides present in the monoglyceride mixture can also react with lactic acid. Another variable in the production of lactylated monoglycerides is the amount of lactic acid reacted with the monoglyceride intermediate. In theory, a monoglyceride can react with 2 moles of lactic acid to yield the dilactylated monoglyceride ester. Commercially, lactylated monoglycerides are available that contain either about 15% or 22% lactic acid. There is an analytical constant known as WICLA (see Chapter 3), which stands for water-insoluble combined lactic acid, used by some companies to characterize lactylated monoglycerides. This value will give an estimation of the amount of active functional lactylated monoglyceride present in the commercial product as opposed to a total lactic acid value that is a summation of the WICLA value and the amount of lactic acid present in a water-soluble form, such as glycerol lactates. Because of the wide range of possible starting monoglycerides and the reaction conditions chosen, all commerciallactylated monoglyceride compositions may not be compositionally the same, and possibly, differences in functionality can exist between products with a similar lactic acid content. The FDA regulations for lactylated mono- and diglycerides permit the use of any edible fat or oil or edible fatty acids to be used in their manufacture. There are no restrictions on the amount of lactic acid that can be present in the lactylated mono- and diglycerides. 2.4.2.2

Lactylated Fatty Acid Esters of Glycerol and Propylene Glycol.

Another

emulsifier, prepared from lactic acid by the reaction of the carboxylic acid group of the lactic acid with the hydroxyl groups of glycerol and propylene gly-

Synthesis and Composition of Food-Grade Emulsifiers

23

col monoesters, is the lactylated fatty acid esters of glycerol and propylene glycol. In this type of emulsifier, propylene glycol is interesterified with an edible fat or oil to yield a mixture of mono- and diglycerides and propylene glycol monoesters. The reaction mixture is then reacted with lactic acid. As with the lactylated mono- and diglycerides, a great variety of propylene glycol monoester and monoglyceride mixtures could be used to react with lactic acid to yield a final composition. In addition, lactic acid can react with any free propylene glycol and free glycerine initially present or formed by a disproportionation of the starting propylene glycol monoesterlmonoglyceride composition. These propylene glycol lactates and glycerol lactates are removed by waterwashing or vacuum distillation of the reaction product. Obviously a complex composition is produced.

It should be noted that only propylene glycol esters prepared by an interesterification process may be used. Propylene glycol mono- and diesters prepared by a direct fatty acid esterification route are not allowed under the pertinent FDA regulation (21CFR172.850). The FDA regulation further specifies the WICLA content of the final ester composition to be 14 to 18%.

2.5

Polyglycerol Esters

Polyglycerol esters have been commercially available to the food industry for over 25 years, but they have been known in the nonfood industry for many more years. The polyglycerol alcohols are most often prepared by the polymerization of glycerine with an alkaline catalyst at elevated temperatures (Harris, 1941; Babayan and Lehman, 1973). The polymerization is a random process and a number of different polyglycerols are produced. This is illustrated in Equation 6. The extent of polymerization is followed by refractive index, viscosity, or hydroxyl value. When the theoretical hydroxyl value for a diglycerol is obtained, the polyglycerol could be called diglycerol. When the hydroxyl value for triglycerol is obtained, the polyglycerol could be called a triglycerol, etc. The hydroxyl values for di- to decaglycerol are summarized in Table 2.2. The theoretical molecular weight of each polyglycerol is also given in Table 2.2. In general, no effort is made to separate the various polyglycyerols, and the entire reaction mixture that contains a distribution of polyglycerols is used to prepare polyglycerol esters. At lower degrees of polymerization, higher concentrations of lower poyglycerols are present; at higher degrees of polymeriza-

24

Food Emulsifiers and Their Applications

heat catalyst

OH

OH

OH

I I

I

OH

OH

OH

I I

I

I

OH

OH

OH

OH

I

I

I

CH 2-cH-cH 2-0-CH 2-CH-CH 2-0H

OH

Diglycerol

CH 2-CH-(H 2-0-CH 2-(H-(H 2-0-cH 2-CH-CH 2-0H

OH

I I

Triglycerol

CH 2-CH-cH 2-G-CH 2-CH-CH 2-0-CH 2-CH-CH 2-0-CH 2-CH-CH 2-0H Tetragl ycerol

and so on, up to decaglycerol + (n- 1) H20 (6) Table 2.2 Polyol Glycerine Diglycerol Triglycerol Tetraglycerol Pentaglycerol Hexaglycerol Heptaglycerol Octaglycerol Nonaglycerol Decaglycerol

Theoretical hydroxyl value

Theoretical molecular weight

1839 1352 1169

92 166 240 314 338 462 536 610 684 758

1072

1012 971 942 920 902 888

Synthesis and Composition of Food-Grade Emulsifiers

25

tion, higher concentrations of higher polyglycerols are present. The number of possible esterification sites in a polyglycerol is the nominal polyglycerol plus 2(n + 2). Thus, a triglycerol has 5 possible esterification sites and an octaglycerol has lO possible esterification sites. The polyglycerol esters may be prepared from the polyglycerols by either a direct esterification with fatty acids or an interesterification with triglycerides. When a fatty acid process is used, the theoretical molecular weight of the polyglycerol is used with the molecular weight of the fatty acids to calculate the reaction charge. Generally, if low degrees of esterification are used, the reaction product is neutralized and allowed to "phase out" at about l00°C. The free polyol is separated and the emulsifier is filtered and packaged. If higher degrees of esterification are used, then no polyol will phase out and the product, neutralized or not neutralized, is filtered and packaged.

If an interesterification process is used, then additional glycerine from the fat or oil is introduced into the reaction mixture. This additional glycerine will modify the polyol distribution of the final product compared to the polyol distribution of the starting polyglycerol. Additional mono- and diglycerides will be produced compared to a direct esterification process, and distribution of fatty acids ester will be different than if a direct esterification process were used. Esters prepared by an interesterification process are still identified by the polyol that was initially used. It is obvious that even if a single fatty acid were used to make polyglycerol esters that the number of compositions possible are very numerous and com-

plex. Since mixtures of fatty acids are used, this makes the polyglycerol esters even more complex. Thus, a triglycerol monostearate polyglycerol ester is a mixture of the stearate and palmitate esters of glycerine, diglycerol, triglycerol, tetraglycerol, pentaglycerol, hexaglycerol, heptaglycerol, octaglycerol, nonaglycerol, and decaglycerol, while a decaglycerol tristearate is a mixture of the stearate and palmitate esters of the same polyglycerols but in different proportions. A wide range of polyglycerol esters are commercially available from liquid esters such as hexaglycerol dioleate to plastic esters like triglycerol monoshortening to solid esters like decaglycerol decastearate. FDA regulations permit the use of edible hydrogenated or nonhydrogenated nonlauric oils and the edible fatty acids derived from them as well as oleic acid from tall oil to prepare polyglycerol esters up to and including decaglycerol.

26

Food Emulsifiers and Their Applications

2.6

Sorbitan Esters

Only one sorbitan ester is currently approved in the FDA regulations as a direct food additive in the United States: sorbitan monostearate. However, a GRAS petition has been filed to permit the use of sorbitan tristearate in confectionery coatings (Federal Register, 1988). The FDA, as of 1996, has not acted on this petition. The most commonly used process for the production of sorbitan esters is the direct fatty acid esterification of sorbitol with stearic acid (Brown, 1943; Japanese Patent, 1974). Generally, the stearic acid used is about a 50:50 mixture of stearic and palmitic acids. The overall reaction is shown in Equation 7. Sorbitan is a monoanhydro sorbitol and sorbide (or isosorbide) is a dianhydro sorbitol, as illustrated in Equation 7. Commercial sorbitan monostearate is the stearate, palmitate ester of a mixture of about 1 to 12% sorbitol, 65 to 72% sorbitan, and 16 to 32% isosorbide. It can be demonstrated that the amount of sorbitan is fairly constant but that the amount of linear sorbitol and isosorbide can vary among manufacturers. The use of an acidic catalyst during the esterification of sorbitol promotes the cyclization of sorbitol to the mono- and dianhydro forms. The use of a basic catalyst promotes the esterification reaction at the expense of color formation. It is possible that each commercial supplier has its own blend of acidic and basic catalysts to generate the ratio of sorbitan esters required to meet tight FDA specifications for hydroxyl number, saponification number, and acid number while minimizing color degradation of the product. Hydrogen peroxide can be used to reduce the color of a sorbitan monostearate. Stockburger (1981) has patented a process for preparing sorbitan esters in which sorbitol is first dehydrated with an acid catalyst to the desired ratio of sorbitol, sorbitan, and sorbide polyols. The mixture of polyols is then reacted with fatty acids and a basic catalyst to yield the desired sorbitan ester with an improved light color. The use of sorbitan monostearate in foods is highly regulated. The reader is referred to 21CFR172.842 for further details on where sorbitan monostearate can be used in food products, and for the required analytical constants.

2.7

Ethoxylated Esters

Four ethoxylated fatty acid esters have FDA approval for use as direct food additives. These are ethoxylated sorbitan monostearate, ethoxylated sorbitan

Synthesis and Composition of Food-Grade Emulsifiers

CH 2-0H

CH 2-DH

I

I

CH-OH

CH-OH

I

CH-OH

27

+

I

catalyst

+

CH-OH

R-COOH

I

I

CH-OH

CH-OH

I

I

CH-DH

CH-OH

I

I

0

II

CH 2-0H

CH 2-0-C-R

Sorbitol

Linear sorbitol monoester

J=l

CHI

L nickel oxide (Wahlgren and Arnebrant, 1991). The similarity between the behavior of the two oppositely charged surfactants indicates that the removability of protein in these cases mainly reflects the binding mode of the protein to the surface. Elwing et al. (1989, 1990) studied the surfactant elutability of proteins adsorbed to a surface containing a gradient in hydrophobicity and found large differences in the amounts removed from the hydrophilic and hydrophobic ends. In the case of a nonionic surfactant (Tween 20), the elutability was largest at the midpoint of the gradient, which can be attributed to enhanced conformational changes of the adsorbed protein at the hydrophobic end, in combination with a lower efficiency of removal by nonionics at hydrophilic surfaces. At hydrophobic surfaces the removal is generally high (Elwing et al., 1989; Wannerberger et al., 1994). However, this may not be considered as evidence for weak binding of the proteins to the surface, but rather as an indication of the strong interaction between the surfactants and surface.

Simple models.

The observed effects of surfactants on adsorbed proteins

can be classified into two types of behavior, a short description of which follows (see Figure 5.4):

l. Complex formation between surfactant and protein that leads to desorption of protein from the surface. In this case the surfactant does not have to adsorb at the surface, but it has to interact with the adsorbed protein. 2. Replacement of protein by surfactant. This implies that the interaction between the surfactant and the surface has to be stronger than the interaction between the protein or the surfactant/protein complex and the surface. Adsorption of the surfactant to the surface is essential in this connection, but binding of surfactant to protein may not be required. Of course, the surfactant might bind to the surface and/or to the adsorbed protein without any net effect on the amount of protein adsorbed. A partial removal according to mechanisms (1) or (2) as illustrated in Figure 5.4 may be the most common observation and has previously been suggested as one indication of the presence of multiple adsorption states of the protein (Horbett and Brash, 1987). It is important to note that surfactant can remove proteins without binding to the surface [case (1), left side of Figure 5.4]. This could be described as a solubi-

106

Food Emulsifiers and Their Applications

•

~·

Figure 5.4 An illustration of surfactant-protein interactions at solid interfaces. The top drawing schematically shows an adsorbed layer of protein consisting of a removable (type 1) and a nonremovable (type 2) fraction. The differences might be due to, e.g., conformational and/or orientational aspects. The bottom-left drawing illustrates formation of desorbing complexes of surfactant and protein (solubilization), and replacement of protein by surfactant is shown to the right.

lization of the proteins by the surlactant. An interesting question is whether the replacement of proteins by surlactant in case (2) (right side of Figure 5.4) is first initiated by solubilization followed by surlactant adsorption. Nonionic surlactants interact to a very low extent with soluble proteins (Tanford, 1980), as for example can be concluded from the low amounts adsorbed to the adsorbed protein layer (Wahlgren, 1992). These surlactants still remove proteins from hydrophobic surlaces, and it is thus evident that in this case it occurs through replacement of adsorbed protein molecules by surlactant. 5.3.1.2

Adsorption from Mixtures of Proteins and Surfactants.

Proteins and

surlactants can interact in solution to form surlactant/protein complexes that may have different properties from those of the pure protein (Tanford, 1980; Ananthapadmanabhan, 1993). Ionic surlactants are known to interact with proteins in solution, and the interaction is generally stronger for SDS than for cationic surlactants (Nozaki et al., 1974; Subramanian et al., 1986; Ananthapadmanabhan, 1993). Nonionic surlactants are known to generally interact poorly with soluble proteins (Tanford, 1980) unless specific hydrophobic binding sites exist. Three types of interactions are observed: l. Binding of the surlactant by electrostatic or hydrophobic interactions to

specific sites in the protein, such as for ~-lactoglobulin (Tanford, 1980;

Protein/Emulsifer Interactions

107

Jones and Wilkinson, 1976; Coke et al., 1990: Frapin et al., 1990; O'Neill and Kinsella, 1987; Kresheck et al., 1977; Clark et al., 1992; Creamer, 1995), serum albumin (Tanford, 1980; Nozaki et al., 1974; Brown, 1984; Ericsson and Hegg, 1985), and specific lipid-binding proteins such as puroindoline from wheat (Wilde et al., 1993). 2. Cooperative adsorption of the surfactant to the protein without gross conformational changes. 3. Cooperative binding to the protein followed by conformational changes (Few et al., 1955; Subramanian et al., 1986; Su and Jirgensons, 1977; Nelson, 1971). These different interactions can occur in the same system upon increasing the surfactant concentration. The conformational changes that occur in case (3) can involve changes in secondary structure (Nozaki et al., 1974; Subramanian et al., 1986; Su and Jirgensons, 1977). Several models for the protein/surfactant complexes have been suggested, e.g.: rigid rod (Reynolds and Tanford, 1970), pearl and necklace ( Shirahama et al., 1974), and flexible helix model (Lundahl, 1986). In the cooperative region (2 and 3), above the critical association concentration (cac ), the interaction is mainly one of hydrophobic character (Tanford, 1980; Subramanian et al., 1977; Nelson, 1970). The adsorption from surfactant/protein mixtures to hydrophobic solid surfaces is to some extent analogous to the adsorption at air/water or oiVwater interfaces, which have been the subject of frequent studies (Courthaudon et al., 1991a, b; Clark et al., 1994). Competitive adsorption between proteins and surfactants at these interfaces has recently been reviewed by Dickinson and Woskett (1989). They conclude that, as expected, small surface-active components above a certain critical concentration will dominate over proteins at these interfaces, since such components normally have higher surface activity (superiority in lowering interfacial tension). Experimentally it is observed that the presence of surfactants in protein solutions may influence the amount of proteins adsorbed to solid surfaces in three different ways (Wahlgren 1992; Wahlgren and Arnebrant, 1991, 1992; Wahlgren et al., 1993, 1995):

l. Complete hindrance of protein adsorption 2. Reduced amounts of adsorbed protein compared to adsorption from pure protein solution 3. Increased amounts adsorbed

108

Food Emulsifiers and Their Applications

The complete lack of adsorption in case (1) could be explained by complex formation with a surfactant resulting in an entity that has no attraction to the surface or direct/preferred surfactant adsorption, due to their higher surface activity and diffusivity, unpending adsorption of proteins, or protein/surfactant complexes. In cases (2) and (3), the formation of complexes in solution leads to a decrease or increase in the amounts of protein adsorbed, respectively. The presence of surfactant influences the total amount of protein adsorbed by steric effects or changes in the electrostatic interaction between complexes as opposed to native protein. In addition, the complex may adsorb in a different orientation than the pure protein, resulting in a positive or negative effect on the adsorbed amount. Due to the different shapes of the adsorption isotherms of surfactants and proteins, the interaction with the interface is of course, as for protein mixtures, strongly dependent on the relative concentration of the components. The special character of the surfactant adsorption isotherms featuring the sharp increase in adsorbed amount in the range of their critical association concentration will influence these events in a very pronounced way. Studies regarding these surfactant/protein "Vroman effects" have been reported; for example, adsorption of fibrinogen from mixtures containing Triton X-100 passes through a maximum (Slack and Horbett, 1988). The adsorption from ~-lactoglobulin/SDS mixtures at different degrees of dilution was studied by Wahlgren and Amebrant (1992) (see Figure 5.5). At concentrations above the erne for the surfactant, the amount adsorbed corresponded to a layer of pure surfactant and was found to increase after rinsing. At lower concentrations, the adsorbate prior to rinsing appeared to be a mixture of protein and surfactant, and the total amount adsorbed passes through a maximum. The composition of the adsorbate after rinsing is most likely pure ~-lactoglobulin, since interactions between the surface or protein and SDS are reversible. At high degrees of dilution of the mixture, the absence of surfactant adsorption to the methylated silica, the nonreversible adsorption of ~-lactoglobulin, and the observed partial desorption of the adsorbate from the mixture imply that some SDS molecules are bound to ~-lactoglobulin molecules with a higher affinity than to the surface (see Figure 5.5). The amount of protein adsorbed is larger, even after rinsing, than for adsorption from pure ~-lactoglobulin solutions, and it can be concluded that SDS binding in this case facilitates the adsorption of protein.

Conclusions. Generally, it can be concluded that surfactants may interact with interfaces through solubilization or replacement mechanisms, depending on sur-

Protein/Emulsifer Interactions

109

0.18

......-: --

0

..-...: .-- .

0.12

0.06

0 1000

100

Degree of dilution

10

Figure 5.5 The amounts adsorbed to a methylated silica surlace as a function of degree of dilution for a mixture of ~-lactoglobulin and SDS (0.2 w/w), in phosphate buffered saline pH 7, I= 0 .17. The figure shows the adsorbed amount (!lg/cm2) after 30 minutes of adsorption (e) and 30 minutes after rinsing(+). In addition, the figure shows the adsorption of pure ~-lactoglobulin, after 30 minutes of adsorption (•) and 30 minutes after rinsing (x). Finally, the adsorption isotherm of SDS is inserted (0). (From Wahlgren and Arnebrant, 1992.)

factant surface interactions and surfactant/protein binding. Solubilization requires complex formation between protein and surfactant, and replacement requires adsorption of the surfactant to the surface. As for protein adsorption, one of the most important protein properties affecting surfactant-induced desorption appears to be conformational stability. Differences between a competitive situation and addition of surfactant after protein adsorption may derive from the alteration in surface activity of protein/surfactant complexes formed in solution compared to pure protein, the difference in diffusivity of surfactants and proteins affecting the "race for the interface," and time-dependent conformational changes resulting in "residence time" effects. The effects observed at low surfactant concentration, below the erne, mvolve the specific binding of surfactant to some proteins and are not fully understood. Further, the exact prerequisites for solubilization versus replacement as well as detailed information on molecular parameters such as aggregation numbers are not known.

110

Food Emulsifiers and Their Applications

5.3.2 Protein/Surfactant Interactions at Liquid/Air and Liquid/Liquid Interfaces Interactions between proteins and surfactants at air/water and oil/water interfaces has attracted considerable study in recent years because the consequences of competitive adsorption of these two species at these interfaces can often strongly influence dispersion (foam or emulsion) stability against coalescence. The majority of proteins have high affinity for interfaces, which they saturate at comparatively low concentrations compared to low molecular weight (LMW) surfactants (Dickinson and Woskett, 1989; Coke et al., 1990). Thus, on a mole for mole basis at low concentrations, proteins reduce the surface tension to a greater extent than LMW surfactants. However, the opposite effect is observed at high concentrations, because at saturation coverage with LMW surfactants, the interfacial tension of the interface is usually lower than that achieved by proteins, and as a result, the latter molecules will be displaced from the interface. The region where the two different components coexist in the interfacial layer is of greatest interest, since it is in this region that the stability of the system to coalescence is most greatly affected. A clearer understanding of this has emerged from direct study of the structures that separate the dispersed-phase of foams or emulsions, under conditions of high dispersed-phase volume (i.e., foam or emulsion thin films). Such structures form rapidly in foams following limited drainage but may occur only in emulsions after creaming of the dispersed phase. 5.3.2.1

Foam and Emulsion Film Stabilization.

Thin films are stabilized by

two distinct mechanisms; the one that dominates is dependent upon the molecular composition of the interface (Clark, 1995). Low molecular weight surfactants such as food emulsifiers or polar lipids congregate at the interface and form a fluid-adsorbed layer at temperatures above their transition temperature (see Figure 5.6a). When a surfactant-stabilized thin film is stretched, local thinning can occur in the thin film. This is accompanied by the generation of a surface-tension gradient across the locally thin region. Surface tension is highest at the thinnest point of the stretched film, due to the local decrease in the surface concentration of emulsifier in the region of the stretch. Equilibrium surface tension is restored by adsorption of surfactant from the interlamellar liquid, which is of very limited volume in a drained thin film. This process is called the "Gibbs effect." Alternatively, migration of the surfactant by lateral diffusion in the adsorbed layer toward the region of highest surface tension

Protein/Emulsifer Interactions

111

may also occur (Clark et al. 1990a). Here, the surfactant drags interlamellar liquid associated with the surfactant head group into the thin region of the film and contributes to the restoration of equilibrium film thickness. This process is often referred to as the "Marangoni effect" (Ewers and Sutherland, (1952). In contrast, the adsorbed layer in protein-stabilized thin films is much stiffer and often has viscoelastic properties (Castle et al., 1987). These derive from the protein/protein interactions that form in the adsorbed layer (see Figure 5.6b). These interactions result in the formation of a gel-like adsorbed layer, recently referred to as a "protein-skin" (Prins et al., 1995), in which lateral diffusion of molecules in the adsorbed layer is inhibited (Clark et al., l990b). Multilayer formation can also occur and serves to further mechanically strengthen the adsorbed layer (Coke et al., 1990). When pure protein

(o) Syrfnctnru-alonc

(b) Pmtein-olpne

h igh mobility

~

~

Film sttetchiog

~ diffusion~

~Prot ~ cin

rapid

dcfonnntion

" " ' (c) Mixed mlem rc:duc:ed mobility

/ no int.emct.i:ons

·

Pilm stretching No Protein defonnation

J

Slow diffusion

P'lm rui l r e.

-

i

-

Figure 5.6 Schematic diagram showing the possible mechanisms of thin-film stabilization. (a) The Marangoni mechanism in surfactant films; (b) the viscoelastic mechanism in protein-stabilized films; (c) instability in mixed component films. The thin films are shown in cross section and the aqueous interlamellar phase is shaded. (Reprinted with kind permission of the Royal Society of Chemistry, London.)

112

Food Emulsifiers and Their Applications

films are stretched, the change in interfacial area is dissipated across the film, due to the cohesive nature of the adsorbed protein layer and possibly the deformability of the adsorbed protein molecules. Thin-film instability can result in systems that contain mixtures of proteins and low molecular weight surfactants (Coke et al. 1990; Clark et al., 1991a; Sarker et al., 1995), as is the case in many foods. The origin of this instability rests in the incompatibility of the two stabilization mechanisms: the Marangoni mechanism relying on lateral diffusion, and the viscoelastic mechanism on immobilization of the protein molecules that constitute the adsorbed layer. One can speculate that in a mixed system, competitive adsorption of low molecular weight surfactant could weaken or interfere with the formation of protein/protein interactions in the adsorbed layer and destroy the integrity and viscoelastic properties of the adsorbed layer (see Figure 5.6c). This could be a progressive process, with the presence of small quantities of adsorbed surfactant initially introducing faults or weaknesses in the protein film. Adsorption of more surfactant could induce the formation of protein "islands" in the adsorbed layer. These structures could be capable of slow lateral diffusion but would be too large to participate in Marangoni-type stabilization. Indeed, they could impede surfactant migration in the adsorbed layer. Adsorption of progressively more surfactant would reduce the size of the protein aggregates still further until the adsorbed protein was in its monomeric form. Ultimately, all the protein would be displaced from the interface by the surfactant. Two types of interaction are shown in the schematic diagram of the mixed system. First, there is an interactive process associated with the coadsorption or competitive adsorption of the two different species at the interface. Second, many of the functional proteins used in food production have physiological transport activities and therefore possess binding sites, which may allow the formation of complexes with surfactants. Let us consider each of these processes in tum. The transition in adsorbed-layer structure at the air/water and oil/water interface caused by competitive adsorption between protein and emulsifiers has been studied in detail. Oscillatory surface shear (Kragel et al., 1995) and dilation (Clark et al., 1993: Sarker et al., 1995) measurements have been carried out at the air/water interface and show an emulsifier-induced reduction in surface shear viscosity and surface dilational elasticity at critical emulsifier/protein ratios. This is consistent with the cartoon depicted in Figure 5.6, where at a specific molar ratio the emulsifier will break down protein/protein interactions in the adsorbed layer, resulting in a reduction in surface shear viscosity and dilational elasticity. Similar

Protein/Emulsifer Interactions

113

observations have been made at the oil/water interlace under conditions of constant shear in experiments where both components were present in solution when the interlace was formed (Courthaudon et al., 1991) and when the competing surfactant was added subsequent to formation of the protein-adsorbed layer (Chen and Dickinson, 1995). Direct measurements of changes in adsorbed-layer rheological properties in foam and emulsion films is possible using the fluorescence recovery after photobleaching (FRAP) technique (Clark et al., 1990a; Clark, 1995). This method relies on the positioning of a fluorescent reporter molecule in the adsorbed layer either by covalent labeling of the protein of interest with a fluorescent moiety such as fluorescein isothiocyanate (FITC) or by use of an amphipathic fluorescent molecule [e.g., 5-N-(octadecanoyl)amino fluorescein, ODAF] at low (submicromolar) concentrations that are insufficient to alter adsorbed-layer structure. FRAP allows direct measurement of the lateral diffusion coefficient of the fluorophore in the adsorbed layer of the thin film. The presence of an extensive network of protein/protein interactions in the adsorbed layers arrests lateral diffusion of the probe molecule, as is the case in all films stabilized by protein alone (Clark et al., 1990b). This situation persists in the presence of emulsifier until a critical ratio of emulsifier/protein is achieved. This is marked by the onset of surlace lateral diffusion in the adsorbed layer. The technique serves as a useful means of (i) comparing the resistance of different proteins to emulsifier-induced adsorbed layer disruption, (ii) evaluating the effectiveness of protein modification strategies at improving the resistance of proteins to competitive displacement, and (iii) investigating the usefulness of natural food ingredients as crosslinkers of proteins in the adsorbed layer. 5.3.2.2

Specific Binding of Proteins and Emulsifiers.

Let us now consider the

effects of specific binding of emulsifiers by food proteins on adsorbed-layer properties at the air/water and oil/water interlace. There are many examples of proteins that possess binding activity, including bovine serum albumin and ~­ lactoglobulin (see Section 5.3.1.2). Investigation of the binding properties of these proteins has been generally confined to studies in bulk solution. For example, the presence of a fluorescent tryptophan residue in the hydrophobic cleft of ~-lactoglobulin (Papiz et al., 1986) has facilitated the study of emulsifier binding by fluorescence titration. Subsequent analysis of binding by conventional methods such as that of Scatchard (1949) allows determination of the dissociation constant (Kd) of the complex formed. Typical examples of KJs for ~-lactoglobulin

are shown in Table 5.1. The effect of complex formation can

114

Food Emulsifiers and Their Applications

usually be detected by shifts in the surface-tension (y) curve (Dickinson and Woskett, 1988). An example of this is shown for Tween 20 and ~-lactoglobulin in Figure 5.7 (Coke et al., 1990). Surface-tension/concentration (y-c) curves for Tween 20 alone and in the presence of a fixed concentration of ~-lactoglob­ ulin (0.2 mglml; 10.9 J1M) are shown. Table 5.1

Typical dissociation constants of emulsifier/P-lactoglobulin complexes Emulsifier

Tween 20 L-a lysophosphatidylcholine, palmitoyl Sucrose monolaurate Sucrose monostearate Sucrose monooleate Sodium stearoyl lactylate, pH 7.0 Sodium stearoyl lactylate, pH 5.0 Lauric acid Palmitic acid

Dissociation constant

Reference

4.6 j.iM 166.J.!M

Wilde and Clark, 1993 Sarker et al., 1995

11.6 j.iM 1.02 j.iM 24.8 j.iM 0.26 j.iM

Clark et al., 1992 Clark et al., 1992 Clark et al., 1992 Clark, unpublished

0.30 j.iM

Clark, unpublished

0.7 j.iM 0.1 j.iM

Frapin et al., 1993 Frapin et al., 1993

The general features described earlier are evident with a comparatively low concentration of protein causing a significant reduction in y. In the absence of protein, yreduces gradually with increasing Tween 20 concentration. The gradient of the reduction in surface tension reduces at higher Tween 20 concentrations (> 30 J1M) but doesn't become completely flat due to failure to attain equilibrium y, possibly due to the presence of a mixture of surface-active species in the Tween-20 sample. In contrast, the curve in the presence of protein maintains a relatively steady surface-tension value of about 50 mN/m up to Tween-20 concentrations of 25 j.iM due to adsorption of the protein. This means that the curve for the sample containing protein crosses that of Tween 20 alone. This is strong evidence for complex formation between the two components, since the curves cross due to a reduction in the concentration of free emulsifier in solution due to that which interacts with the protein to form the complex. Thus, great care must be taken when considering the surface properties of

Protein/Emulsifer Interactions

115

80

70

~

5 ~

60

·u.;0 ~

Q) ~

Q)



50

$.... ;::l r:n.

40

30

0

20

40

60

80

100

Figure 5.7 Surface tension isotherm for Tween 20 in the absence (e) and presence (•) of 0.2 mg/mL ~-lactoglobulin. The data were recorded after 20 minutes adsorption and are therefore not at equilibrium.

solutions containing mixtures of interacting components. In the simplest case of a single binding site, the two-component system becomes a three-component system comprising free emulsifier, free protein, and emulsifier/protein complex. The relative proportions of the components present can be calculated in the following manner (Clark et al., 1992). In the simplest case, the interaction of an emulsifier (E) with a protein (P) can be described by the expression P+E~PE

(l)

where PE is the emulsifier/protein complex. Thus the dissociation constant

(Kd) for the complex can be expressed as

[P] [E] [PE]

(2)

where the square brackets indicate molar concentrations of the different species. It is also the case that

116

Food Emulsifiers and Their Applications

[P] = [P101]

-

[PE]

(3)

[E] = [E101]

-

[PE]

(4)

where [P101] and [E101] are the total protein and emulsifier m the system. Substituting (3) and (4) in (2) gives

which can be solved for [PE] and can be used to calculate the relative concentrations of the three components. In addition, the binding data, which may comprise a change in a parameter (e.g., intrinsic fluorescence) caused by formation of the complex may be fitted using this equation, provided there is a single active binding site and the titration is carried out to saturation. Alternatively, it is possible to determine the dissociation constant and number of binding sites from the Scatchard (1949) equation

v

[E]

(6)

where v is the fraction of protein with occupied sites (i.e., [PE]/[P101]). If the Scatchard plot of v against v/[E] gives a straight line, it indicates the presence of only one class of binding site. The gradient of this line is -l!Kd, and the intercept on the xaxis gives the number of binding sites, n. If the Scatchard plot does not give a straight line, then the shape of the curve obtained can be used to identify if the observed binding is positively or negatively cooperative or the presence of multiple independent sites. In the former case the Hill equation can be used to determine the Kd and a cooperativity coefficient (Hill, 1910). Evidence for the formation of a specific complex in solution by direct measurement or by crossovers in surface-tension/concentration isotherms is not sufficient to allow the conclusion that intact complex adsorbs directly at the air/water or oil/water interface. There are few studies that provide convincing data that support such a hypothesis, and that which is provided often only indirectly points toward the presence of adsorbed complex at the interface. One of the best understood systems is that of Tween 20 and ~-lactoglobulin (Coke

Protein/Emulsifer Interactions

117

et al, 1990; Wilde and Clark, 1993), which are known to interact in solution to form a 1:1 complex characterized by a Kd = 4.6 ~' which has an increased hydrodynamic radius of 5. 7 nm compared to 3.5 nm for P-lactoglobulin alone (Clark et al., 1991b). Detailed measurements of the properties of foam films formed from a constant concentration of 0.2 mg/mL mixed native and fluorescein-labeled P-lactoglobulin as a function of increasing Tween-20 concentration (Wilde and Clark, 1993; Clark, 1995) have been reported. This study revealed that between molar ratios (R) of Tween 20 to P-lactoglobulin of 0.2 to 0.9, there was a progressive increase in the thickness of the foam films and a corresponding decrease in the amount of adsorbed protein to an intermediate level of approximately 50% of that which was originally adsorbed (see Figure 5.8). These changes occurred prior to the onset of surface diffusion of the labeled protein as determined by the FRAP technique at R = 0.9 (Coke et al., 1990). The increase in foam-film thickness was unexpected since protein displacement by the Tween 20 should have reduced the thickness of the thin film. One persuasive interpretation of the data is that coadsorption or trapping of the Tween-20/P-lactoglobulin complex in the adsorbed multilayers could account for adsorbed-layer thickening (Clark et al., 1994), since the complex is known to have an increased hydrodynamic radius (Clark et al., 1991b). Calculations reveal that this is a distinct possibility, since 16 to 49% of the P-lactoglobulin present in solution will be in the complexed form in the R-value range, 0.2 to 0.9. Further confirmation of this explanation comes from measurements of foam-film thickness at different P-lactoglobulin concentrations but at constant R value. Film thickness data for P-lactoglobulin at 0.2 and 1.0 mg/mL are also shown in Figure 5.8. The completely different thicknesses observed at the two protein concentrations can be rationalized in terms of the amount of Tween-20/P-lactoglobulin complex formed. The sharp reduction in film thickness observed in the 0.2 mg/mL P-lactoglobulin sample at R = 0.9 occurs when there is 5.41-LM complex present in the sample. An equiv-

alent amount of complex is present in the 1 mg/mL sample at R = 0.1 and could account for the immediate reduction in film thickness observed with the 1 mg/mL P-lactoglobulin sample and the complete absence of a film thickening step at low R values. Further evidence supporting direct adsorption of the complex formed between

~-lactoglobulin

and Tween 20 comes from dynamic surface-tension

(Ydyn) measurements performed using the overflowing cylinder apparatus (Clark et al., 1993). The Yclvn isotherm for Tween 20 showed classical sig-

118

Food Emulsifiers and Their Applications

40 0 0

--,._,

_..,

C l)

~

;::S 0

u

30

OJ

u

43 ... ;::S

CIJ

8

-E Cl) Cl)

OJ

20

];a u

~ 4

Molar ratio (R)

Figure 5.8 A comparison of foam-film thickness and surface concentration data for ~­ lactoglobulin samples as a function of Tween 20 concentration. Surface concentration of FITC/~-lactoglobulin (0.2 mg/mL) as determined by fluorescence counts (.&); foamfilm thickness for samples containing 0.2 mg/mL (•) and l.O mg/mL (e) ~-lactoglobu­ lin. R refers to the molar ratio of Tween 20: ~-lactoglobulin.

moidal behavior hut was shifted to increased surfactant concentration by approximately 2 orders of magnitude compared to the static measurements. Inclusion of ~-lactoglobulin (0.4 mg/mL) in the initial solutions caused only a small reduction in the measured

Ydyn

to 71 mN/m. This remained unaltered in

the presence of Tween 20 up to a concentration of 15 f.!M. Above this concentration a small hut significant further reduction in

Ydyn

was observed. The ef-

fect resulted in a small inflection in the Ydyn curve in the region corresponding to 15 to 40 J.LM Tween 20. At higher Tween-20 concentrations, the curve for the mixed system followed that of Tween 20 alone. The inflection in the

Ydyn

isotherm observed for the mixed system at concentrations of Tween 20 greater than lO JlM could not he due to adsorption of Tween 20 alone since under the prevailing conditions, the concentration of free Tween 20 was reduced by its association with ~-lactoglobulin. Using Equation (5) it can he shown that the Tween-20/~-lactoglohulin

complex is the dominant component in solution in

the Tween-20 concentration range of 15 to 35 flM (Clark et al., 1993). Indeed, the

Ydyn

isotherm indicates that there is very little difference between the sur-

Protein/Emulsifer Interactions

119

face activity of the three components present in solution, Tween 20, ~-lac­ toglobulin, and the complex, since

'Ydyn

behavior is dominated by the compo-

nent present in the highest concentration. Such observations provide important evidence for direct adsorption of intact complex, and in this particular case provides evidence that the observed "induction period" in static y isotherms could be due to the formation of protein islands (de Feijter and Benjamins, 1987) and can be abolished if interactions between the adsorbed protein molecules can be prevented, as is the case with the Tween-20/~-lac­ toglobulin complex. Direct adsorption of complex at the air/water interface also appears to have importance in functional properties of certain lipid-binding proteins from wheat called "puroindolines" (Blochet et al., 1991; Wilde et al., 1993). These proteins show unusual behavior in the presence of lipids that they bind, in that their foaming properties are generally unaltered and in some cases enhanced. A systematic study of the influence of interaction with lysophosphatidyl cholines (LPC) of different acyl chain lengths has been completed (Husband et al., 1995) and has produced persuasive evidence of the importance of the complex on foaming activity. First, two isoforms of the protein were investigated, puroindoline-a and -b (the b form has also been referred to as "friabilin"). Puroindoline-b has a significantly increased Kd for LPC compared to puroindoline-a (i.e., 20-fold weaker binding) and the enhancement of foaming properties is correspondingly reduced in the b form. Further stud-

ies of the binding of LPC to the a form revealed that the binding became tighter with increasing acyl chain length, and higher concentrations of the short-chain-length LPC are needed to achieve optimal foam stability enhancement. One interesting observation was that the micellar form of LPC was the species that bound to the protein. This finding emerged from the observation that lauryl-LPC showed no interaction with the puroindoline-a until the levels present exceeded the critical micelle concentration of 400

~·

This indicates a cooperative binding since it takes place in this concentration range, and any of the suggested structures for the protein/surfactant complexes described in Section 5.3.1.2, e.g., the pearl and necklace structure, could be applicable. It seems increasingly likely that the functional properties of the puroindolines are linked to a role in the transport and spreading of lipid at the air/water interface analogous to the role of amphipathic lung surfactant proteins such as SP-B, with which they have striking structural homology (Hawgood and Clements, 1990).

120

5.4

Food Emulsifiers and Their Applications

Protein/Phospholipid Interactions

Introduction. In this section we will discuss the interaction between phospholipids and proteins. Both proteins and phospholipids are major components of biological membranes, and therefore it is not surprising that a vast number of publications concerning protein/phospholipid interactions are related to understanding the biomembrane processes. This aspect has recently been reviewed in a book by Watts (1993). In pharmaceuticals, phospholipids are often used as colloidal drug carriers in drug delivery systems in various physical forms like liposomes or emulsions. These drug delivery systems are cleared from the circulation (bloodstream) by the reticuloendothelial system. It is believed that this clearance is triggered by adsorption of serum proteins on the phospholipid interface and will depend on the properties of both the protein and the phospholipid (Eidem and Speiser, 1989; Tabata and lkada, 1990; Patel, 1992). In untreated milk the fat globule is stabilized by a lipid membrane, composed mainly of sphingo- and phospholipids. Homogenization of milk results in a total area increase of the fat globules by some 6- to 10-fold, where the increased surface is stabilized by proteins adsorbed from milk during the process. Phospholipids, particularly phosphatidyl-choline Oecithin), are added to various processed foods, where they act as emulsifiers alone or together with proteins. Therefore, proteins and phospholipids, separately as well as in complexed form, contribute significantly to the physical properties of many systems of technological interest (e.g., emulsions and foams). The intention of this section is to emphasize the diverse nature of phospholipid/protein interaction and to point to some implications of this for the physicochemical as well as the biological properties of phosholipidlprotein systems. It is also our intention to point at some of the major forces involved in phospholipid/protein interactions. We will highlight only some properties of importance for the understanding of phospholipid/protein interactions. Therefore the classification of interactions made in this section, when the lipid is dispersed in solution, at different interfaces and with lipid phases, is arbitrary. Assignment according to polar/nonpolar, anionic/cationic, or soluble/insoluble phospholipids could also have been possible.

5.4.1

Protein/Phospholipid Interactions in Dispersed Systems

Many proteins have the biological role of transporting molecules with hydrophobic properties, which are bound to a hydrophobic pocket in the protein. ~­ Lactoglobulin is thought to transport retinol (Papiz, 1986; Sawyer, 1987; North,

Protein/Emulsifer Interactions

121

1989) but has also been shown to have high affinity for phospholipids, fatty acids, and triglycerides (Diaz de Villegas, 1987; Creamer, 1995; Sarker et al., 1995; Kristensen, 1995). An important application of lipid/protein interactions was reported by Kurihara and Katsuragi (1993), who found that a lipid/protein complex, formed between ~-lactoglobulin and phosphatidic acid, could mask bitter taste. This property was suggested to be specific for phosphatidic acid since no effect was observed for mixtures of ~-lactoglobulin and phosphatidylcholine, triglycerides, and diglycerides. Differential scanning calorimetry measurements confirm the presence of a specific interaction between phosphatidic acid and ~-lactoglobulin since the presence of distearoylphosphatidic acid (DSPA) as well as dipalmitoylphosphatidic acid (DPPA) thermally stabilized the protein, which was not observed when the protein was mixed with phosphatidylcholine, phosphatidylethanolamine, or phosphatidylglycerol (Kristensen et al., 1995). No interaction could be observed if the lipid contained unsaturated fatty acid residues or if it was mixed in the gel state with the protein. Thus, the results show that the interactions between ~-lactoglobulin and phospholipids are strongly dependent on the acyl chain as well as the head group. This is not simply a question of having a negatively charged head group since no interaction was observed for phosphatidylglycerol. The influence of protein structure on lipid/protein interactions has been demonstrated by Brown et al. (1983), who observed that native ~-lactoglobulin is unable to bind to phosphatidylcholine vesicles. However, if the protein was dissolved in a-helix-forming solvent, binding to the phospholipid was observed. Brown suggested that the acyl chains of the lipid interact with the hydrophobic interior of the a helix, while the polar head group is likely to interact with the hydrophilic exterior of the protein (Brown, 1984). The partially unfolded proteins formed during food processing may give helix structures when interacting with the lipids and these lipid/protein complexes can improve the emulsification process (Brown, 1984; de Wit, 1989).

5.4.2

Protein/Phospholipid Interactions at Solid Surfaces

A few studies have demonstrated the use of deposited phospholipid layers, deposited via the Langmuir-Blodgett technique or by spincoating, to follow the interaction between proteins and phospholipids in situ by using ellipsometry (Malmsten, 1994, 1995; Corselet al., 1986; Kop et al., 1984). This approach can also be used to analyze the kinetics of interaction (Corsel et al., 1986; Kop et al., 1984). The work of Malmsten (1994, 1995) showed that the interaction

122

Food Emulsifiers and Their Applications

of human serum albumin, lgG, and fibronectin from human plasma with phospholipids spin-coated onto methylated silica surfaces depends on the phospholipid head group. He found no interaction of proteins with phospholipids that have no net charge or shielded charges like phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, and phosphatidylinositol, whereas interaction was observed with the phospholipid surfaces containing unprotected charges like phosphatidic acid, diphosphatidylglycerol, and phosphatidylserine. No differences in adsorption behavior were found for spin-coated surfaces and Langmuir-Blodgett-deposited phospholipid layers. The consequences of nonspecific interactions with negatively charged dioleoylphosphatidylserine (DOPS) bilayzrs observed for fibrinogen and albumin in contrast to the specific ones observed for prothrombin have been demonstrated by Corsel et al. (1986). By analyzing their data in terms of intrinsic binding and transport rate, they found that the initial rate of adsorption of prothrombin was transport-limited, whereas the rate-determining step for the albumin interaction was the binding. The adsorption rate of fibrinogen was either transport-limited or controlled by the binding, depending on pH and ionic strength. Since the DOPS bilayer contained biological binding sites for prothrombin, the interaction was completely reversible. However, the interaction of fibrinogen and albumin with the bilayer probably induced conformational changes of the proteins and as a consequence the interaction was irreversible. Kop et al. (1984) found that a high density of DOPS in the bilayer was needed for the high-affinity binding of prothrombin. Consequently, an introduction of dioleoylphosphatidylcholine (DOPC) into the bilayer markedly decreased the affinity for binding.

5.4.3

Protein/Phospholipid Interactions at liquid/air Interfaces

Electrostatic interactions between protein molecules and lipid monolayers have been shown to be important for phospholipid/protein interactions at the liquid/air interface. A model food emulsion was used to study the interaction between nitroxide homologs of fatty acids and milk proteins by following the mobility of the nitroxide radicals using electron spin resonance (Aynie, 1992). It was found that at pH 7 the lipid/protein interaction was correlated with the number of positive charges on the protein. Thus, the importance of the interaction in the emulsions was found to decrease in the order ~-lactoglobulin > ~-casein, suggesting that the interaction was of electrostatic nature. The work of Quinn and Dawson (1969a, b) concerning the inter-

Protein/Emulsifer Interactions

123

action between cytochrome c (positive net charge below pH 10) and phospholipids from egg yolk also suggest that it is determined by electrostatics. Their results show that the limiting pressures for penetration are 20 and 24 mN/m for phosphatidylcholine and phosphatidylethanolamine, respectively, whereas penetration into the phosphatidic acid and diphosphatidylglycerol (cardiolipin) monolayers occurred up to pressures (< 40 mN/m) close to the collapse pressure of the film. Furthermore, the presence of sodium chloride decreased the interaction. Later, Kozarac et al. (1988) confirmed the findings of Quinn and Dawson with their reflection spectroscopy results. Cornell (1982) observed a specific interaction between ~-lactoglobulin and egg yolk phosphatidic acid (e-PA) in spread mixed films at low pH (1.3 and 4) where ~-lactoglobulin carries a positive net charge. No interaction was observed in the neutral pH range or for egg yolk phosphatidyl choline, (e-PC). ~-lac­ toglobulin, adsorbing from solution into a spread monolayers of palmitoyloleoylphosphatidylcholine (POPC) and palmitoyloleoylphosphatidylglycerol (POPG), was found to interact with the lipids only in the acid pH range (Cornell and Patterson, 1989). The highest amounts of ~-lactoglobulin (Cornell and Patterson, 1989), a-lactalbumin, or BSA (Cornell et al., 1990) bound to mixed monolayers of POPC and POPG were observed below the isoelectric point of the protein, when the lipid layer and the proteins carry an opposite net charge, whereas less was adsorbed around and almost nothing above the isoelectric point. The interaction was also found to be reduced in the presence of calcium as well as if sodium chloride was added (Cornell et al., 1990). Bos and Nylander (1995) used the film balance to study the incorporaffon of ~-lactoglobulin into monolayers of distearoylphosphatidic acid (DSPA), distearoylphosphatidylcholine (DSPC), and dipalmitoylphosphatidic acid (DPPA) and some of their results are shown in Figure 5.9. The highest rate of incorporation was observed for ~-lactoglobulin into the negatively charged DSPA monolayer. The rate also increases with ionic strength of the subphase, which probably is due to a decrease of the repulsion within the phosphatidic acid protein monolayer. The incorporation into the zwitterionic DSPC monolayers is, as expected, less salt-dependent. The importance of electrostatic interactions for the incorporation of proteins and peptides in lipid layers have also been reported for a number of non-food-related systems like adsorption of SecA (Breukink et al., 1992), actin (Grimard et al., 1993), IgG (Lu and Wei, 1993), and opioid peptides and opiate drugs (Bourhim et al., 1993) into phospholipid monolayers.

124

Food Emulsifiers and Their Applications

DSPC

. I ''I'

, I 'I

DPPA

-3 [t (j)

-3.5

~ -4

t

r

0_0

-4.5 0

5

10

15

20

25

30

ri (mN/m)

Figure 5.9 The rate of incorporation of P-lactoglobulin into monolayers of distearoylphosphatidic acid (DSPA), distearoylphosphatidylcholine {DSPC), and dipalmitoylphosphatidic acid (DPPA) versus surface pressure (II). The data were recorded at constant surface pressure by measuring the area increase of the lipid monolayer spread on a protein solution containing 1.15 mg/L in 10 11M phosphate buffer pH 7, with 0 11M (e), 50 11M (•), or 150 11M (A) sodium chloride. The rate in mg/m 2 was calculated from the area increase using the IT-area isotherm of spread monolayers of P-lactoglobulin. Data adopted from Bos and Nylander (1995), where the experimental details are also given.

Besides electrostatic interactions, hydrophobic interactions (based on the hydrophobic effect (Tanford, 1980) between protein and phospholipid are also important. Para-K-casein, a product of the cleavage of K-casein, retains its ability to interact with DMPC monolayers due to its more hydrophobic nature, whereas the macropeptide does not (Griffin et al., 1984). The adsorption of~-

Protein/Emulsifer Interactions

125

lactoglobulin into phosphatidic acid monolayers (Bos and Nylander, 1995) showed that incorporation was faster into a distearoyl monolayer than into a dipalmitoyl monolayer, especially at higher surface pressures (see Figure 5.9). This shows that the incorporation also is dependent on hydrophobic interactions. Bougis et al. (1981) showed that for the incorporation of snake venom cardiotoxins into lipid interfaces, not only electrostatic interactions but also hydrophobic interactions are important. Structure of Protein/lipid Monolayers. The structure of mixed protein/ phospholipid films depends on both the properties of the components and their interaction. It has been shown that conformational changes of the proteins during or after the adsorption at the liquid/air and liquid/liquid interfaces influence the

5.4.3.1

properties of the protein film (Graham and Philips, 1979; Mitchell, 1986; Dickinson and Stainsby, 1982). Circular dichroism spectra of ~-lactoglobulin bound to phospholipid monolayers were found to be similar to those recorded in solution, indicating that the conformation of the protein did not change significantly when interacting with the lipid monolayer (Cornell and Patterson, 1989; Cornell et al., 1990). Katona et al. (1978) showed that the~ form of a hydrophobic myelin protein was more able to interact with sphingomyelin than the "' "0 u

Soya lecithin

---·YN

~\

110

....

-

~\

0.3

.... --

--- 1----------04

0.5

Lee ith 1 n

Brookfield viscosity measurements of milk chocolate at three levels of shear. Comparison of effeet of soya lecithin and YN lecithin. (Minifie, 1980.)

242

Food Emulsifiers and Their Applications

-

700

c:;-

5% cocoa butter

E ..s?. Ul

600

0.3% lecithin

Q)

c:

>

500

~ Ul Ul Q)

--+-

0.3% YN

__.._

400

.... ....

+'

Ul

300

ctl

Q)

..c:

(/)

200

Figure 9.5

0

10

20

30

Shear rate (s-1)

40

50

Viscosity plot comparing lecithin, YN, and cocoa butter. (Bradford, 1976.)

These interactions result in higher viscosities compared to coatings containing only cocoa solids and sugar for surfactant adsorption. Details of how these interactions occur are absent from the literature.

9.2.3

Polyglycerol Polyricinoleate (PGPR)

PGPR is a surfactant used in the chocolate and compound industries in Europe and other parts of the world, excluding the United States. It has a unique role to play in modifying the viscosity behavior of chocolate coatings. It is made by reacting polyglycerol with castor oil fatty acids under vacuum. The resultant material is a colorless, free-flowing fluid with little or no odor. PGPR is also claimed to he a moisture scavenger in chocolate and compound coatings, preventing thickening of coatings over time (Application Notes Admul WOL, Quest International). Its chemical structure is, in general form,

where R= H or a fatty acyl group derived from poly condensed ricinoleic acid and n is the degree of polymerization of glycerol.

Emulsifiers in Confectionery

243

A number of studies have been published that compare the effects of PGPR with lecithin and YN. Most conclude that PGPR, when added to chocolate or compound coatings at 0.5% or less, can reduce the coating yield value to almost zero (Application Notes Admul WOL, Quest International; Bamford, 1970). The practical benefit of such a feature is that in a chocolate bar molding operation, PGPR addition would allow the chocolate to flow easily into even complicated mold shapes without entrapping air bubbles and also to flow around inclusions. Furthermore, the opportunity exists to reduce the fat content of the chocolate as well as the coat of chocolate formulations. A typical comparison of lecithin and PGPR additions to a milk and to a dark chocolate using a Rotovisco viscometer is given in Tables 9.1 and 9.2 (Application Notes Admul WOL, Quest International). The values in Tables 9.1 and 9.2 indicate that in milk chocolate it is possible to reduce the yield value to almost zero. The presence of lecithin in the emulsifier mix allows the plastic viscosity to be minimized, and this blend pro-

Table 9.1

Casson plastic viscosities and yield values of a milk chocolate when cocoa butter, lecithin, and PGPR are added Casson plastic viscosity (poise)

Casson yield value (dynes/cm2 )

2.0 4.0 5.0

45 29.8 26.5 16.3 15.3

97 62 58 58

Lecithin

0.05 0.1 0.2 0.4

30.0 26.7 20.0 15.6

79 54 40 37

PGPR

0.075 0.175 0.3 0.5 0.6

30.0 29.2 26.8 30.5 32.0

86 38.5 22 2.5 2.0

Lecithin + PGPR

0.1 0.2 0.3

14.1 13.4 12.7

34 32 29

Addition

Amount

Cocoa butter

0.0

l.O

llO

244

Food Emulsifiers and Their Applications

Table 9.2 Casson plastic viscosities and yield values of a dark chocolate when cocoa butter, lecithin and PGPR are added Addition

Amount

Casson plastic viscosity (poise)

Casson yield value (dynes/cm2)

Lecithin

0.3 0.7 0.97 1.3

18.5 17.1 14.4 12.4

155 221 297 285

PGPR

0.0 0.1 0.2 0.5 1.0

12.9 12.5 14.8 14.9 15.9

199 151 82 13 0

vides the optimum solution. In dark or semisweet chocolate the effect of PGPR on plastic viscosity is small, while it can reduce yield values to very low values at 0.5% addition. The mechanism by which PGPR affects yield value is not understood but its practical benefits are widely reported. PGPR is also claimed to be advantageously used in ice cream coatings since it allows low apparent viscosities in the presence of low levels of moisture (Bamford, 1970). Also claimed is PGPR's beneficial effect on fat-phase crystallization leading to easier tempering, improved texture, and longer shelflife of coatings (Application Notes Admul WOL, Quest International.). The author has found that the viscosity-reducing properties of PGPR does lead to significantly reduced viscosity at temper and a level of temper, as measured by a tempermeter, which is easier to maintain over long periods in an enrober without significant recirculation of chocolate via melt-out and retempering circuits. PGPR's most recognized benefit remains that of fat reduction, and manufacturers claim that a blend of 0.5% lecithin and 0.2% PGPR allows cocoa butter reductions of approximately 8%.

9.3 Antibloom Agents in Chocolate and Compound Coatings There are many references in the literature to uses of emulsifiers as additives to influence the physical appearance and texture of chocolate and compound coatings. One of the main problems to be overcome when making cocoa but-

Emulsifiers in Confectionery

245

ter-based chocolate is to ensure that the cocoa butter crystallizes in the correct crystal form or polymorph. Cocoa butter has several different polymorphic forms that have melting points ranging from 17 to 35°C. The forms are represented by the greek letters y, a, pt, and~· As the polymorphic form increases in stability it also increases in melting point. To make chocolate in the familiar glossy, fast-melting form with good snap, it is necessary to crystallize the cocoa butter in the highest melting polymorph, which is ~· This form of cocoa butter is also needed to ensure good contraction in molded products and the long bloom-free shelf life expected for good quality chocolate goods. Bloom is the phenomenon in which liquid fat is forced to the surface of a product and spontaneously crystallizes there as a grayish layer that looks to the uninformed consumer as if the product has gone moldy. The liquid fat is forced out to the surface in this way by the following mechanisms: l. Chocolate is not preconditioned (tempered) correctly such that insufficient concentration of seeds in the ~ form is present in the crystallizing chocolate mass. This leads to a higher level of less stable Wforms in the

chocolate mass that later transform to the more stable ~ form. This transformation causes the chocolate coating or bar to contract and squeeze liquid fat to the surface. Chocolate contains liquid fat even at room temperature, where cocoa butter attains a maximum solid fat content of approximately 85%. This liquid fat at the surface crystallizes in an uncontrolled fashion and is a mixture of ~' W, and even possibly some a forms. 2. Chocolate is tempered correctly, but in storage or distribution the product is subjected to wide temperature variations, resulting in partial melting and resolidification of the chocolate. Under these conditions uncontrolled recrystallization takes place and extensive bloom can occur. This kind of change is often referred to as "heat damage" and the product is classified as not heat resistant. 3. In molded bars that contain peanuts or other nutmeats as solid inclusions, or in enrobed products that have centers containing quantities of soft vegetable oil or dairy butter oil, this oil can "migrate" from the center to the chocolate shell. The soft oil will cause the chocolate to become soft and cocoa butter will dissolve. This will cause severe damage to the product due to physical handling prior to consumption or due to discoloration and bloom of the chocolate shell, which will now be far more heat-sensitive.

246

Food Emulsifiers and Their Applications

4. Long-term changes in cocoa butter crystal structure via ~(V) to ~(VI) transitions can also be a cause of bloom in some cases, although this may not be as common as the mechanisms above. In this scenario cocoa butter in the stable ~ state can exist in two forms, given the nomenclature V and VI. At the time of manufacture only the form V can he formed. Form VI has a slightly lower energy than form V, but the transformation from one to the other takes place at a very slow rate because there is a significant kinetic harrier to he overcome. This bloom mechanism occurs only in solid dark (milk-fat-free) chocolate bars. Milk fat present at low levels (2%) in chocolate will prevent this type of bloom. (See also the reference to STS as a bloom inhibitor in Section 9.3.1.) In all the cases above, the negative impact of uncontrolled crystallization is discoloration and bloom. This phenomenon is also seen in compound coatings based on other vegetable fats, hut since they are not polymorphic in the same way as cocoa butter, the mechanism of bloom formation is different. Problems of discoloration tend to stem from types 2, 3, and 4 above rather than type l. The final result is, however, the same, with an unattractive dull finish becoming apparent on the coating surface. Emulsifiers can have a role in helping control the rate of crystallization of cocoa butter and other vegetable hard butters both at the time of production and during subsequent storage and distribution. This in turn can promote bloom prevention.

9.3.1

Sorbitan Tristearate (STS)

STS is an emulsifier often associated with bloom prevention; it is claimed that when added to chocolate in the liquid state at 2% it slows down the crystallization rate of cocoa butter, thereby reducing the concentration of the most unstable

a form. The more stable

Wform is still produced hut this transforms into

the~ form thus deterring bloom (Anon., l99la). In this way STS behaves as a

crystal modifier. The situation is further complicated, however, because there exists not one hut two ~ forms of cocoa butter, usually referred to as forms V and VI. In this classification system the Wform is called form IV and transitions from form IV to form V, the stable form, occur via the liquid phase only. The transformation of form V to form VI takes place only via the solid phase and can take many months to occur. Also, identification of form VI is difficult and requires specialized x-ray diffraction techniques. However, this ~transformation is also as-

Emulsifiers in Confectionery

24 7

sociated with bloom in solid chocolate that has been well tempered. Work done by Garti et al. (1986) has indicated that STS is particularly effective at blocking this V to VI transformation and, hence, preventing bloom even after extensive temperature cycling between 20 and 30°C. Other emulsifiers studied by Garti included sorbitan monostearate and Polysorbate 60, but these were only half as effective as STS. STS is a highmelting-point emulsifier (approximately 35°C} whose structure is more closely related to cocoa butter triglycerides than to most other emulsifier types. It is speculated that it is due to this similarity that STS co-crystallizes with cocoa butter from the melt and, due to its rigid structure, binds the lattice in form V. Other more liquid or less triglyceride-like emulsifiers tend to depress the melt point of crystallized cocoa butter, increasing liquidity and promoting form IV to V transformations in preference. This is presumably why STS is a more effective antibloom agent in solid chocolate than in enrobed chocolate items, where soft center oils can soften cocoa butter crystals via migration and lead to type IV-V bloom occurring (see type 3 bloom previously mentioned). Krog (1987), however, claims that STS locks fats in the less stable Wform and prevents the transformation to ~­ Berger (1990) also claims that STS performs well as a bloom inhibitor or gloss enhancer in palm kernel oil-based compound coatings used to enrobe cakes

by stabilizing the Wform of the vegetable fat, a situation also observed by the author in several practical cases using lauric coating fats but with much less reliability when using domestic fats such as soybean or cottonseed-based coating fats. Such products tend to have longer bloom-free shelf lives in many cases so that the need for antibloom additives is not so imperative. The use of STS in food in the United States is limited to chocolate and compound coatings for which there is a petition pending for acceptance by FDA as a food additive. This uncertain status has not deterred United States food companies from enjoying the benefits that STS can bring to coating appearance. STS is, however, more widely accepted as an additive in EC countries.

9.3.2

Sorbitan Monostearate (SMS) and Polysorbate 60

SMS and polysorbate 60 [also known as polyoxyethylene (Player, 1986) sorbitan monostearate] are also used as antibloom agents, especially in compound coatings based on vegetable butters. They are not as effective as STS, but they have the advantage of being already accepted by FDA as food-grade emulsifiers. They are usually used in combination, where the SMS acts as a crystal

248

Food Emulsifiers and Their Applications

modifier and the polysorbates act as hydrophilic agents to improve emulsification with saliva and aid flavor release (Dziezak, 1988; Lees, 1975). SMS can also be used at high levels in coatings to increase heat resistance due to its high melt point, 54°C; unfortunately, the addition of SMS also causes the coating to become waxy. Up to 1% of this combination can be added to coatings to improve initial gloss and bloom resistance. The optimum ratio of SMS to polysorbate 60 is 60:40 (Woods, 1976). These emulsifiers are claimed to function by forming monomolecular layers of emulsifier on the surface of sugar and cocoa particles, thereby inhibiting the capillary action that causes liquid fat to migrate to the surface and cause bloom. Lecithin is still needed in these systems to control coating viscosity and reduce fat content. In another nomenclature system, SMS is also called Span 60 and polysorbate 60 is called Tween 60 (Lang, 1974). Spans and Tweens are also claimed to reduce the rate of fat crystallization; therefore, to develop proper crystal size a suitable tempering system needs to be employed. They are employed in both chocolate and compound coatings and may be used with advantage iffast crystallization of the coating would be disadvantageous.

9.4

Other Emulsifiers Used in Coatings

Mono- and diglycerides are also used as additives to chocolate and compound coatings, often as their purified or distilled forms. They can act as seeding agents especially when in high-melting-point forms such as glycerol monostearate (GMS). They are more commonly used as antibloom agents in laurictype palm kernel oil compound coating to extend useful shelf life. A typical usage level would be 0.5%. Berger (1990) claims good results in hydrogenated palm kernel oil coatings when using glyceryllacto palmitate at 1 to 5% as a gloss improver; the application was as a coating for a baked product. Moran (1969) found that a polyglycerol ester of stearic acid reduced the viscosity of fat sugar systems better than lecithin as well as retarded crystallization, improved gloss, and better demolding. Lactic acid esters of monoglycerides have also been used to control gloss in compound coatings (Hogenbirk, 1989; Dziezak, 1988) and to improve demolding performance (Anon., 1991b). Woods (1976) describes the use of triglycerol monooleate in compound coating chocolate to improve initial gloss and gloss retention, and triglycerol monostearate as a whipping agent to aerate coatings

Emulsifiers in Confectionery

249

giving them a lighter texture for filling applications. Herzing (1982) describes in detail the types of polyglycerol esters needed to optimize the glossy properties of lauric and nonlauric compound coatings: triglycerol monostearate, octaglycerol monostearate, and octaglycerol monooleate. These emulsifiers are added to the coating fat at up to 6% by weight. Polyglycerol esters have also been claimed to speed up the setting time of chocolate panning coatings when used at levels of 0.4 to 0.6% (Player, 1986). Hogenbirk (1989) has found advantages of viscosity reduction to some degree with examples of mono- and diglycerides, diacetyl tartaric acid esters of monoglycerides (DATEM), acetylated monoglycerides, and propylene glycol monoesters. Musser (1980) has published results showing the benefits of adding up to 1.5% DATEM to chocolate and compound coatings to modify viscosity properties and to improve the rate of crystallization of coating fat phases. In a series of experiments, Musser found that the addition of DATEM to fully lecithinated milk and dark chocolates, and dark sweet coatings, could further reduce the viscosity of the coatings as measured by a Brookfield viscometer. At the same time Musser found that the DATEM was acting as a seeding agent in chocolate systems, improving the speed of crystallization and resulting in a finer grain and better gloss in molded bars. Musser's conclusions relative to the effect of DATEM on viscosity is supported by the author's own published study on chocolate viscosity and emulsifiers (Weyland, 1994).

9.5

Emulsifiers in Nonchocolate Confectionery

Unlike in chocolate and compound coatings, the continuous phase of sugar confectionery is not oil or fat but is either sugar or a sugar syrup (in this case "sugar" means any nutritive carbohydrate sweetener). For this reason the role of an emulsifier in sugar confectionery is to enable small quantities of lipophilic material to be finely dispersed within a sugar matrix to achieve a desired effect. This effect may involve the dispersion of color, flavor, or some other fat-soluble ingredient, or the direct physical interaction of the emulsifier with the sugar phase to achieve the desired textural properties. A major factor in consumer acceptance is the mouthfeel of a confection. Vegetable fats and emulsifiers are used to improve texture and lubricate the product to achieve better chewing characteristics. A well-chosen surface-active agent can improve this aspect as well as slow down the release of added flavorings. They will affect the viscosity characteristics of the sweet and influence the

250

Food Emulsifiers and Their Applications

crystal shape present in grained confections. The improvement in fat dispersion throughout the confection will slow the rate at which the ingredient becomes rancid as the amount presented or migrating to the surface is lessened. For the purposes of this review I will divide the use of emulsifiers into the following categories: (i) chewing gum; (ii) caramels, toffee, and fudge; and (iii) jellies and gums.

9.5.1

Chewing Gum

Chewing gums contain fats and emulsifiers that act as softening agents or plasticizers to the gum base. In this role, emulsifiers can also act as carriers for colors and flavor aiding in the dispersion of these important ingredients within the gum base. Up to 1% lecithin can be used to soften chewing gum to the desired consistency (Patel et al., 1989) and can be hydrated or mixed with a vegetable oil or suitable fatty emulsifier such as mono- and diglycerides, to aid in dispersion within the chewing gums. Chewing gums prepared in this way have the desirable soft, chewy properties popular in today's top products. Other emulsifiers are also used in chewing gum to provide suitable textural and antistick properties to the chewing gum base; and these include monoand diglycerides, glyceryl lacto palmitate, sorbitan monostearate, triglycerol monostearate, triglycerol monoshortening, and polysorbates 60, 65, and 80. Lecithin is also used to provide a protective coating to chewing gum pieces prior to a hard panning process (Dave et al., 1991). Normally, only hard chewing gums can be hard panned in this way, but by using a hydrated lecithin coating it is possible to candy coat the gum and then allow the lecithin to soften the chewing gum in storage prior to consumption. By this technique the emulsifier coating, when set, forms a suitable base for syrup-based candy coatings.

9.5.2

Caramels, Toffee, and Fudge

Emulsifiers acting as surface-active agents increase the resistance of caramels and similar fat-containing confections to stick on cutting knives or to oil out due to manipulation in the process. The use of glycerol monostearate (GMS) and similar products such as mono- and diglycerides do produce an improvement in lowfat products such as in toffee and nougat. It is also claimed that the addition of these agents can help bind the oil and oil-based flavoring into a confection, reducing sweating and problems with rancidity. One property of emulsifiers that is particularly important is the improvement in emulsification in high-fat-content

Emulsifiers in Confectionery

251

confections such as butterscotch and caramels. During the manufacturing process, a high-sugar-content syrup is produced in which fat globules are dispersed. The finer these globules are the better will be the eating qualities. Consumer acceptance is based on flavor, appearance, texture, and chew. The last two factors are influenced directly by the number and size range of fat globules present in the product. The lower the size and the more even the dispersion of fat globules, the smoother the confection. Fat-containing products of this type exhibit non-Newtonian flow with a yield stress, which means that it is necessary to apply a sufficient level of stress to cause flow. Fat makes a minor contribution to the viscosity in relation to that due to the milk protein, but its presence is extremely important for lubrication. The higher the level of water left in a confection of this type, the higher the danger of stickiness and graining. GMS is a highly effective emulsifier to ensure maximum fat dispersion and minimum stickiness, but glycerol monooleate and lecithin are also quite effective. A usage level of 0.25 to 0. 7% is normal. Fudges are fondants that contain milk protein and fat having a flavor characteristic of toffee and caramel. Its texture can vary widely from a hard product often sold as a cut tablet to a soft form used in starch-molded products. In fudgemaking, an emulsified milk phase is prepared consisting of sweetened condensed milk, vegetable fat such as hardened palm kernel oil, and an emulsifier, usually GMS. The fat is emulsified into the syrup solution in a highspeed mixer at 120 to l40°F. Without GMS present the fat is more likely to separate during the subsequent cooking and working process or during the storage life of the fudge. This emulsified milk phase is added to a sugar/corn syrup mix and cooked to the desired moisture content of 8 to 15%. During this cooking process the characteristic Maillard or caramelized flavors develop. Finally, fondant is added during the cooling stage to provide the correct level of sugar seeds to make the desired sugar crystal size in the fudge. The fudge is then sheeted, deposited, or extruded.

9.5.3

Jellies and Gums

Some emulsifiers and surface-active agents such as GMS and saturated ethoxylated monoglycerides or polyglycerate 60 are adsorbed onto starch granules. This property can be used to modify the texture of starch-based sugar confectionery. Gel formation in starch-based jellies and gums is mainly due to the water-soluble fraction of starch, the amylose. Interaction between amylose

252

Food Emulsifiers and Their Applications

and emulsifiers creates a water-insoluble helical complex and creates an irreversible textural effect. This interaction was quantified by Krog (1977) using the amylose-complexing index or ACI. The ACI is defined as the percentage of amylose precipitated at 60°C after l hour and after reacting 5 mg of the emulsifier with 100 mg of amylose in solution. See Table 9.3.

Table 9.3

ACI values of some food emulsifiers

Glycerol monostearate (85%) Glycerol monooleate {45%) Mono- and diglycerides (50% monoester) DATEM Sorbitan monostearate Lecithin Polysorbate 60 Acetylated monoglycerides

87 35 42 49 18 16 32 0

To be an active amylose-complexing agent an emulsifier must have a high level of saturated monoglycerides and some degree of water dispersability. An example of the use of emulsifiers in starch-based confectionery is in the making of Turkish delight, where it is possible to use emulsifiers with high ACI values (GMS) to avoid pastiness or cheesiness. Usage levels are typically 0.025%.

9.6

Processing Aids

Emulsifiers are sometimes used in small amounts in confectionery products either to control aeration or to prevent product sticking to machinery and packaging. They can also be used to displace starch from starch-molded jellies and gums and provide a shiny attractive appearance as well as a barrier to degradation from atmospheric oxygen and moisture. Aeration of protein systems containing small amounts of fat, such as nougats, can be facilitated by the addition of triglycerol monostearate. Liquid fat or lipophilic emulsifiers such as GMS or acetylated monoglycerides usually tend to destabilize forms and cause deaeration. Emulsifiers are also useful release agents providing barrier properties between product and molds, tables, metal, conveyor belts, utensils, and machin-

Emulsifiers in Confectionery

253

ery, especially on cooling. Release agents must be food-grade materials and have high stability to resist oxidation and hydrolysis. Acetylated monoglycerides are used as release agents or as oiling and polishing agents because they form stable films on the surface of confectionery items. They have a-crystalline stability, plastic, nongreasy texture, and neutrality of flavor, color, and odor. They reduce shrinkage, harden through moisture loss, and prevent fat degradation and mold growth. They retain moisture and other desirable properties of the foodstuff and prevent contamination by moisture or dust. They are usually applied directly to the confectionery product by spraying. Melting points used are in the range 30 to 46°C. Typical applications include nuts and dried fruits and certain panned confectionery items. Lower melting-point forms (l0°C) can be sprayed directly onto conveyers and molds to release goods with high sugar contents such as fondant creams and jellies. Another release agent used often on chocolate-enrobing tunnels is a mixture of lecithin and cocoa butter. This is sprayed onto the band before the candy center is deposited to ensure clean separation of the centers from the band prior to chocolate-enrobing.

References Anon. (199la). Confectionery Production, 57(2), 136-7, 140. - - - (l991b). Confectionery Production, 57(6), 451-2. Bamford, H.F., eta!. (1970). Rev. Int. Choc. (RIC), 25, 6. Berger, K.G. (1990). World Conference on Oleochemicals into the 21st century, AOCS, Champaign, IL, pp. 288-91. Bonekamp-Nasser, A. (1992). Confectionery Production, 58(1), 66, 68. Bradford, L. (l976).Int. Flavors Food Addit., 7(4), 177-9. Dave, ].C., eta!. (1991). U.S. Patent 5,135,761, March 28. Dziezak, J.D. (1988). Food Techno!., 42(10), 171-86. Garti, N., eta!. (1986). ]. Assoc. Off. Chem. Soc., 63(2) 230-236. Gregory, D.H. (1982). Confectionery Production, 48(10), 437-9. Harris, T.L. (1968). Surface Active Lipids in Foods, Monograph No. 32, Society of Chemical Industry, England. Herzing, A.G., eta!. (1982). U.S. Patent 4,464,411, November 5. Hogenbirk, G. (1989). Confectionery Production, 55(1), 82-3. Jeffrey, M.S. (1991). Manufacturing Confectioner, 71(6), 76-82. Klienert, J. (1976). Rheol. Texture Food Qual., pp. 445-73, AVI, Westport, CT. Krog, N. (1977). ]. Assoc. Off. Chem. Soc., 54(3), 124--31. Lang, M. (1974). Confectionery Manufacturing and Marketing, 11(2), 3-5, 13. Lees, R. (1975). Confectionery Production, 41(6), 296,298, 304.

254

Food Emulsifiers and Their Applications

Minifie, B.W. (1980). Manufacturing Confectioner, 60(40), 47-50. Moran, D.P.J. (1969). Rev. Int. Choc. (RIC), 24,12. Musser, J.C. (1980). 34th PMCA Production Conference, Lancaster, PA. Nakanishi, Y. (1971). Rev. Int. Choc. (RIC), 26, 8. Patel, M.M. et al. (1989). U.S. Patent 5,041,293, December 28. Player, K. (1986). Manufacturing Confectioner, 66(10), 61-5. Weyland, M. (1994). Manufacturing Confectioner, 74(5). Woods, L.C. (1976). Gordian, 76(2), 53-7.

TEN Margarines and Spreads Eric Flack

10.1

Introduction

The invention of margarine in the 1860s is attributed to the French chemist Hippolyte Mege Mouries, in response to a competitive challenge initiated by the French Government under Napoleon III for a less expensive and less perishable substitute for butter. Mege had already undertaken research in this field at the Imperial farms, where he had observed that although underfed or hungry cows lost weight, they still produced milk, though of lower than normal yield, and that the milk contained fat. Thus, he deduced that milk fat was derived from normal body fat, i.e., tallow. However, since tallow itself does not possess the melting property of milk fat, he construed that through some metabolic process, a fractionation of the fat occurred, the lower melting fractions of which were transported to the mammary glands of the udder whereby, through the enzymatic action of pepsin, it became transformed to butter fat and dispersed as an emulsion in the milk plasma, while the harder fractions were utilized by the animal as a source of energy (Andersen and Williams, 1954). Having arrived at these conclusions, Mege set out to imitate this natural process by carefully rendering fresh tallow at body heat (about 45°C) using ar-

255

256

Food Emulsifiers and Their Applications

tificial gastric juices to facilitate separation of tissue from pure fat and then, following crystallization at 25 to 30°C, extracting under pressure about 60% of a soft semifluid fraction-oleomargarine-and about 40% of a hard white fat-oleostearine. The softer fraction had a melting point similar to butter fat, a pleasant flavor not unlike melted butter fat, a pale yellow color, and could easily be plasticized, and although different in fatty acid composition from butter fat, it offered a useful basis for the production of a substitute. He assumed, therefore, that this new butter fat substitute consisted of glycerides of margaric and oleic acids (the former then considered to be a C17 homolog of the saturated fatty acids, although now known to be a eutectic mixture of palmitic and stearic acids) that solidified in crystals having a pearly luster. The name margarine was derived from the Greek word "margarites," meaning pearl and thus is pronounced with a hard "g" according to its derivation. Mege's process was to take a proportion of the soft fat with appropriate quantities of milk and water, into which a small amount of udder extract was stirred. Following agitation, a stable emulsion similar to thick butter cream formed that, on further churning, thickened to resemble butter. While this process may now sound rather rudimentary, it nonetheless comprised all the elements of margarine production as we know them today.

10.2

Early Development

Mege took out patents in France and England, but the next major development took place in Holland when, in 1871 in the absence of patent law in Holland at that time, he sold his invention to the butter merchants Johannes and Anton Jurgens in the village of Oss. Also in the same locality was another family of butter merchants-Simon and Henry Van den Bergh-who were to commence production shortly afterward and who later were to join forces with the Jurgens and eventually become the largest margarine manufacturers in the world (Schwitzer, 1956). Production followed in most countries in Europe-Austria (1873/4), Italy (1874), Germany (1874), Norway (1876), and Denmark (1883), which was later to become the largest per capita consumer of margarine. Mege applied for a United States patent that was granted in 1874. Many variations were developed in the following years and patents on new formulations and processes were taken out. At the same time there was strong opposition to the introduction of margarine into the market by the farming

Margarines and Spreads

257

community, and in some places antimargarine legislation was introduced. Opposition from such quarters continued well into the twentieth century and is not entirely unknown today.

10.3 Yellow-Fat Consumption Despite the restrictions encountered in some countries, the consumption of margarine has continued to grow, and in many cases has overtaken the consumption of butter. Consideration of available statistics may be complicated since they do not always distinguish between the use of products for spreading, baking, or frying. Nonetheless, the variation in consumption of spreads, especially before, during, and after the Second World War, is clearly marked. In the United States, according to the National Association of Margarine Manufacturers, the change in comparative levels of consumption of margarine versus butter is significant. See Table 10.1. Table 10.1

United States-Average consumption of butter and margarine (lb per capita)

Year

Butter

Margarinet

1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1991 1992 1993 1994

17.8 17.6 17.0 10.9 10.7 9.0 7.5 6.5 5.3 4.7 4.5 4.9 4.4 4.2 4.2 4.5 4.8

2.8 3.0 2.4 4.1 6.1 8.2 9.4 9.9 11.0 11.0 11.2 10.8 10.9 10.6 11.0 10.8 9.9

t From 1975; includes spread products. Source: USDA Economic Research Service.

258

Food Emulsifiers and Their Applications

A similar development has been seen in Europe (Table 10.2), where in recent years (and also forecast to continue) the trend is for a reduction in yellowfat consumption generally, with small reductions in both butter and margarine in the order of 4 to 5% and an increase in spreads of 17 to 19% by 1997. Table 10.2 Europe-Average consumption of butter, margarine, and spreads (kg per capita)

1987 Country Belgium/ Luxembourg Denmark France Germany Greece Ireland Italy Netherlands Portugal Spain

UK Total EC

1992 (Est.)

Butter

Margarine

Spreads

Butter

Margarine Spreads

8.3 10.2 8.8 8.3 0.9 5.8 2.3 4.1 0.8 0.5 4.9 5.1

12.8 16.9 3.9 7.7 1.4 4.5 1.2 13.7 3.4 1.6 7.5 5.4

3.2 3.5 0.4 0.3 0.1 3.4

7.4 9.0 8.2 6.7 1.0 3.1 1.9 3.4 1.0 0.5 3.9 4.5

11.7 14.4 3.4 8.0 1.4 4.2 1.3 11.9 3.0

3.3 0.1 0.8 0.6 0.7

2.2

6.1 5.1

5.1 6.2 0.9 0.9 0.2 6.8 4.0 0.3 1.6 2.4 1.4

Source: Food Source '92 (1992), Frost & Sullivan, New York.

The reason for the change in consumption patterns in recent years-which is expected to continue into the future-is principally related to concerns over health following recommendations to reduce overall fat consumption and especially saturated fats from many authorities, for example, the National Academy of Sciences in the United States and the Committee on Medical Aspects of Food Policy (COMA) in the UK. Reduction in the consumption may also be due to factors such as the decline in bread consumption. There have also been significant structural changes within the markets, as will be discussed later.

10.4

Definitions and Descriptions

The name and basic composition of margarine, or oleomargarine, has been more or less established since Mege's original formulation-that is, it should

Margarines and Spreads

259

be similar to butter. However, with the new developments during more recent years involving different components and varying combinations of vegetable oils, animal fats, and milk fat, a range of new descriptions have come into being such as low-fat spreads, low-calorie spreads, and yellow-fat spreads. In 1993, Moran listed the varieties then available, as shown in Table 10.3. Table 10.3

Some current spreads Approx. fat content(%)

High-fat spreads

Low-fat spreads

Butter Margarine: Packet Soft Polyunsaturated fatty acids (PUFA) spreads Vegetable/butter-fatblended spreads Vegetable fat spreads

80 80 80 80 80 70 60

40 Vegetable/butter-fatblended spreads Butter-fat spreads Very low-fat spreads Water-continuous spreads

70

40 40 20-30 15 9

5 Source: Moran (1993).

In Europe, the adoption of Council Regulation (EC) No. 2991/94 of 5 December 1994 brought all products, including butter, under the one description, "Spreadable Fats" and described them as "products in the form of a solid, malleable emulsion-with a fat content of at least 10% but less than 90% by weight. The fat content, but excluding salt, must be at least two-thirds of the dry matter." These terms are further qualified as "products which will remain solid at a temperature of 20°C and which are suitable for use as spreads." The definitions and sales descriptions are detailed in Table 10.4. Clause 2 of Article 3 of this regulation states that the sales descriptions "minarine" and "halverine" may be used in place of "half-fat margarine."

g

10

l. Butter

A. Milk fats Products derived exclusively from milk and/or certain milk products for which fat is the essential constituent of value

l. Blend

C. Fats composed of plant and/or animal products Products derived from solid and/or liquid vegetable and/or animal fats suitable for human consumption, with a milk-fat content of between 10 and 80%

Source: Official Journal of the European Communities, 1316, Vol. 37,9/12/1994.

2. Three-quarter-fat blend 3. Half-fat blend 4. Blended spread xo/o but not more than

l. Margarine 2. Three-quarter-fat margarine 3. Half-fat margarine 4. Fat spreads xo/o

B. Fats Products derived from solid and/or liquid vegetable and/or animal fats suitable for human consumption, with a milk-fat content more than 3% of the fat content

2. Three-quarter-fat butter 3. Half-fat butter 4. Dairy spread xo/o

Sales description

Definitions and descriptions for spreadable fats

Fat-group definitions

Table 10.4

Not less than 39%; more than 41% Products with fat content: • Less than 39% • More than 41 %; less than 60% • More than 62%; less than 80% Product from a mixture of vegetable and/or animal fats with fat content of not less than 80% but not more than 90% Not less than 60%; not more than 62% Not less than 30%; more than 41% Products with fat content: • Less than 39% • More than 41 %; less than 60% • More than 62%; less than 80%

Milk-fat content not less than 80% but less than 90%. Max. water 16%; max. dry nonfat milk materials 2% Milk-fat content not less than 60% but not more than 62% Milk-fat content not less than 39% but not more than 41% Products with milk-fat content: • Less than 39% • More than 41 %; less than 60% • More than 62%; less than 80% Vegetable and/or animal fats not less than 80%; less than 90% Not less than 60%; less than 62%

Product categories (additional description with indication of% fat content by weight)

Margarines and Spreads

261

Whether the listed descriptions will gain greater prominence other than as the required secondary descriptions is doubtful since consumers, presumably, will prefer to favor the brand names that have been applied to the broad range of products now available. Fat spreads falling outside these standards, for instance those with fat contents below 10% and concentrated products with fat contents of 90% or more, will not be classed as spreadable fats. EC legislation does not specify vitamin fortification, which is left for decision at the national level. However, in the UK the requirement will remain as previously specified in the Margarine Regulations (Sl 1867) 1967. That is, each 100 g of margarine shall contain 800 to 1000 mg of vitamin A and 7.05 to 8.82 mg of vitamin D. This does not apply to other spreads, so that vitamin fortification in these cases is a matter for individual decision by the manufacturers and/or retailers. Legislation in the United States and Canada is currently less detailed than in Europe, but both require a minimum of 80% fat. In the United States, FDA §156.110 describes margarine (or oleomargarine) as "food in plastic form or liquid emulsion" containing not less than 80% fat and describes a method for fat determination. It specifies vitamin A fortification to be not less than 15,000 I.U. per pound but leaves vitamin D as an optional ingredient while stating not less than 1500 I.U. per pound. While spreads are not specified in the legislation, low-fat spreads were stated in 1990 as the fastest growing category, with spreads from 20 to 72% fat on the market (Borwanker and Buliga, 1989). The National Association of Margarine Manufacturers of the United States describes spreads as having fat contents ranging from 18 to 79%. Details of market shares in the United States are shown in Table 10.5.

United States retail market share of Table 10.5 margarine and spread products Type

Stick margarine Soft margarine Liquid margarine Low-fat vegetable oil spreads Total retail market

1980

1990

65 19 1 15

44

100

100

l3 2

41

Source: National Association of Margarine Manufacturers.

262

Food Emulsifiers and Their Applications

Canadian Standard B.09.016 states that margarine shall be "a plastic or fluid emulsion of water in fat, oil or fat and oil that are not derived from milk" and shall contain not less than 80% fat and not less than 3300 I.U. vitamin A and 530 I.U. of vitamin D. Calorie-reduced margarine is specified in Standard B.09.0l7 as containing not less than 40% fat and having 50% of the calories normally present in margarine. The conversion of International Units of vitamins A and D to microgram equivalents is complicated in the case of vitamin A since it depends upon the origin of the fat. Thus, to convert vitamin A from I. U. to f..Lg retinol in foods of animal origin, the I.U. of retinol should be multiplied by 0.3. However, for foods of plant origin, the I.U. of beta-carotene should be divided by 10. This arises because l I.U. of vitamin A is equivalent to 0.3 f..Lg retinol or 0.6 f..Lg beta-carotene. The conversion of the units for vitamin D is straightforward, i.e., li.U. vitamin D = 0.025f..Lg.

10.5 Structure and Raw Materials Margarine is a water-in-oil (W/0) emulsion; that is to say, the water (the disperse phase) is distributed as droplets within the oil (the continuous phase). In margarine, the levels of each largely simulate that found in butter and are regulated in most places by legislation, viz., minimum 80% fat, maximum 16% water, the remainder consisting of salts, proteins, emulsifiers, vitamins, colors, and flavors. Whereas production initially was based upon the use of fractionated animal fats such as tallow and lard, these were later superseded by vegetable oils and, for a period, marine oils, both of which offer a much greater flexibility in physical characteristics and economy. Being the main and most expensive ingredient, the fat blend is also the most important factor in the formulation of margarine. As oil prices fluctuate, it is essential to have a fat blend providing the desired quality at minimum cost. Thus, it is vital to be able to utilize alternative formulations based on prevailing price conditions while still maintaining quality. Therefore, a full understanding of the physical characteristics of the individual oils composing the blend is critical. In this respect, factors of importance for the fat phase include the solid/liquid fat ratio, crystallization rate, and melting properties. In the early days of margarine production, large quantities of milk and water in almost equal proportions were used for emulsification with the fat, with much of the excess water being pressed out during kneading to arrive at a final

Margarines and Spreads

263

moisture content of 16% or lower. Nowadays, the aqueous phase is added at optimum levels and usually consists of a simple solution of skim milk powder or whey powder in water, with the addition of salt and the pH adjusted to 5.5 to 6.0 by using, for instance, citric acid.

10.5.1

Oils and Fats

Oils and fats, otherwise known as triglycerides, are esters of glycerol and fatty acids having a basic formula

where R 1, R2 , and R3 are the fatty acid residues, which may be the same but, invariably, are different according to the source of the fat. Examples of the variations in fatty acid compositions of different oils and fats are shown in Table. 10.6. Modification of the fat by, for instance, hydrogenation, whereby some of the unsaturated links (double bonds) become saturated (for instance oleic C18:1 to stearic CIS) offer the opportunity of considerable variation in the melting points of fats, especially the liquid vegetable oils. The exact physical character of a fat depends upon that of the constituent fatty acids that can vary widely in melting point, as illustrated in Table 10.7.

10.6

Fat Crystallization

Variations in the crystallization properties of fats and differences between batches of a similar origin may cause problems in production even though processing techniques are fully controlled and highly automated (Madsen, 1983). The crystallization rates of some individual and blended fats are shown in Table 10.8 Oils and fats are polymorphic and can crystallize in more than one form, which can differ in terms of melting point, density, heat of fusion, and rate of crystallization. The three crystal forms are commonly known as alpha (a), beta prime (W), and beta (~), with the a form having the lowest values, the Winter-

""'

~

0.2 1.6 tr 25-30 2.5-3.5 15-25 35-45 7-12 0.5-1 1-4 59-70

0.2 3-4 0.5-1 26-28 2-3 23-27 30-35 1-1.5 0-1

45-57

4-8

-

-

Lard

9.2-13.9 tr 2.2-4.4 36.6-65.3 15.6-40.7 tr 2-8 84-105

7.7-9.7 2.3-3.2 5.4-7.4 1.3-2.1 tr tr 7.5-10

-

tr

-

13-17

Groundnut

45.9-50.3 16.8-19.0

-

Coconut

tiodine value is a measure of the degree of unsaturation of the fat.

C-10 & lower; capric, etc. C12lauric C14 myristic C14:1 myristoleic C16 palmitic C16:1 palmitoleic C18 stearic C18:1 oleic C18:2 linoleic C18:3 linolenic C20 & higher Iodine valuet

Fatty acid

Beef tallow

Table 10.6 Fatty acid compositions of oils and fats (%m/m)

tr 0.8-1.3 tr 43.1-46.3 tr 4.0-5.5 36.6-65.3 9.4-11.9 0.1-0.4 [xx]1 50-54

Palm

1.9-3.0 11.9-18.5 1.4-3.3 tr [xx]1 16-19

-

7.2-10.0

43.6-51.4 15.3 17.2

Palm kernel

3.4-6 0.2-0.6 l.l-2.5 52-65.7 16.9-24.8 6.5-14.1 1-6 109-126

tr

-

Lowerucic rapeseed

9.9-12.2 tr 3.6-5.4 17.7-25.5 50.5-56.8 55-95 [xx]l.5 125-136

tr tr

Soya

5.6-7.4 tr 3.0-6.3 14.0-34.0 55.5-73.9 tr [xx]l.5 85

tr

Sunflower

Margarines and Spreads

265

Table 10.7 The melting points of fatty acids Fatty acid

No. of double bonds

C12lauric C14 myristic C 14: 1 myristoleic C16 palmitic C16:1 palmitoleic C18 stearic C18:1 oleic C18:2 linoleic C18:3linolenic C20 arachidic

M.P. eC) 44.2 54.4 Liquid 62.9 Liquid 69.6 16.2 Liquid Liquid 74.4

1 1 1 2

3

Source: Andersen and Williams (1954).

Table 10.8

The crystallization rates of fats

Fat ( 0 C)

Time (min)

Temp.

Coconut Coconut/palm 1:1 Coconut/palm, interesterified Palm-hardened Palm-hardened/palm 2:1 Lard Lard/palm 1:1 Palm Sheafat

3 4 5 5 8 14 15 27 45

20 15 18 17 13 lO 10 lO 10

Source: Madsen (1983).

mediate, and the most stable ~ form the highest values. Transition from one form to another is from

a

~

W~ ~ and is not reversible without remelting the fat.

The polymorphism of crystalline fats may cause problems with the consistency of margarine and spreads. During production, the fats initially crystallize in the a

form and normally will rapidly transform to the Wform. This is the desirable form for spread production since the small needle-shaped

Wcrystals (about l!lm long) Wform to the much

impart good plasticity. Should the crystals transform from larger

p form (> 20 Jlm) they will give the spread a grainy consistency known as

"sandiness," as can be seen in Figure 10.1 (Madsen and Als, 1968).

266

Food Emulsifiers and Their Applications

(a)

(b)

Figure 10.1 Fat crystals in (a) normal margarine with good consistency and (b) a margarine with large ~crystals causing a "sandy" texture. (Magnification 200x.) (Courtesy

of Danisco Ingredients, Denmark.)

Concurrently, the specific area of the crystal surface will decrease, allowing the liquid oil to penetrate to the surface of the margarine, which may then lead to oiling out, especially if the margarine comes under pressure. Some vegetable oils such as partially hardened sunflower or low erucic rapeseed are particularly prone to form ~ crystals and thus can cause sandiness in spreads. In this case, sorbitan tristearate at 0.3% of the fat has been found to inhibit the

transition from the Wto the ~ form

The crystal-modifying effect of a range of emulsifiers-sorbitan esters, ethoxylated sorbitan esters, ethoxylated fatty alcohols, citric acid esters of monoglycerides (Citrem), diacetyl tartaric acid esters of monoglycerides (DATEM), sucrose monostearate, sodium stearoyl lactylate, and polyglycerol esters- has been investigated on the polymorphism of tristearin (glyceryl tristearate) (Garti et al., 1982). In these trials it was found that sorbitan monostearate and Citrem (Cl6/Cl8 fatty acids) were the most effective in preventing the recrystallisation (from a to ~ form) of tristearin. It should be noted that when used in emulsions, surface-active materials will

Margarines and Spreads

26 7

be adsorbed at the oil/water interface and that only lipophilic emulsifiers with high solubility in the oil phase can perform as crystal inhibitors in emulsions. Varying the level of saturated fat affects the degree of crystallinity of the oil phase (Borwanker and Buliga, 1989). Spreads with 40% fat were made using oil phases of varying crystallinity by blending either liquid soyabean oil or stick margarine oil with soft margarine oil. The textures of the spreads made with these blends were visibly very different, increasing in softness in the same direction as the oil itself. As a consequence of increased firmness, the stability of the resulting spread was expected to increase with increasing crystalinity in the oil phase. A centrifugation procedure was used to measure the stability of the emulsions (Figure 10.2). The higher amount of water and/or oil (especially water) released corresponds to a less stable emulsion.

10.7

Emulsifiers

The main function of emulsifiers in processed foods is to reduce the interfacial tension between the phases of an emulsion-usually oil and water. In such two-phase systems, one phase is dispersed as large droplets within the other.

60 "0

+-'Cil

c

Ul

Cll co u Cll Cll Cll

....

-

.s-.: >.0 ..~I...

==o ..c.._ co Cll +-'+J CJ)co

3:

""' '"--

50 40 30

-a...___

20

O Oil

"-~

10

O Water

~

~

0 4.5

6.3

8.6

10.4

13.0

Crystallinity (enthalpy, J/g)

50 Soft 50 liquid

75

25

Soft

75

25

50 Soft 50 Stick

Figure 10.2 Effect of the degree of crystallinity on the emulsion stability of 40% fat spreads as measured by ultracentrifugation. (From Borovanker and Buliga, 1989.)

268

Food Emulsifiers and Their Applications

They are either oil-in-water (0/W) emulsions, where the continuous phase is water (such as in milk or ice cream) or water-in-oil (W/0), where the continuous phase is oil (as in butter and margarine). The stability of two-liquid phase emulsions is kinetic stability, i.e., the system is not thermodynamically stable (Friberg et al., 1990). Thermodynamically stable emulsions would spontaneously reform following separation by, for instance, centrifugation, while experience shows that an emulsion that has separated remains so unless mixed by some external action. In reality, the two separated phases are in the most stable state to which all emulsions will tend. Thus, a stable emulsion is one in which this inevitable trend has been retarded so that it is not noticeable during the normal life of the product--even if it be several years. Margarine is a water-in-oil emulsion in principle only because, in reality, it is a dispersion of water droplets in a semisolid fat phase, containing fat crystals and liquid oil (Krog et al., 1983). Preparation of the emulsion requires considerable energy to reduce the droplet size of the disperse phase, thereby creating an increase in the surface area between the two immiscible phases. The initial water-in-oil emulsion is prepared in mixing tanks with vertical or horizontal stirrers to ensure emulsification but without incorporating too much air. It is rather coarse in water-droplet size and fairly unstable if not kept agitated. In modern continuous production, the emulsion exists for only a brief period before passing into the chilling unit where final emulsification and crystallization of the fat phase take place. Thus, the emulsion need not be very stable against coalescence as the water droplets become fixed within the semisolid phase. However, the droplet size is important when considering flavor release and microbiological spoilage. Thus, emulsifiers are used to lower the interfacial tension between the oil and water phases, which will generally result in a smaller water-droplet size. Distribution of the water droplets in the range 2 to 4 11m will give better stability against deterioration such as mold growth. However, it is still desirable for some of the water droplets to be larger in size-10 to 20 11m-to give a better flavor release in the mouth. For these purposes, therefore, lipophilic emulsifiers such as mono-/diglycerides of long-chain fatty acids (C16-C18) are used at levels of 0.1 to 0.3%, often in combination with 0.05 to 0.1% refined soya lecithin. Comparisons of the water-droplet distribution in margarine emulsion and in finished margarine are shown in Figure 10.3. Droplet size in the emulsion is further reduced during the cooling and kneading processes in the tube chiller. The water droplets in finished margarine are stabilized by adsorbed fat

Margarines and Spreads

(a)

269

(b)

Figure 10.3 Water-droplet size distribution in (a) margarine emulsion and (b) the finished margarine. (Magnification 200x.) (Courtesy of Danisco Ingredients, Denmark. )

crystals, as seen in Figure 10.4 showing the microstructure of margarine by freeze-fracture transmission electron microscopy. It is clearly seen that the water droplets are covered by fat crystals, oriented flatly along their surface. Margarine is frequently used for frying when it is especially important that it does not spatter. Spattering is caused when the margarine melts in the frying pan, the emulsion breaks, and the coalesced water droplets, due to gravity, form a film of water covered with molten fat on the frying pan. When the temperature reaches boiling point, the increase in vapor pressure will cause spattering-sometimes explosive-of the water phase. It is desirable, therefore, that the margarine allow gradual evaporation of the water from the small water droplets and the formation of a fine, golden brown sediment that does not adhere to the frying pan. Both formulation and processing play important roles in reducing the tendency to spatter. The presence of salt and milk are desirable as is a high pH, up to say 6, while sugars and starches will increase the tendency to spatter. The selection and addition of the emulsifier is of considerable importance in producing a margarine with good frying properties. While a combination of mono-/diglycerides and lecithin will have only a

270

Food Emulsifiers and Their Applications

Figure 10.4 Freeze fracture electron micrograph showing the microstructure of margarine. Water droplets (w) are covered with fat crystals. (Bar: l!lm.) (Courtesy of Dr. W. Buchheim, Keil.) limited effect in reducing spattering in low-salt margarine, there are other emulsifiers that, either alone or with lecithin, will help prevent coalescence of water droplets during frying. In this respect, citric acid esters of mono- and diglycerides (Citrem), polyglycerol esters, and thermally oxidized soybean oil interacted with mono- and diglycerides used at 0.3 to 0.4%, together with soya lecithin can be very effective.

10.8 Processing Typical modern processing involves the separate processing of the oil and water phases. The oils and fats are kept in storage tanks at temperatures just adequate to maintain them at the required fluidity. Preferably, they should be bottom fed to avoid splashing and aeration. It is essential that the plant, i.e., tanks, pipes, and pumps, be entirely free from copper or copper alloys to avoid the high risk of oxidation. The final oil blend together with oil-soluble components such as emulsifiers, colors, flavors, and vitamins, is prepared separately from the water phase

Margarines and Spreads

271

that may contain milk components such as whey powder, skim milk powder, or sodium caseinate and also salt, gelatin, or thickener, water-phase flavors where appropriate, and preservatives such as potassium sorbate for low-fat products. Modern methods involve the feeding of the phases by computer-controlled load cells, which ensures fast throughput and constant composition. A second emulsion tank is used for maintaining quantities of finished emulsion for feeding the cooling and kneading equipment. Cooling and kneading can be carried out by either of two different methods: (i) tube chiller or (ii) chilling drum-complector. In the former, cooling and kneading take place in a closed system and in a single process. In the latter, the cooling and kneading are carried out separately-cooling on the chilling drum and kneading in the complector. The advantage of the chilling drum-complector method is that it allows the product to rest between cooling and kneading, which is important with formulas based on slower crystallizing fats, for instance, puff pastry margarine. By comparison, the tube chiller is relatively more compact considering throughput, is easy to operate, and reduces the possibility of spoilage. Most types of margarine can be made very satisfactorily using the tube chiller method, although in some cases extra working units (pinning machines) may prove advantageous. However, the chilling drum-complector has been the preferred method for puff pastry margarine, although tube chillers are now · widely used, and is perfectly satisfactory for normal table margarine and for cake margarine. The suitability of both methods is summarized in Table 10.9. Table 10.9

Comparison of processing methods Chilling drum-

Type

Tube chiller

complector

Block/stick margarine Soft table margarine Low-fat spread Cake and creaming margarine Puff pastry margarine Shortening W/0 emulsion with high water content

XXX

XXX

XXX

X

XXX

X

XXX

XXX

XX

XXX

XXX

X

XXX

X

XXX

= Excellent;

XX

= acceptable; X = poor.

Source: Madsen (TPlOl).

272

Food Emulsifiers and Their Applications

The comparative merits of the two methods were investigated using four different fat combinations (see Table 10.10) in puff pastry margarines that were then evaluated by various parameters including a "finger" judgement (see Table 10.11) of plasticity after one week (Madsen, TPlOl). Table 10.10

Dilatation, iodine value, and melting points of fat blends used for comparison of puff pastry margarines Solid fat index Fat blend

so

10°

15°

20°

25°

Iodine value

l. 2. 3. 4.

37 40 43 37

37 40 42 35

34 36 37 31

27 31 29 25

22 24 23 19

67 7l 66 74

l8°Ct animal 18°Ct vegetable 12°Ct animal soct animal

M.P.

eq

37 37 41 37

tThe figures indicate storage and rolling temperature of the puff pastry margarine. Madsen (fPlOl).

Source:

Table 10.11

Plasticity judgement by finger method

Fat blend

Method

Plasticity judgment

Score

l. l8°C animal

Chilling drum Tube chiller

5 0

2. 18°C vegetable

Chilling drum

Fine plasticity Lumpy/gritty, a little firm, becoming slack and very greasy when worked Good plasticity, tending to become greasy Gritty, firm, becoming slack and greasy when worked Fine plasticity

Tube chiller 3. 12°C animal

Chilling Drum Tube chiller

4. soc animal

Source:

Madsen, TPlOl.

Chilling drum Tube chiller

Short and gritty, very, firm, becoming soft and greasy when worked Fine plasticity Short and gritty, very firm, becoming soft and greasy when worked

4 1 5 0

5 0

Margarines and Spreads

273

Similar results were found when the same products were judged after 3 weeks' storage. This rather critical evaluation did not fully take into account the differences that might result from the use of varying techniques possible with tube chillers, which was investigated separately.

Table 10.12 Plasticity judgment by means of the finger method in puff pastry margarines made on tube chiller with varying production techniques Production technique

Fat blend

l. Normal

Animal Vegetable

2. Intermediate crystallizer

Animal Vegetable

3. Pinning machine

Animal Vegetable

4. Resting tube + pinning machine 5. Low capacity

Animal Vegetable Animal Vegetable

Plasticity judgment after I week at l8°C

Points

Lumpy and gritty, a little firm but becomes slack and greasy when worked Gritty, firm but becomes slack and greasy when worked A little lumpy and soft, very greasy when worked A little firm but becomes soft and greasy when worked A little lumpy and fairly soft; very greasy when worked Becomes easily soft and greasy when worked Soft and greasy

0

Too soft and very greasy Fine homogeneity but too soft, fairly good plasticity Fine homogeneity, a little too soft, fairly good plasticity

l 3

l 1

2 l

2 0

4

Source: Madsen, TPlOl.

The important issue relates to the postcrystallization of the fats, which was further investigated (Madsen, 1981 ). A good plastic puff pastry margarine can be bent without breaking and the plasticity evaluated by repeated handworking to check stability, firmness, and greasiness (Figure 10.5). In the case of cake margarine, the most important points are that the fat blend is soft and easy to incorporate into the batter and has good creaming properties. This, therefore, suggests the use of lauric fats (coconut, palm kernel) that crystallize quickly and, thereby, facilitate creaming.

274

Food Emulsifiers and Their Applications

Figure 10.5 Evaluation the plasticity of puff pastry margarine by hand. (Courtesy of Danisco Ingredients, Denmark.)

10.9 Reduced- and Low-Fat Spreads As has been previously highlighted, low-fat spreads have been the only growth area in a gradually declining market. They can have fat contents from lO to 79% and, except in the case of very low-fat spreads, are W/0 emulsions. However, with low-fat products, it is necessary to strike a balance between stability and mouthfeel, which can be affected both by the composition and the method of processing. Margarine is essentially a stable product and the appropriate fat blend and the combination of milk proteins, lecithins, and/or saturated mono- and diglycerides used in production ensure both stability and the desired eating characteristics (Flack, 1992). However, in reduced- and low-fat spreads in which the dispersed phase (aqueous) can exceed the phase volume of the continuous (fat) phase, problems can arise with stability, meltdown, and flavor release (Moran, 1993). While milk proteins are in high-fat products to improve mouthfeel and flavor, they also act as hydrophilic 0/W-emulsion stabilizers, and thus their use in low-fat products, together with the considerable energy input needed, could result in phase inversion. These problems can be overcome by a combination of formulation and processing. Important factors in the formulation include the melting characteristics

275

Margarines and Spreads

of the fat blend, the type and level of emulsifier, and the addition of thickeners such as gelatin, sodium alginate, pectin, and carrageenan to the aqueous phase. Low levels of whey protein may be used to improve flavor release with the further advantage that the pH of the aqueous phase can be lowered to improve keeping properties because, unlike casein, whey proteins do not precipitate at low pH. The speed of processing, i.e., the rate of throughput and the emulsion temperature, are also important factors in the stability of the spread. Examples of the effect of various types of emulsifiers on the stability of lowfat spreads with fat contents of 40% and 20% are shown in Tables 10.13 and 10.14, respectively.

Table10.13

Effect of types and blends of emulsifiers on the stability of a 40% fat

spread Water separation % after

Levels of use

Types of emulsifier

5 min

10 min 15 min 20 min

0.6%

Distilled monoglyceride from

1.6

2.6

9.5

15.8

0

l.O

2.6

6.3

0

0

0

0

0.6% plus 0.2%

0.4% plus 0.2%

vegetable oil. IV approx. 80 Distilled monoglyceride from vegetable oil. IV approx. 80 Polyglycerol ester of fatty acids. IV approx. 80 Distilled monoglyceride from vegetable oil. IV approx. 80 Polyglycerol ester of interesterified ricinoleic acid. IV approx. 85

IV = Iodine value. Formulation of spread: Water phase

56.4% water 0.5% whey powder

pH 4.5 1.5% gelatin

1.5% salt 0.1% potassium sorbate Fat phase

39.2-39.4% fat blend 0.{H).8% emulsifier (as above) 4 ppm beta-carotene

Source: Madsen (1989).

276

Food Emulsifiers and Their Applications

Table 10.14 Effects of types and blends of emulsifiers on the stability of a 20% fat spread Levels and types of emulsifiers

Results

0.8 % distilled monoglyceride from sunflower oil. IV approx. lOS O.S % distilled monoglyceride from sunflower oil. IV approx. lOS plus O.S% polyglycerol ester of interesterified ricinoleic acid. IV approx 8S

Emulsion split into separate phases in tube chiller Produced a fine, stable spread with good spreadability and mouthfeel

IV = Iodine value.

Formulation of spread: Water phase

69.9% water 4.0% skim milk powder

pH6.8

3.0% gelatin

l.S% sodium alginate 1.5% salt

0.1% potassium sorbate Fat phase

19.0-19.2% fat blend 0.8--1.0% emulsifier (as above) 8 ppm beta-carotene

Source:

Madsen (1989).

The trial batches in both cases were made on a three-tube Perfector pilot plant using a fat blend composed of 60 parts soya oil 30 parts partially hydrogenated soya oil lO parts coconut oil Both examples indicate the potential instability of these emulsions and the variation in the stabilizing effects of different emulsifier blends even when used at low dosage levels. These results suggest that emulsifier structure at the interface plays a critical role in retarding water-droplet flocculation and coalescence. While the evaluation of spreads by measuring water separation provides quantifiable results, a quicker and more practical evaluation of the stability of

Margarines and Spreads

277

spreads can be made by spreading a sample with a knife on cardboard, as shown in Figure 10.6, where the desired qualities of good spreadability and low moisture loss are shown in the right-hand photograph. A rheological measurement to obtain quantitative data could also be carried out.

It is rather more difficult to produce low-fat butter spread from butter oil due to the relative hardness of the fat at low temperatures. Nonetheless, spread with a butter fat content of about 40% has been produced using 5% sodium caseinate plus 2% sodium alginate in the water phase and 0.5% distilled monoglyceride, IV approximately 55, in the fat phase.

Figure 10.6 Evaluating margarine by spreading on cardboard. (Courtesy of Danisco Ingredients, Denmark.)

However, in this case it is not possible to lower the pH of the aqueous phase without precipitating the caseinate, which will reduce its emulsifying properties, and therefore, the keeping properties of the spread will be limited. However, a satisfactory low-fat butter spread can be produced from dairy cream, using a distilled monoglyceride with high iodine value (80 to 105) in the cream and a thickener such as sodium alginate. In this case, phase inversion from 0/W to W/0 can be achieved in the tube chiller, using normal or slightly reduced cooling and operating at 40 to 50% of the usual capacity. To obtain a satisfactory working effect, a high rotor speed in the tube chiller cooling cylinder would be preferable (Madsen, 1989). Factors that may affect the efficiency of phase inversion in low-fat emulsions are listed in Table 10.15.

278

Food Emulsifiers and Their Applications

Table 10.15

Factors promoting the inversion of oil-in-water emulsions

l. Increased rotor speed 2. Controlled temperature (maintenance of optimum fat solids level) 3. Use oflow-HLB emulsifiers 4. Increased oil-droplet size entering unit Source: Moran (1993).

Most of these factors concern the increase in rate of collision of oil droplets upon which the rate of coalescence is dependent (Moran, 1993). The emulsifier(s) likely provide steric hindrance to keep droplets separated.

10.10 Oil-in-Water Spreads According to Moran (1993), the advantages of 0/W spreads over the more conventional W/0 spreads may be attributed to •

Product structure not dependent on the type of fat used

• •

Any level of fat can be used from 1% to more than 50% High levels of protein are possible

•

Processing is easier and cheaper

•

Flavor release is quicker on the palate

Against this, however, one major drawback is that unless products are prepared at comparatively low pH, then ultra-high-temperature processing and possibly an aseptic filling procedure must be followed if shelf lives comparable to conventional spreads are required. Oil-in-water spreads remain a relatively unexplored area of the spreadable fats market, possibly due to the problem of microbiological deterioration, but may offer a potential for future expansion in markets where adequate levels of preservatives are permitted. In contrast to W/0 emulsions, these systems would utilize high-HLB emulsifiers to stabilize the water-continuous emulsion.

10.11 Liquid Margarine Liquid margarine is used primarily for frying and is available particularly in markets such as the United States, Germany, and Sweden, where butter or margarine are normally used for frying (see Table 10.5).

Margarines and Spreads

279

In markets such as the UK that have traditionally used solid fats like lard or cooking fat or, more recently, liquid vegetable oils, there is less interest in using liquid margarine. A typical composition has a fat phase of about 82% based on soya or sunflower oil, in which emulsifiers perform two functions. First, an emulsifier such as citric acid ester of monoglyceride (Citrem) at, say, 0.4% plus 0.2% soya lecithin produces a stable water dispersion with limited spattering during frying; and second, a selected mono- and diglyceride blend prevents oiling out on storage and thus gives a homogenous product with low viscosity. If the margarine is not intended for frying, the Citrem can be replaced with 0.2% distilled monoglyceride. The water phase may contain proportions of skimmed milk powder and salt as well as a preservative such as potassium sorbate. Flavoring may be added to both phases. The aqueous phase should be adjusted to 4.5 to 6.5 pH and pasteurized at 80°C. The fat phase should be tempered to about 60°C and the emulsifiers melted into a small amount of the liquid oil to a temperature of 65 to 70°C, which is then stirred into the main part of the fat phase. The water phase is added to the fat phase under continuous agitation before cooling through the tube chiller with an outlet temperature of approximately 5 to 7°C. The emulsion should be rested for 2 hours to allow proper fat crystal formation and then stirred vigorously for 15 minutes before topping off for packaging.

10.12

Summary

Standard margarines containing 80% fat are, under normal conditions, relatively stable, requiring minimal quantities of lecithin and/or mono- and diglycerides over and above the quantities of milk proteins usually present. However, where the margarine is required for special purposes, i.e., cakemaking or frying and particularly in products with reduced fat levels, emulsifiers specific to the unique functional requirements of the application should be selected (see Chapter 8 for applications of emulsifiers in baking products).

References Andersen, A.J.C., Williams, P.N. (1954). Margarine, 2d ed., Pergamon, Oxford. Borwanker, R.P., Buliga, G.S (1989). Emulsion properties of margarines and low fat spreads, in Proc. Food Emulsions and Foams-Theory and Practice (eds. P.G. Wan eta!.), San Francisco, pp. 44-52.

280

Food Emulsifiers and Their Applications

Flack, E. (1992). The role of emulsifiers in reduced fat and fat free foods, in Food Technology International Europe (ed. A. Turner), Sterling Publications, London, pp. 179-181. Friberg, S.E. et al. (1990). Emulsion stability, in Food Emulsions (eds. K. Larrson and S.E. Friberg), Marcel Dekker, New York, pp. 1-40. Garti, N., et al. (1982).]. Am. Oil Chem. Soc., 59, 181. Krog, N., et al. (1988). Applications in the food industry, in Encyclopaedia of Emulsion Technology, Vol. 2: Applications of Emulsions (ed. P. Becher), Marcel Dekker, New York, p. 321. Madsen, J. Puff Pastry Margarine: A Comparison of the Chilling Drum and Tube Chiller Methods of Production, TP101, Grinds ted, Denmark. - - - (1981). Post-Crystallisation in Puff Pastry Margarine, at 11th Scandinavian Symposium on Lipids, Bergen, Norway. - - - (1983). Product Formulation and Processing of Margarine and Yellow Fat Spreads, at Margarine and Yellow Fat Seminar, Coventry, England. - - - (1989). Low Calorie Spread and Melange Production in Europe, at World Conference on Edible Oils and Fats Processing, Maastricht, Holland. - - - , Als, G. (1968). Sandiness in Table Margarine and the Influence of Various Blends of Triglycerides and Emulsifiers Thereon, at /Xth Int. Soc. of Fat Research Congress, Rotterdam. Moran, D.P.J. (1993). Reduced calorie spreads, in Porim Technology, No. 15., Feb '93, Palm Oil Research Institute of Malaysia. Schwitzer, M.K. (1956). Margarine and Other Food Fats, Leonard Hill, London.

ELEVEN

Emulsifier Trends for the Future Gerard L. Hasenhuettl

As in many other industries, forecasting the future is usually done by examining the trends of the past and extrapolating the changes for several years into the future. While this works well for continuous functions, discontinuous events often produce dramatic changes in market structures. Forecasting technology is essentially an observation of technical events, extrapolating the trends, and trying to estimate which technologies are about to jump to the next S curve. Food technology abhors radical change. Development of new crops is contingent on being able to diffuse the crop into the massive agronomic supply chain. Issues such as cross-pollination and identity preservation may pose significant problems. When a new product is brought to market, it needs to be thoroughly tested or examined for its safety. Programs like HACCP are aimed at institutionalizing safety into the industry. Even if the government is assured of a product's safety, consumer acceptance is by no means assured. Controversies around genetically engineered and irradiated foods are testimony to this principle. As we stated in Chapter l, development of totally new emulsifiers is unlikely because of the time and cost involved with regulatory approval. However, this by no means sounds a death rattle for innovations in the field of 281

282

Food Emulsifiers and Their Applications

food emulsifiers. Some social, demographic, and technical developments may cause discontinuities in the underlying science involving food emulsions. A few of these trends will be examined.

11.1

Globalization in the Food Industry

The food industry has traditionally been multidomestic. A number of factors such as local taste, perishability, and low value-to-volume ratios in shipping were responsible. However, counter trends such as increased income in developing nations, more international communication and travel, and increased consolidation in the processed food industry are exerting globalization pressures. Development of food products for the global market will change some of the rules for higher value products. Emulsions will require more microbiological and physical stability to withstand shipping long distances and the absence of refrigerated storage in some countries. Some lessons may be learned from the pharmaceutical and cosmetic industries that are further advanced in the application of emulsifiers to produce long shelf lives. One example of a new global product might be a margarine that is stable without refrigeration. In addition to a higher melting fat, a more robust emulsifier system will be required because coalescence of water droplets could cause separation into a phase that would be vulnerable to microbial growth. As global population continues to explode, food emulsifiers will also need to adapt to new lower cost sources of protein, carbohydrate, and fat emulsions formed at lower temperature and mechanical shear can also contribute to energy savmgs.

11.2 Nutritionally Driven Changes in Foods Nutritional studies in the area of diet and health or the counterpart, diet and disease, are continually being carried out and reported, often with apparently contradictory interpretations. Assessing trends in this area can be confusing unless one stays with a few areas where there is general consensus. Saturated fat has been long associated with its ability to raise serum cholesterol, notably LDL. The FDA's NLEA regulations recognized this consensus by requiring labeling of saturated fat for all packaged foods. Food processors have therefore been making a substantial effort toward substitution of solid fats with liquid oils. This poses a formidable challenge in some products where solid fat is

Emulsifier Trends for the Future

283

part of the physical structural or primary functionality of food. For example, the development of high liquid-oil margarines will require an emulsifier that can stabilize a W/0 emulsion where the continuous phase is liquid. Adjunct technologies, such as the development of molecular networks to thicken the oil phase can make a significant contribution to providing structure to the processed food. Solid fat is implicated in such functions as aeration of whipped toppings and formation of evenly dispersed air cells in cakes. Replacement with liquid oil places more of a functional burden on the emulsifier system. Health authorities have recommended that total dietary fat should not exceed 30% of calories. Some consensus is also building that some forms of cancer may correlate to total caloric consumption. Since fat represents 9 cal/gram, cutting fat consumption will also reduce total calories (if the same weight of food is consumed). If consumers respond to these recommendations, pressures for availability of reduced-fat and fat-free foods will continue or even increase. Elimination of fats from products normally containing high levels creates enormous challenges to maintain texture and flavor. Flack (1992) has speculated that emulsifiers can play an important role in reclaiming some of these qualities. Structured emulsifier phases have been patented as the basis for formation of a pseudo-fat phase (Heertje, et al., 1994; Kleinherenhrink et al., 1995). This trend toward replacement of fat functionality with emulsifiers will undoubtedly continue.

11.3 Trends toward Safer Emulsifiers Interest in natural and minimally processed foods has waned and resurged many times over the last half century. As previously mentioned, phospholipids and proteins are the only "all natural" emulsifiers. The discovery and elimination of dioxane in polysorhates illustrates many of the concerns voiced about synthetic food additives. Testing and surveillance of additives will continue and more definitive assays will he developed to assure their safety. Toxicological evaluations are also becoming more sophisticated and specialized. For example, Larsson (1994) has described a model that tests the effects of surfactants on gastric and intestinal lumina cells. Concerns about penetration of single-chain food emulsifiers, such as lysophosphatidylcholine and sodium stearoyllactylate, have been expressed. Microbes have long been used in the food industry to produce cultured products such as cheese and yogurt. Microbes have also been used to produce

284

Food Emulsifiers and Their Applications

very efficient surfactants for application such as enhanced oil recovery and oilspill control. A logical extension of these technologies would be to develop food-grade organisms that produce natural surfactants. However, extensive evaluation would still be essential to ensure the safety of these products when consumed in processed foods.

11.4 Emulsifier Structure and Interactions with Other Ingredients Chapter 6 of this book has discussed the formation of mesophases of food emulsifiers in aqueous environments. Although this property has been known for a few decades, functional implications are just beginning to emerge (Heertje et al., 1994; Kleinherenbrink et al., 1995). lsraelachvili (1985) has described mesophase formation as a function of intermolecular forces. He proposes a model, shown in Figure 11.1, where a free energy minimum is achieved by formation of a structure that balances attractive forces of hydrophobic alkyl chains and the repulsive forces between polar head groups. The author has calculated a "critical packing parameter" from the effective head group area, length of the alkyl chain, and volume of the cone defined by the previous two factors. Table 11.1 lists the structures expected for ranges of critical packing parameters. The significance of this technology is that once

Interfacial (hydrophobic) attraction

, . - - / H e a d-group (hydrophilic) repulsion

~

Volume v

·-._ \

Area a 0

Figure 11.1

Determination of critical packing parameter {lsraelachvili, 1985).

Emulsifier Trends for the Future

Table 11.1

285

Amphiphilic packing of surfactants. (From lsraelachvili, 1985.)

Lipid type

Critical packing shape

Critical packing parameter (VIaJ.)

Structures formed

Single-chain lipids with large head group areas Single-chain lipids with small head group areas Double-chain lipids with large head group areas Double-chain lipids with small head group areas Double-chain lipids with small head group areas

< l/3

Cone

Spherical micelles

l/3-l/2

Truncated cone

Cylindrical micelle (hexagonal)

l/2-l

Truncated cone

Flexible bilayers, vesicles

-l

Cylinder

Planar bilayers (lamellar)

>l

Inverted truncated cone

Inverted micelles

the functional role of a mesophase is defined, rational design of head and tail groups can he accomplished and the emulsifier synthesized by techniques described in Chapter 2. Emulsifiers may he viewed as one class of functional food ingredients. As Chapters 4 and 5 have pointed out, these ingredients may interact with carbohydrates and proteins to produce a number of technical effects. The area of ingredient interactions is the subject of a recent book by Gaonkar (1995). New experimental techniques such as scanning tunneling microscopy and interfacial rheology have the potential to provide greater understanding of these interactions. Emulsifiers can then be designed to form more selective interactive structures that may result in improved or entirely new functionalities.

11.5

Enzymatic Synthesis of Food Emulsifiers

Production of emulsifiers involves contacting lipid and polar phases that are mutually insoluble. To achieve homogeneity, temperatures as high as 500°F are applied and held until reaction is complete.

286

Food Emulsifiers and Their Applications

A consequence of this drastic processing is the production of undesirable and often unidentified byproducts from side reactions. These byproducts can impart metallic, soapy, or bitter off-flavors in finished food products. For example, high temperatures cause caramelization of sucrose esters. To avoid this problem, solvents such as dimethyl sulfoxide and dimethyl formamide have been used. However, removal of these solvents from the product poses another serious problem. An alternative approach is to catalyze esterification or interesterification reactions with enzymes such as lipase or esterase. Since these reactions are carried out at much lower temperatures, formation of odors and off-flavors can be significantly reduced. This is particularly advantageous for unsaturated fatty acids that can be oxidized by high temperatures and small quantities of air. Another potential advantage for enzyme synthesis would be the ability to produce high concentrations of monoesters without the need for short path distillation. To accomplish this, the reaction could be carried out at a temperature just below the melting point of the monoester. As the reaction proceeds and monoester selectively precipitates, the equilibrium will shift to produce more monoesters. Examples of emulsifier synthesis are recent works of Vulfsen (1993) as well as Arcos and Otero (1996). Shah and coworkers (1994) have studied lipase-

catalyzed reactions in monolayers and microemulsions. The major disadvantages of enzyme-catalyzed interesterification are high enzyme cost (relative to sodium or calcium hydroxide catalysts), longer reaction times, and the tendency of enzymes to denature. However, the problems are surmountable and the use of enzyme technology is expected to increase.

References Arcos, J.A., Otero, C. (1996). ]. Am. Oil Chem. Soc., 73:673-82. Flack, E. (1992). Food Techrwlogy International-Europe, 79-81. Gaonkar, A. (ed.) (1995). Ingredient Interactions: Effects on Food Quality, Marcel Dekker, New York. Heertje, 1., et al. (1994). European Patent 0 558 523 Bl, July 13. lsraelachvili, J.N. (1985). Intermolecular and Surface Forces: With Applications to Colloidal and Biological Systems, Academic, New York, pp. 246--62. Kleinherenbrink, F.A., et al. (1995). International Patent Application WO 95/35035, December 28. Larsson, K. (1994). Lipids-Molecular Organization. Physical Functions and Technical Applications, The Oily Press, Ayr, Scotland, pp. 156--62. Shah, D.O., et al. (1994). ]. Am. Oil Chem. Soc., 71:1405-9. Vulfsen, E.N. (1993). Trends Food Sci. & Techno!., 4:209.

Index

Index

A

hydrocarbon chain packing, 151 thermodynamics, 150 albumin, 102 "all natural" ingredients, 5 amino acid, peptide chain, 97 amphiphilic packing of surlactants,

acetylated diglycerides, 33 acetylated monoglycerides, 33, 44,

60,253 preparation of, 33-36 acetylated monoglyceride citrate,

285

33-36

ampoules, flame-sealed, 153 amylopectin molecules, 68, 79, 80 amylose-complexing index, ACI, 252 amylose molecules, 68, 79 amylose leaches, 226 amylopectin, 226 anionic emulsifier: sodium stearollactylate, 219 anionic surfactants, 221 AOAC, Association of Official Analytical Chemists, 40, 56 method, 51 AOCS, 56 association structures, 154-155 associative adsorption, 167, 169

preparation of, 33-36 acid value/free fatty acid, 44 adsorbed proteins: binding strength of, 101 interactions of surfactants, 101 influence of, 102 adsorbed surfactant molecules, 101 adsorption, emulsifier: associative, 167 competitive, 167 layer, 167 surface, 167-169 aeration, bakery products, 214, 217 aggregation structures: association structures, 151, 152

289

290

Index

B baked products: cream icings, 232 crumb-softening, 226 emulsifiers, 216 applications, 225 extruded snacks/cereals, 232 fat-free products, 232 dough conditioning, 225 monoglycerides in, 217, 218 production influences, 229 shortening, 215 yeast in, 217 Bancroft rule, 162, 166 birefringence, loss of, 78 bovine milk, 173 composition of, 174 bovine serum albumin 98 102 113 ' ' ' ' 126 bread dough, 85

Brewster angle microscope (BAM), 96 Brookfield viscosity measurements ' 241 butter, 1, 174, 202, 257, 259 butter and margarine consumption: content of, 259, 260 in Europe, 258 market share of, 261 in the U.S., 257 butterscotch, 251

c cake batters, 212, 230 calcium stearoyl-2-lactylate, 20, 57 calcium hydroxide, 17 capillary melting point, 53

carboxylic acid group reaction, 20 caramels, 251 casein, 122, 124, 126, 134, 170 micelles, 173 caseinate, 134 casson viscosities, yield values: chocolate, 243, 244 cationic surfactant (CTAB), 199 cetyl-trimrthyl ammonium bromide ' CTAB, 199 cheese, 174 manufacture, processed, 198 chemically leavened products, 229 cookies, crackers, 230 layer and snacks cakes, 229 spread ratios, 231 chewing gum, 250 lecithin, 250 mono- and diglycerides, 250 chocolate, 7 antibloom agents, 248--249 bloom, 245--248 coatings, viscosities, 244 compound coatings: antibloom agents, 244--248 confectionery, 236 lecithin, 237-242 crystallization, 248--249 diglycerides, 248 fat, crystallization of, 244 milk, 241, 243 monoglycerides, 248 plastic viscosity, 237 polyglycerol polyricinoleate, PGPR, 242-244 polysorbate 60, 24 7 sorbitan: tritearate, STS, 246--24 7 monostearate, 24 7 synthetic lecithin, 240

Index

viscosity, 8, 237, 241, 243, 248-249 viscosity, apparent, 237 yield value, 237 chromatography/mass spectrometry, 2 circular dichroism, CD, 96 clathrate complex, starch, 68 coalescence, 95 cocoa butter: antibloom agents, 248--249 crystallization rate, 246-24 7 polymorph, 245-247 coffee creamers, 195 column chromatography, 40-42 competitive adsorption, 167 hydrophoblic interaction, 167 critical micelle concertration, 168 ionic surfactants, 168 nonionic surfactants, 168 compound coatings: antibloom agents, 248--249 gloss, 248 crystallization, 248--249 viscosity, 248-249 confectionery emulsifiers, 235-236 chocolate, 235, 236 compound coatings, 236 sugar, 235 concentrated milk, 199-202 production of, 201 products, 199 congeal point, 53 critical micelle concentration (erne), 148,167 cream, 174 fat globule coalescence, 183 destabilized, 187 recombined whipping, 185-186, 186 stabilization, 187

291

whipped, whipping, 183-187 cream liqueurs, 191-195 composition of, 192 cream stability, 192-195 manufacture of, 193 production of, 191 shelf life, 194 cream, coffee whiteners, 195197 recombined, 195-196 formulation, whiteners, 196 cream icings, 232 citric acid esters, monoglycerides, 266 cubic phase, monoolein/water, 131 cubic monoglyceride phase, 132 crystal size of shortenings, 216 cryo scanmng: ice cream, 177 whipped cream, 184, 188 crystals (see also crystallization): fat, bakery products, 217 fat, margarine, 266 fat, effect, emulsifiers, 266-267 crystallization: effect on margarine, 267 fat, confectionery, 239 fat, chocolate, 248 fat, margarine, 265 cytochrome c, 102, 123, 126, 130

0 dairy applications, emulsifiers, 202 decaglycerol decastearate, 25 decaglycerol tristearate, 25 derivatives, bakery products, 217 diacetyl tartaric acid esters of: monoglycerides (DATEM)

292

Index

diacetyl tartaric acid esters (continued) esters, 31, 32, 44, 59,228,

233,249,266 differential scanning calorimetry

(DSC),53,87,96,131 diglycerides, 6, 15, 23, 25, 33, 40,

41,49,55,60,182,198, 200,204,212,227,240, 249,250,268,274,279 hydroxyl values, 23, 24 interesterification process, 15, 17 diacetyl tartaric acid, 31 dimyristoylphosphatidic acid, 126 dioleoyl PC, PE, 160 dioleoylphosphatidylserine, DOPS, 122 dioleoylphosphatdylcholine, 125 dioleoylphosphatidylethanolamine, 125 dipalmitoylphosphosphatidic acid, 121 diphosphatidylglycerol, 122 dipalmitoylphosphatidic acid, DPPA, 123 dipalmitoylphosphatdylcholine, 126 distearoylphosphatidic acid, 121, 123 DMPG, 130 dodecyl sulfate, SDS, 78 DOPG, 130 DTAB, adsorption, 100

E egg yolk, 123 electron microscopy, 2, 266, 269, 270 ellipsometry, 121, 171 emulsifiers: anionic, 219 analytical methods for, 39 baked foods, 211-216 bakery products, role of, 212-214 breakdown, process of, 95

bilayers, 154 binary mixture, liquid-crystalline,

150 carbohydrate interactions, 67 l3C chemical shifts, 61 chocolate confectionery, 235, 236 classified as, l l classification, 161 coalescence, 6, 176 color of, 50 compound coatings confectionery,

236 consistency, 54 crumb softeners in bread, 70 dairy applications, other, 202 determination of, 40--52 destabilization, whipped toppings,

189 dispersion, stabilize, 154 emulsifier/starch-complex formation, 69, 79 enzyme synthesis, 286 fat, crystal structure of, 180 flocculation, 6 food additives, 2-5 functionality, 7-9 future trends, 281-286 hexagonal phase, 149 high-melting, 148 ice cream, 175 instrumental methods, 54--62 interaction, ingredients, 284--285 interfacial viscosity, 154 lactoglobulin, 114 lamellar phase, 149 margarine, function of, 267-270 melting point of, 52-54 mesophases, 284--285 micelles, 149, 154

Index

molecular solution, 149 nonchocolate confectionery, 249 nutritional studies, 282 phase diagrams, 153-156 properties of, 96, 153, 154 properties, physical, 52 polyhydric, 219 polysorbate 60, 219 processing aids, 252-253 shortenings, 211-213 solution properties of, 149 solubilization sequence, 149 sorbitan, icings, 219 specification for, 62 starch, characterization of, 85 starch-complexing, 77-78, 83 structure, S--7, 61 sugar confectionery, 235, 249 surface activity, 147-149,230 surfactants, 212 synthetic, 1 testing and surveillance of, 283 regulatory status, FDA, EEC, 215 whipped toppings, 190 emulsifier classification: geometry of molecule, 164 homogenization role, 165 hydrophilic/lipophilic balance,

163-164 layers for, 170 phase inversion, 162 solubility, 161 emulsifier interaction, bakery components, 221 emulsifier surface, 167-169 emulsion stability, 154--155 emulsion phase diagrams, 154--155 entropy, gain of, 148 enzymatic synthesis, food, 285

293

enzymolysis in starches, 81 ethoxylated esters, 11, 26, 169, 266 sorbitan monostearate, 26 sorbitan monoolate, 27-28 sorbitan tristearate, 28 mono- and diglycerides, 28 surfactants, 169 preparation of, 28--29 polyoxyethlene (20) sorbitan, 28 ethoxylated fatty alcohols, 266 ethoxylated monoglycerides, 228 ethoxylated nonyl-phenol and xylene,

153 evaporated milk, 201 European Economic Community (EEC), 40 baked goods in, 214 extruded snacks/cereals, 232

F fat content, solid, SFC, 180 crystallization: margerine, 263-267 polymorphic, 263-265 whipped toppings, 189 fat: crystals of: bakery products, 217 margarine, 266 effect of emulsifiers on,

266-267 crystallization: confectionery, 239 chocolate, 248 margarine, 265 fat, yellow, consumption, 257 fat-free baked products, 232

294

Index

fat plasticity, 272, 274 fat spreads, 274 stability of, 275-276 spreadability of margarine, 277 fatty acids, 12 composition of, 264 lactylic esters, 19 metal salts of, 19, 20 melting points of, 265 soaps, 51 sorbitan esters, 58 fibrinogen, adsorption of, 108 flocculation, 95 fluorescence recovery after photobleaching, FRAP, 113 fluorescence microscopy, 126 Food and Drug Administration (FDA), 40 regulatons of, 40 baked goods, 214 GRAS status, DATEM esters,

32 hydroxyl, 26 propylene glycol, 18 sorbitan monostearate, 26 succinylated monoglycerides,

30 Reichert-Meiss! value, 34 form stability, bakery products, 217 Fourier transform infrared spectrosopy, FTIR, 59 food emulsifiers, solution properities,

155-156 free fat acids, 60 measuring, in olive oil, 60 freeze fracture, margarine, 270 fruit acid esters, 11, 31-33 tartaric acid-derived esters, 31 fudge, 251-252

G gas-liquid chromatography GLC), 46,

55-57 Gibbs effect, 110 performed on lipids, 55 GLC, 56 gliadin, 132 glyceryl monostearate (GMS), 86,

197 gelatin, 134 gelatinization, 78, 89 gelatinization endotherm of starches, 88 globalization, food industry, 282 globular proteins, interior, 97 hydrogen bonding, 98 hydrophobic interreaction of, 98 van der Waals interaction, 98 gluten structure, 215

gluten proteins, 224 glycerollactopalmitate (GLP), 191, 250 glycerol monostearate (GMS), 178,

180-18,189,236,248, 250,251,252 glycerol monooleate, 189 GRAS, 2-3, 15, 26 monosodium phosphate, 36 status of, 32 gums, 251

H helix starch, structure of, 79 hexaglycerol dioleate, 25 hydroxyl value, 48 high-performance liquid chromatography (HPLC), 47, 52,57-58 detectors of, 58

Index

separations of phospholipids, 58 homogenization, 166 hydrated distilled monoglycerides, 227 hydrodynamic interactions, 166 hydrophile/lipophile balance (HLB), 6-8,151,163-164,169, 220,236 hydrophilic, 5, 11, 100 hydrated lime, 17 hydration: force, emulsion droplets, 155 repulsion, monopalmitin, 155

295

J jellies, 251 ACI values, 252

K kosher, 5, 13 Krafft temperature, 148

L

ice cream, 95, 174-183 aging of, 178 composition of, 175 coalesence stability of, 176 cryo scanning of, 177 emulsifiers, 175, 178 fat globles in, 179 fat crystallization in, 180-182 interfacial viscosity, 177 manufacture of, 175 orthokinetic stability, 177 inclusion complexes, starch, 68 interesterification process, 17 interfacial tension, role, 165-166 in bakery products, 217 iodine dilation value, margarine, 272 melting point, fat blends, 272 value, 45--46 binding of starches, 77 ionic surfactants, 100 isotherm adsorption, 100 isotherm surface tension, 115 IUPAC, 56

lactic acid, 236 analyses of, 49 water-in-soluble combined, (WICLA), 22 esters of: glycerol, 22 monoglycerides, 187, 248 propylene glycol, 22 lactalbumin, 102, 123, 125, 130, 185 lactoglobulin, 102, 104, 106, 109, 113-114,117, 118, 120-121,122,124,125, 126,130,133,134,185 lactylated esters, 18-23, 41 hydroxyl group reaction, 19 fatty acids of, 19 metal salts of, 19, 20 preparation of, 19-23 lactylated monoglycerides, 20-22, 23,44,227,230 preparation of, 20-22 lamellar liquid-crystalline phase, emulsifiers of, 153 lamellar phase, monoglycerides, 154 Langmuir-Blodgett technique, 121 layer adsorption, 167, 169, 171

296

Index

layer adsorption, (continued) surface, protrin, 171 phospholipid, 171 ellipsometry, 171 lecithin, 42, 50, 60, 120, 155-161,

173,199,202,220,223, 228,231,233,236, 238-239,248,250,253, 268,274 phosphorus, procedures for, 51-52 phosphatidyl, 171 phosphatidylcholine content in,

60,155 soy lecithin, 51, 239 synthetic, 240 viscosity, 54 linear molecules, starches, 68 lipid emuisifiers, liquid-crystalline,

156 lipid fractions, topping emulsions,

190 lipid materials, effects of 69, 96 lipid/protein interaction, 122 lipid structures, 129, 133 lipids in baked foods, 225 lipophilic, 5, ll lipolytic emzymes, 133 liposomes, 84 liquid chromatography, 42 liquid-crystaline mesophases, whipped toppings, 191 liquid margarine, 278-279 low-fat spreads, 274-278 low molecular weight (LMW), 96 lysolecithin, 84 lysophosphatidyl cholines (LPC),

119,159,283 lysophosphatides (LPC), (LPE), 156,

158 lysozyme, 102, 104

M Marangoni effect, Ill margarine, l, 255, 258-279 emulsifiers, 267-270 liquid margarine, 278 low-fat spreads, 274-276 market share, United States, 261 oil-in-water (0/W) spreads, 7, 278 phase inversion, 277-278 processing, 270-27 4 puff pastry margannes, 272-274 plasticity, 272-427 reduced fat spreads, 6, 274 spreadability, 277 structure, 262 fat crystallization, 263, 265-266 fat melting points, 272 polymorphism, 263-265 oils and fats, 263-426 melting points, 265 raw materials, 262 water-droplet distribution,

268-269 water-in-oil (y//0) emulsion, 7,

268,274,277-278 mass spectrometry, 60 mayonnaise, l melting point, 12, 52-53 melittin interactions, 125 Mettler dropping point, 53 micelles, 84, 148, 165 microemulsion process, 37 milk, l, 173 composition of bovine milk, 174 concentrated, 199-202 fat globule membrane (MFGM),

173,184,185 proteins, 122, 135 recombined, 199-201

Index

shelf life, 200 minarine, 259 moisture, 50 molded products, 175 molecular aggregation, 165 molecular distillation, 15, 17 monoglycerides, 3, 6, 8, 11, 13-15,

21-22,25,40-44,55-57, 59--61, 134, 149, 154--156, 178, 182, 198--200, 202, 212, 217-219,227,230--1240, 248--250,252,268--270, 274,279 acetic acid esters of, 187, 236, 249,252-253 acetylated, 33, 44, 60 preparation of, 33-36

297

yeast-raised bakery products, 217 monoglyceride citrate, 33 monomargarine, 55, 56 monoolein, 130, 156 monopalmitin, 155, 224 monostearate, 231 cubic, water phase, 131 mouthfeel, 249 myelin protein, 125

N near infrared reflectance (NIR), 46,

48,59 nougat, 250 nuclear magnetic resonance (NMR),

2,59,60

citric acid esters of (CITREM),

266,270,279 diacetyltartaric acid esters of (DATEM), 3, 31-33, 41,

44,59,228,249,252,266 distilled, 22, 30, 233 distilled saturated, 156 distilled unsaturated, 156 ethoxylated, 231, 250 lactic acid esters of, 20--22, 44,

187,230,236,248 phase behavior, 178 phases of: cubic phase, 156 lamellar phase, 156 reversed hexagonal, 156 phosphated, 3, 11, 236 propylene glycol esters of, 60, 187 stearyl monoglyceride citrate, 33 succinylated (SMG), 30, 213, 227,

278,231 tartaric acid esters of, 197, 236

0 oil-continuous emulsions, 154 oleic acids, 11-13, 256 oleomargarine (see margarine) oleostearine, 256 organic acid esters, 156 diacetyl tartaric acid, 156 monoglyceride ester, 156 orthokinetic stability, 177 Oswald ripening, 95 olalbumin, 102

p packing parameter, 165 palmitic acids, 11-13, 256 palmitoyloleoylphosphatidylcholine,

123

298

Index

palmitoyloleoylphosphatidylglycerol,

123 para-K-casein, 124 peanut butter, 7 penetrometer, 54 pentosan, 214 peptide chain, 97 peroxide value, 46, 4 7 phase diagrams, 153, 166 emulsion stability, 154 lamellar liquid crystalline phase,

153 water and dioleoylphosphatidylcholine, 157 phase inversion, concept, 162 phase inversion temperature (PIT),

162 phosphated esters, 36 monosodium phosphate, 36 preparation of, 36 phosphatides, mixtures of, 158 phosphatidic acids, 122, 158, 240 dioleoyl, 159 lysophosphatidylcholine (lyso PC),

159 phosphatidylglycerol, 135 phosphatidylcholine (PC), 52, 57-61,

122,130,155,157-159 dimyristoyl, 159 dioleoyl, 159 dipalmitoyl, 159 distearoyl, 159 egg, 159 soybean, 159 transition temperature for, 158 phosohatidylserine, 122 phosphatidylethanolamine (PE), 52,

60, 61, 122, 130, 156-159,173 dioleoyl, 159

dipalmitoyl, 159 soybean, 159 phosphatidylinositide, 173 phosphatidylinositol (PI), 122, 156,

158,159 soybean, 159 phosphatidyl serine (PS), 156, 173 phospholipids, 41, 42, 52, 57-61,

159,166,171,173,186, 200,202 liquid-crystalline phases, 159 phosphoric acid, 15, 17 phosphorus pentoxide, 240 photobleaching, fluorescence recovery, 113 polar lipid: classes, 127 cubic phase, 127 lamellar phase (LJ, 127 liquid crystalline phase, 127 hexagonal phase, 127 hydrophobic interaction, 127 micelle concentration (cnc ), 127 phase behavior, 126 surfactants, 127 structure, 128, 129 plasmalogens, 173 plasticity, 5 polyglycerate 60, 251 polyglycerol, 59 polyglycerol esters, 3, 11, 23, 54, 58,

59,213,233,249,266, 270 of stearic acid, 248 preparation of, 23-25 polyglycerol polyricinoleate (PGPR), 8,56,236,242-244 polyhydric emulsifiers, 219 polyglycerol esters, 219 sucrose esters, 219

Index

polylactic acid, 20 polymerization, 242 polymorphic form, 245, 246 polyoxyethylene (20), sorbitan monostearate, 28, 29, 114, 115,

118,156,182,220,232 polyoyl, 56 polyphosphates, 198 polysorbates, 3, 29, 59, 61, 178, 182, 219,236,250 polysorbate 60, 29, 213, 220, 227, 230,233,236,247-248, 250,252 processed cheese, 197-199 manufacture of, 198 programmed temperature x-ray diffraction, 53 propylene glycol, 17 propylene glycol esters, 15, 17, 23,

55,232 propylene glycol lactates, 23 propylene glycol monoesters

(PGME), 11, 17, 18, 22-23,213,230-232, 236,249 prepartion of, 15 propylene glycol monostearate

(PGMS), 15, 189-191 proteins, 162, 69, 71, 89 adsorption, 169 desorption, 189 strenghthening, 214 protein complexes in baked foods,

224 protein/emulsifier: interactions, 95-135 food applications, 132 lipolytic enzymes, 132, 133 lipid structure, 133 protein stability, adsorption, 97

299

protein, lipid: interactions, 126 monolayers, 125 protein hydrolysates, 149 protein/phospholipid interactions, 120 dispersed systems, 120, 121 solid surface interactions, 121 protein stability, 97 protein/surfactant interactions, 98--119 adsorption: binding to, 107 competive, 111 cooperative, 107 isotherm, 99 mixtures of, 106 adsorbed: surface properties, 103 complex formation, 105 replacement of, 105 binding, protein and emulsifiers,

113 coadsorption, 112 dissociation constant (Kd),113 emulsifier properties, 134 foam, emulsion stabilization, 110 hydrophobic surfaces, 103 hydrophilic surfaces, 103 Krafft temperature, 103 liquid air, 110 liquid/liquid interfaces, 110 lactoglobulin, 117 electrostate repulsion, 103 monolayer of, 99 nonionic surfactants, 106 interactions, solid interfaces, 106 ionic surfactants, 99, 106 solid surfaces, 98 solution influence, 107 micelles, critical concentration of,

99

300

Index

protein properties of, 102 surface tension, llO protein/phospholipid interactions,

122 protein/protein interactions, ll2 puddings, 77 puroindolines, ll9

R refractive index, 54 regulatory agencies, 40 Reichert-Meiss! value, 34, 49 reverse osmosis, 201 reversed aggregates, 165

s saponification number, 26, 4 7 sauces, 77 Scatchard equation, ll6 shelf life, 200 milk, 200 salad dressings, 2 shortening, 2ll-216 emulsified, 2ll-213 fluid, 230 melting point, 216 nonemulsified, 213 plasticity, 216 solid-fat index, 216 sodium caseinate, 192 sodium dodecylsulfate, SDS, 98 sodium hydroxide, 17 sodium lauryl sulfate (SLS), 78, 134 sodium hydroxide, 17

Sodium caseinate, 192 sodium stearoyl fumarate, 197, 213,

221,231 sodium stearoyllactylate (SSL), 20,

41,42,44,156,197,203, 213,219,221,224,227, 228,230-232,266,283 softening point, 53 solubility, 161 Bancroft rule, 162 sorbide, 26 polyoyls, 26 sorbitan, 26 polyoxylated (20), 231 monostearate (SMS), 26, 56, 219, 230,231,247,248,250, 252 tristearate (STS), 56, 246, 24 7, 266 sorbitan esters, ll, 26, 162, 164, 169,220,233,266 ethoxylated, 26, 28, 266 production, 26 polyxyethylene (20), 156 sorbitan monooleate, 156 sorbitan monostearate, 156, 247 sorbitan stearate, 156 soy lecithin, 8 soybean phospholipids, 161 phase diagram, 161 spectroscopy, 59 sphingomyelin, 125, 173 spread ratios of cookie dough, 231 spreadable fats, 259, 260 starch: complexes, in baked foods, 222 complexing, 77, 214 differential scanning calorimetry, 85

Index

inclusion complexes of, 68 iodine binding capacity, 77 composition of, 68 gelatinization of, 85, 86 temperature, Tlf Tm, 89 glass transmission, 89 crystallite melting, 89 granule, 82--83 lysolecithin, 85 nuclear magnetic resonance, 85 properties: amylose helix, 82 effects of lipid materials, 69 fatty acids, 81 gelatinization, 77 module, 78 monoglyceride binding, 82 pasting, 70 retrogradation, 79, 80, 223 viscosity, 70, 77, 79 saturated fatty acid monoglycerides, 224 types of, 83 viscosity profile, 83 emulsifier complexes, 77, 78, 79,

83,85-90 electron spin responce, 85 infrared spectroscopy, 85 pH effects, 83 temperature, 83 paste gelation, 79 unsaturated fatty acid monoglycerides, 224 waxy, table of, 75 starch/emulsion complexes: V-type x-ray diffraction pattern, 69 statistical experimental design, 8 fractional factorial, 8

301

response surface methodology (RSM), 8 staled bread, 80 stearic acids, 11-13, 26, 256 stearoyllactylate, 213 succinylated esters, 11, 29 preparation of, 29, 30 sucrose esters, 3, 11, 42, 58, 59, 182,

213,227,236 preparation of, 36--38 sucrose monopalmitate, 231 sucrose monostearate, 231 sucrose distearate, 231 sucrose monostearate, 266 sucrose polyesters, 233 Olestra™, 233 surface activity, 148, 167 components, 167 polar interactions, 148 surfactants, 5 surface tension, emulsifiers, 147,

227 surfactants, 168, 199, 201, 212 anionic, 199, 201, 224 cationic, 199 cetyl-trimethyl ammonium bromide (CTAB), 199 ionic, 99, 100, 168 interaction of, 101 lecithin, 199 molecules, arraingments of, 101 nonionic, 168, 201, 224 properties, 102 sodium dodecyl sulphate (SDS),

199,201 solidlaqueos interfaces, 99 sucrose ester, 223 zwitterionic, 199

302

Index

T tetraglycerolesters, 156 monolaurin, 156 tetraglycerol, 156 thin film stabilization, 111, 112 tocopherols, 50 toffee, 250 triglycerides, 2, 12-5, 17, 204, 240,

263 glycerolysis of, 204 triglycerol, 23 triglycerol monooleate, 248 triglycerol monoshortening, 250 triglycerol monostearate, 248, 252 triglycerol monoshortening, 25 triglycerol monostearate polyglycerol ester, 25 tripropylene glycol monoesters, 18

u ultrafiltration, 201

vitamin fortification, 261 Vroman effects, 108

w water-continuous emulsions, 154 water-insoluble combined lactic acid

(WICLA), 49 waxy starch table, 75 wet chemical analysis, 43-50 titration, 43-49 wheat flours, 214 whipped cream, whipping cream,

183,185 electron micrograph, 188 recombined, 185, 186 whipped toppings, 187 emulsion destabilization, 189 fat crystallization, 189 powder composition, 187 protein desorption, 189 Wiley melting point, 53

y

v van der Waals interaction, 98 vesicle bilayers, 131 viscosity, 8, 54,177,237,241-244 ,

248 apparent, 237 interfacial, 177 plastic, 237, 243, 244

yeast-raised products, 225 crumb-softening, 225--227 dough conditioning, 225 dough strenghthening, 225, 226 emulsifier functionality during processing, 227 yield value, 237 yoghurt, 202