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Contents vii This page has been reformatted by Knovel to provide easier navigation.. viii Contents This page has been reformatted by Knovel to provide easier navigation.. Contents ix Thi

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Dairy Science and

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Dairy Science and

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Dairy Science and

Technology Handbook

3 Applications Science, Technology, and Engineering

EDITOR

VCH

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3006 4 4 S " Street

Eureka, California 95501

U.S.A.

A NOTC TO THE READER:

This book has been electronically reproduced from digital information stored at John Wiley & Sons, Inc We are pleased that the use of this new technology will enable us

to keep works of enduring scholarly value in print as long

as there is a reasonable demand for them The content of this book is identical to previous printings.

Copyright O 1993 by Wiley-VCH, Inc

Originally published as ISBN 1 -56081 -078-5

No part of this publication may be reproduced, stored in aretrieval system, or transmitted in any form or by any means,electronic, mechanical, photocopying, recording, scanning orotherwise, except as permitted under Sections 107 and 108 ofthe 1976 United States Copyright Act, without either theprior written permission of the Publisher, or authorizationthrough payment of the appropriate per-copy fee to theCopyright Clearance Center, 222 Rosewood Drive, Danvers,

MA 01923, (978) 750-8400, fax (978) 750-4744 Requests tothe Publisher for permission should be addressed to thePermissions Department, John Wiley & Sons, Inc., 605 ThirdAvenue, New York, NY 10158-0012 (212) 850-6011, fax

(212) 850-6008, e-mail PERMREQ@WILEY.COM for

ordering, call 1-800-CALL-WILEY.

Printed in the United States of America

10 9 8 7 6 5 4

Library of Congress Cataloging-in-Publication Data

Dairy science and technology handbook / editor, Y.H Hui.

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Although there are many professional reference books on the science and technology

of processing dairy products, this 3-volume set is unique in its coverage (topics selected, emphasis, and latest development) and its authors (experts with diversified background and experience).

Volume I discusses four important properties and applications of milk and dairy ingredients: chemistry and physics, analyses, sensory evaluation, and protein Each chapter is not a comprehensive treatment of the subject, since more than one reference book has been written on each of the four disciplines Rather, each chapter discusses the basic information in reasonable details that are supplemented by new research data and advances This assures that each chapter contributes new information not available in many reference books already published.

Volume II discusses the manufacture technology for yogurt, ice cream, cheese, and dry and concentrated dairy products The direction of each chapter is carefully designed to provide two types of information Each chapter details the currently accepted procedures of manufacturing the product and then explores new advances

in technology and their potential impact on the processing of such products in the future The fifth chapter in this volume discusses microbiology and associated health hazards for dairy products The goal of this chapter is obvious, since there are so much new information on this topic in the last few years The authors have done an excellent job in reviewing available data on this highly visible field.

Volume III is unique because it covers five topics not commonly found in sional reference books for dairy manufacture: quality assurance, biotechnology, computer application, equipment and supplies, and processing plant designs The length

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profes-of each chapter is limited by the size profes-of the book As a result, I assume full sibility for any missing details since I assigned a fixed length to each chapter.The appendix to Volume I alphabetically lists products and services in the dairyindustry Under each product or service, the appendix describes the names of com-panies that provide those products and services In Volume III, the appendix providesinformation for each company listed in Volume I This includes contact data and thetypes of products and services for each company The appendixes for Volumes I andIII are not repeated in Volume II in order to assure a reasonable price for the books.

respon-As for the expertise of the authors, you are the best judge since most of them areknown among scientists, technologists, and engineers in the dairy discipline.This three-volume set is a reference book and will benefit dairy professionals ingovernment, industry, and academia The information is useful to individuals en-gaged in research, manufacturing, and teaching In general, the texts form an excel-lent background source for professionals who just enter the field For expert dairyprofessionals, these books serve as a subject review as well as a summary of what

is new Any chapter in the three volumes can be used as a supplement material for

a class teaching a specific topic in or an overview of the science and technology ofprocessing diary products

Y.H HuiOctober 1992

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Illi-Norman J Klipfel, Baskin-Robbins International Company, Glendale, CA, U.S.A.

K Rajinder Nath, Kraft General Foods, 801 Waukegan Road, Glenview, IL 60025, U.S.A.

Khem Shahani, Department of Food Science and Technology, Food Industry plex, University of Nebraska, Lincoln, NE 68583-0919, U.S.A.

Com-Joseph Tobias, Agricultural Bioprocessing Laboratory University of Illinois, Urbana,

IL 61801-4726, U.S.A.

P.C Vasavada, Department of Animal and Food Science, University of Wisconsin, River Falls, WI 54022

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Jeffrey K Kondo, Marschall Products, Rhone-Poulenc, Inc., 601 Science Drive, Madison, WI 53711, U.S.A.

Robert L Olsen, Department of Research and Development, Schreiber Foods, Inc., Green Bay, WI 54307-9010, U.S.A.

Jim Shell, Consultant, Ellicott City, MD 21043, U.S.A.

John E Stauffer, Stauffer Technology, 6 Pecksland Road, Greenwich, CT 06831, U.S.A.

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v

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Contents

Preface vii

Contributors (Volume 1.) ix

Contributors (Volume 2.) x

Contributors (Volume 3.) xi

Volume 1 Principles and Properties

1 Chemistry and Physics 1:1

1.1 Introduction 1:2

1.2 Composition 1:5

1.2.1 Proteins 1:9

1.2.2 Lipids 1:18

1.2.3 Lactose 1:26

1.2.4 Minor Components 1:28

1.3 Structure 1:30

1.3.1 Casein Micelles 1:30

1.3.2 Fat Globules 1:41

1.4 Physical Properties 1:49

1.4.1 Density 1:49

1.4.2 Viscosity 1:50

1.4.3 Freezing Point 1:52

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2.2.2 Sampling of Liquid Products 1:87

2.2.3 Sampling of Dry Products 1:88

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Contents vii

2.4 Tests for Milk Quality 1:102 2.4.1 Titratable Acidity 1:102 2.4.2 Added Water 1:105

2.4.3 Sediment 1:106

2.4.4 Antibiotics 1:107 2.4.5 Acid Degree Value 1:112 2.4.6 Iodine and Hypochlorites 1:113

2.4.7 Aflatoxins 1:113

2.4.8 Pesticides 1:114 2.5 Tests for Abnormal Milk 1:115

2.5.1 “Cow-Side” Tests 1:115 2.5.2 Wisconsin Mastitis Test 1:116 2.5.3 Somatic Cell Count 1:117 2.6 Microbiological Methods 1:120 2.6.1 Aerobic Plate Count 1:121 2.6.2 Coliform Count 1:126 2.6.3 Tests for Specific Spoilage Bacteria 1:131

2.6.4 Tests for Specific Pathogenic

2.8 Sensory Analysis 1:146

2.8.1 Sensory vs Chemical and

Microbiological Methods 1:146

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viii Contents

2.9 Summary 1:148 2.10 Future Developments 1:148 2.11 References 1:149

3 Sensory Evaluation of Dairy Products 1:157

3.2.1 Introduction 1:166

3.2.2 Affective Testing 1:168 3.2.3 Discrimination Testing 1:170 3.2.4 Descriptive Analysis 1:171

3.3 Application of Sensory Analysis to Dairy

Products 1:174

3.3.1 The Philosophy of Judging of Dairy

Products 1:175 3.4 Descriptive Sensory Defects of Dairy Products 1:175 3.4.1 Fluid Milk and Cream 1:175

3.4.2 Cottage Cheese 1:185

3.4.3 Butter 1:198 3.4.4 Ice Cream and Related Products 1:214

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Contents ix

4 Functional Properties of Milk Proteins 1:277

4.2 Composition and Principal Physicochemical

Properties of Major Milk Proteins 1:280 4.2.1 Major Protein Components in Milk 1:280

4.2.2 Principal Physicochemical Properties

of Milk Proteins 1:281

4.3 Major Functional Properties of Milk

Proteins 1:282 4.3.1 Water-Protein Interactions 1:282 4.3.2 Protein-Protein Interactions 1:292 4.3.3 Protein-Surface Interactions 1:302

4.4 Some Selected Processing Effects on the

Functional Properties of Major Milk Proteins 1:325 4.4.1 Effects of Heat Treatments 1:325 4.4.2 Membrane Separation Processes 1:329

Volume 2 Product Manufacturing

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x Contents

1.2.2 National Yogurt Association Criteria

for Live and Active Culture Yogurt 2:10

1.2.3 Frozen Yogurt 2:11

1.3 Yogurt Starters 2:13

1.3.1 Taxonomy of Yogurt Bacteria 2:15

1.3.2 Production of Yogurt Starters 2:20

1.4 General Principles of Manufacture 2:22

1.4.1 Ingredients and Equipment 2:22

1.5.1 Yogurt Ingredients and Flavor,

Texture, and Rheological Aspects 2:28

1.5.2 Yogurt Starter and Its Contribution to

Texture and Flavor 2:31

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Contents xi

2 Ice Cream and Frozen Desserts 2:57

2.2.1 Sources of Dairy Products 2:62

2.2.2 Nonconcentrated Milk Products 2:63

2.2.3 Concentrated Milk Products 2:67

2.2.4 Perishable Concentrated Milk

2.2.8 Other Dry Ingredients 2:74

2.2.9 Preserved Fluid Concentrated Milk

Products 2:74

2.2.10 Frozen Concentrated Milk Products 2:75

2.2.11 Substitutes for Dairy Products 2:75

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xii Contents

2.3 Calculations and Mix Standardization 2:92

2.3.1 Calculating MSNF in Skim Milk and

Cream 2:92

2.3.2 Standardization of Ice Cream Mixes –

the Simplest Case 2:93

2.3.3 The Serum Point Method of Mix

2.3.7 Calculating Density and Degrees

Baume (Be) 2:109

2.4 Formulation 2:110

2.4.1 Premium and Superpremium

Products 2:112 2.4.2 The "All-Natural" Designation 2:113

2.4.3 Formulations for a Plain (White) Ice

Cream Mix 2:114

2.4.4 Formulations for a Chocolate Ice

Cream Mix 2:114 2.4.5 Fruit Ice Cream 2:115 2.4.6 Products Containing 2 to 7% Fat 2:116 2.4.7 Products Containing 0 to 2% Fat 2:117 2.4.8 Sherbets and Ices 2:117

2.4.9 Direct-Draw Shakes 2:118 2.4.10 Frozen Yogurt 2:119 2.4.11 Other Frozen Desserts 2:119 2.4.12 Nonstandardized Products 2:120

2.5 Mix Processing 2:121

2.5.1 Pasteurization 2:121

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Contents xiii

2.5.2 Homogenization 2:125 2.5.3 Mix Cooling and Storage 2:127 2.6 Flavoring of Frozen Desserts 2:129 2.6.1 Flavor Character and Intensity 2:132 2.6.2 Quantity of Flavoring 2:133

2.6.3 Propriety Flavorings 2:134

2.6.4 Vanilla Flavor 2:134 2.6.5 Chocolate Flavor 2:135 2.7 Freezing of the Mix 2:136 2.7.1 Amount of Water Frozen 2:138 2.8 Ice Cream Hardening 2:142 2.9 Defects of Ice Cream 2:145 2.9.1 Defects Identified by Sight 2:146 2.9.2 Defective Container 2:146 2.9.3 Product Appearance 2:146

2.9.4 Meltdown Characteristics of Ice

Cream 2:146 2.9.5 Defects of Texture 2:147 2.9.6 Defects in Body 2:147

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xiv Contents

2.11.2 Ice Cream Structure 2:155 2.11.3 Processing and Freezing 2:156 2.12 References 2:157

3 Cheese 2:161

3.1.1 Classification 2:164 3.1.2 Cheese Production and Composition 2:165 3.2 Heat Treatment of Milk for Cheesemaking 2:169 3.3 Cheese Starter Cultures 2:173 3.3.1 Types of Cultures 2:174

3.6 Culture Production and Bulk Starter

Propagation 2:191

3.6.1 History 2:191

3.6.2 Concentrated Cultures 2:191 3.6.3 Bulk Starter Propagation 2:192

3.6.4 pH-Controlled Propagation of

Cultures 2:194

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Contents xv

3.6.5 General Comments 2:196 3.6.6 Helpful Points to Phage-Free Starters 2:196 3.7 Manufacture of Cheese 2:197 3.7.1 Cheddar Cheese 2:200

3.7.2 Stirred Curd or Granular Cheddar

Cheese 2:200

3.7.3 Colby Cheese 2:200

3.7.4 Swiss Cheese 2:201

3.7.5 Parmesan Cheese 2:201 3.7.6 Mozzarella and Provolone Cheese 2:205 3.7.7 Brick Cheese 2:205 3.7.8 Mold-Ripened Cheese 2:206 3.8 Cheese from Ultrafiltered Retentate 2:207 3.9 Salting of Cheese 2:210 3.10 Cheese Ripening and Flavor Development 2:210 3.10.1 Proteolysis of Caseins 2:211 3.10.2 Proteolysis in Cheese 2:212 3.10.3 Amino Acid Transformations 2:213 3.10.4 Flavor Development 2:213

3.11 Microbiological and Biochemical Changes in

Cheddar Cheese 2:215 3.11.1 Fate of Lactose 2:215 3.11.2 Fate of Casein 2:216 3.11.3 Microbiological Changes 2:217 3.11.4 Fate of Fat 2:218 3.11.5 Flavor of Cheddar Cheese 2:219

Swiss Cheese 2:219 3.12.1 Fate of Lactose 2:220

3.12.2 CO2 Production 2:220

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xvi Contents

3.12.3 Eye Formation 2:221 3.12.4 Fate of Proteins 2:222 3.12.5 Flavor of Swiss Cheese 2:222

Gouda Cheese 2:222 3.13.1 Fate of Lactose 2:223 3.13.2 Fate of Proteins 2:223 3.13.3 Fate of Fat 2:224 3.13.4 Microbiological Changes 2:224 3.13.5 Flavor of Gouda Cheese 2:224

Mold-Ripened Cheese 2:224 3.14.1 Blue Cheese 2:224 3.14.2 Camembert and Brie Cheese 2:226

Bacteria Surface-Ripened Cheese 2:227 3.15.1 Brick Cheese 2:227

Mozzarella Cheese 2:227

Parmesan and Romano Cheese 2:228 3.18 Accelerated Cheese Ripening 2:229 3.19 Processed Cheese Products 2:229

3.19.1 Advantages of Process Cheeses over

Natural Cheese 2:231 3.19.2 Processing 2:231 3.19.3 Emulsifiers 2:231 3.19.4 Heat Treatment 2:234 3.19.5 pH and Microbiological Stability 2:234 3.20 References 2:235

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Contents xvii

4 Concentrated and Dried Dairy Products 2:257

4.1 History and Definitions 2:258 4.2 Unsweetened Condensed Milk 2:259

4.2.1 Processing Chart and Preparing Raw

Milk 2:259 4.2.2 Preheating and Evaporation 2:259

4.2.3 Homogenization and Second

Standardization 2:265 4.2.4 Packaging, Sterilization, and Storage 2:266 4.3 Sweetened Condensed Milk 2:267

4.3.1 Processing Chart and Raw Milk to

First Standardization 2:267

4.3.2 Heat Treatment, Evaporation, Sugar

Addition, and Second

Standardization 2:267 4.3.3 Cooling with Crystallization 2:270 4.4 Other Concentrated Dairy Products 2:270 4.5 Dried Dairy Products 2:271 4.5.1 Milk Powder 2:271 4.5.2 Instant Milk Powder 2:278

4.5.3 Infant Formulas 2:282

4.5.4 Other Products 2:285 4.6 Dried Dairy Ingredients 2:286 4.6.1 Whey Powder 2:286 4.6.2 Whey Protein Concentrates 2:289 4.6.3 Casein Products 2:290

4.6.4 Lactose 2:296

4.7 References 2:299

5 Dairy Microbiology and Safety 2:301

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xviii Contents

5.2 General Dairy Microbiology 2:304 5.2.1 Morphological Features 2:305 5.2.2 Microorganisms Associated with Milk 2:305

5.3 Growth of Dairy Microbes in Milk and Dairy

Products 2:321

5.3.1 Relative Growth Rates of

Psychrotrophs 2:321 5.3.2 Sources of Psychrotrophs in Milk 2:323

5.3.3 Significance of the Presence and

Growth of Psychrotrophs 2:324

5.4 Inhibition and Control of Microorganisms in Milk

and Dairy Products 2:326 5.4.1 Natural Antimicrobial Systems 2:326

5.4.2 Lactoperoxidase 2:327

5.4.3 Lactoferrin 2:330

5.4.4 Lysozyme 2:331

5.4.5 Xanthine Oxidase 2:331 5.4.6 Lactic Acid Bacteria and Bacteriocins 2:332

5.5.5 Factors Affecting the Incidence of

Mastitis 2:341 5.5.6 Detection and Diagnosis 2:341

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Contents xix

5.6 Pathogenic Bacteria in Milk and Dairy

Products 2:342

5.6.1 Listeria Monocytogene 2:344 5.6.2 Yersinia Enterocolitica 2:346 5.6.3 Campylobacter Jejuni 2:346 5.6.4 Escherichia Coli 2:347 5.6.5 Escherichia Coli 0157:H7 2:347 5.6.6 Bacillus Cereus 2:348

5.6.7 Economic Significance of Pathogens 2:348 5.6.8 Mycotoxins and Amines 2:349 5.7 Mycotoxins in Milk and Dairy Products 2:350

5.7.1 Presence of Mycotoxins in Milk and

Dairy Products 2:351

5.7.2 Fate of Aflatoxin M1 in Dairy Product

Manufacture and Storage 2:355 5.7.3 Elimination of Mycotoxins 2:356 5.7.4 Regulation of Mycotoxins in Foods 2:358 5.8 Microbiology of Starter Cultures 2:359

5.8.1 Terminology 2:359 5.8.2 Function of Starter Cultures 2:362 5.8.4 Inhibition of Starter Cultures 2:365

5.8.5 Genetic Engineering for Improving

Starter Cultures 2:366

5.9 Methods for Microbiological Analysis of Milk and

Dairy Products 2:367 5.9.1 Conventional Methods 2:367

5.9.2 Rapid Methods and Automation in

Dairy Microbiology 2:370

5.9.3 Microbiological Tests for Assessing

Sanitation and Air Quality in Dairy

Plant 2:377

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xx Contents

5.9.4 Shelf-Life Tests 2:378 5.10 Microbiology of Milk and Dairy Products 2:378 5.10.1 Pasteurized Milk and Cream 2:379 5.10.2 Dried Milk Powder 2:381 5.10.3 Evaporated Milk 2:381 5.10.4 Cottage Cheese 2:382 5.10.5 Mold-Ripened Cheeses 2:382 5.10.6 Hard Cheese 2:383 5.10.7 Yogurt and Cultured Milks 2:384 5.10.8 Butter 2:385

5.10.9 Ice Cream and Frozen Dairy

Desserts 2:385

5.11 Microbiological Considerations of New

Processing Technologies 2:386 5.11.1 Ultrafiltration and Reverse Osmosis 2:386

5.11.2 Ultrahigh Temperature Sterilization of

Milk and Dairy Products 2:389 5.11.3 Low-Dose Irradiation of Milk 2:391

5.11.4 Microwave Processing of Milk and

Dairy Products 2:392

5.11.5 Use of Carbon Dioxide and

Supercritical Carbon Dioxide for

Reduction of Microbial Populations 2:392

5.12 Assuring Microbiological Quality and Safety of

Milk and Milk Products: HACCP Approach 2:393 5.12.1 HACCP Principle 2:394 5.12.2 Elements of the HACCP System 2:394 5.13 Conclusion 2:395 5.14 References 2:395

Appendix: Food and Drug Administration,

Part 135 – Frozen Desserts, April 1, 1992 2:427

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Contents xxi

Volume 3 Applications Science, Technology,

1.1.3 Organization and Management 3:4

1.2 Hazard Analysis and Critical Control Points 3:4

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1.5.4 Imitation and Substitute Foods 3:57

1.5.5 Open Date Labeling 3:59

1.5.6 Kosher Certification 3:59

1.6 Packaging 3:60 1.6.1 Functional Needs 3:60

1.8.1 Importance of Process Controls 3:67

1.8.2 Need to Avoid Recontamination 3:68

1.9 Future Developments 3:68

1.9.1 The Promise of Biotechnology 3:68

1.9.2 Internationalization of the Dairy

2.2 Applications and Successes 3:78

2.2.1 Low-Fat Dairy Products 3:79

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Contents xxiii

2.2.2 Bacteriocins as Food Preservatives 3:80

2.2.3 Bacteriophage Resistance 3:83

2.2.4 Accelerated Cheese Maturation 3:84

2.3 Yesterday and Tomorrow: Tools for

Biotechnology 3:85

2.3.1 Conjugation and Cell Fusion 3:85

2.3.2 Transformation and Gene Delivery

3.2.1 Knowledge Representation 3:109

3.2.2 Searching and Inference

Strategies 3:113

3.2.3 Uncertainty 3:116 3.3 Building Expert Systems 3:117

3.3.1 Feasibility 3:117 3.3.2 Knowledge Acquisition 3:118

3.3.3 Tool Selection 3:120 3.4 Expert Systems and Process Control 3:121 3.4.1 Preexpert System Developments 3:121

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xxiv Contents

3.4.2 Expert System Applications 3:123

3.4.3 Knowledge Representation in Process

Control 3:126 3.4.4 Commercial Examples 3:127 3.5 Business and Manufacturing Operations 3:128 3.5.1 Physical Goods Management 3:128

3.5.2 Time Management: Planning and

Scheduling 3:130 3.5.3 Computer Integrated Manufacturing 3:132 3.6 Quality Management Applications 3:138 3.6.1 Quality Control Programs 3:138

3.6.2 Laboratory Systems 3:140 3.6.3 Quality Defect Analysis 3:142

3.7 Strategic Operations 3:143

3.7.1 Simulation 3:143 3.7.2 Research and Development 3:146

3.7.3 Training 3:149 3.8 Future Trends 3:150

4 Dairy Equipment and Supplies 3:155

4.1 Dairy Equipment and Supplies 3:156 4.2 Equipment Common to all Dairies 3:160 4.2.1 Tanks 3:160 4.2.2 Heat Exchangers 3:171

4.2.3 Pumps 3:179 4.2.4 Pipe, Valves, and Fittings 3:195

4.2.5 Centrifuges 3:203

4.2.6 Homogenizers 3:213 4.2.7 Cleaning Dairy Processing Systems 3:217

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4.3.5 Cottage Cheese and Other Cultured

Products 3:277 4.3.6 High-Temperature Processes 3:281

4.3.7 Membrane Separation 3:288

5 Engineering: Plant Design, Processing, and

Packaging 3:295

5.1 Introduction 3:296 5.2 Plant Construction and Arrangement 3:296 5.2.1 Construction Considerations 3:297

5.2.2 Plant Layout 3:303 5.3 Processing Engineering 3:307 5.3.1 Dimensions and Units 3:307 5.3.2 Fluid Flow Characteristics 3:309

5.3.3 Heat Transfer 3:310 5.3.4 Principles of Homogenization 3:316 5.3.5 Material Handling 3:318 5.3.6 Preventative Maintenance Program 3:319 5.4 Product Packaging 3:320 5.4.1 Fluid Milk Packaging 3:320

5.4.2 Aseptic Packaging 3:321

5.5 Regulations 3:326 5.5.1 Plant and Equipment 3:326

5.5.2 Product 3:327

5.6 Summary 3:327

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xxvi Contents

5.7 Future Developments 3:327

Appendix: Company Listing 3:331

A & B Process Systems Corp to FrigoTech 3:331 Fristam Pumps, Inc to Quest International 3:356

Quest International Flavors, Inc to Zurn

Industries, Inc 3:385

Index 3:409

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Oxidation, 24 Lactose, 26

1.2.3.1

1.2.3.2

Biochemical Properties, 26 Physicochemical Properties, 26 Minor Components, 28

1.2.4.1

1.2.4.2

Vitamins, 28 Minerals, 29 Structure, 30

Destabilization, 48 Physical Properties, 49

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1.4.5 Surface Tension, 561.4.6 Acid-Base Equilibria, 57L4.7 Heat Capacity and Thermal Conductivity, 601.4.8 Optical Properties, 60

Today, the majority of milk for human consumption is secreted by the

domesti-cated cow, genus Bos, although milk from goats, buffaloes, and sheep, in addition

to human milk, is also consumed in significant quantity

Milk is defined by the United States Code of Federal Regulations as "the lacteal

secretion, practically free from colostrum, obtained by the complete milking of one

or more healthy cows, which contains not less than 8.25% of milk solids-not-fat andnot less than 3.25% of milkfat".3 Reviews of the composition of goat's milk,4-5

ewe's milk,6 buffalo's milk,7 camel's milk,8 human milk,9 and the milk of otherspecies1011 are available in the literature This chapter is limited to a discussion ofcow's milk

Milk is synthesized in the mammary gland An average cow in North America

produces 5400 kg of milk in a 305-day lactation period

The components of the mammary gland at various magnifications are shown in

Figure 1.1 The alveolus is the milk-producing unit within the gland In the alveolus,

a single layer of epithelial secretory cells surrounds a central storage area, the lumen,which is connected to a duct system These secretory cells are, in turn, surrounded

by a layer of myoepithelial cells and blood capillaries The raw materials for milkproduction are transported via the bloodstream to the secretory cell Within the cell,components are synthesized mainly by the endoplasmic reticulum and its attachedribosomes, which are supplied with energy from the mitochondria and then passedalong to the Golgi apparatus, which is responsible for their eventual movement out

of the cell Vesicles containing many of the aqueous nonfat components are released

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Figure 1.1 Bovine mammary gland at various magnifications (Reprinted from ref 12,

p 794, by courtesy of Marcel Dekker.)

by the Golgi apparatus, pass through the cytoplasm and the apical plasma membrane, and are deposited in the lumen of the alveolus Lipid droplets, synthesized by the endoplasmic reticulum, also pass through the cytoplasm and the apical plasma membrane and are deposited in the lumen.

As is discussed further in Section 1.3.2.1, it is believed that the milk fat globule membrane (FGM) is comprised of the apical plasma membrane of the secretory cell, which continually envelops lipid droplets as they pass into the lumen The apical cell membrane is continually being replaced from endomembrane material synthesized in the endoplasmic reticulum and transported from the Golgi in the form of vesicles containing aqueous nonfat components The vesicle membrane fuses with the apical cell membrane as the contents of the vesicle are released Milk components stored in the lumen of the alveolus are released into the duct system as a result of hormonal stimulation The duct systems within the mammary gland, a complex net- work, flow into the teat cistern from which they are milked Further details of milk biosynthesis and mammary physiology are beyond the scope of this chapter and have been reviewed extensively elsewhere 13 " 15

Milk is estimated to contain more than 100,000 molecular species However, the average gross composition of milk can be simplified to 4.1% fat, 3.6% protein (75% casein protein and 25% whey protein), 4.9% lactose, and 0.7% ash, with the balance

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ALVEOLUS I 1 WUTUN.

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MCtKMLU

^ytfrtl NUCLEUS

LMD OtKWLET

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consisting of water 16 (Details of the composition of milk are covered in Section 1.2.) Variation in milk composition can be caused by inherited characteristics (breed), physiological characteristics (stage of lactation, pregnancy, age, nutritional balance, season, and udder health), and milking procedure (within milkings and between milkings) 3

Although milk is a fluid food, it has considerable structural organization scribed in further detail in Section 1.3) Milk can be described as:

(de-• an emulsion of milkfat globules which contain the milk lipids, fat soluble vitamins, and the components of the FGM;

• a colloidal suspension of casein micelles (which contain casein proteins, calcium, phosphate, citrate and water), globular proteins, and lipoprotein particles; and

• a solution of lactose, soluble proteins, minerals, vitamins, acids, enzymes, and other components.

Milk plasma is defined as milk minus the milkfat globules, which is close in composition to separated or skim milk, although separation is never complete Milk serum is defined as milk plasma minus casein micelles, which is close to the com-

position of whey, except for the presence of some proteolytic products from mosin 16 The casein micelles and the milkfat globules are the principal structure- forming constituents that form the basic structural elements of most dairy products 17 ' 18

chy-Dairy foods make a significant contribution to the total nutrient intake of the North American population, supplying, for example, one-fourth or more of individuals' protein, calcium, phosphorus, and riboflavin requirements Dairy foods are an excellent source of vitamin B 12 as well as an adequate source of vitamin A, thiamine, niacin, and magnesium Vitamin D is added to most liquid dairy products; vitamin

A is added to most low-fat fluid products Only iron, vitamin C, and folacin are present in somewhat deficient amounts 1219 The nutrient composition of whole milk

is listed in Table 1.1.

From a nutritional viewpoint, milk has been described as nature's most nearly perfect food, owing mainly to its biological role as the only source of nutrition for the infant mammal Milk proteins are slightly deficient in methionine and cysteine, the sulfur amino acids Milk lipids are slightly high in saturated fats and cholesterol and thus may have an impact on cardiovascular disease The nutritional significance

of milk proteins and lipids has recently been reviewed 19 " 21

A small but significant part of the population, particularly among African and Asian peoples, produce less than average intestinal /3-galactosidase This leads to

lactose intolerance, or malabsorption, which causes diarrhea, abdominal cramps, and

intestinal gas if dairy products are consumed Lactose intolerance has recently been reviewed 22

The purpose of this chapter is to serve as a reference for many of the processes and technologies described in other chapters and volumes of this set In this chapter,

we review the basics of milk composition and milk structure as they affect the utilization of milk in industrial practice and provide a comprehensive bibliography for further reading This chapter is not designed to be a comprehensive review of

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From ref 12, p 822 Reprinted courtesy of Marcel Dekker.

a Average Recommended Dietary Allowances for all males and females above

age 11.

b Retinol Equivalents: 1 u,g retinol or 6 u,g ^-carotene.

c Niacin Equivalents: 1 mg niacin or 60 mg dietary tryptophan Only 10% of the

NE in milk corresponds to niacin.

the tremendously growing fields of dairy chemistry and physics Several very recentexcellent reviews and monographs of aspects of dairy chemistry are available andrecommended for those seeking more detail.16^23"28

1.2 Composition

The gross composition of milk is defined as the fat, protein, lactose, ash, and total

solids content Gross composition for large numbers of samples is determined byindirect methods calibrated against chemical methods.29 The most common chemicalmethods for milkfat determination are gravimetric (solvent extraction by the Mo-jonnier or Roese-Gottlieb procedure) or volumetric (the Babcock or Gerber pro-cedure).30 For raw milks, the Babcock procedure produces slightly higher results(0.021% fat) than does the Mojonnier procedure and has significantly lower inter-and intralaboratory repeatability.30

Total protein is generally determined as Kjeldahl nitrogen multiplied by the factor6.38 This factor is still in common use, although a more representative one is 6.34.31

It is also common to report protein as crude protein (total N X 6.38), which estimates true protein content (protein N X 6.38) by about 4 to 8% The most

over-Table 1.1 NUTRIENT COMPOSITION OF WHOLE MILK

0.94 mg 0.038 mg 0.162 mg 0.85 NE C

%RDA a in 250 ml 17.2 8.9 4.2 8.2 30.0 13.9 5.4 3.2 30.7 32.0 25.0 10.2 0.9 6.5

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common method of lactose analysis is polarimetric determination of lactose in aclarified milk extract.32 Lactose is frequently reported (especially in the older liter-ature) as lactose monohydrate, which overestimates the amount of lactose by 5.26%.3

Total solids of milk are most frequently determined by an oven method involvinginitial drying on a steam bath followed by further drying in a forced air oven at 98

to 1000C,32 although a longer drying time in the oven without initial boiling off onthe steam bath may be more accurate.33 Ash content is normally determined by dryashing at about 5500C.32 Ash content is not equivalent to the total content of salts.Milk salts are discussed in Section 2.4

In the determination for payment purposes of the gross composition of producermilk, the largest source of error is bulk tank sampling error Standard deviationsassociated with bulk tank sampling error of 0.01% for milk protein and 0.093% formilk fat have been reported.34 Corresponding standard deviations associated withlaboratory analyses were 0.01% for both fat and protein Milk analysis is discussed

in detail in Chapter 3

Many factors affect the gross composition of milk The factors most significant

to the processing of milk and milk products are breed, feed, season, region, and herdhealth.35 In the short term, the only factors available to the farmer to alter milkcomposition are selection of breed and feed.36 The gross composition of milk ofvarious breeds is listed in Table 1.2 Note that breeds producing high-fat milk alsoproduce milk with lower ratios of protein to fat This is certainly significant tomultiple component pricing37"42 and suggests that genetic selection can achieverelatively rapid increases in the ratio of milk protein to fat, provided the change isachieved by lowering fat content.43 A large negative correlation between fat contentand protein/fat ratio but a small correlation between protein content and protein/fatratio have also been reported.44 Heritabilities (based on milk records of 32,000 first-lactation cows) of percent composition of milk fat, protein, and protein/fat ratio were0.61, 0.59, and 0.58.44

The effects of feed on milk composition have been reviewed.45'46 The most portant dietary factors are the amount and type of roughage, the forage/concentrateratio, and the carbohydrate composition of the concentrates and lipids.46"49 Feedingfrequency does not affect milk composition, provided the total feed intake is con-stant.50 The greatest effects of feeding are on the concentration of milkfat, withsmaller changes in protein concentration

im-Table 1.2 GROSS COMPOSITION OF MILK OF VARIOUS BREEDS, g/100 g3

Protein 3.29 3.48 3.75 3.98 3.64

Lactose 4.68 4.60 4.71 4.83 4.94

Ash 0.72 0.72 0.76 0.77 0.74

Total Solids 12.16 12.77 14.04 14.42 13.08

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1988 Figure 1.2 Seasonal variation of protein and fat content of Ontario milk Primary standard

methods were Mojonnier for fat and semi-micro-Kjeldahl for protein Protein is total nitrogen

X 6.38 Data represent means of 10,000 herds tested four times each month at the OntarioCentral Milk Testing Laboratory

In the Northern Hemisphere, maximum annual fat contents occur during the ter months, usually peaking in November or December; minimum fat contents occur

win-in August as shown win-in Figure 1.2.51 Seasonal trends in protein contents follow asimilar trend, with some significant differences: the seasonal variation is not as great,the minimum occurs in July, and the maximum occurs in October (Fig 1.2).51 Thesedifferences cause seasonal variation of the protein/fat ratio of milk, which is ofsignificant economic consequence, especially to cheese manufacturing.51 Small sea-sonal variations in lactose content have also been reported.52 Although there is someevidence that climatic conditions affect milk composition, the principal effect ofclimatic factors is on milk production.53 It is likely that the observed seasonal effects

on milk composition are primarily due to variations in feed and stage of lactation.3'54

Variations in feed and stage of lactation probably also account for most regionalvariations in milk composition Regional variations in the Ontario, Canada, milkfatcomposition for the years 1978 to 1988 are shown in Figure 1.3 These data andearlier unpublished data (Ontario Central Milk Testing Laboratory, Guelph) goingback to 1971 show a continual increase in average fat content of Ontario milk overtime, with little or no increase in protein content The result is a significant decrease

in the protein/fat ratio of Ontario milk There has also been a gradual increase inaverage lactose content of Ontario producer milks, from 4.80% lactose monohydrate(w/v) in 1970 to 5.2% (w/v) in 1988

With respect to herd health, yield and compositional effects of greatest economic

Protein Fat

Jan Feb Mar Apr May June July Aug.Sept Oct Nov Dec.

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Y e a r

Figure 1 3 Regional and annual variation of fat content of Ontario milk Primary standard method was Mojonnier Data represent annual means within each region Herds were tested four times per month.

significance are due to mastitis 55 Average yield losses due to udder infection may exceed 1 kg of milk per cow per day 56 Somatic cell counts in excess of 300,000 indicate subclinical mastitis 57 In 1989, average somatic cell counts for all Ontario producer milks were 350,000/mL (Ontario Central Milk Testing Laboratory, Guelph, Ontario, Canada) In the United Kingdom, the national average was 390,000/

mL 58 Elevated somatic cell counts are correlated with reduced lactose content 52 and

a corresponding increase in mineral content to maintain osmotic equilibrium Casein content is reduced, but total protein content increases with increasing somatic cell counts due to increased whey protein content 59 Modest levels of somatic cells may affect cheese yield 60 due to increased proteolysis, 61 but effects of somatic cell counts

<2,000,000 m l " 1 on cheese texture and flavor are probably more significant than yield effects 58

Production aids may also affect milk composition Supplementation of dairy tions with the antibiotic Flavomycin increases feed conversion efficiency, milk production, and the percent composition of both fat and protein 62 Like other factors affecting milk composition, the effect on fat content is greater than on protein content Numerous authors have reported minimal or no effects of bovine somatotropin (BST) on gross composition of milk "

WESTERN SOUTHERN NORTHERN EASTERN CENTRAL ONTARIO

1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988

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1.2.1 Proteins

The nitrogen content of milk is distributed among caseins, whey proteins, and protein nitrogen (NPN), excepting some minor proteins that are associated with theFGM (Section 1.2.2)

non-Nitrogen distribution is normally determined by the classical Rowland ation,67 which separates caseins from whey nitrogen by precipitation at pH 4.6 andseparates total proteins from whey NPN by precipitation with sodium acetate andacetic acid at pH 5.0 Based on this procedure, average milk nitrogen distribution isabout 76% casein, 18% whey protein, and 6% NPN This operational classification

fraction-of proteins is still used for both research and process control However, a cation system of milk proteins based on their amino acid sequences (Table 1.3) hasbeen developed by the American Dairy Science Association's (ADSA) Committee

classifi-on Milk Protein Nomenclature, Classificaticlassifi-on and Methodology.68 The amino aciddistributions of the principal milk proteins are summarized in Table 1.4

1.2.1.1 Caseins

The casein content of milk is about 26 g/kg, representing about 80% of milk protein.The principal casein fractions are asl-casein (10 g/kg), as2-casein (2.6 g/kg),/3-casein (9.3 g/kg), y-casein (0.8 g/kg), and /c-casein (3.3 g/kg).16 These fractionsare all included in the pH 4.6 precipitate from milk, but y-caseins are now reclassified

as carboxyl terminal fragments of /3-casein The corresponding N-terminal ments,—formerly classified as proteose-peptones70—are also classified as caseinsubfractions.68 These fractions result from cleavage of ^-casein by the milk protease,plasmin The carboxyl terminal fragments (y-caseins) remain associated with thecasein micelle and are recovered by rennet coagulation and by pH 4.6 precipitation.The N-terminal fragments are hydrophilic and appear as heat-stable fractions in bothcheese whey and the pH 4.6 supernatant Carboxyl terminal fragments correspond

frag-to /3-casein subfractions 2, 3, and 4; and the N-terminal fractions correspond frag-to/3-casein subfractions 5 to 9, as listed in Table 1.3 The N-terminal fractions do notcontain aromatic amino acids (Table 1.4) and, therefore, show no absorbency at

280 nm

The nomenclature used for the caseins consists of a Greek letter with or without

a numerical subscript to identify the family of proteins; and an uppercase Latin letter

to indicate the genetic variant Post-translational modifications such as tion or formation of subfractions are indicated after the genetic variant.68 For ex-ample, the notation /3-casein B-5P (fl-105) indicates that the protein belongs to the/3-family of caseins, is the B genetic variant, contains five phosphate groups, andrepresents an N-terminal fragment of /3-casein B from amino acid residues 1 to 105.69

phosphoryla-In most breeds of dairy cattle, asl-casein is >90% variant B Exceptions areGuernsey and Jersey cattle, which produce about 75% variant B and 25% variant

C.71 The A variant of /3-casein occurs with nearly 100% frequency in most dairybreeds, excepting Jersey and Brown Swiss, which produce significant levels of/3-casein B Significant effects of milk protein genetic variants on heat stability,72

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