Advances in Fat Rich Dairy Products 2002
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Advances in Fat Rich Dairy Products 2002...
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FEBRUARY 5 - MARCH 6, 2002
CENTRE OF ADVANCED STUDIES DAIRY TECHNOLOGY DIVISION NATIONAL DAIRY RESEARCH INSTITUTE KARNAL -132001
Lecture Compendium
Advances in Fat-Rich Dairy Products
The Fourteenth Short Course
Organised under the aegis of
Centre of Advanced Studies in Dairy Technology
February 5 – March 6, 2002
Dairy Technology Division National Dairy Research Institute (ICAR) Karnal -132 001
Head, Dairy Technology Division & Director, CAS (DT) Dr. G.R. Patil
Course Coordinator Dr. B.B. Verma
ALL RIGHTS RESERVED No part of this lecture compendium may be reproduced or use in any form without the written permission of the Director, NDRI, Karnal
Editing & Compilation Dr. A.A. Patel Dr. V.K. Gupta Dr. Sudhir Singh Mr. A.K. Singh
Cover Design & Page Layout Dr. B.B. Verma
R.B. Verma Mr. Aniruddha Kumar
FOREWORD Dairy Technology Division of this Institute, under the Centre of Advanced Studies Programme, has done a very commendable service to the State Agricultural Universities and ICAR Institutes by offering thirteen short courses for training their academic staff. Through these efforts a large number of the teaching faculties of the SAU‟s and Research Scientists engaged in the National Agricultural Research System have been exposed to the latest developments in the field of Dairy Technology. In this manner, the Dairy Technology Division has fulfilled the task assigned by the Education Division of the ICAR for dissemination of the expertise available at various departments of the National and International repute. The Centre of Advanced Studies is now ready to offer 14th short course of 30 days duration entitled „Advances in Fat Rich Dairy Products”. The course intends to provide insight and awareness to the teachers involved in teaching the UG/PG students about the advancements in the field so that they can transmit the new knowledge to their students. A phenomenal growth of the dairy industry has taken place since 1971 with an annual increase of 4-7 % in milk production, as a result of which India has become the largest producer of milk in the world. The increasing milk production, though has boosted the confidence of our planners, dairy/animal R & D workers, milk producers and dairy entrepreneurs and has offered lot of opportunities, but at times, the problem of handling surplus milk needs to be ably tackled. Indian dairy industry, over the years, has been converting surplus milk for the manufacture of fat rich dairy products, especially ghee and butter, and skim milk powder because of several environmental, technological and economical reasons. More than one third of the total milk production is being utilized for the production of ghee and butter where in milk lipids the most expensive constituents of milk are concentrated and preserved. Milk lipids play many diverse roles, some of which are essential for human health. Many of the desirable flavour and textural attributes of dairy products are due to their lipid components, consequently, butter fat has, traditionally, been highly valued. Significance of fat can also be realized from the fact that the consumers perception of food quality is largely based on the percievable rich taste. Unfortunately, milk lipids are subject to chemical and enzymatic alterations which can cause flavour defects referred to as oxidative and hydrolylic rancidity, respectively. The storage stability of high fat products are strongly influenced by these changes. High proportion of saturated fatty acids in butterfat has been the subject of controversies in recent years, particularly in their possible role in aggravating coronary heart diseases. Considerable progress has been made in different areas of fat-rich dairy products, such as development of continuous ghee and butter making equipment, fractionation of butter fat for different uses, milk fat spreads, nutritive health aspects of butterfat, microstructure and preservation of fat rich dairy products. All these and other related basic aspects have been effectively discussed in the lecture compendium by the subject experts. It is hoped that the compendium so ably brought out by the course organizers will serve as a reference work of immense importance to the participants of the course.
(B.N. MATHUR) DIRECTOR
ACKNOWLEDGEMENT We express our gratefulness to the ICAR for having recognized the Dairy Technology Division of this Institute as a Centre of Advanced Studies based on the excellent performance in the VIII Plan and subsequent renewal of the programme during the IX Plan period. I express my gratitude to Dr. (Mrs.) Tej Verma, DDG (Education) and Dr. H.S. Nainawate, ADG (HRD-II), ICAR, New Delhi for taking keen interest in this programme and timely release of funds. I am grateful to Dr. B.N. Mathur, our Director who has always taken keen interest in all the activities by the Division and encouraged me to perform to the expectations of the ICAR and NDRI, in addition to providing all the infrastructural facilities for the smooth and successful conduct of this course. For this short course on “Advances in Fat Rich Dairy Products” we are thankful to the guest speakers from Dairy Industry, State Agricultural Universities and the ICAR Institutes who contributed the lectures in time and travelled in all the way to Karnal in such a cold weather to share their valuable expertise with the participants. I must convey my special thanks to our faculty for timely submission of lectures and for actively participating in conduct of theory and practical classes. The faculty of other division particularly, Dairy Chemistry, Dairy Microbiology Division, Computer Centre, Dairy Engineering needs special mention for helping us in this endeavour. Successful conduct of any programme requires the efforts of a team of active workers. Though all the staff of D.T. Division, Scientists, Technical Officers and other staff contributed in one way or other for the conduct of this course, special appreciation needs to be made for Dr. B.B. Verma, Senior Scientist and Course Coordinator, Dr. A.A. Patel, Dr. S.K. Kanawjia, Dr. Dharam Pal, Sh. F.C. Garg, Dr. Sunil Sachdeva, Dr. R.S. Mann, Dr. Sudhir Singh, Sh. A. K. Singh, Sh. Aniruddha Kumar, Mr. R.B. Verma and Mr. Tanveer Alam for their help in preparation of the compendium, purchase of the material required for the course and arranging boarding and lodging of the participants. The help rendered by Mr. Lakhvinder Singh for word processing and logistic support during the course is sincerely acknowledged. I am thankful Mr. A.K. Sharma, Dairy Supdtt. and all technical staff of Exp. Dairy and Library for helping us in smooth conduct of practical training of the participants.
(G.R. PATIL) Head, Dairy Technology Division and Director, CAS(DT)
Committees for organisation of the short course
Organising Committee Dr. G.R. Patil Dr. A.A. Patel Dr. R.S. Mann Dr. S.K. Kanawjia Dr. Dharam Pal Dr. B.B. Verma
Receiption Committee Dr. S.K. Kanawjia Dr. D.K. Sharma Dr. D.K. Thompkinson Dr. (Mrs.) Latha Sabikhi
Chairman Member Member Member
Hospitality Committee Dr. R.S. Mann Dr. G.K. Goyal Dr. C.N. Pagote Dr. Sunil Sachdeva
Chairman Member Member Member
Course Director Member Member Member Member Course Coordinator
Technical Committee Dr. A.A. Patel Dr. V.K. Gupta Dr. Sudhir Singh Dr. R.R.B. Singh Mr. A.K. Singh
Chairman Member Member Member Member
Purchase Committee Dr. Abhay Kumar Dr. Dharam Pal Mr. F.C. Garg
Chairman Member Member
CONTENTS
1
Status of fat-rich dairy products
Dr. G.R. Patil
1
2
Chemical characteristics of cow and
Dr. B.S. Bector
6
buffalo milk fats 3
Physical characteristics of milk fat
Dr. A. A. Patel
12
4
Developments in cream separator
Prof. I.K. Sawhney
18
5
Cream and consumer cream products
Dr. C. N. Pagote
22
6
Developments in preservation of cream
Dr. R. R. B. Singh
30
7
Technology of butter manufactureconventional process
Dr. B.B. Verma
38
8
Developments in continuous butter making
Dr. Abhay Kumar
46
9
Additives in fat rich dairy products
Dr. Sudhir Singh
51
10 Biotechnological developments in
Dr. R. K. Malik &
56
enhancement of butter flavour
Naresh Kumar
11 Imitation butter and related products
Mr. A.K. Singh
62
12 Rheology of butter-technical considerations Dr. G. R.Patil and measurements
69
13 Dairy spreads
Dr. P.S. Prajapati
76
14 Application of electron microscopy in fat rich dairy products
Dr. D.N. Prasad &
87
Dr. S.K.Tomar 15 Anhydrous milk fat-butter oil
F.C. Garg
92
16 Milk fat fractionation
Dr. T. Rai
96
17 Properties and utilization of fractionated milk fat
Dr. Sumit Arora
101
18 Application of fat modification techniques for improving the usability of milk fat
Dr. D.K. Sharma
110
19 Alternative sources of milk fat for recombined milk
Dr. B. D. Tiwari
117
20 Industrial practices in production and
Dr. Dharam Pal
121
preservation of ghee 21 Developments in continuous ghee making
Dr. A.K. Dodeja
128
22 Regional preferences for flavour of ghee and methods for simulation
Dr. G. S. Rajorhia
134
23 Utilization of sour/curdled milk for ghee making
Dr. Vijay Kumar Gupta
138
24 Developments in the packaging of butter and ghee
Dr. G.K. Goyal
144
25 Ghee flavour and its simulation-a review
Dr. (Mrs.) B.K. Wadhwa
149
26 Quality evaluation of butter and ghee
Dr. Sunil Sachdeva
153
27 Fat constants- basic principle, their determination and significance in quality control of ghee
Prof. K.L. Arora
158
28 Cholesterol and its management:
Dr. (Ms) Latha Sabikhi
166
29 Rancidity in fat rich dairy products and its prevention
Dr. D.K. Sharma
173
30 Renovation of oxidised butter fat
Dr. M.P. Bindal
179
31 Recent trends in detection of adulterants in milk fat
Dr. Dharshan Lal
183
32 Medicinal value of ghee
Dr. S. K. Kanawjia
192
33 Nutritional attributes of milk fat
Dr. Vinod K. Kansal
202
34 Fat-rich dairy powders
Dr. Sitaram Prasad
208
35 Developments in processing and utilization of ghee-residue
Dr. B.B.Verma
214
36 Application of systat statistical software packages to dairy research
Dr. D.K.Jain & Adesh K. Sharma
219
37 Multimedia presentation: a modern technique for effective teaching
Adesh K. Sharma
233
38 Search techniques for printed and online
Y.K. Sharma and B.P. Singh
240
facts and figments
information sources for dairy research
LIST OF PARTICIPANTS
1.
Mr. S.H. Qureshi Asstt. Professor Deptt. Of Dairy & Food Technology Maharana Pratap University of Agrilculture & Technology Udaipur-313001 (Rajasthan)
2.
Dr. (Mrs.) Manorama Sr. Asstt. Professor College of Dairy Technology I.G.K.V., Krishak Nagar Raipur-492012
3.
Mr. Kamble Dinkar Keshav Asstt. Prof. Deptt. Of Animal & Dairy Science College of Agriculture Kolhapur-416004
4.
Mr. Awatirak Manik Ganogi Astt. Prof. Deptt. Of Animal Husbandry & Dairying College of Agriculture, Ambajogai Distt. Beed-431517
5.
Dr. Mukesh Jaghubhai Solankey Assc. Prof. Dairy Technology Deptt. SMC College of Dairy Science GAU, Anand Campus Anand-388110 (Gujarat)
6.
Mr. Sunil Kumar Magaubhai Patel Asstt. Prof. Dairy Engineering Deptt. SMC College of Dairy Science GAU Anand Campus, Anand-388110 (Gujarat)
7.
Dr. Vivek Sharma Scientist Dairy Chemistry Division NDRI, Karnal-132001
8.
Dr. Jai Singh Yadav Lecturer Deptt. Of Animal Husbandry & Dairying J.V. College, Baraut, Bagpat (U.P)
9.
Mr. Bhagat Singh Lecturer in Animal Husb. & Dairying Govt. P.G. College Sawai Madhopur-322001 (Rajasthan)
10.
Dr. Rajan Sharma Scientist Dairy Chemistry Division NDRI, Karnal-132001
11.
Sh. Shinde Anant Tatesaheb Deptt. Of Animal Husbandary & Dairy Science College of Agrilculture Latur (Maharashtra)
12.
Sh. V.K. Mairal Asstt. Professor Deptt. Of Animal Husbandry & Dairy Science College of Agriculture Latur (Maharashtra)
13.
Dr. Devesh Gupta Asstt. Prof. (A.H & Dairying) J.V.C. Baraut Shantipuram Gali No. 2 Nehru Road, Baraut (Baghpat) U.P
14.
Mr. Charanjiv Singh Lecturer Deptt. Of Food Technology SLIET, Longowal (Sangrur) Pb.
15.
Dr. Shalik Gram Shukla Sr. Lecturer A.H. & Dairying R.M.P. (PG) College, Narsan Haridwar-249406
16.
Dr. Pramod Kumar Omre Jr. Research Officer Deptt. Of Process & Food Engg. College of Technology Pant Nagar-263145
STATUS OF FAT-RICH DAIRY PRODUCTS IN INDIA AND ABROAD
Dr. G.R. Patil Head Dairy Technology Division NDRI, Karnal-132001 1.0
INTRODUCTION
Milk production in India has been increased steadily during the last five years at a rate of 4 - 4.5% annually, culminating in India surpassing the America in 1998-99 to become world leader in milk production with 74 million tones. India has maintained its position since then by producing 77 million tones of milk in 1999-2000. Of this, buffalo milk accounts for roughly 52% while cow milk makes of most of the balance. About 12% of the total milk produced in the country is processed in 567 dairy factories for conversion into milk and milk products, valued at Rs. 69.34 crores annually. Presently, the organized dairy sector has been penetrating more vigorously the milk and milk product market in India, which had been the exclusive zone of the unorganized sector. Verma et al. (1999) have studied the productivity performance of dairy industry across the country & have registered an annual growth of 17.14% for the country as a whole with highest market share of 23.49% by Maharashtra followed by Gujarat (17.22%). They suggested that management & inputs and product mix contribute significantly in productivity realization and efforts should be made to industry more viable. Considering the importance given to fat and popularity of fat-rich dairy products, these products can find place in viable product mix. Our strength lies in the fact that we are the largest producer of buffalo milk in the world. Buffalo milk is better suited for the manufacture of fat-rich dairy products as compared to cow milk due to its higher fat, bigger size of globules and higher production of solid fat leading to the higher yield, lesser low of fat in buttermilk or skim milk, easier separation of cream or butter and better texture (Sindhu, 1996). The manufacture of fat rich dairy products such as cream butter, ghee, butter-oil, cream powder, butter powder, butter spreads, Malai and Makkhan from buffalo milk has been reviewed extensively by Gokhale et al (2001). The present status of production, trade, consumption, etc. in India and abroad in briefly discussed in this presentation. 2.0
PRODUCTION OF FAT-RICH DAIRY PRODUCTS
In 1998-99 the production of butter in India amounted to 26000 tonnes and production of ghee was 48000 tonnes, which was lower than the production in 1997-98 (Butter: 30000 tonnes & ghee 52000 tonnes). The world butter production including anhydrous milk fat (AMF) etc. remained stable since 1998 and this trend will continue in 2000 at 4.2 million tones. More will be produced in United States, New Zealand and possibly Russia because milk production is increasing in these countries. This growth, however, will be offset by reductions in other countries and the E.V. In 1998-99, butter production remained almost the same after a decline in previous years (Table-1)
Table 1: Dairy Butter Production ‘000 t EU 15 1) Iceland Switzerland Norway Baltic States 2) Bulgeria 1) Czech Republic Slovakia Slovenia Poland Romania Hungary Russia Ukrine Belarus Croatia Canada Mexico USA Argentina Brazil Chile Uruguay China 3) India 3) India 1) Iran 3) Israel Japan South Africa Australia 4) New Zealand 1.4)
1995 1 809.3 1.4 41.2 20.7 50.0 2.1 72.3 16.0 1.9 122.8 16.1 15.7 421.0 161.4 60.8 2.4 92.5 15.2 568.8 51.3 85.0 6.7 13.0 3.4 26.0 3.3 4.2 80.3 14.1 153.1 277.5
1996 1 815.1 1.3 39.6 19.4 59.2 2.1 68.9 15.0 2.0 129.7 13.4 10.8 310.0 116.5 61.8 3.0 93.2 12.7 525.9 52.2 85.0 6.5 14.5 3.5 36.3 5.4 4.2 86.3 8.1 157.8 351.0
1997 1 762.2 1.4 39.7 24.1 63.8 2.1 61.9 14.5 1.9 136.5 9.2 9.4 277.0 79.0 70.8 2.6 89.7 15.0 520.7 49.0 90.0 9.6 15.0 3.5 33.2 80.8 5.0 4.7 87.2 10.8 164.2 344.0
1998 1687.4 1.4 40.5 22.6 59.2 2.1 65.4 16.5 3.1 141.2 9.0 13.0 271.0 76.0 72.8 2.4 85.9 15.0 529,8 49.0
1999 1 701.2 1.5 34.9 22.9 41.2
11.2 16.4 4.0 31.2 82.0 4.7 88.9 17.3 186.9 339.0
141.5
65.4 16.3 4.1 133.0 13.8 257.4 72.0 3.7 88.6 578.4 687.0
5.0 74.0 5.0 85.3 10.5 190.1 360.0
1)
Incl. Butteroil in butter equivalent. Extonia, Latvia and Lithuania. 3) Table Butter. 4) Dairy years ended June or May of the following 2)
3.1
TRADE IN FAT-RICH DAIRY PRODUCTS
The international trade in dairy products is continuing to grow. The long-term growth trend was interrupted in 1998 and 1999 by the economic crisis in many parts of the world. These crises particularly affected emerging markets for dairy products such as south-east Asia, Latin America or Russia. The world trade in butter is also recovering again (Table 2 & 3) with regard to future market development, it is really a question of whether the trade 2
volume in future years will continue to follow the long-term downward trend or if it will stabilize at certain level. It is true that market access arrangements will have stabilizing influence. New Zealand is the major exporter of butter/butter oil followed by EV & Australia (Table-2). Russia continues to be the major importer followed by Egypt (Table-3) & India’s trade of Fat-rich dairy products in the international market is negligible. Table 2: World Trade in Dairy Products (Exports) ‘000 t Butter/Butteroil World EU USA Australia New Zealand Other countries
1996
1997
1998
1999*
2000*
761 189 21 64 237 250
875 219 21 100 314 221
800 164 11 106 317 202
725 158 6 117 277 170
770 150 2 310 -
Table 3: World Trade in Dairy Products (Imports) ’000 t Butter/Butteroil World EU Russia Poland Algeria Egypt Morocco Mexico Brazil Iran Jordon USA
4.0
1995
1996
1997
1998*
1999*
846 72 246 0 22 49 22 20 16 17 22 1
761 96 126 0 14 50 28 19 10 27 15 5
875 92 190 5 10 38 16 25 6 10 15 13
800 96 83 1 9 35 16 27 6 10 15 27
725 100 38
27
15
CONSUMPTION AT FAT-RICH DAIRY PRODUCTS
The long-term trend of butter consumption in the major areas of production and consumption is characterized by a slight decline. In some cases, the declining trend has been arrested, but not generally reversed. In the European Union, the demand from private households in continuously falling, whereas the demand from catering outlets and food services is growing one major factor for the stabilization of butter consumption is the subsidized disposal of butter in special schemes for utilization in bakery, confectionery, icecream and other food items. The general impression is that butter is inevitably losing its market share to the yellow fat market. This can not be confirmed since recent developments in countries such as Poland, 3
Argentina and some other show a partial recovery (Table 4). While the per capita annual consumption of butter in some developed countries is an high as 6-8 kg, in India it is only 1.75 (largely in the form of ghee). Table 4: Butter Consumption ‘000 t 1997 Austria 37 Belgium/Luxembourg 64 Denmark 10 Finland 37 France 485 Germany 578 Greece 9 Ireland 14 Italy 124 Netherlands 54 Portugal 16 Spain 22 Sweden 59 UK 182 European Union 1672 Norway 18 Switzerland 46 Iceland 1 Bulgaria 3 Croatia 4 Hungary 7 Poland 133 Slovakia 14 Estonia Latvia 5 Russia Ukraine 71 Canada 78 USA 503 Argentina 43 Australia 59 New Zealand 28 Japan 90 South Africa 12
1998 38 61 10 37 490 5525 10 13 133 51 16 22 53 172 1609 18 46 1 3 2 8 135 16 2 5 64 87 515 43 60 28 83 14
1999 38 10 490 548 12 134 51 188 1593 17 44 8 138 16 5 88 87 545 59 62 11
4
Kg per capita 1997 1998 4.6 4.7 6.3 6.1 2.0 2.1 5.8 5.9 8.3 8.3 7.1 6.8 0.9 1.0 3.5 3.5 2.3 2.3 3.5 3.3 1.6 1.6 1.0 1.0 6.7 6.0 3.1 2.9 4.5 4.3 4.1 4.1 6.2 6.2 4.4 4.4 0.3 0.3 0.8 0.5 0.7 0.8 3.4 3.5 2.5 2.9 1.7 1.9 2.0 1.4 1.2 2.6 2.9 1.9 2.0 1.2 1.2 3.2 3.2 7.5 7.5 0.7 0.7 0.3 0.3
1999 4.7 1.7 8.3 6.7 3.2 2.3 3.2 4.2 3.9 6.1 0.8 3.6 3.0 2.2 1.8 2.8 2.2 1.6 3.2 0.3
Table 5: Butter Prices in Selected Countries US$/kg 1999 Argentina 1.80 Australia Canada 4.10 Croatia 4.07 EU 3.28 Norway 3.05 Poland 2.01 USA 2.14 South Africa Slovakia 2.11 World market (fob Western 1.30 Europe)
5.0
2000 1.60 1.17 4.62 3.67 3.16 2.90 2.61 2.94 2.76 2.08 1.48
PRICES OF HIGH FAT-PRODUCTS
The prices of butter in the World market has increased in 2000 to US $ 1.48/kgs. From US $ 1.30 in 1999. 6.0
REFERENCES
Gokhale, A.J., Upadhyay, K.J. & Pandya, A.J. (2001). Fat-rich dairy products from buffalo milk. Indian Dairyman 53 (3) : 17-25. IDF (2000). World Dairy Situation 2000. IDF Bulletin No. 355. Sindhu, J.S. (1996). Suitability of buffalo milk for products manufacture. Indian Dairyman 48: 41-47. Verma, M.H., Agarwal, S.B., Rana, R.K. (1999). Performance of Dairy Industry. Indian J. Dairy Sci. 52 (6): 377-382.
5
CHEMICAL CHARACTERISTICS OF COW AND BUFFALO MILK FATS Dr. B.S. Bector Principal Scientist Dairy Chemistry Division NDRI, Karnal-132001 1.0
INTRODUCTION
The bulk (>98%) of milk fat exists as tiny spherical droplets, called fat globules, in an oil-in water emulsion. Each globule (size varies from 0.1 µ to 22 µ with an average of 4 µ) consists mostly of triglycerids but a complex mixture of other lipids such as cholesterol, phospholipids, and traces of free fatty acids, hydrocarbons including carotenoids and fat soluble vitamins A, D, E and K are associated with it, especially at the surface. This surface of the fat globules is coated with an absorbed layer of material commonly known as the fat globule membrane which contains phospholipids and proteins in the form of a complex. The phospholipids-protein complex is involved in stabilizing the emulsion of the fat in milk and preserving the identity of individual globules. Milk lipids are found in three distinctly different phases of milk. These are fat globules, membrane surrounding the globule and milk serum. Table 1. Lipids of milk S.No. 1. 2.
Range 98-99% 0.2-1%
3.
Constituent Triglycerides Phospholipids (Lecithin, Cephalin, Sphingomyelin) Sterols (Cholesterol, Lanosterol)
4.
Free fatty acids (various)
Traces
5. 6. 7.
Waxes Squalene Fat soluble vitamins Vitamin A Carotenoids Vitamin E (Tocopherols) Vitamin D Vitamin K
Traces Traces Traces 7.0-8.5 µg/g fat 8.0-10.0µg/g fat 2-50µg/g fat
0.25-0.40%
Location Fat globules Globule Membrane and serum Fat Globule, globule membrane and milk serum Fat globule and milk serum Fat globules Fat globules Fat globules
Traces Traces
Table 1 shows the lipids composition in milk, range of occurrence and location in milk with respect to the three phases of milk, as mentioned above. The lipids of milk differ in their chemical nature. Fresh milk fat normally has mild delicate flavour. However, it can be the source of a multitude of flavour compounds that may result in desirable flavour or in
undesirable off-flavours. The chemical and physical properties of milk fat are important in determining its utilization in dairy and other foods. Variations in the physical properties can be modified by crystallization of the fat during processing, e.g. temperature treatments of cream before churning of butter. Another approach is to modify it chemically by interesterification or hydrogenation. 2.0
CHEMICAL CHARACTERISTICS OF COW AND BUFFALO MILK FATS
The short chain fatty acids (4:0 to 12:0) and unsaturated fatty acids contribute to softness of fat, the long chain saturated fatty acids contribute to its hardness. Buffalo milkfat is distinctly harder than cow milkfat. This is because it contains large amounts of long chain saturated fatty acids (16:0 and 18:0) as compared to cow milk fat (Table 2). For the same reason the amount of high melting triglycerides is significantly higher in buffalo (8.7%) than in cow milkfat (4.9%). Due to this difference, the triglycerides crystallize much earlier in buffalo milkfat than in cow milk fat and at a given temperature the amount of crystallized fat is much higher in case of buffalo milkfat than in cow milkfat. Table 2. Average Fatty acid composition of milk fat. Fatty acid 4:0 6:0 8:0 10:0 10:1 12:0 14:0 14:1 15:0 16:0 16:1 17:0 18:0 18:1 18:2 18:3
Cow milk-fat 3.2 2.1 1.2 2.6 0.3 2.8 11.9 2.1 1.2 29.9 1.8 0.3 10.0 28.4 1.5 0.6
Buffalo milk-fat 4.4 1.5 0.8 1.3 1.8 10.8 1.3 1.3 33.1 2.0 0.6 11.9 27.1 1.5 0.5
Cow milk fat contains 52.9% of High Molecular Weight Triglycerides (HMT), 18.9% of Medium Molecular Weight Triglycerides (MMT) and 28.2%n of Low Molecular Weight Triglycerides (LMT). The corresponding values for buffalo milk fat are 42.4, 17.1 and 40.5%. Cow milk fat contains higher proportions of HMT and lower level of LMT than buffalo milk fat. The difference in the proportions of HMT and LMT fractions are due to 4:0, 18:0 and 18:1. The lower content of LMT in cow milkfat as compared to buffalo milk fat is due to lower amount of 4:0 in cow milk fat. Similarly, higher content of HMT in cow milk fat as compared to buffalo milk fat is due to the higher proportions of 18:1. Since the buffalo milk fat contains greater levels of saturated acids, the physico-chemical constants of buffalo milk fat reveal a higher saponification number, lower iodine value and higher melting range (Table 3). Similarly, the difference in the short chain fatty acids of two mien fats is reflected 7
in higher Richert Meissl and Kirschner values and lower Polenske value of buffalo milk fat as compared to cow milk fat. Table 3. Sr.No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 3.0
Physico-chemical constants of milk fat.
Characteristics Solidifying point °C Melting point °C Butyro-refractometer reading at 40°C. Saponification value Reichert-Meissl value Kirschner value Polenske value Iodine value Colour (Yellow units/g) Tintometer
Cow milk fat 15.0-23.5 28.5-41.0 41.2
Buffalo milk fat 16.0-28.0 32.0-42.5 42.0
227.3 28.5 22.1 1.8 33.8 8.8
230.1 32.3 28.5 1.5 29.4 0.8
MILK PHOSPHOLIPIDS
The milk phospholipids are minor constituents of milk fat (1% of total lipids), but are important structural components of the milkfat globule membrane surrounding the core triglycerides. Phospholipids consists of a polyhydric alcohol, usually glycerol but not always, which is esterified with fatty acids and also with phosphoric acid. The phosphoric acid in turn is combined with basic nitrogen containing compound.. The phospholipids are present in five major subclasses: phosphatidyl choline (PC), phosphatidyl ethanolamine (PE), phosphatidyl serine (PS), sphingomyclin (SM) and phosphatidyl inositol (PI). In addition to these, traces of cerebrosides and plasmalogens are also present. One of the principal functions of phospholipids in milk is to maintain the milkfat in a finely emulsified state i.e. they are active emulsifying agents. They concentrate around the normal fat globules in the fat globule membrane and tend to stabilize the system. They are rich in unsaturated fatty acids and essentially oxidized and give rise to “oxidized’ flavour to milk. They also impart richness flavour to fluid milk products. 3.1
Phospholipids Content in Milk
Most of the recent work indicate that the phospholipid content of milk varies from 20 to 40 mg per 100 g. The average phospholipid content of cow and buffalo milks has been reported as 39.2 and 38.7 mg per 100 g, respectively. Thus, there is no appreciate difference in the phospholipid content of cow and buffalo milks. Similarly, there is no appreciable difference in the phospholipid content of different breeds of cows and buffaloes. Season appears to exert some influence on the phospholipid content of milk. During winter the phospholipid of cows and buffaloes milk is higher compared to summer. The stage of lactation has significant effect on the phospholipid content of milk. Colostrum is rich in phospholipids and it comes to normal level in about 4 days. Then phospholipids remain more or less steady till 5th or 6th month when it start rising readily till the end of lactation, almost approaching those obtained during the colostrum period. At levels of phospholipids per unit weight of fat are 1.54-4 folds greater in fore milk than in residual milk. 8
3.2
Phospholipids Content in Cream
During the mechanical separation of milk it is generally observed that the phospholipid content of cream increased with increasing fat content (55-58% fat) and then further decrease with the further increase in the fat percent. Skim milk contains about 40% of the original phospholipids in producing a cream of 15-20% fat, and further increase in fat of 20-55% removed very little of phospholipids . 3.3
Phospholipids Content in Bbutter
The distribution of phospholipids in butter varies depending upon the raw material and also the method of manufacture. Phospholipid content of creamery butter increase with the increase in fat content of the cream. Approximately 30-45% of the total phospholipid content of the cream passed into butter in the churning process. Butter from sweet cream has less phospholid content than that obtained from acid-cream. Desi-butter from buffalo milk contain less phospholipid than Desi-butter from cow milk. Both acidity of the cream and washing of butter has no effect on phospholipid content of butter. 3.4
Factors Affecting Phospholipids Content in Cream and Butter
The distribution of phospholipids during separation of milk and churning of cream is influenced by the stage of lactation and species of the milk used. The proportion of transfer of phospholipids to cream and butter is slightly greater in milks of buffaloes than that of cows. Phospholipids passed from early, middle and late lactation milks to cream and subsequently preparation of butter decreased as the lactation progressed. Since much of the phospholipids in milk is in fat globule layer it is likely that the variations in the distribution of total phospholipids between cream and skim milk in the separation of milk, and between butter and butter-milk in the churning of cream are due to differences in the sizes of the fat globules of milk. The greater transfer of phospholipids in cream and butter from milks containing higher average fat globules size may be due to the affinity of the bigger fat globules to go along with the cream and butter, and of the smaller ones to skim milk and buttermilk during separation and churning, respectively. The composition of phospholipids in milk, cream, skim milk, butter and butter-milk is almost the same as that of milks from which they are prepared. Table 4. Phospholipid content of cow and buffalo milks and their products.
Cow Buffalo
Milk 34.4-41.9 Av 39.2 32.4-41.4 Av 38.7
Cream 137.5-246.6 Av 191.1 180.0-249.4 Av 200.4
Butter 180.0-238.0 Av 206.1 177.6-278.6 Av 232.6
Butter milk 26.9-32.1 Av 30.0 20.4-35.0 Av 30.0
Ref: Ramamurthy and Narayanan (1966).
3.5
Phospholipids Content in Ghee
Although milk contains about 1% phospholipids of the total fat, much of it lost in skim milk, butter milk and ghee residue during manufacture of ghee. The final amount of phospholipids that remains with ghee has been shown to depend upon the phospholipid 9
content of butter and method of manufacture. During the manufacture of ghee from cream and butter, only small quantities of butter phospholipids are transferred to fat phase and rest remains in the ghee-residue. Ghee prepared from butter by heating just to 120°C contains only traces of phospholipids (about 10 mg per 100 g). But on increasing the period of heating there is a gradual increase in the phospholipid content of ghee. A maximum transfer of phospholipids (132 mg/per 100 g) amounting to 57.7% of the total phospholipids take place after 40 min. On further heating, there was progressive decrease in the phospholipid content of ghee accompanied by a progressive browning in ghee. The initial increase observed in the phospholipid content of ghee with the increased holding time may be due to efficient removal of moisture and greater liberation of phospholipids from the phospholipid protein complex of ghee residue. However, there is a decrease in the percentage distribution of PC, PE, PS, Spl. and PL inositol and increase in the lysophospholipid as the period of heating increased. 3.6
Fatty Acid Composition of Milk Phospholipid:
In contrast milkfat, the phospholipids from both colostrum and milk do not have lower chain fatty acids of less than 12 carbon atoms. There is no marked differences in the fatty acid composition of phospholipids obtained from cow and buffalo colostrum and that of milk collected at different stages of lactation. The major fatty acids of colostrums phospholipids are palmitic, stearic, oleic and linoleic acids and their amount being 16.7-17.5, 15.1-15.9, 32.9-34.5 and 12.7-14.1% respectively. The acids above 18:0 constitute about 13% of the total acids. About 53% of the total fatty acids of colostral phospholipids are unsaturated. Palmitic and stearic acids are the major saturated fatty acids, whereas oleic and linoleic acids are in maximum quantities among the unsaturated acids. There is slight increase in the total unsaturated fatty acids, as the lactation progressed and they constitute about 41, 42 and 54%, respectively of easily, middle and late lactation the total fatty acids. The late lactation milk phospholipids are somewhat similar in fatty acids composition as that of colostral phospholipids. Cephalin fraction is the most unsaturated of the three fractions.(Oleic acid 48.0%, stearic 19%). Lecithin fraction contains oleic acid 35.9%, palmitic acid 30.2% and stearic acid 11.6%. Sphingomyelin fraction contains mainly saturated fatty acids. Higher chain fatty acids like behenic acid (22:0), tricosanoic acid (23:0) and ligmoceric acid (24:0) totaling approximately 30% is notable. 4.0
ROLE OF MILK PHOSPHOLIPIDS IN THE AUTOXIDATION OF MILK AND MILK PRODUCTS
Milk phospholipids behave in a different manner in aqueous and non-aqueous systems. When phospholipids present in aqueous phase of milk triglycerides are relatively more stable and phospholipids are preferentially oxidized. In dried milk products, such as ghee, phospholipids serve as antioxidants. The antioxidant activities of phospholipids depend upon their concentration in ghee. Higher the concentration of phospholipid greater being its oxidative stability. Phospholipids are shown to have synergistic action with -locopherols which is a natural antioxidant in ghee. They have also shown to possess chelating action on copper which may otherwise catalyse oxidation of ghee. Among the various phospholipids only cephalin fraction is shown to have antioxidant properties in ghee. 5.0
REFERENCES
Arumughan, C. and Narayanan, K.M. (1979). Grain formation in ghee (butterfat) as related to structure of triglycerides. J. Food Sci. Technol. 16, 242-247. 10
Arumughan, C. and Narayanan, K.M. (1982). Triacylglycerol composition of buffalo milkfat. J. Dairy Res. 49, 81-85. Arumughan, C. and Narayanan, K.M. (1982). Influence of stage of lactation on the physical and chemical characterisitcs of buffalo milkfat. Indian J. Anim. Sci.; 52(9), 731-735. Arumughan, C. and Narayanan, K.M.(1982). Triglycerol composition of cow milkfat. J. Food Sci. Technol. 19, 71-74. Bector, B.S. and Narayanan, K.M. (1972). The role of milk phospholipids in the autoxidation of butterfat. Indian J. Dairy Sci. 25, 222-227. Jenness, R. and Patton, S. (1959). Principles of Dairy Chemistry. John Miley & Sons, New York. Kuchroo, T.K. and Narayanan, K.M. (1973). Distribution of phospholipids during curd formation. Indian J. Anim. Sci. 43, 171-173. Kuchroo, T.K. and Narayanan, K.M. (1976). Effect of stage of lactation on the distribution and composition of phospholipids and composition of phospholipids in milk products. J. Food Sci. Technol. 13 (5), 246-248. Kuchroo, T.K. and Narayanan, K.M. (1977). Effect of sequence of milking on the distribution of fat globule and phospholipid composition of milk. Indian J. Dairy Sci. 30 (3), 225-228. Kuchroo, T.K. and Narayanan, K.M. (1977). Distribution and composition of phospholipids in ghee. Indian J. Anim. Sci. 47, 16-18. Kuchroo, T.K. and Narayanan, K.M. (1977). Effect of stage of lactation on distribution of fat globule and phospholipid content of milk. Indian J. Dairy Sci. 30, 99-104. Kuchroo, T.K. and Narayanan, K.M. (1978). Effect of stage of lactation on fatty acid composition of milk phospholipids. Indian J. Dairy Sci., 31 (3), 272-275. Kuchroo, T.K. and Narayanan, K.M. (1981). Composition of fat globule membrane phospholipids. Indian J. Dairy Sci. 34, 16-18. Pruthi, T.D., Narayanan, K.M. and Bhalerao, V.R. (1970). Role of milk phospholipids in the autoxidation of butterfat. Part I. Indian J. Dairy Sci. 23, 248-252. Pruthi, T.D., Narayanan, K.M. and Bhalerao, V.R. (1971). The role of milk phospholipids in the autoxidation of butter-fat Part-2. Effect of individual phospholipids. Indian J. Dairy Sci. 24, 185-189. Pruthi, T.D., Narayanan, K.M. and Bhalerao, V.R. (1972). Fatty acid composition of milk phospholipids of Indian Zebu Cattle. Milchwisscnschaft 27 (5), 294-296. Pruthi, T.D., Narayanan, K.M. and Bhalerao, V.R. (1972). Fatty acid composition of buffalo milk phospholipids. Indian J. Dairy Sci. 25, 16-24. Pruthi, T.D., Kapoor, C.M. and Pal, R,N. (1972). Phospholipid content of ghee prepared by direct clarification and pre-stratification methods. Indian J. Dairy Sci. 25, 233. Pruthi, T.D. (1980). Phospholipid content of ghee prepared at higher temperatures. Indian J. Dairy Sci. 33 (2), 265-267. Rama Murthy, M.K. and Narayanan, K.M. (1966). A method for the estimation of phospholipids in milk and milk products. Indian J. Dairy Sci. 19, 45-47. Rama Murthy, M.K., Narayanan, K.M. and Bhalerao, V.R. (1968). Effect of phospholipids on the keeping quality of ghee. Indian J. Dairy Sci. 21, 63-68.
11
PHYSICAL CHARACTERISTICS OF MILK FAT
Dr. A. A. Patel Principal Scientist Dairy Technology Division NDRI, Karnal-132001 1.0
INTRODUCTION
Physical properties of milk fat, in its globular form or in bulk, have profound influence on the sensory attributes, texture, in particular, of fat-containing dairy foods. For instance, the extent of crystallization or the crystal status of globular fat could greatly affect the optical and rheological properties of milk and cream. The viscosity of these products is also a function of the physical state of fat globules. Even more important is perhaps the stability of the globules themselves with regard to fat solidification. In its bulk form, milk fat has its physical characteristics determining the textural properties of fat-rich dairy products such as ghee, cheese, butter and spreads. The crystallization behaviour also influences processes such as fractionation, a method of fat modification. Extensive literature is available on crystallization of milk fat, although not much work has been carried out in recent times. Certain other physical properties e.g., refractive index, primarily determined by the chemical nature of the triglycerides, constitute parameters (called ‘constants’) useful in identification of the product / type of fat. A brief account of various physical properties of milk fat and their technological relevance is presented hereunder. 2.0
CRYSTALLIZATION OF MILK FAT
2.1
Stages in Crystal Formation
The major constituent of milk fat is triglycerides with different chemical compositions and different physical properties. When the triglyceride molecules are in a molten state, they have high kinetic energy, and therefore, the individual molecules have a rather free mobility since the inter-molecular forces tending to hold the molecules together are not strong enough to counteract the thermal motions. However, when molten fat is cooled the thermal motions of the molecules decrease, and the inter-molecular forces viz., hydrogen bonds and van der Waals’ forces, draw the triglyceride molecules closer together simultaneously with an incipient parallel-ordering of the fatty acid chains, as the first step towards crystallization. The whole process of crystallization consists of nucleation and growth phases. Crystallization starts with the formation of crystal nuclei (centres of crystallization) in the molten fat as a few molecules gather in molecular aggregates where the potential energy is reduced to a minimum. These aggregates, in which molecules are continuously replaced, grow into real crystals at a stage when the probability of a molecule being adsorbed is greater than the probability of a molecule being liberated. The crystallization process is started when the melt is inoculated with pre-formed crystals (heterogeneous nucleation) or by a strong super-cooling of the melt (homogeneous nucleation). The nucleation rate is increased by falling temperature until a maximum is reached. The reason why further cooling result in a reduced nucleation rate is the increased
viscosity of the melt causing a reduction in the rate of diffusion, which is a critical factor also with regard to the second stage crystal growth. The growth of crystal nuclei takes place by successive single layers of molecules being deposited on an already ordered crystal surface. The rate of growth depends on the probability of the incorporation of these molecules into the crystal lattice as well as on the material density and on the temperature. Milk fat crystallization has been found to correspond to a first-order reaction with an activation energy of 11.0 kcal mol-1. The constants of the crystallization process have been found to be related to the iodine value. One of the complications associated with crystallization of fat is that during crystallization there is no distinct difference between solute and solvent. Lowering the temperature will cause some of the solvent to change to the role of solute. Thus, the solubility of a given solute fraction is decreased while the amount of available solvent is also diminished. 2.2
Polymorphism
Like other fats containing long-chain aliphatic fatty acids, milk fat exhibits polymorphism, i.e. it tends to exist in more than one crystal form due to different patterns of molecular packing in the crystal. The three well recognized polymorphic forms (viz., , , and ) have different crystal lattices and different melting points. While the form (with triclinic packing) is stable, the and forms (hexagonal and ortho-rhombic forms) are metastable, which gradually transform into the stable form having the highest melting point. On rapid cooling, a metastable -form is produced reversibly from the liquid phase. The form may then be transformed irreversibly into the more stable -form and further into the most stable -form. However, not all triglycerides are known to form all three crystal forms. Many complex triglyceride mixtures have been reported to exhibit four crystal forms, viz. , , 2 and 1, in the order of increasing stability. Milk fat is also believed to exhibit a similar pattern. Among the major implications of polymorphism in milk fat is the existence of multiple melting points, such as three melting points in the high-melting fractions and two in the low-melting fractions reported by some workers. X-ray diffraction techniques combined with electron microscopic examination of butter showed that the -crystal form dominates in the outer shell of the fat globules while the predominant part of the modification is found in the lower-melting crystal layers in the interior of the globules and in the free inter-globular fat phase where the content of unsaturated fatty acids is particularly high. 2.3
Solid Solutions
Part of the complexities in multi-component systems such as fats is formation of mixed crystals or solid solutions. A solid solution is exactly analogous to a liquid solution and consists simply of a lattice in which the component atoms or molecules have been partially replaced with dissimilar atoms or molecules. As in a liquid, the foreign molecules are distributed through the structure at random. The matter is even more complicated because polymorphism must also be considered when the formation of mixed crystals is discussed. The meta-stable crystal modifications (, ) form mixed crystals more easily than the more stable -modification. It has also been shown that in heterogeneous triglyceride systems the incorporation of different molecules in the same crystal lattice implies that the life of metastable crystal forms is prolonged. 13
Further, the melting point of milk fat is highly dependent on the rate and temperature of crystallization. If cooling occurs very rapidly, a considerable number of the low-melting triglycerides are built into a lattice formed by high-melting glycerides. This involves the formation of relatively uniform mixed crystals with nearly the same melting point. Such crystals adsorb a considerable amount of the low-melting triglycerides, and therefore milk fat that has been cooled rapidly contains less liquid fat at a given temperature than milk fat that has been cooled slowly or stepwise with suitable holding times. In the last case, the solid phase consists of a heterogeneous blend of mixed crystals, characterized by different melting points depending on the temperature treatment employed. On slow or stepwise cooling a considerable part of the crystallization process probably takes place by glyceride molecules being deposited on pre-formed crystal surfaces built up of other triglycerides. The so-called ‘overlaid crystals’ formed in this way have a sort of laminated structure in which highmelting glycerides often form the nuclei of the crystals with the low-melting components located in the outer layers. Since the formation of mixed crystals influences the content of liquid fat in the fat mixture, it has a great influence on the rheological properties of butter. At least part of the effect of temperature treatment of butterfat and cream is due to its influence on mixed crystal formation. Moreover, formation of mixed crystals influences the rheological properties of products made from mixtures of different fat fractions. Addition of liquid fat to solidified fat results in a greater reduction in firmness of the product than addition to the melt. 2.4
Crystallization of Bulk Fat vs. Globular Fat
Bulk fat contains sufficient catalytic impurities to initiate heterogeneous nucleation with little super-cooling. A liquid crystal phase is formed in the melt during cooling after which a mono-crystalline nucleus emerges from the high-melting glycerides. The nucleus has the shape of a spherolite consisting of crystals radiating outward from a common center. During the growth of the spherolite the rather elongated needle-shaped crystals thicken and assume a feather-like structure characteristic of a typical spherolite. The external form and the size of the crystals growth from the nucleus depend not only on the internal structure but also on the external treatment. The size of milk fat crystals may vary considerably depending on the rate of crystallization; if milk fat is cooled rapidly, numerous very small crystals with a maximum diameter of 1-2 m are formed while slow cooling results in the formation of a few large crystals with diameters up to 40 m. Recrystallization of the fat affects the size of the crystals but a much greater effect could be found when the fat is cooled stepwise, with formation of large spherolitic crystal aggregates. Further not only single crystals but also spherolites can agglomerate; such spherolite agglomerates can vary considerably in size, i.e. from 100 to 1000 m, and their shape frequently diverges from spherical. Spherolite agglomerates can be disrupted very easily by mechanical treatment. Stirring during cooling process causes crystallization of fat into smaller spherolites, which only agglomerate loosely. Very low and very high agitation speeds result in the formation of very fine crystals and a high agitation speed seems to prevent the flocculation of crystals. In absence of stirring, the solidified fat tends to flocculate into a network held together by van der Waals’ attraction forces. When crystallization is so far advanced that almost all of the remaining liquid phase is bound in to the network, the mass appears as a complete solid, though it does consist of certain liquid fat. Work-softening of the thixotropic butter and spreads is believed to disrupt the crystal networks building in them during quiescent stage. Crystallization of globular fat differs considerably from the crystallization of bulk fat. The main difference is that crystals in the emulsified state cannot 14
grow larger than globules; thus a solid network of crystals can form only within the globules unless the globules are clumped. A deeper super-cooling is needed to initiate crystallization when the fat is in the emulsified state. Also, a slower crystallization rate is obtained in a more finely dispersed fat, which has been attributed to differences in nucleation. At least one nucleus must be formed in every globule to achieve full crystallization and the time needed to obtain the first nucleus is proportional to the volume of the globule. This implies that a lower temperature is needed for a finer dispersion. It is recognized that there is not a sharp temperature at which crystallization suddenly starts in all globules. The formation of nuclei is a stochastic process following the principle of random distribution and the probability of the presence of a catalytic impurity that will start nucleation depends on the size of globules, which varies throughout the emulsion. The surface layer of a fat globule probably acts as a catalytic impurity. Tiny tangentially oriented fat crystal needles in the outer layer of the globules have been observed. It is believed that crystallization might start at the globule boundary. In study employing polarizing microscopy, four types globules were found at temperatures where part of the fat is solidified. In one type nothing could be seen except possibly a reflection at the globule boundary; in a second type there were tiny needle-shaped crystals throughout the globule; a third type had a birefringent outer layer, which was thought to be formed by the rearrangement of the needle crystals into a tangential orientation along the globule boundary; and a fourth type showed small crystals throughout the globule as well as in the bright outer layer. Thus, in conclusion, very small, more-or-less needle shaped crystals are initially formed and flocculate into a random network giving the globule a certain firmness. On holding, growth, transformation and rearrangement of the crystals into a tangential orientation along the globule boundary take place. 2.5
Solid Fat Index
The crystallization behaviour implies that milk fat has no sharp, well-defined melting point but melts over a wide temperature range. It is liquid above 40C and completely solidified below -40C. At intermediate temperatures, it is a mixture of solid and liquid fats. The content of solid fat in the mixture is very important because the rheological properties of many dairy products depend more on this than on the size and form of the crystals. Information about the ratio of solid to liquid fat at a given temperature is, therefore, essential in many aspects of cream and butter manufacture. Furthermore, the ratio determined directly in butterfat, after a standardized pre-treatment, can be used to characterize the physical properties of the butterfat and is highly correlated to the iodine value of the fat. The ratio measured corresponds to the solid fat index (SFI) measured by the official American Oil Chemists’ Society (AOCS) method based on dilatometry. The determination of the content of solid fat by dilatometry is based on the specific volume change that occurs when fat goes from the solid to the liquid state upon heating under controlled conditions. This change in specific volume can be observed when fat is in a socalled ‘dilatometer’. Based on the expansion of the fat sample during heating, the specific volume can be recorded as a function of temperature and from the graph showing this relationship, the ratio of the solid and liquid fractions can be calculated. Most dilatation measurements have been made on pure fats, e.g. butterfat, but the method can also be used on fat emulsions, e.g. cream. Naturally, in such cases the thermal expansion of the water phase must also be considered in the calculations. This method, however, cannot be used directly on butter. Though inexpensive and easy to perform, the dilatometric method is rather timeconsuming and the calculation of solid or liquid fat is based on the assumption that the 15
dilatation of solid and liquid fats, respectively, is constant over the complete melting range. However, this is not the case, because different triglycerides and different crystal modifications have different melting dilatations. The content of solid or liquid fat can also be determined by other methods viz. Differential scanning calorimetry (DSC) and Nuclear magnetic resonance (NMR) spectroscopy. The DSC method, offering sufficient precision, is based on the thermal transitions that occur in milk fat during heating or cooling. In a thermogram of a fat sample the energy transfer to or from the sample necessary to raise or lower the temperature, respectively, is recorded as a function of the temperature of the sample. Such a graph gives an illustration of the phase transitions, which occur within the complete melting range. The method can be used for the examination of pure milk fat, cream or butter. The water content in cream butter complicates interpretation of the melting curve because the aqueous phase transition mask a significant amount of lipid melting below 0C. The analysis is timeconsuming and the calculation of solid or liquid fat is based on the assumption that the heat of fusion is constant over the complete melting range, which is not the case. On the other hand, the analysis gives a good picture of the phase transitions that occur over the whole melting range. SFI determination by NMR spectroscopy has been widely used. Protons in the sample placed in a strong magnetic field can, under certain conditions, absorb energy from electromagnetic waves. This absorption, called nuclear magnetic resonance, depends on the physical state of the protons. The commonly used pulsed NMR analysers emit a short intense pulse of electromagnetic radiation at the resonance frequency into the fat sample and the free induction decay of the signal following the pulse is observed. The relaxation time is strongly related to the mobility of the protons and hence the physical state of the sample. Based on registration of the signal a suitable time after the pulse, the content of the solid phase can be calculated. Besides pure fat samples fat emulsions can also be analysed for solid fat by NMR methods but the contribution of water protons to the signal represents a complication. The performance of the NMR measurements is easy and very rapid, but one of the disadvantages of the methods is that the equipment is rather expensive. The results obtained seem to be quite similar to those obtained by dilatometry and DSC measurements. In a comparative study employing pulsed NMR spectroscopy, it was found that over a temperature range of 030C, Indian buffalo milk fat exhibited a higher solid fat content than did European (German) cow milk fat, whereas Indian cow milk fat (summer) had the higher solid fat content of all milk fats at 0-15C but showed intermediate values between 20 and 30C. Holding at 0C for up to 3 h resulted in consistently smaller solid fat content in European milk fat vis-à-vis Indian cow and buffalo milk fats. 3.0
OTHER PROPERTIES
3.1
Melting Range
Melting, (or, the reverse of crystallization) of milk fat occurs over a wide temperature range because of the wide range of constituent triglycerides with their varying melting points. The melting curve (% solid fat vs. temperature) is not smooth, but there are several optimum melting temperatures giving rise to the so-called ‘group melting’. However, melting point in terms of ‘capillary slip point’, ‘drop point’ or ‘clarification point’ has often been measured on milk fat for comparison purposes. While the melting range for milk fat may fall within 2816
43C depending on the method and other factors, a slightly higher values of softening and melting points (34.3-36.3C and 33.4-35.8C, respectively) have been reported for buffalo milk fat as compared cow milk fat (33.5-35.9 and 33.7-35.2C, respectively). The broader melting range is 32.0-43.5C and 28.5-41.0C for buffalo and cow milk fat, respectively. A DSC stydy showed that buffalo milk fat melted over a higher temperature range (11-38C) than did cow milk fat (5-35C), the DSC clarification point being 39.1-39.2C for the former and 36.3-37.0C for the latter. The respective drop points were in the range of 34.9-35.1C and 31.2-32.9C. 3.2
Refractive Index
Valuable as a physical constant, the refractive index (RI) of milk fat is a characteristic function of its fatty acid composition. While the effect of animal species (cow vs. buffalo) may not be very definite, milk fat has a typical RI range of 1.453-1.457 which is lower in comparison with vegetable oils. It, therefore, forms a basis for detection of adulteration of milk fat with other fats as judged by the butyro-refactometer reading (40-45 at 45C). 4.0
CONCLUSION
The crystallization behaviour of milk fat in systems containing globular fat and / or bulk fat is the single most important physical property in relation to consistency characteristics. The size of the fat globule restricts the crystal growth in it unlike in bulk fat. Essentially a first-order reaction, the process of crystal formation and its impact on the product properties are greatly complicated by the phenomena of crystal polymorphism, compound or mixed crystals and recrystallization conditions that determine the crystalline nature of milk fat which, in turn, govern the physical properties of the product. It is, therefore, conceivable that post-production temperature history is as important as the production process itself. The solid fat content in conjunction with the type of crystal structure determines the physical behaviour of the product. Crystal networks in products like butter and spreads impart a thixotropic character, which is related to phenomena such as work-softening and brittleness. Methods of determining solid fat index include dilatometry, differential scanning calorimetry and pulsed NMR spectroscopy, the last being simple and precise. Among other physical properties of milk, refractive index is useful as a ‘constant’ for the purpose of examining purity of the fat. 5.0
REFERENCES
AOAC (1995) Official Methods of Analysis of AOAC International (P. Cunniff, ed.), 16 th Ed., Vol. II, AOAC International, USA. Mortensen, B.K. (1981) Methods for determining the ratio of solid to liquid fat in dairy products particularly in butter. IDF Bull., 84: 28-34. Patel, A.A. and Frede, E. (1991) Studies on thermal properties of cow and buffalo milk fats. LebensmittelWissenschaft u. Technologie, 24: 323-327. Walstra, P., van Vliet, T. and Kloek, W. (1995) Crystallization and rheological properties of milk fat. In: Advanced Dairy Chemistry-Lipids, Vol. 2, Second Ed., (P.F. Fox, ed.), Chapman & Hall, London, pp. 179211.
Walstra, P. (1987) Fat crystallization. In: Food Structure and Behaviour. (J. M. V. Blanshard and P. Lillford, eds.), Academic Press, London, pp. 67-86.
17
DEVELOPMENTS IN CREAM SEPARATOR
Prof. I.K. Sawhney Principal Scientist Dairy Engineering Division NDRI, Karnal-132001
1.0
INTRODUCTION
Cream-separator is the equipment of great importance in dairy industry. The process of separation of cream from the skim milk is based upon the density difference between the milk fat in the globules and aqueous phase in which they are dispersed. Milk fat at 20°C temperature has a specific gravity of 0.93 and the skim milk has a specific gravity of 1.034. Due to this density difference, the fat globule with lower density tends to rise in the surrounding medium, if placed undisturbed in earth’s gravitational field. The rate of rise of the fat globule can be estimated from the principles of Stoke’s Law. The velocity with which the fat globules in the milk rise also depends upon temperature of milk and the agglomeration of fat globules. The rate of rise of fat globule is very low, usually of the order of half a millimeter per hour. Thus the separation process is very slow. In order to increase the rate of separation, centrifugal forces may be used to accentuate the differential forces on components. 2.0
SEPARATION BY CENTRIFUGAL FORCE
The velocity () of fat globule in the gravitational field is described by Stoke’s Law in the following equation =
g ( ρ s -- ρ f ) 2
d
-------------------(i) 18 μ where d = diameter of globule, g = acceleration due to gravity, ρ s = density of serum, ρ f = density of fat globule and μ is the co-efficient of viscosity. For separation process by centrifugal force, the Stoke’s formula still applies but the value of ‘g’, i.e. 9.81 m/s2 is replaced by much greater value representing the centrifugal acceleration (a). In a circular motion the acceleration from centrifugal force is a=R ω2 where ω is angular velocity in rad per sec and R is the radial distance from the center of rotation. Substituting the value of centrifugal acceleration in place of acceleration due to gravity in equation (i) the expression for velocity of globule is:
=
d2 (ρ s — ρ f ) ω 2 R 18 μ
--------------------(ii)
In a centrifugal field rate of separation will be increased by increasing the radius of the paths of flow and the rotational speed. The velocity of separation, as high as 4 m/s, could be achieved in centrifugal field. The above two parameter, however, could not be increased at will because of the limiting strength of the centrifugal bowl. 3.0
TUBULAR CENTRIFUGE
Tubular bowl centrifuge has a small diameter cylindrical bowl rotating at a very high speed. The diameter being very small, down to 10 cm, the tubular centrifuge is suitable only for a slim line construction. Due to higher rotating speed, it allows a high rate of sedimentation of heavy particles and rise of lighter particles, that is, high rate of cream separation. However, due to small separating area, it is unsuitable for a high throughput. This needs a large separating area and separating distance as small as possible for the particles moving in the centrifugal field. An ideal solution which satisfied both the requirements was the introduction of conically shaped discs in to the bowl of the centrifuge. 4.0
DISC BOWL CENTRIFUGE
The disc bowl separator has closely spaced cone-shaped discs in the bowl, which rotate with the bowl. The number of discs is up to 120, placed one above the other. Their angle of inclination to the horizontal is 45°C to 60°C and the outer diameter is 200 to 300 mm. The discs are made of stainless steel with a wall thickness of approximately 0.4 mm. The spacing between the discs is 0.4 to 2 mm and is ensured by welding plate or bar shaped spacer on the discs. The main component of disc bowl centrifuge are bowl base, disc holder, disc stack, the separating disc, bowl lid, feed inlet and outlets for the separated liquid streams. Special features of the disc are holes, which lie one above the other and thus forms a channel for the ascending liquids. The liquid feed entering through these channels is dissected to the zone where maximum separation occurs. From these the light phase travels in wards toward the axis of rotation and the heavy phase towards the bowl wall. The discharge of the light and heavy phases occurs via over flow lips. Disc bowl centrifuges used for cream separation today, rotate on average at 5500 to 6000 rpm at mass flow rates of 20,000 kg/h. About 2.5 to 5 kg/cm2 pressure can be obtained, depending upon the rotational speed and diameter of the disc. Thus the liquid can be easily forced from centrifuge into heat exchangers or storage tanks connected in services. 5.0
DEVELOPMENTS IN SEPARATOR DESIGNS
In the process of enhancing the efficiency of cream separation, number of separator models have been developed. Designs also provide the ejection of sludge through sediment collector during the separation process. In the open type designs, the feed is fed into the rotating bowl through a fixed pipe. The light and heavy components are discharged from the bowl via regulating ring dams. They are discharged tangentially from the bowl into separate but open collectors in the hood of the machine. They are taken off through open or closed discharge lines. The fixed feed 19
pipe and fixed collector hoods must clear the rotating bowl, so that bowl is free to swing outwards without touching them while in rotation. The same-open separator provides a special outlet device for cream and milks, which is known as paring disc. In these, the kinetic energy of the rapidly rotating milk and cream is converted into pressure so that the paring discs pump the separated skim milk and cream out of the machine. Both the discs are submerged in the separated liquid phases and discharge them under pressure. Because of this design, the semi open separators are usually called paring-disc separators In the hermetic separator, the milk is supplied to the bowl from below through a channel in the bowl spindle. A centrifugal pump pumps the milk. The bowl of a hermetic separator is completely filled with milk during operation, with no air in the center. The hermetic separator therefore is regarded as part of a closed pipe system. The pressure generated by the centrifugal pump is sufficient to overcome the flow resistance through the separator and provide a moderate discharge pressure for cream and skim milk. 6.0
FAT CONTROL AND STANDARDIZATION
The whole milk supplied to the separator is discharged as two flows of cream and skim milk. The proportion discharged as cream determines the fat content of the cream. The volume of the cream discharged from the separator is controlled by means of a throttling valve in the cream outlet. If the valve is completely closed all the milk will be discharged from through the skim-milk outlet. Progressively larger amounts of cream with progressively diminishing fat content will be discharged from the cream outlet if the valve is gradually opened. The size of the valve aperture is adjusted with a screw. Any change in the cream discharge will be matched by an equal and opposite alteration in the skim milk discharge. This means that the pressure in the down stream lines will be changed. A control unit is therefore fitted in the skim milk at the outlet constant, regardless of the changes in the rate of cream flow. The cream screw is, however, affected by variations in fat content of the incoming whole milk and by variation in flow line. The fat standardization process control for cream could also be integrated to the cream separator for specified constant fat in the milk. A flow transmitter continuously monitors the flow of cream from the separator. A density transmitter continuously measures the fat constant of cream in terms of density of cream. Both these signals are transmitted to microprocessor. The microprocessor resets the flow-regulating valve to restore the exact fat content in cream. The standardization of milk could also be achieved by providing a ratio controller, which mixes cream of fat content with skim milk in the necessary proportions to give standardized milk of specified fat content. 7.0
SOLID-EJECTION
The solids that collect in the sediment space of the separator consist of dirt particles, udder cells, white and red blood corpuscles, bacteria etc. Sour milk contains more sediment and the sediment space will be filled quickly if coagulated milk is separated. For solid ejection a number of discharge slots are placed round the periphery of the bowl body and level with the angular sediment receiver built in to frame hood. A sliding bowl bottom is located under the bowl. The space between the bowl bottom and the floor of bowl is filled with water and the bowl is closed by the hydraulic pressure. When the water is drained from 20
the space, the sliding bowl descends, thus opening the narrow gap through which the sediment slots in to the sediment receiver. The space under the sliding bottom is again filled with water and bowl bottom is once more forced upwards and against the seal ring. The whole process of solid ejection occurs during the separation and bowl is opened only for a very short time so that there is no less of any product. A specified volume of water at a specified pressure is applied to the machine in order to operate the discharge system properly. In modern plants, water is supplied through the pneumatically operated constant pressure valve, which are operated by compressed air. 8.0
CREAM SEPARATING ATTACHMENT FOR FOOD PROCESSORS AND MIXIES
Cream separators developed for industrial scale applications require large-scale production and efficient cold storage network for post handling operations. In Indian conditions the availability of fresh cream and low fat milk on market racks is quite difficult. If it is made possible to have skim milk and fresh cream as and when required in domestic operations the instant users will be immensely helped. Presently, these are around 10 million mixies and food processors in use in the country. These units have numerous small attachments needed in the kitchen for domestic uses. Addition of cream separation attachment to these units would further add to the convenience of the users. An attempt has been made at DE Division of NDRI Karnal to develop such an attachment, which could be adopted to different mixies and food processors without major alterations. Most of the domestic food processors and mixies available in our country are directly coupled to single phase universal electric motor. These units are usually provided with variable speed control and have a speed variation from 1400 to 18000 rpm. The full load power requirement varies from 200 to 400 watts. Since there is no rigid foundation and the mechanical strength of the driving unit being poor, a low speed centrifuge was designed. The unit designed consisted of raw milk, cream and skim milk pans sized to match the requirement. The lowest pan has built-in power transmission assembly. It fixes with the mixie and gives a fairly rigid base to the bowl. The bearings are designed to prevent vibrations and over heating. The number of discs was reduced to 8 or 9 and the cream outlet diameter modified. The optimum operational speed was fixed at 3250 rpm. The unit can be adapted to different mixies by altering the plastic transmission assembly at the lowest pan in accordance with the selected mixie. Cream of 40% richness was obtained and fat content in skim milk varied between 0.5 to 1 per cent. It requires about ten minutes to separate 4 litres of milk. Milk heated to 55°C gave better cream separation results. 9.0
REFERENCES
Agrawala, S.P., Sawhney, I.K., and Biktam Kumar (1993). Development of cream separating attachment for food processors and mixies. Indian Dairyman 45, 3, 113-114. Ahmed, T. (1997) Dairy Plant engineering and management, Kitab Mahal, Allahabad, 237-272. Kessler, H.G. (1981) Food Engineering and Dairy Technology, Verlag A. Kessler, Freising, Germany, 59-81. McCabe, W.L. and Smith, J.C. (1985) Unit operations of chemical Engineering. Third Edition. McCraw-Hill, Kogakusha Ltd. Robinson, R.K. (1986) Advances in Milk Processing-Modern Dairy Technology, Elsevier Applied Sci. Pub. London. Towler, C. (1986). Developments in cream Separation and Processing. Elsevier Applied Science Publisher, London. 21
CREAM AND CONSUMER CREAM PRODUCTS Dr. C. N. Pagote Senior Scientist Dairy Technology Division N.D.R.I., Karnal-132001 1.0
INTRODUCTION
Cream is one of the most important portion of milk which has been known from time immemorial as the fatty layer that arises to the top of the milk when it stands undisturbed for some time. It is the prime component of milk, which gives adequate profit to the person who involved in dairy-business or dairy-industry. Cream is sold in many varieties as its products. This topic has covered definition, classification, legal standards and composition of cream, and technology of selected cream products, such as: coffee cream, sour cream, whipping cream, clotted cream, etc. 2.0
DEFINITION AND CLASSIFICATION
2.1
Cream
2.1.1
Definition
Cream may be defined as "that portion of milk which is rich in milk fat", or "that portion of milk into which a large portion of milk fat has been gathered", or "when milk fat is concentrated into a fraction of the original milk, that portion is known as cream". 2.1.2
Classification
Cream is not a definite specific substance. It contains all the milk constituents but in varying proportions. The milk fat in cream may vary from 18 to 85 percent; the solids-not-fat constituents in lower proportions than in milk. Cream may be broadly classified as: a. Market cream:- which is used for direct consumption, and b. Manufacturing cream:- which is used for the manufacture of dairy products. The various types of cream and their fat contents are as follows: i. Table cream, ii. Light cream, and iii. Coffee cream...
20-25% milk fat.
iv. Whipping cream and v. Heavy cream
...
30-40% milk fat.
vi. Plastic cream
...
65-85% milk fat.
2.2
Cream Products
2.2.1
Definition
...
Cream products are products that are enriched to a varying degree with milk fat; they are non-acidified, acidified, whipped and may or may not have additives.
2.2.2
Classification
Cream products are classified according to the application, manufacturing process and the fat content. In Germany, two standard products are known: i. Coffee cream (10% milk fat) and ii. Whipping cream (35% milk fat). Other types of cream and their milk fat content are: Sour cream (30%), Sweet cream (28%), Cake cream (36%), Butter cream (30-45%), and Plastic cream (60-75%). 3.0
LEGAL STANDARDS
3.1
According to the PFA Rules (1976)
Cream, excluding sterilized cream, is the product of cow or buffalo milk or a combination thereof which contains not less than 25 percent milk fat. 3.2
United Nations Food and Agricultural Organization and World Health Organization (1977)
The United Nations Food and Agricultural Organization and World Health Organization (1977) have suggested the following standards for market cream: a. Pasteurized, sterilized & UHT treated cream b. Half-cream ... c. Whipping cream ... d. Heavy whipping cream ... e. Double cream ... 3.3
... ... ... ... ...
18% milk fat 10-18% milk fat 28% milk fat 35% milk fat 45% milk fat
According to FAO standards
According to FAO standards, the following classification is made according to the fat content: a. Cream ... b. Light cream (or coffee cream) c. Whipping cream d. Heavy cream e. Double cream 4.0
18-26% > 10% > 28% > 35% > 45%
COMPOSITION
The increasing fat content of cream, changes the percentages of all other components. Cream with a fat content of 30% has the following composition (in Germany). The chemical composition of cream with 25% fat and 50% fat (both form USA) has given in the following table: 23
Table 1. Chemical composition of cream Constituents
Fat Water Serum: Protein Lactose Minerals/Ash Total solids Solids-not-fat
Percentage
30 64 02.4 03.5 00.4 36 06
25.00 68.20 02.54 03.71 00.56 31.80 06.80
50.00 45.45 01.69 02.47 00.37 54.55 04.55
In addition, vitamins, enzymes, trace elements and acids are present in cream. It will be observed from the above composition that the higher the fat percentage in cream, lower the solids-not-fat content. The formula for determining the percentage of solidsnot-fat in cream is: %SNF in cream = [(100 - %fat in cream) / (100 - %fat in milk)] x [%SNF in milk]. 5.0
CREAM PRODUCTS
5.1
Coffee Cream
5.1.1
Terms and Required Characteristics
Coffee cream is a shelf-stable product with a fat content of >10%. It is homogenized and UHT processed, filled aseptically or sterilized in the container. Its shelf life is longer, similar to UHT milk. Its key function is to whiten coffee, but it is also used in the preparation of food and drinks and for direct consumption. The important quality criteria are taste, whitening power and stability in hot coffee. 5.1.2
Method of Manufacture
First, the fat content must be standardized as required. Coffee cream treated by the UHT process, is filled aseptically into one-way containers of standard net volumes [10 ml (portion pack) up to 0.25 l]. When preserving coffee cream by the sterilization process, it is first fat standardized, then pasteurized at 90°C, homogenized, filled into bottles, closed by crown corks and finally sterilized in retorts. Importance of homogenization: Coffee cream must be homogenized. This prevents a fat layer or fat plug in the container, thus improving taste, whipping power and stability. Homogenization has a direct influence on the flocculation stability of coffee cream in hot coffee. A double-stage homogenization is optimal for UHT cream. The first homogenization is done before the UHT treatment; the second aseptic one is done after the UHT treatment. For both process, the pressure in the first stage should be about 200 bar and in the second 24
stage about 50 bar. When sterilizing cream in the pack, homogenization has to take place before the sterilization, which again is a double-stage process using the same pressure (200/50 bar). Flocculation of cream in hot coffee is due mainly to casein precipitation. For example, homogenized casein-free cream, enriched with whey proteins has significantly improved flocculation stability when it is preheated at 90°C for 5 min because of whey protein denaturation. 5.2
Sour Cream
5.2.1
Terms and Required Characteristics
This is a heavy-bodied ripened cream of high acidity (0.6% as lactic acid), clean flavour and smooth texture. It should have following organoleptic criteria. Appearance: White to yellowish, slightly creamy. Flavour: Clean, slightly acidic, rich. Taste: Clean, milk-sour, flavorful. 5.2.2
Method of Manufacture
Take a sweet cream and standardize to get 18-20% milk-fat. It is then pasteurized, homogenized (preferably at a low temperature to promote formation of homogenization clusters) and chilled to 15-20 °C, and the final fat content is set. Then, it has to be inoculated with an aerobic starter (i.e. lactic acid/butter culture) @ 2-4% at 20°C, and allow for fermentation until the desired qualities are obtained. During the acid production, the homogenization-clusters flocculate, resulting in a highly viscous cream. To increase the firmness, rennet or thickening agent are sometimes added to the sweet cream. When the pH has reached to 4.5 (or once the cream has reached an SH-value of 25-35), the cream is further cooled with gentle stirring and then chilled to 2-4 °C and packed (by filling into one-way containers or bottles). Alternatively, souring in the package may be applied. Sour cream is mainly used in prepared foods, less often in drinks or beverages. 5.3
Whipping Cream
5.3.1
Terms and Desirable Properties
Terms: Whipping cream is one of the food foam. This concerns 35-40% fat cream. It is widely accepted due to its multiple applications in decorating and refining of food. The cream is usually whipped immediately prior to consumption, either by the consumer or in the catering outlets (restaurants, bakeries and others). It is therefore, primarily designed to be beaten into foam, often with sugar added. It is mostly available as a pasteurized product in small bottles, plastic cups, or large cans. It is also sold as in-can sterilized cream, and even supplied with sugar and a driving gas in an aerosol-can that delivers a ready-made whipped cream. Desirable Properties: The most important specific requirements for the desirable product are: 25
(a) Flavour: The product is eaten for its flavour, which obviously must be perfect. Rancid and tallowy flavours in the original milk should be rigorously avoided; this requirement is even more essential than for coffee cream. Not everybody appreciates a sterilization flavour or even a pronounced cooked flavour, and partly because of this the cream usually is pasteurized. (b) Keeping quality: Many kinds of spoilage can occur, but it is often desirable to store the cream for a prolonged time. The original milk should contain not more than a few heatresistant bacteria, above all. Bacillus cereus is a disastrous microorganism in whipping cream (it causes the fat emulsion to become unstable). Nor should growth of psychrotrophs occur in the original milk because they form heat-resistant lipases. To allow for a fairly long shelf life, the pasteurized cream should be packed under strictly hygienic or even aseptic conditions. Recontamination by bacteria arises many complaints. Therefore, whipping cream is often heated by in-can or in-bottle pasteurization. Contamination by even minute amounts of copper causes autoxidation and hence offflavour. Some coalescence of the fat globules during processing can readily lead to cream plug formation during storage. A cream plug implies that the product can hardly be removed from the bottle; moreover, it will readily churn rather than whip during beating in of air. (c) Whippability: The cream should quickly (i.e. in a few minutes) and easily whip-up to form a firm and homogeneous product, containing about 50% (v/v) of air (i.e. 100% overrun). (d) Stability after whipping: The whipped cream should be firm enough to retain its shape, remain stable during deformation (as in "decoration"), not exhibit coarsening of the air cells, and show negligible leakage of liquid. Sometimes carrageenan is added as a thickening agent. 5.3.2. Method of Manufacture The classical manufacture of whipping cream is fairly simple. In which, cream obtained from pasteurized milk is taken and standardized to 36% milk fat. After adding thickening agent, it has to be pasteurized at 85°C for 30 minutes, and then cooled to 5°C and packed. The pasteurization of the cream should at least be sufficient to fully inactivate milk lipase. Usually, the heat treatment is far more intense in order to improve the bacterial keeping quality. The way of heating, as well as the heating intensity, varies widely; holder pasteurization (e.g., 30 min at 85°C), heating in a heat exchanger (possibly over 100°C), and in-can (bottle) heating (e.g., 20 min at 103°C) are used. Likewise the manufacturing sequence, separation temperature, and so forth vary widely. Sometimes the cream is stirred in an open vat at rather high temperature in order to deodorize it; vacreation is not suited because it damaged the fat globules. Such damage, especially (partial) coalescence of the fat globules, should be avoided. The milk, and especially the cream, should be handled gently. The cream should not be processed or pumped unless the fat is completely liquid or largely solid, i.e., only at temperatures below 5°C or above 40°C. Hence, bottle filling of hot cream followed by cooling would be preferable, but it is rather uneconomical. 26
Sterilization of whipping cream may cause problems. In-bottle or in-can sterilization, often causes coalescence, unless the cream is first homogenized. However, most homogenized cream cannot be whipped. Accordingly, UHT heating is to be preferred, also because of the flavour (direct UHT heating causes strong homogenization); the cream should then be homogenized aseptically at low pressure and the composition should be adjusted ("emulsifier" added). A disadvantage of UHT whipping cream is that the temperature fluctuations to which it may be subject (it is often stored un-cooled for a time) can cause "rebodying". This implies a considerable increase in viscosity that, moreover, strongly impairs the whipping properties (churning rather than whipping). To be readily whippable on delivery, the cream needs first to be kept refrigerated for a day in order to ensure that all fat globules contain some solid fat. To prevent creaming during storage, a thickening agent is generally added (e.g., 0.01% k-carrageenan). 5.3.3. Whipping Process When skim milk is beaten, a foam with very rich in air is rapidly formed on top of the liquid. This, proceeds more slowly when cream is beaten and the air bubbles stay in the liquid for a longer time. This is partly because of the higher viscosity but also because the fat globules directly penetrate the air-water interface, attaching themselves to the air bubbles and spreading some liquid fat onto the bubble surface. Because of this the films between closely approached air bubbles are rather unstable and initially the bubbles coalesce readily. The far globules are so highly concentrated that they readily show partial coalescence (clumping). In this way a structure of clumped fat globules formed, enclosing the air bubbles and giving a rigid a d stable foam. To achieve this, air cells and fat clumps should be similar size, preferably 10-100 m. The foam increases in firmness during whipping, but it also becomes coarser. On prolonged beating, the clumps become so large and few that they cannot stabilize but a few large air cells: the whipping becomes churning and the clumps become butter grains; the air bubbles coalesce and disappear again. The balance between foaming and churning partly depends on the way of beating. If this is too slow, the cream may churn prematurely. Vigorous beating causes a high overrun and finely structured and smooth foam. The smaller the air cells, the less clumping is needed to enclose the bubbles and to produce a firm foam. It is also possible to foam an emulsion without clumping occurring. Such a product may be sold in aerosol cans; thus it is not beaten, but the foam forms when the gas pressure is released. Obviously, time does not suffice for sufficient clumping to occur. The fat globules curtail the overrun. They should not destabilize the air bubbles. This may be achieved by considerably reducing globule size. Proteins or other surfactants may cause some foam stability. But since encapsulation of air bubbles with fat globules does not occur, the foam is mostly unstable to manipulation and it soon becomes coarser due to Ostwald ripening of the air cells. On the other hand, these products often have a high overrun, over 200%, instead of around 100% for ordinary whipped cream. 5.3.4. Factors for Whippability Several properties of the cream affect the whipping process.
27
(a) Fat content has a considerable effect (see Fig. 15.7). But the influence depends on the conditions during whipping. The more intensive the beating, the lower the fat content of the cream allowing a stable foam to form, and the higher the overrun. (b) Crystallization of the fat is essential for clumping. If the amount of liquid fat is high, clumping is too rapid and the foam becomes unstable. Hence, deep cooling and a sufficient cooling time of the cream are essential, as is a low temperature during storage and at whipping. Obviously, the composition of the fat has an effect: There may be more problems in summer than in winter. (c) Further composition of the cream. Presumably protein is needed, especially when beating starts, to form foam cells. Addition of thickening agents hardly affects whipping, but leakage of liquid is considerably reduced. (d) Homogenization considerably impairs the whippability; the globules become too small to clump rapidly. This may, however, be better than expected if the fat globules have formed homogenization clusters because far less clumping is needed in that case. Homogenization at low pressure (1-4 MPa), preferably in two stages (e.g., 2 and 0.7 MPa at 35°C), can give clusters of some 15-20 m in diameter. (e) Supplying the surface layers with other surface-active substances decreases the formation of clusters and increases the tendency to clumping; then homogenization at higher pressure may be applied. The surfactant added may be a mono-glyceride or a Tween; the latter drastically affects the whipping properties. 5.4
Clotted Cream
5.4.1. Terms and Required Characteristics Clotted cream is exceedingly rich, containing form 60-70% milk fat. This fat is present in the cream in a finely emulsified condition, which renders it usually digestible. The product will have a peculiar boiled taste and rough appearance, and will exhibit a whiteflaked surface. The average composition of clotted cream will have: 67.50% milk fat; 4.90% protein; 1.00% lactose, 0.50% ash and 26.10% water. 5.4.2. Method of Manufacture There is no standardized method of preparing clotted cream. Several systems are used, varying chiefly as regards the method of obtaining the raw cream, and resulting in considerable variation in the texture, flavour and appearance of the finished product. The flavour and physical consistency of cream are depends upon: i. the acidity of original milk, ii. the temperature of scalding, and iii. the time allowed for scalding. The several methods of manufacture in common use are: a. Earthen bowl method b. Shallow pan system c. Scalding over separated milk, and d. Direct scalding method. The last two methods make use of cream mechanically separated from the original milk. These methods are used with milk of unknown or doubtful cleanliness. Whereas, first two system may sour the product during scalding process, when cream will possess a poor keeping quality. It is prepared by heating cream to 77-88 °C in shallow pans and then allowing it to cool slowly. The surface layer consists of clotted cream, which is skimmed off and strained. 28
Clotted cream was long considered a luxury product but it has been widely recommended by the medical profession as an excellent fatty food, particularly for use in the dietary of invalids. 5.5
Canned or Sterilized Cream
5.5.1
Required Characteristics
Canned cream generally possesses a peculiar flavour due to its processing, and high viscosity due to homogenization. Texture should be smooth. It should be free from lumpiness and separation of serum. Sterilization spoils its whipping quality. The fat content is about 2025%, and solids-not-fat content may vary between 6.5-9.5%. 5.5.2 Method of Manufacture The various steps are: i. Fresh-sweet cream is first standardized to 20% milk fat. ii. Pre-heated to 80°C without holding. iii. Then, double homogenized at 80°C, using 2500-3000 psi in the first stage and 500 psi in the second stage. iv. Immediately cooled to 16°C. v. Filled into tin-cans or bottles, and immediately sealed. vi. Sterilized in retorts (as for evaporated milk) employing 15 minutes for coming-up, 12-14 minutes for holding at 118°C, and 15 minutes for cooling to room temperature. 5.6
Plastic Cream
5.6.1
Terms and Required Characteristics
Plastic cream is highly viscous than any other type of cream. Its texture is resembles to paste. Its fat content is between 65-85%. It can be used directly for the manufacture of butter-oil. 5.6.2. Method of Manufacture This is obtained by i. re-separating normal cream (30-40% fat) in a normal cream separator, or by ii. separating milk in an especially designed 'plastic cream separator'. In both the above cases, the initial product is pasteurized at about 71-77 °C for 15 minutes and cooled to 60-66 °C before separation. 6.0
FURTHER READING
'Dairy Technology'-Principles of Milk Properties and Processes. Editors: Walstra P., Geurts T.J., Nooman A., Jellema A. and M.A.J.S. van Boekel; Publ.: (c) 1999 by Marcel Dekker, Inc. 'Milk & Dairy Products Technology'. Editor: Edgar Spreer; Publ.: (c) 1998 by Marcel Dekker, Inc. 'Milk Products'. Editors: WM Clunie Harvey and Harry Hill; Second Edition, 1999. Publ.: Biotech Books, Delhi. 'The Butter Industry': Hunziker O.F., La Grange, Illinois (1940).
29
DEVELOPMENTS IN PRESERVATION OF CREAM
Dr. R. R. B. Singh Sr. Scientist Division of Dairy Technology NDRI, Kanal-132 001 1.0
INTRODUCTION
Cream is a high moisture product and is therefore perishable. Processing of cream is essential to prevent spoilage and extend keeping quality. This could be accomplished by application of unit operations such as chilling, freezing and thermal treatments. Pasteurization of cream for extending the keeping quality to a period longer than its natural shelf life has been practiced for a very long time. Extremely limited shelf life and formation of cream plug which could sometimes totally solidify into a gel are major defects of pasteurized cream. The free fat content may result from disruption of the membranes during thermal processing or from mechanical treatment through pumping or air incorporation. There are however other processing technologies available which could overcome these difficulties and extend the shelf life to acceptable levels. 2.0
IN-PACKAGE STERILIZATION
Thermal treatment to cream so as to destroy microorganisms and enzymes coupled with suitable packaging to prevent post processing contamination result in significant increase in shelf life of the product. The conventional method of sterilization requires the product to be packaged and the complete package and material subjected to heating in a retort or hydrostatic sterilizer using temperature-time regimes of 110-120oC for 10-20 min. The can and glass bottles have been the traditional containers but the retortable plastic materials are now available for packaging. The severe heating during in-package sterilization induces gross changes in the cream with protein denaturation, Maillard browning and fat agglomeration resulting in texture and flavour defects. Calcium sequestering agents such as sodium citrate or sodium phosphates have been found to make more casein available for stabilizing the emulsion. The unit packaging volumes are generally small (60-41-20-80 0.3 Margarine >80 0.2 Reduced 60-75 0.3 Fat Low fat 38.40 0.2-6.5 Very low 20.25 0-8.3 Fat Water 5.12 12.20 Continuous = denotes an optional
Emulsifier/ emulsifying salt
Stabilizer
Preservatives
+ +
-
-
Colour Flavour and Vitamins + + +
+ +
= =
+ +
+ +
+
=
=
+
(Moran, 1994)
6.0
FUNCTIONS AND PROPERTIES OF FAT SPREADS
The function of a fat spread is multiple and include lubrication of bread when eating, energy source, flavour carrier, vitamins transports, source of essential fatty acids, coolness taste contribution during eating, and provide product structure. Properties of the spreads can be classified into two groups i.e. Organoleptic and spreadabilty. Organoleptic tests are normally carried out by trained panelists and can embrace flavour and texture profiling techniques. The taste of the products with fat spreads is controlled through emulsion inversion. The melting of the product in the mouth simultaneously causes disruption of the crystal network and the breakdown of the emulsion. The emulsion stabilizing shells of fat around the aqueous melt, with saliva, create an O/W emulsion from the original W/O spread. As a result, the viscosity of the emulsion on the palate falls rapidly to a point where swallowing taking place, and a rapid diffusion of aromatic compound into nasal occurs (Moran, 1993). Spreadabilty is one of the most important properties for spreads from consumer view point. It is desirable that products should be spreadable at 5°C. To have the desired plasticity/spreadabilty in the product, there must be following three essential requirements: 1 2 3
7.0
There must be two phases, solid and liquid. The solid phase must be so finely dispersed that the crystal mass is held together by lateral cohesive forces. There must be proper proportion of solid and liquid phase. If the solid content is too high, the interlocking crystals coupled with insufficient liquid, will cause shortening of the product and break subsequently to be brittle (Crabtree, 1989). TECHNOLOGY OF SPREADS MANUFACTURE
Technology of spread processing.
manufacture comprising of selection of ingredients and 79
7.1
Selection of Ingredients
The important constituents of spreads are milk fat, milk proteins, emulsifiers, stabilizers, emulsifying salts, acidiluants, common salts, colouring and flavouring materials, vitamins, preservatives, antioxidants, etc. Each ingredients has specific importance in production of good quality spread. 7.1.1
Function of fat
Fat provides structure, energy and taste including creaminess. It act as carrier of flavour and vitamins and also source of essential fatty acids. The physical properties of spreads, namely spreadability, firmness, plasticity and thixotropy are mainly determined by the ratio of liquid to solid fat content. Fat are usually selected from milk fat and its fractions or vegetable fats/oils or combination of both. Milk fat include cream, butter and butter oil. On the basis of flavour and composition corn, safflower, sunflower, soybean and groundnut oils have been preferred for spread. 7.1.2
Function of proteins
Milk proteins are added to the spread for their organoleptic functional and nutritional properties. They imparts creamy taste, thereby improving consumer acceptability. They contribute viscosity and water holding capacity to the aqueous phase, thereby improving emulsion stability during processing and storage. Milk proteins supply the essential amino acids and improve the nutritional value of the product. The main source of milk proteins are skim milk, butter milk, caseinates, whey solidsin the form of concentrated or dried or retentate form. Use of cheese in spread would not only provide protein but also help in imparting cheese flavour to the product (Shiller et al., 1977 and Sprenger, 1981). Soy protein isolate, vegetable proteins, can be used in manufacture of spread because of high water holding capacity (Kinsella,1978), high protein quality (Gupta and Kapoor, 1978). It can be also used in the form of protein-lipid concentrate so as to utilize the polyunsaturated soys oil as well. 7.1.3
Emulsifiers
In combination with milk proteins (when used) emulsifiers are generally of the fat soluble type and primarily help to reduce the size of aqueous droplets and contribute a dairy like taste to the product. Mostly they function by creating stabilizing films at the water/oil interface and by altering the other characteristics such as the wettability by water of the fat crystals. They have ability to yield the softer and more easily spreadable product with stable emulsion. Various emulsifiers used in spread are monoglycerides (MG) of saturated and unsaturated fatty acids, egg yolk solids, lecithin, combination of lecithin and MG, etc. The proportion of emulsifier in spread varies from 0.1 to 0,6%. 7.1.4
Emulsifying salts
In addition to assisting the emulsification process, emulsifying salts also improve the texture of the spreads. These salts are believed to modify the emulsification of fat. They are known to contribute to the texture of products like spreads especially of O/W type. The 80
common emulsifying salts used are tri sodium citrate, di-sodium phosphate and their combination, etc. and are added at he rate of 1to 4%. 7.1.5
Stabilizers
Stabilizers are especially important in reduced/low fat spreads and help to promote water in W/O by inhibiting coalescence of aqueous phase droplets during product processing and in use situations, and by balancing the viscosity of the two phases which make up the spread, namely water and fat. High water holding ability of stabilizers play an important role in improving body and texture of spreads. Various stabilizers like gelatin, carboxyl methyl cellulose, starch, modified starch, sodium alginates, carrageenan, etc. can be used alone or in combination at the rate of 0.1 to 0.5 %. 7.1.6
Plasticizer
Plasticizers like glycerol, sorbitol, glycol, etc. may be used in spreadable products to impart pliability or plasticity to them. They have an ability to depress the water activity of the aqueous phase (Holscher and Dijkshoorn, 1980). This may help in extending the shelf life of the product. Addition of glycerol and sorbitol at the rate of 0.5 to 1.0 % in soy based low fat spread, improve the mouth feel without any adverse effect on firmness of the spread (Patel and Gupta, 1988). According to Seas and Spurgeon (1975), use of 2 to 4 % sorbitol in cheese flavoured dairy spread could partially limit lactose crystallization. 7.1.7
Acidifying agent:
Spreads, particularly low fat types, have low storage stability because of their high moisture content. A low pH in the food system retards bacterial growth and thus helps in extending the shelf life. Best body and least ‘weeping’ have been obtained with pH 5.7- 5.9 (Spurgeon et al., 1973). Lactic, acetic, citric acid, glucono- delta- lactone etc. can be use as acidifying agent. 7.1.8
Common salts
Sodium chloride or table salts usually added in spreads, which not only provides taste and palatability to the spread but also retards the growth of bacteria and thereby acting as preservative. Generally the salt content in spreads varies from 0.25 to 2%. 7.1.9
Colouring materials
In order to simulate the colour of the spreads, the colouring matters used are annatto and beeta carotene. Use of beeta carotene enhances not only the nutritive value but also the oxidative stability t the product. 7.1.10 Flavouring material Dairy spreads are blend of different ingredient, dairy or non-dairy, it may or may not have the desired flavour. It is thus essential that external flavouring are added to evelop or impart desired flavour. Butter starters, butter culture flavour concentrate, starter distillate, synthetic butter flavour etc. used successfully for butter flavoured spreads. Diacetyl, lactones, phenols, delta-lactone etc. can be used in such spreads. 81
Cheese flavoured spreads involve the use of cheese flavour concentrate, aged Cheddar cheese, smoked aged Cheddar and blue cheese. Shiller et al., (1977) added melted cheese as a protein ingredient and obtained a low fat spread with a flavour of matured ripe cheese and high overall quality. According to Lang and Lang (1970), other flavours used which include ham, herbs, shallots, garlic cocolate, vanilla, honey, nuts, etc. 7.1.11 Preservatives To inhibit the growth of spoilage organisms and yeast and mold , in addition to heat treatment, addition of various preservatives is required. The various preservatives used include sorbic acid, salts of sodium, potassium and calcium , nisin, propionates, sodium benzoate etc. and can be added at the rate of 0.03 to 0.1%. Other additives like anti-oxidants, vitamins, sweeteners, etc. can be incorporated to spreads. 7.2
Processing
The formulation and processing of spreads generally determine the final product quality such as appearance, taste, spreadability and keeping quality. The processing of spreads making involve preparation of aqueous and fat phase and their mixing, heat treatments, emulsification, cooling/crystallization, working, filling, packaging and setting. 7.2.1
Preparation of Phases
Aqueous phase preparation involves of dissolving of water soluble dairy and non dairy ingredients namely protein, stabilizer, salt, etc., Blending temperature between 40 to 80°C is generally used for faster dispersion and solubilization of ingredients. Flavouring ingredients should be incorporated at the end of heating to minimize the loss of volatile flavour. Pasteurization, homogenization and cooling are given before addition/blending into fat phase. Desired flavour and melting characteristic is very important in spread making and is influenced by the fat phase preparation. Blending involves melting of fat, mixing it with other fat soluble vitamins and colouring ingredients. Spreads preparation also involve mixing of all required ingredients together rather than preparation of two phases separately. The temperature used for mixing varies from 15 to 65°C. 7.2.1
Heat treatment
It is suggested to pasteurize the aqueous and fat phase before emulsion formation to minimize microbial contamination and to make the product safe for human consumption. The time temperature combinations used are 75°C for 30 min., 85°C for 5 min. and 95°C without holding. 82
7.2.2
Cooling of fat phase
It is commonly known to prepare fat compositions by cooling liquid fat or aqueous emulsion of fat, very often during cooling the desired crystal structure is not obtained and, therefore, taste, spreadability and other physical properties are impaired. In order to obtain outstanding properties of the final product a very specific crystal structure is required. This can be achieved by rapid cooling of the fat phase (Prajapati et al., 1991 and Verma, 1996). 7.2.3
Emulsification
Emulsification is an important process to get stable product during handling and storage. Emulsification process can be carried out by blending, homogenization, shearing action, churning, heat shock cooling etc. Blending of two phases can be carried out using Hobart Food Mixer, high shear mixer, etc. Various other methods have been suggested, namely Stephan thermizing unit, kneading action, plasticizing by cutting action with sharp blades, SRS vacuum cooler and colloidal mill methods. 7.2.4
Working
The process of working ideally disperse the fat crystals throughout the emulsion and if the process is carried out satisfactorily, the product will be plastic and spreadable; if not it will be greasy. Degree of working by scraped surface cooling affects the characteristics of low fat spread. Preparation of high moisture spreads of W/O type emulsion requires more intensive working at high refrigeration temperature than margarine. Maximum working at low temperature produces the hardest product. By churning method, butter with additional water requires working to manufacture low fat butter. 7.2.5
Packing
Water and air proofs Containers are required for packaging of spread. Various kind of packaging materials namely ice-cream cups, plastic coated cartoons, semi-plastic containers, plastic coated paper packs, polyethylene lined paperboard containers, parchment paper, colorued glass containers and polystyrene cups are used. 7.2.6
Setting
Setting is the phenomenon where the spread is usually kept at low temperature for several hours to get desired degree of consistency. Crystallization of fat during setting helps in attainment of final body characteristics. Setting temperatures govern the rheological properties of the product by influencing the number of crystal particles. Number of crystal particles vary even with slight changes in temperature. Higher temperature of setting yields a butter with lower hardness in comparison those set at lower with temperature. Setting temperature and duration varies from 0 to 15 C for 4 hours to 48 hours, respectively. 8.0
SPREAD DEVELOPMENT IN INDIA
Recent findings indicate that an increasing number of spreads have fat content in the range of 38-44 % rather than the traditional 80 % butter or high fat spreads. This is because increasing the demand for the low fat or reduced fat or low calorie spreads by consumers. A variety of spreads are developed in number of western countries. In our country, a butter 83
flavoured low fat spread was developed based on soy concentrate and vegetable fat (Patel, 1982), butter flavoured Prajapati, et al., 1991) and cheese flavoured (Prajapati, et al., 1992) spreads using hydrogenated fat and soybean oil (50:50) and butterfat based, particularly cream based, spread (Verma,1996) are formulated. Chemical composition of developed spreads are given in Table 4. The schematic diagram for the manufacture of these spreads are given in Figures 1, 2 and 3. Recently, Amul Dairy had launched "Amul Lite" low fat spread in the market. Table 4. Chemical composition of developed spreads Constituent
Butter-flavored spread
Total solids Fat Protein Carbohydrate Ash Caloric value, Kcal/100g 9.0
57.38 40.64 5.15 8.79 2.79
Cheese flavoured spread 57.59 40.36 7.92 6.27 3.03
421.52
420.00
Cream based Soy based butter flavored spread spread 62.35 51.4 45.58 39.4 5.37 6.3 9.12 2.29 1.7 468.18
-
SHELF LIFE OF THE SPREADS
Spreads, particularly Low-fat spread, have poor shelf life varying from 7-90 days at different storage temperature (4°C to 30°C). The shelf life of the product is affected by various factors namely type of emulsion and dispersion, moisture content, processing treatment, type of ingredients, salt content, packaging material, storage temperature, pH of the product and use of preservative. 10.0
CONCLUSION
Cold spreadable butter, recombined butter, butter blends and low calorie butter spreads are products which assist in the development of food industries in areas where dairying is un economic. At the same time the products help the utilization of the surplus of butterfat of the main dairy producing regions. A high quality product close to traditional butter can be obtained if the best raw materials, dairy hygiene, and good manufacturing techniques are chosen. Research work is required in the area enhancing the shelf-life of the spread. 11.0
REFERENCES
Crabtree, R.H. 1989. Table spreads. The Australian J. Dairy Technol.,42:2:101. Forman, L. 1990. Industrial processes for milk fat spreads. Proc. XXIII Int. Dairy Congr., Brussels, Vol.2:1791 Gupta, S.K. and Kapoor, C. M. 1978. food value of soybean. Agric. Res. Newsletter, 5:1. Holscher,E.J. and Dijkshoorn,J. 1987. Edible ware-in-oil emulsion with a reduced fat content and use of said emulsion for producing bakery products. European Pat. Appln. 0218277. cited from Food Sci. technol. Abstr. 19:10:v112. IDF. 1989.The market position of imitation products. Bullatin of the Int. Dairy Fedn. No. 239 pp5. IDF. 1993. Guidelines for fat spreads. IDF Standards.166:1993;2 cited from J. Soc.Dairy Technol., 47:1:1477. Kinsella, J.E. 1978. Functional properties of soy proteins. J.Amer.Oil Chemists’ Soc. 56:242. Lang, F. and Lang, A. 1977. New development in butter and in use of butterfat-2. Milk Ind. 79:10:19 84
Mann, E. 2000. Butter related spreads. Dairy Ind. Int. 62:11:20. Moran, D.P.J. 1993. Yellow fat spreads.J. Soc. Dairy Technol., 46:1:2. Moran, D.P.J. 1994. Fats in spredable products. In Fats in food products (Moran, D.P.J. and Rajah, K,K. eds.) Blackie Academic and Professional, London, p.155. Nichols, B. 1993. The current market and legal status of butters, margarine and spreads. Lipid technol.,5:3:57. Patel, A.A.1982. Development of a low calorie protein rich table spread. Ph.D. Thesis , Kurukshetra Uni. Kurukshetra. Patel, A.A. and Gupta, S. K. 1989. Rheological studies on a protein enriched low fat spread. J. Fd. Sci. Technol,. 26:1:36 Patel, A.A. and Gupta, S.K. 1988. Studies on a soy based table spread. J. Food Sci.(USA)53:455. Prajapati, P.S.; Gupta, S.K.; Patel, A.A.and Patil, G.R.1991a. Ingredient selection for production of low fat butter flavoured spread. J. Food Sci. Technol.,28:4;204. Prajapati, P,S.; Gupta, S.K.; Patel A.A. and Patil, G.R. 1991b. Processing of low fat bytter flavoured spread. J. Food Sci. Technol., 28:4:208. Prajapati, P,S.; Gupta, S.K.; Patil, G.R. and Patel, A. A. 1992. Development of cheese flavoured low fat spread. Cultured Dairy Prod. J. Seas, S. M. and Spurgeqn, K. R. 1975. Development of cheese flavoured type dairy spread with controlled fat content. Food Prod. Development. 9:9:68. Shiller, G.G.; Vyshemirskii, F.A. and Silin, V. M. 1977. Method for production of butter with cheese flavour.. USSR Pat. 565657. Cited from Dairy Sci Abstr. 40:3845. Sprenger, M. 1981. Cheese spread and process for preparation of the same. Europ. Pat. Appln. 0033635. Cited from Dairy Sci. Abstr.,45:2049. Spurgeon, K.R.; Seas, S. W. and Dalaly, B. K. 1973. Effects non-milk solids and stabilizers on body, texture and water retention in low fat dairy spreads. Food Prod. Devrlopment 7:4:34. Verma, R. B. 1996. A study on technical aspects for development of low fat butter spread. M.Sc. thesis, Gujarat Agricultural Univ., S.K.Nagar. Weckel, K. G. 1065. Dairy spreads. Manufactured milk Prod. J. 56:7:5.Bullock, D. H. 1966. A preliminary study of a new low fat dairy spread. Canad. Dairy Ice cream J. 45:1:26 Zillen, M.1977. Nordisk Mejeriindustri, 4:5:263. Cited in Flang L and Lang A, 1979. New development in butter and uses of butter. Milk Ind.79:10:19.
85
Buffalo milk cream (70 % fat & 2.75 % SNF) Sweet cream butter milk Heating (90 C/30 mins) 0
Heating (85-900C/20-30 mins) Cooling (300C) Cooling (600C) Condensing (40 % TS)
Tempering (30-400C)
Storing in deep freezer (-810C/10-12 hr.) Tempering (30-400C) Mixing (Standardization to 45% fat and 15 % SNF)
Heating (55-600C) Pasteurization (750C/30 min) Homogenization (100 kg/cm2) Annatto butter colour 1.85 ml/kg spread Starter distillate (1.25 % v/w)
Additives CMC - 0.25 % GMS - 0.30 % Sorbic acid – 0.10 % BHA - 0.02 % Salt - 1.5 % Added in hot water (50-600 C)
Mixing Cup filling (100 ml/500 ml polystyrene cups) Setting (510C for 10-12 hrs.)
Storage (510C) FIG. :3 SCHEMATIC DIAGRAM FOR MANUFACTURE OF LOW FAT BUTTER SPREAD 86
APPLICATION OF ELECTRON MICROSCOPY IN FAT RICH DAIRY PRODUCTS Dr. D.N. Prasad1 and Dr. S.K.Tomar2 Head1and Sr.Scientist2 Dairy Microbiology Division NDRI, Karnal 1.0
INTRODUCTION
Electron Microscopy (EM) is being increasingly used to study the microstructure of individual components in milk products and modifications these entities undergo either alone or by interactions with each other or with additional ingredients during manufacturing processes. Such studies can be used for food structuring, texture-structure conclusions and quality evaluation (Aguilera and Stanley, 1999). The EM techniques render a markedly higher magnification at a considerable better resolution than light microscopy. Instead of light, a beam of electrons generated from an incandescent tungsten or lanthanum hexaboride electrode is employed to magnify the image of the sample. There are two major EM modes- Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Magnetic lenses are used to focus the electron beam in both kinds of microscope. The specimen is placed into the path of electron beam in the TEM but in the SEM, it is placed at the end of focussed electron beam path. The image is produced in the form of a shadow on a fluorescent screen in TEM. In SEM, reflected and secondary electrons are processed by an electron detector to form a quasi three dimensional image on a monitor screen. To avoid the absorption of electrons by air, the whole operation is carried out in vacuum. An anode with an orifice in its centre is positively charged and those in the centre pass accelerated through the orifice toward the specimen. Accelerating voltage of 3 to 20 kV has been used to do SEM and 60 to 80 kV has been used in TEM of Dairy foods. 2.0
PREPARATION FOR ELECTRON MICROSCOPY
2.1
Fixation and Dehydration
As a pre-requisite to the observation of a sample with electron microscope, it is necessary to dehydrate the specimen and to fix (preserve intact) the structure in their natural orientation. The fixation and dehydration process must be carried out carefully in stages to avoid distortion of the image. Common fixatives used for this purpose are OsO4 (glutaraldehyde, formaldehyde and acrylic aldehyde) and permanganates (Potassium and barium permanganates). Other specialised compounds used for this purpose include uranyl acetate, chromium, mercury salts and phosphotungstic acid etc. Dehydration of dairy products can be accomplished by air-drying, freeze-drying and critical point-drying (Prasad, 1998).
2.2
Encapsulation
This technique is used to prepare highly viscous product like fat rich dairy product for both TEM and SEM. In this technique the specimen is concentrated in agar or other gel capsules and such sealed capsules are handled as larger solid samples. A special encapsulation technique as devised by Veliky and Kalab(1990) are in vogue for heat-sensitive products such as cream and butter. A special apparatus is used for this purpose. A double-needle assembly consists of a central needle 1mm in diameter concentrically located in a wider needle.. The assembly is connected to two 5-ml syringes with piston to allow the food sample flow through the inner needle and a 3% sodium alginate solution is injected from another syringe to coat the food sample. Food sample and sodium alginate solution are extruded simultaneously into a 0.05 M calcium chloride solution, pH 6.5, where sodium alginate immediately forms a gel and immobilizes the food sample. The 100 to 200 mm long columns of encapsulated food so prepared may be cut into shorter segments and transferred in to a fixative for subsequent processing of sample for EM. 3.0
TRANSMISSION ELECTRON MICROSCOPY
The TEM can be performed using various techniques as discussed in the following sections.
3.1
Conventional Technique
The conventional method consists of embedding the specimen in a resin cutting thin sections(15 to 90 nm thick) with the help of an ultramicrotome, staining the structures within the sections(using heavy metal salts e.g. osmium, lead and uranium) and placing the sections in the path of the electron beam. 3.2
Special Technique
The EM investigation of fat rich products offers a number of difficulties. Such studies are hampered by the solubility of the fat in dehydrating agents and embedding media leading to destabilization of the fat globules and unpredictable extraction of fat. As a result, conclusions drawn from such electron -micrographs are dubious. For these reasons, fat rich dairy products are studied employing following special techniques (Kalab, 1981): 3.2.1
Negative Staining
This is relatively a simple procedure used for TEM. The specimen is in the form of submicroscopical particles semitransparent to the electron beam. Addition of phosphotungstic acid (PTA), sodium phosphotugstate, or ammonium molybdate solutions to the specimen makes the medium electron-dense but spares the particles. The thin layer of specimen so prepared is dried and finally placed into the microscope. The electron beam passes only through the semi-transparent structures under study and is absorbed by the surrounding stain of heavy metal. The structures appear light against a dark background in the micrographs. 3.2.2 Metal Shadowing Metal shadowing is a suitable technique for studying suspensions. In this technique, the specimen is fixed and dried on a translucent film. The dried film is subsequently 88
shadowed with platinum or a platinum and palladium alloy. During TEM study, as the electron beam passes through the shadowed area and exposes photographic material, the shadow appears dark on the negative whereas areas with platinum deposit produce light image. This image depends on the topography of the specimen's surface. 3.2.3 Freeze Fracturing and Freeze-etching Though laborious, these techniques enable to examine the specimen without altering it chemically (fixation) or physically (dehydration, embedding, drying).The specimen is allowed to freeze rapidly followed by freeze-fracturing at a temperature below -110o C. The fracture plane is subsequently replicated with platinum and carbon either immediately or after certain period of freeze etching, during which a thin layer of ice in the specimen sublimes off and reveals underlying structures. The specimen is thawed; replica is separated from the specimen, and examined in the microscope. 4.0
SCANNING ELECTRON MICROSCOPY
In this system, a focussed electron beam is employed to examine the specimen. Some of these electrons get reflected while others are able to generate secondary electron from the gold coating. These secondary electrons are used to form an enlarged image of the specimen surface. In order to neutralize the negatively charged incident electrons, the specimen should be electrically conductive. This is accomplished by coating of specimen generally with gold with the help of an ion sputter coater. Gold-palladium alloy, platinum and iridium are other heavy metal used for this purpose.. 5.0
MICROSTRUCTURE OF FAT RICH DAIRY AND RELATED PRODUCTS
5.1
Fat Spreads
Fat, an integral and indispensable part of our diet is consumed in large amounts as margarine and butter and is used for baking and frying and as spreads. In fat spreads, the fat molecules of high-melting fats are crystallized in a regular arrangement into solid crystals. The type and the size of the crystals depend on the source of the fat blend and the processing conditions (Heertze & Leunis, 1997).Common fat spreads used in daily life are Shortenings, Margarine, and Butter . Shortenings are frequently used in bakery applications. They are composed of liquid oil and fat crystals only unlike margarine and butter which contain about 16% water, in addition. While oil forms a liquid phase, fat crystals attain the form of a plate-like three dimensional crystalline network, with crystal bridges. The microstructure of margarine is characterized by presence of water-droplet in the backdrop of a fat crystal network. Water droplets of a few micrometers in diameter are formed during intensive mixing of fat and water phases during processing. Crystals orient at the water droplet surface and thus stabilize droplet. Fat forms familiar network composed of plate-like crystal aggregates. In products (creaming-, cake- and puff pastry), the nature of the fat crystalline network differs with respect to the size, the shape, and the aggregation of the fat crystals (Heertze, 1993).
89
Butter offers a distinctly different microstructure exhibiting a discontinuous structure of fat globules and a crystalline fat matrix. The fat globules remain intact through the churning process. Amount of globules and the inter-globular fat phase varies with ripening procedure of the cream and other processing conditions. 5.2
Whipped Cream
A comparison of whipping of homogenized and non-homogenized cream reveals various features. The homogenized cream is characterized by smaller size of fat globules and homogenization clusters. The air bubbles decrease in proportion as the time of whipping increases and are much smaller in homogenized than in non-homogenized cream. During whipping, µlatter disrupt fat globule membrane resulting into agglomeration of fat-globules. Further whipping results in disappearance of the air-bubbles and in the formation of butter granules similar to those found during churning (Schmidt & van Hooydonk, 1980). 5.3
Ice cream
The EM studies of ice cream mix depict it as an emulsion comprising of tiny fat droplets dispersed in the water phase, each surrounded by a membrane of proteins and emulsifiers. The sugars get dissolved in the water phase. During cooling, milk fat partially solidifies so that each droplet consists of solid fat crystals cemented together by liquid fat. Ice crystals and air bubbles are two additional phases which come into existence during whipping and freezing of mix. They are dispersed in the concentrated unfrozen mix. The water contributed by milk or cream in the mix freezes in to ice. As a result, the dissolved sugar get increasingly concentrated in the unfrozen phase as more ice forms.Thus microstructure of ice cream comprises four distinct phase, ice crystals, air bubbles, fat droplets and the unfrozen phase. The process of freezing and aeration of the mix causes the emulsion to undergo a process called partial coalescence. During this process, fat droplets form clusters and aggregates of fat that surround and stabilize the air bubbles as it happens in whipped cream. 5.4
Butter Milk
Fat is present in dispersed state in cream and fat globules measuring 0.5 to 10 µm in diameter are encased in membranes composed of lipoproteins which stabilizes them in the milk and inhibits their aggregation. Most of the fat globule membranes are disrupted during churning leading to aggregation of globules in to butter. Most of the membranes fragments are released into the butter milk while others are retained in the butter. Consequent upon removal of the butterfat, though the composition of butter milk made from sweet cream is similar to that of skimmilk with respect to protein and carbohydrates yet it contains additionally excessive membranous material and slightly higher lipid content. Due to lower price, there is a temptation to blend small amount of butter milk into skim milk; chemical detection of butter milk may prove to be difficult due to identical composition. The EM studies can be used to detect differences in the morphology of butter milk and skim milk particles in blends and also of reconstituted products. Apparently, spray-dried skimkmilk and butter milk appear similar under SEM. Both exist in the form of spheres or clusters of spheres widely ranging in dimensions. A closer look, however, offer some striking dissimilarities. In spray-dried skim milk, majority of spheres are severely wrinkled and occasionally displaying the apple like structure. On the 90
other hand, spray dried butter milk is characterized by less deep wrinkled spheres and absence of collapsed structures frequently found in spray-dried skim milk. The former has been found more porous, a feature related to the fat content. Another possibility of adulteration of blending fluid butter milk with skim milk and spray dry the mixture could not be detected by SEM. This could be ascertained by observing the presence of fragments of fat globule membrane by TEM (Kalab, 1980). 6.0
CONCLUSION
Electron microscopy though a sophisticated and expensive technique is highly valuable in establishing the relationship of various attributes of finished product e.g. composition, rheology as well as manufacturing conditions with its microstructure. The study of microstructure has ample application in quality control, product development and process control.
7.0
REFERENCES
Aguilera, J.M. and Stanley, D.W.1999. Microstructural principles of food processing and engineering.2nd ed.Aspen Publishers,Inc, Maryland, USA. Heertze, I.1993.Microstructural studies on fat research. Food Struct.12:77-94 Heertze, I. and Leunis, M.1997. Measurement of shape and size of fat crystals by electron microscopy. Food Sci. Technol.30:141-146. Kalab, M.1980. Possibilities of an electron microscopic detection of butter milk made from sweet cream in adulterated skimmilk .Pages 645-652.Scanning Elect. Microscopy.1980/III, SEM Inc, AMF O' Hare, USA. Kalab, M.1981. Electron microscopy of milk products: A review of techniques. Pages 453-472. Scanning Elect.Microscopy.1981/III, SEM Inc, AMF O' Hare, USA. Prasad, D.N.1998.Microstructure of traditional dairy products. CAS 4th Short Course on Advances in Traditional Dairy Products (Dec 16,1997-Jan.6,1998) NDRI, Karnal. Schmidt,D.C and van Hooydonk, A.C.M.1980. A scanning electron microscopical investigation of the whipping of cream.Pages.653-658.Scanning Elect. Microscopy.1980/III, AMF O Hare, USA.
91
ANHYDROUS MILK FAT-BUTTER OIL F.C. Garg Scientist (SG) Dairy Technology Division NDRI, Karnal-132001 1.0
INTRODUCTION
During II World War period several attempts were made in Australia and New Zealand, for finding a convenient method of supplying butter-fat to meet the army requirement, saving refrigeration and minimizing the storage space and also for satisfactory disposal of butter and second-grade creamery butter. After trying various methods of manufacturing, wrapping and packaging butter it was concluded that the most practicable method of dealing with butter was to extract from it dry butter-fat, which packed in suitable containers, could be shifted without marked deterioration and saving shipping space. This was followed by the development of continuous method of factory scale manufacturing of butter oil under partial vacuum, applying minimum heat treatment to preserve nutritive value of the product. 2.0
DEFINITION
Butter oil may be defined as fat concentrate obtained exclusively from butter and also cream and resulting from the removal of practically the entire water and solid-not-fat content. According to the norms of the FAO/WHO,anhydrous milk fat should have a minimum fat content of 99.8%, and the water content should not exceed 0.1% (Edgar Spreer,1998). Taking this into consideration, ghee in India and Pakistan or Samna of Egypt produced, long long ago before man knew anything about technology could come under the group of butter oil. However, the product “butter oil” popular in continental countries differs from ghee or Samna in colour, granularity and flavour resulting from difference in method of manufacture. Unlike ghee or Samna it is darker in colour, less granular in appearance and has a bland/flat flavour. 3.0
METHODS OF MANUFACTURE OF ANHYDROUS MILK FAT
Continuous process lines are available for the manufacturing of anhydrous milk fat from frozen butter and also directly from cream (Alfa-Laval ). 3.1
Butter as the raw material
Though it is normally more economical to produce butter oil directly from cream and thus eliminating the need for the churning process, the process line using butter as the raw material is used to convert excess amount of available butter into butter oil which is simpler to store and distribute. Salted butter and butter with high FFA content can also be used for
manufacture of butter oil after proper treatments. In this process butter is taken directly from cold storage to the butter melting equipment, where it is melted by using steam. The molten butter is forced outward by centrifugal force towards the periphery, where it is collected and transferred by positive displacement pump 3 to a heating system consisting of plate heat exchanger 4 with a jacketed pipe, through which hot water is circulated.(Fig.1)
From plate heat exchanger 4 the molten butter is transferred to holding tank 5, where it is held for certain period of time. The purpose of the holding time is to give protein sufficient time to agglomerate and to liberate any air entrained in the molten butter. This procedure facilitates the subsequent separation process. From holding tank 5 the molten butter is transferred to separator 7, where the fat is concentrated to more than 99% purity. The butter milk is discharged to the butter milk tank and used further if possible. If the butter is of poor quality and contains significant amount of FFA, it can be neutralized with a warm alkaline solution. Since the fat still contains a small quantity of water, as much as possible of this water is removed in the vacuum dryer 10. Before drying, the fat is heated in plate heat exchanger 9 and, after drying, it is cooled in the cooling section of the same heat exchanger, and than transferred to butter tank 11 before packaging. 3.2
Cream as the raw material
This method utilizes the principle of the de-emulsification of concentrated cream. The fat globules are broken down mechanically by using clarifixator with a line capacities between 500 and 1000 kgs of butter oil per hour or centrifixator with a line capacity of 15002000 kgs or even more kgs of butter oil per hour. This forms a continuous fat phase containing dispersed water droplets which can be separated from fat phase. Raw material should be of good quality. Sour milk is completely unsuitable, even though fat may not be affected. However, the cream from such milk can be improved to certain extend by pre-treatment in the form of “cream washing” i.e. dilution with water, followed by separation.
93
Cream with a fat content of 35-40% is generally used for the production of anhydrous fat. In order to ensure effective inactivation of lipase enzym, the cream is pasteurized in heat exchanger 3 (Fig-2) and is then cooled regeneratively to 55-58°C. This treatment is recommended even though pasteurized cream may be used as the raw material, since the effect of reactivated enzymes is thus avoided.
After heat treatment, the cream is concentrated in centrifuge. This is of the solidsejecting type. The cream is concentrated to a fat content of 70-75%. The skim milk from contrifuge 4 is separated in separator 9, and the cream thus obtained is transferred back into the process across float hopper 1, upstream of heat exchanger 3. The skim milk discharged by separator 9 is cooled regeneratively in the first heating stage for unseparated cream in plate heat exchanger 3. The concentrated cream flows to the centrifixator 5, where the milk fat is subjected to heavy mechanical working and most of the fat globules membranes are broken down. This liberates the fat and a continuous fat phase is formed (emulsion splitting). The raw butter milk still contains a small percentage of fat in globular form, i.e. the membranes of some fat globules are still intact. This globular fat is removed in separator 6. After this treatment, the fat phase is purified so that it contains up to 99.5% fat. The fat phase, with a water content of about 0.4-0.5%, is pumped to plate heat exchanger 7, where it is preheated to 90-95°C. The oil is then transferred to vacuum dryer 8, where the water content is further removed to below 0.1%. The dehydrated milk fat is cooled to about 35-40°C and is then ready for packaging. During packaging of butter oil, care should be taken to exclude oxygen. Butter fat as it comes out of the vacuum dehydrater it is practically or completely de-aerated. Reaeration should be avoided and air-containing head-space in the container should be minimized. If fat is to be carried through regions of high atmospheric temperature, allowances must be made 94
for expansion of butter-fat which has a fairly high co-efficient of expansion. Both for bulk and retail packaging tin-cans are satisfactory. 4.0
STORAGE
One reason for its popularity is its long shelf-life. Even in tropical climate, anhydrous milk fat can be stored for months at room temperature, provided that the packaging is not translucent and is gas-tight. In chill storage, the shelf life of anhydrous milk fat is up to one year. The natural antioxidants of butter fat, pass mainly into separated serum, except for dry butter fat prepared by direct evaporation. The resistance of butter fat to oxidation can be improved by addition of permitted anti-oxidants, butylated hydroxytoluene anisole (BHA) not exceeding 0.02% by weight except gollate which shall not exceed 0.01% by weight. 5.0
USES i) ii) iii) iv) v) vi) vii)
5.1
Conversion of butter/cream to butter oil is a convenient method of preservation of butter fat if refrigerated storage is not available. It is suitable for recombining and reconstitution of milk, cream & butter. In ice-cream manufacture as a source of fat. As a cooking fat. For manufacture of toffee, chocolate and other confections. For manufacture of various type of fat spreads. For conversion into ghee. SELECTED REFERENCES:
Alfa-Laval, Dairy Hand Book. Alfa-Laval AB Dairy and Food Engineering Division, S-22103 Lund, Sweden. Edgar Spreer, Milk and Dairy Products Technology. Marcel Dekker, Inc. New York (1998). FRe Frederick Henry Mc Dowall, The butter Maker’s Manual Volume 2, (1953). FAO/New Zealand Dairy Training Course (14 January to 25 February, 1974) Vol. I Robert Jenness and Stuwart, Principle of Dairy Chemistry. John Wiley and Sons, INC. New York (1959). W.B. Sanderson, XIX International Dairy Congress Vol. II (1974).
95
MILK FAT FRACTIONATION Dr. T. Rai Principal Scientist Dairy Chemistry Division NDRI, Karnal-132001 1.0
INTRODUCTION
Milk fat is unique in terms of the myriad chemical and functional properties that it possesses and which has made it an important component of most dairy products. Milk fat, in the form of AMF (Anhydrous Milk Fat), butter or cream can be regarded as “natural” with the consumer’s meaning of the term. In India, however, it has mainly been used for the manufacture of butter and ghee over decades because of its very high nutritive value. It contains a higher proportion of short chain fatty acids which contribute to its ease in digestibility and is a good source of essential fatty acids. Further, the main feature for becoming an attractive component is a typical characteristic pleasing flavour that cannot be found in other fats. The flavour is mostly in bound or precursor state which allows it to be released steadily during cooking. In addition, compositionally it is a primarily the even number of saturated and unsaturated C4-C8 straight chain fatty acids that imparted a unique physical spectrum of characteristics in terms of crystallization behaviour and melting range (-40 to +40°C). However, besides having so many virtues, with the advent of novel foods having number of functional properties, the need for modifying the milk fat has been realized. In its native form the use of milk fat in many food formulations has been restricted. As for instance, the wide melting range of milk fat makes it difficult to produce butter of improved plasticity and spreadability at refrigeration temperatures (Rizvi et al., 1995). In addition to poor spreadability at refrigeration temperature, its consumption in developed countries is declining because of high price, low PUFA & high cholesterol content and due to its inability to complete with products like margarine. Since the physical properties of milk fat influences the rheological properties of dairy products, especially butter, there has been considerable interest in the modification of milk fat by physical (fractionation, texturisation, blending with other fats) and chemical (interesterification, hydrogenation and dehydrogenation) means. Due to the fact that fat is composed of triglycerides of various molecular weights with different physical properties, fractionation of milk fat into fractions markedly different from one another in composition and physical properties is the most logical basis of modification. Economic fractionation of milk fat into oil and hard fat fractions will facilitate an increased utilization of milk fat in many food applications, such as chocolate, confectionary and bakery products and in developing new convenient (e.g. freeze spreadable) and dietetic (e.g. cholesterol reduced and short and medium chain enriched triglycerides) butter types. Differences in molecular weight, melting temperatures (molecular weight and entropy of fusion), volatility and intermolecular interaction energy of constitutive triglycerides, can provide the physical basis for fractionation of milk fat triglycerides.
2.0
FRACTIONATION BY CRYSTALIZATION FROM THE MELT (DRY FRACTIONATION)
Milk fat exhibits a wide melting range from about –40°C to about 40°C. This provides the possibilities of crystallizing out a series of glycerides fractions at temperatures below their melting points. Suitable sizes of crystals are developed by controlled cooling of the melt and the crystals are separated from the liquid phase by filteration or centrifugation. Currently the dry fractionation of anhydrous milk fat is performed by two conventional systems, (1) TIRTIAUX and De Smet, both from Belgium, which are bulk crystallization processes. The widely used TIRTIAUX dry fractionations process enables one or up to five step fractionation of anhydrous butter oil at any temperature ranging from 50°C down to 2°C. The milk fat fractions thus obtained can be either used as such or the fractions can be blended in various proportions for use as ingredients in various food fat formulations. The major short coming inherent in this systems is the long residence time (8-12 hrs.) for nucleation and crystal growth. In the industrial operations, the fractionation process is carried out by melting the fat to about 65°C to destroy all the crystal nuclei. Then, by controlled cooling, crystals are developed from the molten fat and allowed to grow. When the fractionation cycle is complete, the higher melting crystals are separated out from the lower melting liquid phase. Various factors affect the fractionation process: the cooling temperature, the cooling rate, the crystal geometry, the efficiency of separation and the milk fat compositions. The separation of crystals from the liquid phase can be achieved by filtration, centrifugation or combination of these methods. The optimal crystal size depends on the choice of the separation method. A crystal size of 200-350m is preferred for filteration while a crystal size of 150-200 m is preferred for centrifugal separation. In the Tirtiaux process a continuous belt Florentine vacuum (50-200 m bar) filter is used to separate the fat crystals (optimum size of 200-300 m) from the liquid phase. Alternatively membrane filter presses from De Smet or Tirtiaux among others are currently available for the separation of the crystals. Separation using centrifugal separators with the aid of a surface active agent (Sodium lauryl sulfate) and an electrolyte (MgSO4) was introduced by Alfa-Lavel (Lanza process) in the early 1970s. This separation process has not received the attention of the dairy industry because of the presence o chemical residues in the milk fat fractions. 3.0
FRACTIONATION USING SOLVENTS
Fractionation by crystallization of fat in organic solvents such as acetone and alcohol is commonly employed in laboratory. Separation of fat crystals from organic solvents is easily accomplished and the fractions obtained can be easily recrystallized and purified. The main advantage being rapid crystallization due to low viscosity of liquid phase and higher efficiency of fractionation than the crystallization from the molten fat (Norris et al., 1971). The fat fractions obtained by solvent crystallization are relatively pure (Lechat et al., 1975). 97
Here cooling of fat diluted with a solvent generally results into formation of the crystal and reduce the tendency to form mixed crystals. The milk fat is mixed with an organic solvent. The mixture is cooled and triglyceride precipitates due to crystallization. The mixture is separated into two liquid phases, one containing liquid butter fat plus solvent and the other is solid phase of glycerides crystals and solvent. Both fractions are separated by centrifugation (Wilson, 1975). Here generally the solvent used are ethanol and acetone. Mucese et al., (1984) used hexane as solvent in place of acetone. However, this method has not gained industrial importance because of loss of flavour compounds of milk fat, pigment alteration and the problem of solvent residue in milk fat fraction (Wilson, 1975). Similar findings have been recorded by various workers for buffalo milk fat fractions (Dilanyan et al., 1972; Avvakumov et al., 1976; Makarenko et al., 1976, Yousaf et al., 1977). 4.0
FRACTIONATION BY SHORT PATH DISTILLATION
Short path distillation offers an excellent opportunity to obtain fractions from milk fat with distinctive chemical and physical properties. Short path distillation is a relatively well known process and consists of evaporation of molecules into a substantially gas free space i.e. vacuum. The controlling factor is the rate at which the molecule escape from the heated surface of the distilling liquid and are received by the cooled condenser surface. Hickman (1944 and 1947) has reviewed in depth, the principles, technology and scope of high vacuum distillation and equipment design. Molecular distillation has been used to recover volatile compounds of butter oil and cholesterol from butter fat and milk has been fractionated by short path distillation (Boudreau et al. 1984). Milk fat being a mixture of triglycerides differing in molecular weight, volatility and inter-molecular interaction energies, is an ideal candidate to effect separation of triglycerdes by short path distillation (McCarthy et al., 1962; Arul et al. 1988) Anhydrous milk fat was fractionated into four fractions, two liquid (LF1 and LF2), one semi solid (IF) and one solid (SF) at room temperature. The fractions were characterized by melting temperature protile, solid fat index and triglyceride and fatty acid compositions. The peaks melting temperatures progressively increased (8.8 to 38.7°C) from liquid to solid fractions. The solid fat content ranged from 0 to 27.5% at 20°C while it was 15.4% for native milk fat. The short chain (C24 to C34) triglycerides were enriched in the fraction LF1, long chain (C42 to C54) triglyceride were concentrated in the SF fraction and the medium chain (C36 to C40) triglyceride in the fraction IF. Short chain (C4 to C8) fatty acids gradually decreased from liquid to solid fractions and trend was reversed for long chain (C14 to C18) fatty acids, both saturated and unsaturated. The gradual increase in the concentration of unsaturated long chain fatty acids from liquid to solid is contrary to that observed in the melt crystallization process for the fractionation of milk fat. Short path distillation thus offers an excellent opportunity to obtain fractions from milk fat with distinctive chemical and physical properties. 5.0
FRACTIONATION BY SUPER CRITIAL FLUIDS
There has been a growing interest in supercritical gas extraction, over the past few years. Liquid like densities of dense gases result in liquid like solvent powers. This property 98
and faster mass transport characteristics relative to liquids due to low dense gas viscosity make dense fluids attractive extraction agents. Substances can be selectively dissolved by changing the density of the gas. Super critical gas (Dense gas) extraction involves the phenomenon of distillation and extraction simultaneously. Enhancement of vapour pressure, ideal solubility and phase separation play a role. A mixture of compounds differing in physical properties i.e. molecular weight, volatility, entropy of fusion and inter molecular interaction energy; such as milk fat triglycerides, can be fractionated with a variation in solvent power of the dense gas. Variation in size and packing regularity of the crystal structure lead to a wide variation in melting points for milk fat triglycerides (TG). Further, variation in molecular weight and unsaturation lead to differences in volatility of TGS. In a homologous series i.e. of similar nature of intermolecular forces, the chohesive energy is a function of the molecular size. Volatility of TGs, therefore, decreases with their molecular weight. Therefore, at low densities of the gas, short chain TGs are dissolved into the supercritical fluid phase. As the pressure (density) of gas is increased at constant temperature, intermediate and higher molecular weight TGs migrate into the mobile phase. Consequently, there is distinctive level of compression at which solubility of a species is observed. Thus this process (Dense gas extraction) involves the phenomenon of distillation and extraction simultaneously, where distillation involves enhancement of vapour pressure as a result substances can be selectively dissolved at a particular density or pressure and extraction involves ideal solubility of a particular fraction and then phase separation. In this process, dense gases are used that has liquid like densities and possess liquid like solvent powers. This property and faster mass transport characteristics relative to liquids due to low dense gas viscosity make dense fluids attractive extraction agents. Among the potential gases, carbon dioxide is attractive as a fractionating agent, being relatively a poor solvent for non-polar substances compared to hydrocarbons such as propane due to molecular volume. Besides, CO2 does not react chemically with food constituents, even in supercritical state. It is neither flammable nor toxic and is available in large quantities at relatively low cost, its use does not pose the problem of processing residues. 6.0
REFERENCES
Arora, Sumit and Rai, T. (1997). Milk fat fractions: Properties and applications: A Review. J. Dairying, Food and Home Sci., 16: 143-155. Arul, J., Boudreaue, A., Makhlouf, J., Taradif, R and Sahasrabudhe, M.R. (1987). Fractionation of anhydrous milk fat by supercritical CO2. J. Food Sci., 52: 1231. Arul, J., Boudreaue, A., Makhlouf, J., Taradif, R. and Grenier, B, B. (1988). Distribution of cholesterol in milk fat fractions. J. Dairy Res. 55: 361-371. Avvakuomov, A.K., Rumyant Serva, N.V. and Morozova, V.I. (1976). Changes in melting temperature of milk fat in relation to its chemical composition. DSA 38: 1182. Boudreaue, A., Makhlouf, J. and Arul, J. (1984). 44th Annual meeting of the Instt. Of Food Technology Antheim, CA, USA. Hickman, K.C.D. (1944). Chem. Rev. 351:51 Hickman, K.C.D.(1947) Ind. Eng. Chem. 391:686. Dilenyan, Z., Kharatyan, V. and Agababyan. (1972). Some physico-chemical indices of buffaloes milk fat. DSA. 34: 2298. 99
Lechat, G., Varchon, P., Kuzdazal-Savoie, S., Longlois, D and Kuzdazal, W. (1975). Fractional crystallization of anhydrous milk fat. DSA 37 : 8142. Makarenko, V.L., Grishehnko, A.I., Avvakuomov, A.K. and Babkin, A.F. (1976). Study of the hard and liquid phase in milk fat using impulse method of NMR. DSA 38 : 525. McCarthy, M.J., Kuksis, A and Beveridge, J.M.R. (1962). GLC fractionation of natural triglyceride mixtures by carbon number. Can. J. Biochem. & Physiol. 40 :679. Norris, R., Gray, I.K., Moedowell, A.K.R. and Dolby, R.M. (1971). The chemical composition and physical properties of fractions of milk fat obtained by a commercial fractionation process. J. Dairy Res. 38 : 179. Rizvi, S.S.H. and Bhaskar, A.R. (1995). Supercritical fluid processing of milk fat : Fractionation, Scale-up and Economics. Food Technol. 49 : 90-96. Wilson, B.W. (1975). Techniques of fractionation of milk fat. Aust. J. Dairy Technol. 30 : 10. Youssef, A.M., Salame, F.A and El. Ghanam, M.S. (1977). Fractional crystallization of cow and buffalo milk fats from acetone. Alexandria J. Agric. Res. 25 : 459. cited DSA (1980). 42 : 2167.
100
PROPERTIES AND UTILIZATION OF FRACTIONATED MILK FAT Dr. Sumit Arora Scientist (SS) Dairy Chemistry Division NDRI, Karnal-132001 1.0
INTRODUCTION
Milk fat has is traditionally used as one of the major dairy products in our country in the form of butter and ghee. Among all natural fats, milk fat is the most varied in its chemical characteristics and functional properties. It is a good source of essential fatty acids and possesses a uniquely pleasing flavour not found in other fats. It contains a higher proportion of short chain fatty acids, which contribute to its ease of digestibility. On the other hand, its high proportion of saturated fatty acids and cholesterol content have resulted in creating a shift away from its direct consumption and its utilization as an ingredient. However, in view of the considerable progress made in the dairy industry in our country, it has become necessary to introduce new technological innovations with regard to the diversified use of milk fat. In western countries, attempts are being made to use fractions of milk fat in the manufacture of dairy products with the object of obtaining desired rheological properties in the products. Functionality of milk fat can be improved by fractionation, the compositional variation between different fractions may help us to prepare a milk fat with low cholesterol, higher vitamin content and better keeping quality by mixing them in desired proportions. 2.0
PHYSICO-CHEMICAL PROPERTIES
Milk fat is a very complex mixture containing more than 437 fatty acids (Patton and Jenssen, 1975) of different chain lengths and unsaturation, formulating varieties of triacylglycerols having wide melting ranges from -40 to 40°C (Hannewijk and Haighton, 1957; Antila, 1966; Lovegren et al., 1973). This characteristic melting behaviour of milk fat lends itself to easy fractionation, having different chemical and physical properties. 2.1
Yield of Milk Fat Fractions
Temperature of fractionation is the main factor influencing the yield of milk fat fraction. Jebson (1970) reported marked effect of temperature on crystallization pattern of milk fat, the level of solid fat reportedly increased from 50 to 90 % when the temperature of crystallization was reduced from 27°C to 24°C. Armugham and Narayanan (1979) found that at 29°C the average per cent of the liquid fraction was 62 % for buffalo milk fat and 83 % for cow milk fat using thermal expansion dilatometer and reported that buffalo ,cow and goat milk fat at 28°C contained solid fat at the levels of 84.4, 66.4 and 22.8 % respectively. It was also observed that 50 % solid fat was obtained at 33°C, 30°C and 25°C in cow, buffalo and goat milk fats. Lakshminarayana and Rama Murthy (1985) reported a yield of 12.4, 53.6, 13.0 and 21.0 % for solid fractions obtained at 31°C, 23°C,15°C and the remaining liquid fraction at 15°C (S31, S23, S15 and L15) fractions obtained by stepwise fractionation for buffalo milk fat and a yield of 10.6, 57.6, 12.4 and 19.4 % for S31, S23, S15 and L15 fractions for cow milk fat.
2.2
Melting Point (MP)
Lakshminarayana and Rama Murthy (1985) reported the MP of three solid fractions at 31, 23,15°C and the remaining liquid fraction at 15°C of buffalo ghee as 37.5 (S31), 31.2 (S23), 19 (S15) and 14.5 (L15), and for cow as 34.2 (S31), 36.5 (S23), 30.5 (S15) and 14°C (L15), respectively. Bindal and Wadhwa (1993) observed that the average MP of goat ghee (28.1-30.2°C) was significantly lower (P < 0.01) than that of cow ghee (32.7-35.8°C) and much lower than that of buffalo ghee (33.4-38.8°C), while solid fractions of these ghee showed a similar trend but in liquid fractions, goat ghee had highest MP followed by buffalo and cow. 2.3
Refractive Index
Dolby (1970) and Norris et al., (1971) observed that the refractive index of the original milk fat was 1.4550 and those of the solids and liquid fractions were 1.4548 and 1.4550, thereby indicating that the refractive index of the fractions were similar to the original fat. Singhal et al., (1973) while studying the properties of three different layers formed in cow and buffalo ghee during storage found no differences in refractive index of those fractions, whereas Stephanenko and Tverdokaleb (1974), while studying the properties of milk fractions obtained at 20° and 11°C observed that refractive index of nonfractionated fat, solid fraction and liquid fraction at 11°C were 1.4555, 1.4550 and 1.4560, respectively. Dobronos et al., (1976) showed that the degree of hardening of milk fat depended upon the refractive index and iodine values of the milk fat. 2.4
Iodine Value (IV)
Kehar et al., (1956) determined the iodine values of cow and buffalo ghee which ranged from 27.4 to 40.5 (av. 34.4). Singhal et al,. (1973) recorded higher iodine values for liquid fractions of cow and buffalo ghee. Kankare (1974) determined IV of milk fat and three of its solid fractions obtained at 24°, 18° and 12°C as well as of the remaining liquid fat as 31.2, 24.9, 24.1, 28.7 and 40.5, respectively. Similar observations have been recorded by Fjaervoll (1969), Dolby (1970) and Norris et al. (1971). Youssef et al. (1977) reported that IV of low melting fractions of milk fat was higher than of the high melting fractions. Lakshminarayana and Rama Murthy (1985) reported the IV of three solid and the remaining liquid fraction of buffalo ghee as 28.8 (S31), 30.2 (S23), 34.8 (S15) and 35.60 (L15), and for cow as 30.1 (S31), 31.2 (S23), 33.4 (S15) and 35.2 (L15), respectively. Bindal and Wadhwa (1993) recorded comparatively higher iodine values for liquid fractions obtained at 28°C than those of solid and pure ghee from cow, buffalo and goat. 2.5
Reichert Meissl Value (RM)
The RM value of cow ghee is generally lower than that of buffalo ghee (Achaya and Banerjee, 1946). Most of the workers have recorded high RM values for liquid fraction than original milk fat and solid fraction (Dolby, 1970; Norris et al., 1971; Black, 1973; Stepanenko and Tverdokaleb, 1974). Lakshminarayana and Rama Murthy (1985) reported the RM values of three solid and the remaining liquid fraction of buffalo ghee as 28.6 (S31), 29.7 (S23), 31.4 (S15) and 33.20 (L15) and for cow as 22.4 (S31), 23.6 (S23), 25.0 (S15) and 26.4 (L15), respectively. 102
2.6
Polenske Value (PV)
Singh and Singh (1960) found that the PV of cow ghee ranged from 1.02 to 2.00, while that of buffalo ghee ranged from 0.35 to1.85. Black (1973) reported that PV of soft fractions of three samples of milk fat was 2.6, 2.0 and 2.4, respectively. The PV of the corresponding hard fraction of the same samples was 2.1, 1.9 and 1.5, respectively. Lakshminarayana and Rama Murthy (1985) reported the PV values of three solid and the remaining liquid fraction of buffalo ghee as 1.0 (S31), 1.28 (S23), 1.39 (S15) and 1.50 (L15) and for cow as 1.4(S31), 1.45 (S23), 1.6 (S15) and 1.65 (L15), respectively. 2.7
Saponification Value (SV)
The SV of goat, cow and buffalo ghee was determined by Singh and Gupta (1982) to be 210.2 ± 1.29, 234.12 ± 3.52 and 236.60 ± 2.45. According to Dolby (1970) the SV of the original cow milk fat, solid fraction and liquid fraction is 232.7, 229.1 and 236. Norris (1971) also observed that the liquid fraction had a greater SV (228.1) than solid (225.8) and original milk fat (226.2). 2.8
Fatty Acid Composition of Milk Fat Fractions
Results of earlier workers (Antila and Antila, 1970; Dolby, 1970; Norris et al., 1971; Timmer, 1974; Kankare, 1974; Lakshminarayana and Rama Murthy, 1985) on the fatty acid composition of cow and buffalo milk fat fractions show that low melting fraction contained more of short chain (4:0 to 14:0) and unsaturated (18:1) fatty acids, whereas the high melting fractions contained more of long chain saturated fatty acids (18:0 and 16:0). However, this trend is more prominent in milk fat fractions obtained from acetone crystallization than in those obtained by direct crystallization. The fatty acid composition of the fractions and their crystallization behaviour are largely dependent upon the conditions of crystallization as well as on the original fatty acid composition of milk fat. Since the fatty acid composition of goat milk fat is distinctly different from cow and buffalo milk fat. The levels of short chain (C4-C8) fatty acids in liquid fractions were 2.10, 1.83 and 1.80 fold to those of solid fraction in goat, buffalo and cow ghee. Again the levels of medium chain fatty acids (C9-C14) especially C10:0 and C12:0 in goat ghee liquid fraction were higher than those of cow and buffalo ghee liquid fraction and still much higher than those of solid fraction. Amongst long chain fatty acids, the levels of C16:0 and C18:0 in liquid fraction were much less (0.6-0.7 times) and those of C18:1 were high (1.4-1.6 times) in comparison to those of solid fraction. The unsaturation ratio was almost double in liquid fraction (0.5-0.54) as compared to that of solid fraction (0.27-0.36) (Bindal and Wadhwa, 1993 and Arora and Rai, 1998). 2.9
Flavour potential of fractionated milk fat
Baker (1970) observed that there is some increase in the level of colour and flavour in the liquid fraction and reduction in the hard fraction. The medium fraction is like normal butterfat in everyway except that it has a more limited melting range. According to Walker (1974) preferential solubility of trace flavours in liquid fat is probably influenced by their polarity and melting points relative to the bulk of triglycerides of milk fat. The occurrence of lactones and methyl ketones in the high melting fractions appear to be due mainly to the physical retention of liquid fat in the crystal matrix. The high melting fraction from anhydrous milk fat has possible applications in the preparation of chocolates, pastries etc 103
but if full flavour potential of milk fat is desired in these products, supplementation with a natural or synthetic butter flavour concentrate may be necessary. Bhat and Rama Murthy (1983) reported that the quantities of monocarbonyls were higher in the low melting fractions (LMF) than in high melting fractions (HMF) of both cow and buffalo milks. 2.10
Grain Formation in Ghee
Joshi and Vyas (1976) and Arumughan and Narayanan (1979) analysed solid (grains) and liquid fractions obtained by granulation of buffalo and cow ghee. The partly granular form assumed by ghee appears to be primarily due to presence of high melting triglycerides. On storage at 29°C granulation was found to be complete in 3 days in both cow and buffalo ghee. The minimum % of liquid fractions (59 for buffalo and 80 for cow) and the maximum grain size (420µm for buffalo and 108 µm for cow ghee) were recorded on the third day of storage. Lakshminarayana and Rama Murthy (1985) studied the size of grains of various cow and buffalo fat fractions which were fractionated at different temperatures and observed that the size of crystals was larger in the fractions obtained at higher temperature than at lower temperatures. 3.0
DISTRIBUTION OF MINOR LIPID COMPONENTS IN MILK FAT FRACTIONS
3.1
Cholesterol
Norris et al. (1971) reported that while original fat contained 240 mg of cholesterol per 100 g of fat, the solid and liquid fractions of the same sample of fat contained 220 mg and 250 mg of cholesterol for 100 g of fat. Arul et al. (1988) reported that cholesterol was enriched in the liquid fractions in particular 80 % of the cholesterol being found in the liquid fraction. 3.2
Vitamin A, Carotene and Tocopherol
Norris et al. (1971) fractionated milk fat by holding it at 25°C for 24 h and found that the concentrations of vitamin A and carotene were more in low melting fractions of milk fat as compared to those found in high melting fractions. The levels of vitamin A and total carotene occurring in original fat, liquid fraction and solid fractions were 8.4, 9.8 and 6.6; 8.8, 9.0 and 7.3 µg/g of fat, respectively. Lakshminarayana (1983) also pointed out that the per cent increase of vitamin A, tocopherol in L15 (liquid fraction at 15°C) fraction as compared to whole milk fat was 54 and 39 per cent in case of buffalo and 32 and 31 per cent in case of cow milk fat, respectively. 3.3
Phospholipids
According to Pruthi (1984), the phospholipid content of unfractionated ghee was found to vary from 36.2 to 330.0 mg/100 g (average 228.9 mg). Phospholipid content of liquid fraction of ghee was found to vary from 8.8 to 47.4 mg /100 g of ghee (average 31.0 mg) and that of solid fraction from 84.1 to 636.5 mg (average 489.8 mg). A major portion of phospholipids thus was found associated with the solid portion of milk fat.
104
4.0
STORAGE STABILITY OF MILK FAT FRACTIONS
4.1
Hydrolysis of Milk Fat Fractions
Rama Murthy and Narayanan (1972) have shown that softer fat is hydrolysed at a faster rate than harder fat. It is known that the longer the chain length of fatty acids of a saturated triglycerides, the slower is the rate of hydrolysis (Jensen et al.,1962 and Patel et al.,1968). According to Armughan and Narayanan (1979) a slower rate of hydrolysis was observed for the solid fraction of each buffalo and cow ghee as compared to the corresponding whole ghee and liquid fraction. Hence, the low melting fractions of milk fat can be expected to be hydrolysed faster than high melting fraction. It has also been reported that the physical state of fat greatly influences the rate of hydrolysis because lipase action is inhibited when fat is in solid state . Lakshminarayana and Rama Murthy (1986) explained the greater resistance exhibited by S31 fraction towards lipolysis may be attributed to its significantly higher content of long chain saturated fatty acids and high melting triglycerides than those found in low melting fractions .The rate of hydrolysis of milk fat fraction may find an important application in obtaining desired rates of hydrolysis during ripening of cheese made from buffalo milk. 4.2
Auto-Oxidation of Milk Fat
Low melting fractions of milk fat contain high amount of unsaturated fatty acids and thus are expected to undergo auto-oxidation at a faster rate during storage than high melting fraction. Pruthi (1984) indicated that distribution of phospholipids among the fractions of milk fat could influence the auto-oxidative stability of milk fat fractions. Since the low melting fractions of milk fat contains more of unsaturated fatty acids, it is expected to undergo auto-oxidation at a faster rate during storage than high melting fraction. However, it was also observed that low melting fractions contained more of tocopherol and carotene than high melting fractions which may act as a natural antioxidant in milk fat. It was observed that the presence of higher concentration of unsaturated fatty acids had a greater influence of accelerating auto-oxidation rates than the higher concentration of tocopherol and carotene which are known to retard auto-oxidation (Lakshminarayana and Rama Murthy, 1985). Bhat and Rama Murthy (1983) reported that in freshly clarified milk fats, quantitatively the monocarbonyls were significantly higher in the low melting fraction than in the high melting fraction of milk fat. No significant differences in the concentration of total carbonyls and ketoglycerides in these fractions was observed in these fractions was observed in milk fat of both cows and buffalo. Both the liquid milk fat and the whole fat of buffalo milk autoxidized faster than those of cow milk fat ,while the development of peroxides was slower in the high melting fraction of buffalo than in that of cow milk fat Murthi et al., (1974) observed that generally the liquid portion obtained at lower temperatures of fractionation is expected to deteriorate faster as they contain more unsaturates. Peroxides of liquids obtained at higher temperatures of fractionation (37°C) deteriorated faster than those obtained at lower temperatures. In general, the solids obtained at higher temperatures of fractionation (37°C) showed greater stability with reference to the peroxide value. The lowest melting fractions S15 and L15 showed significantly higher oxidation rates as compared to whole milk fat, whereas S31 and S23 fractions showed lower rates of auto-oxidation as compared to the corresponding whole milk fats of both cow and buffalo (Lakshminarayana and Rama Murthy, 1986). 105
5.0
APPLICATIONS
The chemical composition and physical properties of the fractions are different from those of original milk fat. The fractionation of milk fat is rather a method of increasing the technical applications of milk fat than a method for improving its nutritional properties. Milk fat fraction can be used in the production of fat containing foods e.g. 5.1
Bakery Products
The bakery industry offers an interesting and wide application area for milk fat fractions. The margarine industry has long been producing special fats for bakeries. Bakeries can use both soft and hard fractions for various purposes and these must be tailor made as agreed between the user and the manufacturers. 5.1.1
Pastry products
Major benefits are obtained when plasticised milk fat hard fractions are used in layered pastry products such as Puff pastry, Croissants and Danish pastry. Plasticised fractionated milk fat gives a good and constant performance, it can be utilized at more convenient temperatures than regular butter and eating quality of products served warm may be improved due to reduced oiliness (Pederson, 1989). 5.1.2
Biscuits and short bread
Milk fat soft fractions are used on a large scale in short bread and biscuits with improved quality, it gives the product a longer shelf life, especially during winter months when temperature cycling can cause fat bloom or surface discolouration of biscuits (Eyres et al., 1989). 5.1.3
Cakes
Cake margarines and shortenings have a very good creaming power, which is due to the combined effect of the fat melting properties, emulsifiers and plasticising procedure. However by blending milk fat fractions and plasticising them, a high creaming milk fat suitable for cakes can be produced (Eyres et al., 1989). 5.2
Chocolate and Sweets
Although it is desirable to add milk fat to chocolate as it is cheaper than cocoa butter and has intrinsic low viscosity, there is a maximum level caused by fat incompatibility, this results in chocolate that is too soft for practical use in temperate climates. Attempts have, therefore, been made to harden milk fat by fractionation, hydrogenation and interesterification. The hard fraction of milk fat has also been reported to act as an antibloom giving dark chocolate a longer shelf-life (Gordon, 1991). Lohman and Hartel (1994) observed that higher melting fractions inhibited bloom, while the lower melting fractions induced bloom as compared with control chocolates. 106
5.3
Dairy Products
5.3.1
Butter
Fjaervoll (1970) indicated that butter with good spreadable property can be prepared by incorporating low melting fraction of milk fat with cream, followed by churning the cream into butter. Similarly, several workers (Dolby, 1970; Lechat et al., 1975; Tucker, 1978; Arora and Rai, 1999) have independently shown that butter of good spreadability could be produced by incorporating low melting fraction into it. Deffense (1987) observed that spreadability can be enhanced by blending a very soft fraction (with a softening point of less than 10°C) with a milk fat hard fraction. A blend of 30 % milk fat hard fraction with 70 per cent very soft fraction gives a spreadable butter of excellent physical properties. Anderson (1991) stated that butter made of milk fat from which highest melting fraction has been removed is spreadable at refrigeration temperatures. On the other hand, it shows rather poor stand up properties at higher temperatures, greater liability to oil off and is less stable against flavour deterioration. By using repeated fractionation, it is possible to remove the triglycerides that melt in temperature range between 5° to 25°C. Such butter will show almost the same melting behaviour as table margarines. Double fractionation is, however expensive and there must be a reasonable use for the removed fat fractions. Such uses could include tailor-made butters for different kinds of bakery products. Kaylegian and Lindsay (1992) reported that butter samples made from low melting fractions or a combination of primarily low melting fractions and a small amount of high melting fractions exihbited a good spreadability at refrigerator temperatures (4°C) but were almost melted at room temperatures (21°C). Butters made with a high proportion of low melting fraction, a small proportion of very high melting solid fractions were still spreadable at refrigerator temperature and maintained their physical form at room temperature. Deffense (1993) reported that oleins from single stage fractionations can be used for softening butter, for creaming applications and for spreads .This can be done either by blending of cream with super olein followed by churning or reconstituting butter with milk fat fractions. 5.3.2
Cheese
Cheddar cheese manufactured from buffalo milk is always criticized for flat flavour and hard crumbly ,dry body and texture even after prolonged period of ripening. Admixing of goat milk with buffalo milk does wonders for obtaining good quality Cheddar cheese, addition of 10 to 20 per cent goat milk to buffalo milk yields good quality cheese. The flavour development and all biochemical reactions, i.e., glycolysis, proteolysis and lipolysis were much faster (Rao,1990) in goat milk added cheeses. Goat milk fat plays an important role in flavour acceleration in cheese The goat milk fat fractions were incorporated in buffalo milk at appropriate proportions for the manufacture of cheddar type cheese, liquid fractions helped to improve its sensory and textural properties (Arora and Rai, 2000). 6.0
CONCLUSION
The liquid and solid fractions obtained at different temperatures have significant variations in their chemical composition and the concentration of various constituents. As a consequence, these compositional variations of various milk fat fractions have their influence on the consistency/textural properties of products containing them. 107
7.0
REFERENCES
Achaya, K.T. and Banerjee, B.N. (1946). On the detection of adulteration of ghee. Indian J. Vet. Sci., 16: 144. Anderson, K. (1991). Uses of milk fat. Bulletin of the IDF. no. 260. Antila, V. (1966). Fatty acid composition, solidification and melting of Finnish butter fat. Meijeritiet. Aikakausk., 27(1): 72. Cited: Dairy Sci. Abstr.(1966), 28, 3250. Antila, V. (1979). The fractionation of milk fat. Milk Industries, 81(8):17. Antila, V. and Antila, M. (1970). Nutritional value of various fractions of milk fat. Fetter Seifen Anstr. Mittel., 72: 285. Cited: Dairy Sci. Abstr. (1970), 32, 3532. Arora ,S and Rai,T.(1998). Fatty acid profile and physico chemical properties of goat milk fat fractions. Indian J. Dairy Sci., 51(1): 20-25. Arora ,S and Rai, T.(1999). Effect of incorporating of goat milk low melting fractions on the Rheological and physicochemical properties of butter. J. Dairy Food and Home. Sci., 18(1): 32 - 36. Arora ,S and Rai,T.(2000). Biochemical changes in buffalo milk Cheddar cheese as affected by the incorporation of goat milk and goat milk fat fractions. Indian J. Dairy Sci., 53(1): 19-25. Arul, J.; Boudreau, A.; Makhlouf, J.; Tardif, R. and Greneir, B. (1988). Distribution of cholesterol in milk fat fractions. J. Dairy Res . 55, 361-371. Arumughan, C. and Narayanan, K.M. (1979). Grain formation in ghee (butter fat) as related to structure of triglycerides. J. Food Sci. Technol., 16: 242. Baker, B.C.(1970). The fractionation of butter fat and the properties of selected fractions. XVIII Int. Dairy Congr.,1E:241. Bhat, G.S. and Rama Murthy, M.K. (1983). Distribution and production of carbonyls during autoxidation in low and high melting fraction of cow and buffalo milk fats. Indian J. Dairy Sci., 36(3): 308-313. Bindal, M.P. and Wadhwa, B.K. (1993). Compositional differences between goat milk fat and that of cows and buffaloes. Small Ruminant Research, 12: 79-88. Black, R.G. (1973). Pilot scale studies of milk fat fractionation. Aust. J. Dairy Technol., 28: 116. Deffense, E. (1993). Milk fat fractionation today: A review. JAOCS, 70(2): 1193-1201. Dobronos, V.; Gulyaev-Zaitsev, S.; Zhuravlena, K. and Mramornov, B. (1976). Degree of milk fat hardening in relation to its chemical composition. Trudy, Litovskii Filial Vsesoyuznogo Nauchno-issledovatel'skogo Institute Maslodel' noi Promyshlennosti, 10: 179. Cited: Dairy Sci. Abstr. (1977), 39, 4012. Dolby, R.M. (1970). Chemical composition of fractions of milk fat separated by a commercial process. XVIII Int. Dairy Congress, 1E, 242. Eyres,L.;Boon,P.M. and Illingworth,D. (1989). Tailored Food Ingradients From Fractionated Milk Fat.Third F.I.E.Food ingradients Europe conference and exibition,session 6 lecture 4,Nov15-17 1988,Wembly. U.K. Fjaervoll, A. (1969). Butter oil and butter fat fractionation. Sevenska Mejeritidn, 61: 491. Cited: Dairy Sci. Abstr.(1970), 32, 1939. Fjaervoll, A. (1970). Anhydrous milk fat fractionation offers new application for milk fat. Dairy Industries, 35(8): 502. Cited: Dairy Sci. Abstr. (1971), 33, 143. Gordon, M. (1991). Monograph on Utilization of Milk Fat. Bulletin of IDF, 260. Hannewijk, J. and Haighton, A.J. (1957). The behaviour of butter fat during melting. Neth. Milk Dairy J., 11: 304. Jebson, R.S. (1970).Fractionation of milk fat into high and low melting components. XVIII Int. Dairy Congr., 1E: 240. Jenson, R.G.; Sampugno, J. and Parry, R.M.J. (1962). Lipolysis of synthetic triglycerides and milk fat by a lipase concentrate from milk. J. Dairy Sci., 45: 1527. Johsi, C.H. and Vyas, S.H. (1976). Studies on buffalo ghee. II. Various conditions affecting the granulation of ghee. Indian J. Dairy Sci.,29(1): 13-17. Kankare, V. (1974). Fractionation of milk fat by crystallization without solvents or additives. Meijeritieteellinen Aikakuskirja, 33: 132. Cited: Dairy Sci. Abstr. (1975), 37: 8138. Kaylegian, K.E. and Lindsay, R.C. (1992). Performance of selected milk fat fractions in cold-spreadable butter. J. Dairy Sci., 75: 3307-3317. Kehar, N.D.; Ray, S., Joshi, B.C. and Raisarkar, B.C. (1956). Stud. Fats Oils and Vanaspatis, p.5. Cited: Dairy Sci. Abstr. (1957), 19, 7670. Lakshminarayana, M. (1983). Fractionation of buffalo milk fat and studies on physico-chemical properties of fractions of buffalo milk fat. Ph.D. Thesis, Kurukshetra Univ., Kurukshetra. Lakshminarayana, M. and Rama Murthy, M.K. (1985). Cow and buffalo milk fat fractions. Part I. Yield, physicochemical characteristics and fatty acid composition. Indian J. Dairy Sci., 38(4): 256-264. Lakshminarayana, M. and Rama Murthy, M.K. (1986). Cow and buffalo milk fat fractions. Part III. Hydrolytic and autoxidative properties of milk fat fractions. Indian J. Dairy Sci., 39(3): 251-255. Lechat, G.; Varchon, P.; Kuzdazal-Savoie, S.; Longlois, D. and Kuzdzal, W. (1975). Fractionated crystallization of anhydrous milk fat. Lait., 55(545/546): 293. Cited: Dairy Sci. Abstr. (1975), 37, 8142. Lohman, M.H. and Hartel, R.W. (1994). Effect of milk fat fractions on fat bloom in dark chocolate. J. Am. Oil Chem. Soc., 71(3): 267-276. Lovegren, N.V.; Gray, M.S. and Feuge, R.O. (1973). Sharp-melting fat fractions from cotton seed oil. J. Am. Oil Chem. Soc.,50, 129. Murthi, T.N.; Manohar, A.; Chakraborty, B.K. and Aneja, R.P. (1984). Thermal classification of ghee. Part II.Keeping quality of ghee fractions and their modified fats. Indian J. Dairy Sci, 37(2): 125.
108
Norris, R.; Gray, I.K.; Moedowell, A.K.R. and Dolby, R.M. (1971). The chemical composition and physical properties of fractions of milk fat obtained by a commercial fractionation process. J. Dairy Res., 38: 179. Patel, C.V.; Fox, P.F. and Tarassuk, N.P. (1968). Bovine milk lipase. II. Characterization. J. Dary Sci., 51: 1879. Patton, S. and Jensen, R.G. (1975). Progress in the Chemistry of Fats and Other Lipids. Vol. 14, p.163 (R.T. Holman, ed.). Pergaman Press, Oxford. Pederson,A.(1988). Puff pastry butter - A new product in the dairy industry. Danish Dairy and Food Industry--Worldwide. 6,53-56. Pruthi,T.D(1984).Distribution of phospholipids between solid and liquid portions of ghee.IndianJ.Dairy Sci.,37(2): 175. Rama Murthy, M.K. and Narayanan, K.M. (1972). Polyunsaturated fatty acids of buffalo and cow milk fat. Milchwissenschaft, 27: 695. Rama Murthy, M.K. and Narayanan, K.M. (1974). Hydrolytic and autoxidative properties of buffalo and cow milk fats as influenced by their glyceride structure. Indian J. Dairy Sci., 27: 227. Rao, K.H. (1990). Flavour enhancement in buffalo milk cheddar cheese by synergistic action of goat milk and microencapsulated enzymes. Ph.D. Thesis, NDRI (Deemed Univ.), Karnal. Singh, I. and Gupta, M.P. (1982). Physico-chemical characteristics of ghee prepared from goat milk. Asian J. Dairy Res., 1(3/4): 201. Singh, K.P and Singh S.N. (1960). Variations in the physico-chemical constants of ghee. Indian J. Dairy Sci., 13: 143. Singhal, O.P.; Ganguli, N.C. and Dastur, N.N. (1973). Physico-chemical properties of different layers of ghee (clarified butterfat). Milchwissenschaft, 28: 508. Stepanenko, T.A. and Tverdokaleb, G. (1974). Chemical composition and physico-chemical properties of milk fat fractions obtained without use of solvents. XIX Int. Dairy Congr., 1E: 206. Timmen, H. (1974). Gas chromatographic detection of milk fat fractionation. XIX Int. Dairy Congr., 1E: 491. Tucker, V.C. (1978). Modified butter products. Dairy Products J., 6: 21. Cited: Dairy Sci. Abstr. (1979), 41, 635. Walker,N.J.(1974). Flavour potential of fractionated milk fat. XIX Int. Dairy Congr.,1E:218. Youssef, A.M.; Salama, F.A. and El-Ghanam, M.S. (1977). Fractional crystallization of cow and buffalo milk fats from acetone. Alexandria J. Agric. Res., 25: 459. Cited: Dairy Sci. Abstr. (1980), 42, 2167.
109
APPLICATION OF FAT MODIFICATION TECHNIQUES FOR IMPROVING THE USABILITY OF MILK FAT Dr. D.K. Sharma Principal Scientist Dairy Technology Division NDRI, Karnal-132001 1.0
INTRODUCTION
Milk fat uniquely combines a natural quality image with a highly distinct & desirable flavor, a significant nutritional value (Vitamin A and E, high short chain fatty acids, high monounsaturated fatty acid content etc.) and important functional properties which make a suitable for numerous food applications. With all these unique features milk fat has some matching problems in relation to its use in modern products and spreadability. For example, milk fat has a fatty acid composition that makes it difficult to produce butter which fulfils the functional requirement of products and meets increasing demand of butter spreadable at refrigerator temperature. To achieve a better spreadability in the butter even at refrigerator temperature attempts have been made to modify fat in different ways. Fundamentally the physical properties of milk fat may be modified either physically through temperature treatment, reworking and increased air content or technically by changing the composition of the fat through feeding mixing with other oils and fractionation; biomodification have been used to modify the characteristics of milk fat. This article deals, in brief, with the principles of these fat modification techniques and how possibly these could be used for improving the quality of milkfat (Butter, Ghee etc.) to increase its usability. 2.0
PRINCIPLES OF FAT MODIFICATION TECHNIQUES
2.1
Fractionation
Fractionation by crystallization is widely used to separate fat with harder and softer fractions. Oil and fats are mixtures of triglycerides. Because of their different fatty acid composition, the oil and fats have melting point spanning from –50 to +80°C. Every oil has its own melting range. Milk fat exhibits a wide melting range from –30°C to about +37°C. This provides the possibility of crystallizing out a series of glycerides fractions at temperature below their melting points. This is called fractionation by crystallization from the melt or dry fractionation. This is basically a thermo-mechanical process by which raw material is separated into two portions by crystallization. The process consists of three distinct stages: supercooling of melt, formation of crystal nuclei or nucleation and crystal growth. The crystals are then separated by low or high pressure filters. Different fractionation methods used for fats & oils include solvent fractionation, detergent fractionation and dry fractionation. Currently, dry fractionation of anhydrous milk fat is performed by two conventional systems. Tirtianx and De Smet, both from Belgium, which are bulk crystallization processes. The widely used Tirtianx dry fractionation process enables one-or up to five step fractionation of anhydrous Butteroil at any temperature ranging from 50 down to 2°C (Black,
1975). The milk fat fractions thus obtained can be either used as such or the fractions can be blended in various proportions for use as ingredients in various food-fat formulations. The major shortcoming inherent in this system is long residence time (8-12 hours) for nucleation and crystal growth.Some other fractionation techniques to improve resources, purity with speed are: fractionation by short-path distillation (Forss and Holloway, 1967); fraction by supercritical fluids (Kaufman et al, 1982; Arul, et al 1987), etc. These processes are high energy and capital intensive and not used commercially for fractionation. Another method of fractionation by crystallization using solvent has some advantages of rapid crystallization of crystals due to low. 2.2
Hydrogenation
The triglyceride of naturally occurring oils composed of unsaturated and saturated fatty acids. The unsaturated fatty acids contain from one to six double bonds. The number double bonds in the carbon chain of fatty acid and its position in triglyceride molecule are responsible for susceptibility to oxidation and physical state of oil and fats at a given temperature. The susceptibility of double bonds to oxidation (Autooxidation) can be decreased by saturating the double bonds with external pure hydrogen under specified conditions. When hydrogen is added to fatty acid double bond, it becomes saturated with constant increase in the oxidative stability and melting point of oil .The process is commonly known as “Hardening” of fat. The beauty of the process is that it can be stopped at any point up to complete saturation. Hence, it is possible to obtain fat of various physical and rheological characteristics by altering the level of hydrogenation. The process is selective and starts from fatty acid having more number of double bond (linolenic Linoleic Oleic stearic). This preferential hydrogenation of polyunsaturated fatty acid is required for improving oxidative stability. Usually, nickel metal is used as catalyst for the process. During the process, isomerization takes place due to the movement of double bonds to new positions to form trans-isomers. The trans fatty acids have higher melting points and thus contribute to increase in the melting point of fat. A similar saturation of double bond is enzymically catalyzed by microorganisms in rumen of cattle or buffaloes (Gurr, 1981). 2.3
Dehydrogenation
Current research interests in the United States are focusing on desaturation of fatty acids using lipase activity. If successful, this can lead not only to a healthier more unsaturated milk fat, but also a more spreadable butter. The anhydrous milk fat could also be used readily in more challenging applications such as mayonnaise and salad dressings without the need of fractionation.However some scientist have major objection to this approach of desaturation. As all know, that desaturase enzymes specific for conversion of 18.0 cis require the free acid as substate. Thus it would be necessary to hydrolyse the triglyceride to some extent, allow the 18:0 component of these acids to be desaturated and finally to re-esterify the free acids. It is quite possible that they do not return to their original positions in the triglyceride moiety, hence the relation of final material to milkfat would be somewhat tenuous. 2.4
Interesterification
The nature of fatty acids esterified in triglyceride is not only factor influencing the physical properties of fat. Another important influence is the distribution of the free fatty acids among the different positions of glycerol molecule. Natural fats tend to have specific 111
asymmetrical distributions of fatty acids in the molecule. Interesterification is a method of altering the melting point of a fat by randomizing the positions of fatty acids. The positions may be exchanged between fatty acids of the same triglyceride molecule (intra molecular exchange) or between fatty acids of different molecules (inter molecular exchange). The fat is heated in presence of catalyst (usually sodium, sodium methoxide, sodium ethoxide) to a temperature of 110-160°C. The interesterified fat is used for the manufacture of margarines, shortenings and confectionery fats (Srinivasan, 1978). An extension of this process is the use of microbial lipases as catalysts for the reaction. There are three type of lipases available to catalyse the process of interesterification. These are, non specific (randomized); 1:3, positional specific o the triglyceride and fatty acid specific. In US, this new area of research related to nonaqueous lipase interesterification is getting a lot of interest and funds, to modify milkfat. An exciting, further extension to this is to separate the modified fat into various fractions using superficial carbondioxide extraction. This lipase-catalyzed interesterification of milk fat improves the nutritional properties and butter flavor. And it was found to be the better fat for infant formulae. (Gregt-W-de et al., 1995). Bystrom and Hartel (1994) used this technique for producing Cocoa butter replacer from milk fat. Christorphe et al (1978) found that milk fat randomized with chemical catalyst does not raise the blood serum cholesterol level. Randomized milk fat appears to be more rapidly digested in vivo than i.e. untreated milk fat. By the process of interesterification, not only the physical properties but also the metabolic effects of the fat can be changed (Gurr, 1984). 3.0
UTILIZATION OF MODIFIED MILK FAT IN VARIOUS PRODUCTS
The fat modification techniques (Fractionation, hydrogenation, dehydrogenation, interesterification, lipase catalyzed interesterification) are used for improving the physical, rheological and nutritional properties of milkfat and its use in a wide range of food products. Significant new applications have been identified for these modified milkfat or fractions. The butter fat is now manufactured as a food ingredient and used in various food items to improve their functionality, nutritive value and sensory score & consumers acceptability. Some of the products which use modified milkfat, as one of the ingredients are summarized hereunder: 3.1
Bakery
Large quantity of low melting fraction are now used in Danish cookie to prevent fat bloom. A similar melting point fraction, at 28°C, texturized, performs extremely well in sponge cake. High melting fractions of MP (36-38°C, and 40-42°C) are used in pastries and puff pastry respectively. These applications are in addition to those which are well established i.e. creaming, aeration in cake batters, butter creams and sweet topping, etc. 3.2
Confectionery
Anhydrous Milk Fat (AMF) is used in chocolate to inhibit bloom formation and overall milk fat adds to flavor. However, its use in chocolate recipes is kept low because it 112
causes softening. But recent research shows that melting fraction of 40-42°C causes significantly less softening and therefore provides opportunities to increase percentage inclusion of milk fat in recipes. Butter is an important component of traditional sweet confections e.g. toffee, caramel, where it adds to flavor following heat treatment of its inherent flavor precursors. It is also a carrier of Maillard flavors produced by the action of milk solid-not-fat contained in butter and in the recipes. 3.3
Mayonnaise and dressings
Low melting fractions can be used in recipes where, for instance mayonnaise is used in food fillings e.g. sandwiches. 3.4
Soups and Sauces
Fresh cream and butter are used directly in the preparation of gourmet soups and sauces for their rich taste and quality image. AMF is used for canned soups in the form of an emulsion with low melting fraction some times being used in preference for its flavour and ease of emulsification. Even ghee can be used in the preparation of rich sauces. 3.5
Yellow fat spreads
The patent literature shows that a blend of milk fat fractions can be used, less the midfraction, to produce spreadable butter. In other applications low melting fractions can be added to increase flavour in dairy spreads and high melting fraction used as the hard stock in margarine blends or to produce 100% dairy puff pastry butter. 3.6
Frying
Butter is used for shallow frying. AMF (ghee) or its fractions can be used for deep frying of Asian and Middle Eastern sweetmeats and savoury meat preparation. In both instances the flavour development during cooking becomes a key criterion for its choice. 3.7
Cooking Butters
The product is prepared for frying and used in the restaurants and catering establishments. These have reduced water content, may have added cultured milk, lecithin, free fat milk solids and added salt. Due to compositional characteristics, the heating is faster, the splattering is reduced and butter keeps better. The added fat-free solids account for browning ability which is one indicator of right cooking temperature of fat. 4.0
FAT MODIFICATION FOR IMPROVING THE QUALITY OF GHEE
Indian Dairy Industry in particular has its own practical problems due to two different types of milk being processed simultaneously in dairy processing plant for manufacture of fat rich products. In organized dairy industry, 60% of milk comes from Buffaloes and rest is mainly from cattle of Indian breeds and crossbred. (Crosses of exotic with Indian breeds). These milk differ widely in their chemical composition in general and fat composition in particular. Another evitable situation faced by dairy industry is the seasonal variation in the quality and quantity of milk. The quality of fat obtained in the summer season is always different from milk fat obtained during winter season. This is mainly governed by the 113
availability of feed in those seasons, stage of lactation and ratio of cow to buffalo milk received at dairy plants. For example the ratio of receipt of buffalo milk to cow milk in summer season (lean season) is about 40:60 approximately, which is changed to 65:35 in the winter season. Under the circumstances the quality of raw material i.e. milk received in dairy plant differs widely and hence it is different to make uniform quality product through-out the year with standardized technologies. Because manufacturing protocols are based on certain basic quality of raw material bound to show their effect. Such a situation is not good for organized dairy business catering to the demand of large segments of consumers. To solve this typical problem mainly connected with milk fat as raw material, the role of fat modification technique is some how evident. With the intervention of these techniques it seems possible to solve some of problems faced by Indian dairy industry in ghee manufacture, storage and marketing. 4.1
Problems of Ghee manufacture:
Due to the variation in raw material, mainly the milkfat, following problems are practically faced by dairy industry:
Variation in the granularity of ghee (body and texture) Variation in the color of ghee Variation in Plasticity or plastic character of ghee Variation in sensory profile for ghee Problem of stability (Oxidative stability) and Renovation
4.2
Variation in the Granularity of Ghee
The reason of variation in granularity of ghee is well understood and mainly based on the variation in available milkfat (which differs with season, breed, feed etc.) for making ghee. Keeping manufacturing procedure or technology same we have to correct the variation in milkfat with the help of fat modification techniques. Some possible solutions gross methods are briefly discussed below: 4.2.1
Fractionation
Granularity in ghee is mainly due to the typical ratio of high melting triglyceride (HMTGD) and low melting triglycerides (LMTGD) at ambient temperature. LMTGD provide a liquid phase and HMTGD give a solid granular phase which are said to be one of the parameter for quality and even purity of ghee. The ratio of LMTGD and HMTGD may be adjusted with the fractionated LMTGD and HMTGD for getting uniform grains in ghee without any variation. And this is possible with little knowledge of fractionation technique (dry fractionation) and required ratio of different triglyceride to be adjusted for best grains. 4.2.2
Hydrogenation
Granularity is indirectly based on the level of saturation and unsaturation in fatty acids of triglyceride molecules and also their positions. The saturated fatty acid and trans unsaturated fatty acid give rise to hard fat (HMTGD) responsible for grains in ghee. Reduction in saturated fatty acids in raw fat due to higher ratio of cow milk fat in winter season may give a ghee without or little grains. The partial hydrogenation under mild 114
condition (not more than 125°C) in the presence of fresh catalyst, it is possible to partially hydrogenate milk fat for adjusting ratio of unsaturated fatty acids. Rumen bacteria may also be employed in vitro for hydrogenation of milk fat most naturally. However, such an approach requires an investigation at research level. Research work on these lines is in progress in Japan (Fujimoto et al., 1993). 4.2.3
Lipase-Catalyzed Interesterification
This is one of the new fat modification techniques to randomize the positional arrangement of fatty acids under the influence of specific lipases. Due to change in the positions of fatty acid in the triglyceride molecule the melting points can be typically adjusted. This technique has a great promise in dairy industry to make range of milkfat and fractions. The grain formation in ghee may also be altered by this biotechnological tool. 4.3
Variation in the Color of Ghee
The reason for this problem is due to two type of fat i.e. cow milk fat and buffaloes milk fat used as raw material for ghee making in organized dairy industry in India. Cow milk fat having dense yellow color due to carotenoids (precursors of vitamins A) changes the color of buffalo milk fat to variable degree, which depends on the level of cow milk fat in the final product. Such odd color is not liked by Indian consumers. The most preferred color for ghee is white, amongst Indian consumers. The chemical and physical methods of removing carotenoids may be employed to remove them from the milk fat. However, such attempt required deep investigation in techno-economic feasibility before its application. 5.0
VARIATION IN THE PLASTIC CHARACTER OF GHEE
The plastic character of ghee is due to the ratio of solid crystal and liquid phase of ghee at any given temperature. The viscosity of ghee is controlled by this ratio. Different type of shortening for frying, bakery or confectionery may be formulated by fractionating (dry fractionation or solvent fraction techniques) ghee into different olein (soft) and stearic (hard) fraction and then blending different fraction in wide range or ratios depending on the end use of shortenings. Such an approach of tailor made ghee for specialized end uses would enlarge the scope of its use and probably open up new markets different from conventional uses. An exciting extension is to interesterify milk fat using lipases and then fractionate it using supercritical carbondioxide fractionation. Such an approach is being tried at laboratory scale in US so as to produce variety of milk fats from natural milk fat. 6.0
VARIATION IN FLAVOUR PROFILE OF GHEE
The flavor components of ghee (lectones, aldehydes, FFA etc.) may be fractionated using supercritical CO2 fractionation technique. To simulate the flavor profile the desi ghee made from curd-butter-ghee route in commercial ghee, the fractionation technique has a wide range of application in Indian dairy industry. The flavour fraction of ghee having all carbonyls (lactones, aldehydes, FFA) may be fractionated using this approach, and can be used to simulate ghee flavors in various milk products without increasing their fat contents. Most of the flavor components are concentrated in very low melting point fractions. The regional preferences of flavor profile may also be tackled through this approach. However, techno-economic feasibility study must be made before applying it in the dairy industry. 115
7.0
PROBLEM OF OXIDATIVE STABILITY
The problem of oxidative stability at micro level may be controlled by reducing the head space oxygen in ghee, avoiding the contamination of metal ions and using antioxidants (BHA, BHT, TBHQ) and synergists (lecithin, Tocopherols, etc.) The problem of stability may also be tackled at molecular level by saturating the unsaturated fatty acids and changing their positions using enzymatic hydrogenation and lipase catalyzed interesterification. But still these approaches are in experimental stage and can be debated for their efficacy as a commercial process. The stability of fat/ghee can be improved along with the change in physical and metabolic characteristics of ghee with the application of these fat modification techniques. 8.0
CONCLUSION
Milk fat is unique in its flavour, textural and nutritional properties. And said to be the best fat for human consumption. However to enlarge area of its usability in bakery, confectionery, shortenings, salad dressings, soups and sauces etc., a mild modification is always required at micro level to suit the requirement of end product using conventional (fractionation, hydrogenation) and new methods (lipase catalysed interesterification, enzymatic hydrogenation and dehydrogenation) of fat modification. These fat modification methods have a significant role to play to solve the problems faced to get uniform quality of ghee having uniform grains, flavor and texture profile. To tackle the problem of oxidative stability of fat, these new technological tools would play a significant role in near future. 9.0
REFERENCES
Arul, J., Boudreau, A., Makholouf, J. Tardif, R. and Sahastrabunde, M.R. (1987). J. Food Sci. 52: 1231. Black, R.G. (1975). J. Dairy Technol. 30: 153. Bystrom, C.E. and Hartel, R.W. (1994). Evaluation of milk fat fractionation and modification techniques for creating cocoa butter replacers. Lebens mittel wissen scheft Technologie 27 (2) 142. Christophe, A., Mathys, F., Geers, R. and Verdonk, G. (1978). Arch. 2nd Physical Biochem. 86, 413. Forss, D.A. & Holloway, G.I. (1967). J. Amer. Oil Chem. Sco. 44: 572. Fujimoto, K., Kimoto, H., Shishikula, M. Endo, Y., and Ogimoto, K. (1993). Biohydrogenation of Linoleic and by anaerobic bacteria isolated from rumen. Bioscience, Biotechnology and Biochem. 57. (6), 1026.
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ALTERNATIVE SOURCES OF MILK FAT FOR RECOMBINED MILK Dr. B. D. Tiwari Principal scientist SRS of N.D.R.I., Bangalore 1.0
INTRODUCTION
The F. A. O. milk committee defines recombined milk (RM) as a milk product obtained from combining of milk fat and milk solids not fat (MSNF) in one or more of their forms with or without water. RM is made by adding individually processed, concentrated and dried dairy products and/or market milk products (milk or cream) and then jointly processing them. Various ingredients used for RM consist mainly a MSNF source, a fat source, emulsifiers and water (Fig. 1) WMP
SMP
BUTTER AMF Veg fat
BMP Emulsifier Stabilizer
Fresh milk Whey water PROCESS Fig. 1
Ingredients for Recombined Milk
Recombination process, in general, involves dispersion of non fat milk powder in water generally at 40-50ºC, addition of milk fat usually anhydrous milk fat (AMF) or refined vegetable fat in the required proportions, standardization to reestablish the product‟s specified fat to MSNF ratio and milk solids to water ratio followed by homogenization and suitable heat processing (Fig 2). However, the product prepared by recombination process but using vegetable or non -dairy fat is termed as Filled Milk and not Recombined Milk. For the manufacture of filled recombined products only highly refined, bleached, de-odorized and hydrogenated oils with low peroxide value and free fatty acids (FFA) should be used. Recombination process is widely used for the preparation of a range of dairy products to meet the regular as well as special demand of domestic market using imported dairy ingredients and to compensate for seasonal fluctuations in the availability of fresh dairy ingredients. It is also used to improve the nutritional status and to promote development of local dairy industry in many countries. Recombination of dairy products in India is mainly used for liquid milk marketing, standardization of buffalo milk and in the manufacture of ice cream and indigenous milk sweets.
Low heat skim (or whole) milk powder Water at 40-50ºC
Powder dispersion Deaeration
Hydration
Melted Fat addition Inline
Mixing tank Homogenization
UHT Fig. 2
2.0
Pasteurization
Milk products
Recombination Process
VARIOUS SOURCES OF MILK FAT
The quality of RM and products made from it is directly related to the physicochemical, microbiological and sensory quality of ingredients, processing parameters, and equipments used for its preparation. Hence their proper selection is absolutely essential to produce a product, which is acceptable to the consumers and competitive in costs. Milk fat is one of the major ingredients of RM, which not only possesses high nutritional value and plays important dietary role but more significantly it enhances the palatability and influences the costs of dairy products. Milk fat influences the palatability by acting as a carrier and source of flavour components and its physical properties contribute to the mouth feel of dairy emulsions (products). 2.1
Anhydrous Milk Fat/ Butter Oil
In most countries including India Anhydrous Milk Fat (AMF) is the sole source of milk fat for RM. However, consumer‟s reaction in India indicated that RM made with AMF is not palatable, unless at least half of the fat in RM is substituted from fresh milk. AMF can be manufactured from fresh cream either directly or via butter or from stored butter and is generally stored at ambient temperature. Hence it is quite susceptible to the development of oxidized flavour and impart off flavour and oily / fatty taste to RM. Reduction of the concentration of pro-oxidants like copper and iron during processing, maintaining low concentration of dissolved oxygen during filling and flushing the headspace with nitrogen prior to sealing the packages ensures good shelf of AMF. Australian workers suggest use of synthetic antioxidants for improving the keeping quality but such use is considered unnecessary in good quality AMF which has been packed correctly with low levels of dissolved and head space oxygen. Use of unsalted butter in place of AMF improves the palatability of RM. Use of unsalted butter in place of AMF improves the palatability of RM 118
Deep Frozen Butter The flavour of stored AMF lacks the fresh creamy notes of butter flavour due to the absence of a serum phase. Good quality unsalted butter has a superior flavour and an excellent shelf life of at least 2 years under frozen storage conditions (
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