High Temperature Processing of Milk and Milk Products

This book covers many aspects of thermal processing of milk and milk products with particular focus on UHT processing. It commences with an overview of the major thermal processing technologies: thermisation, pasteurisation, extended-shelf-life (ESL), UHT and in-container sterilisation.  It discusses the principles of the technologies, the processing and packaging equipment used, processing issues such as temperature-time profiles, heat stability, fouling and cleaning, and the quality and safety aspects of the products produced. It provides a balance of the engineering aspects of the processes and the chemical, microbiological and sensory aspects of the products.  The changes that occur in products during processing and storage, and the related defects which can arise, are central to the book.  The discussions of these changes will be an aid to industry personnel in identifying the causes of quality defects in these products and devising measures which can be taken to eliminate or minimise the defects.

About the Authors xv

Preface xvii

List of Abbreviations xxi

1 History and Scope of the Book 1

1.1 Setting the Scene 1

1.2 Scope of the Book 7

1.3 Reasons for Heating Foods 7

1.4 Brief History of Sterilisation Processes 8

References 12

2 Heat Treatments of Milk – Thermisation and Pasteurisation 15

2.1 Introduction 15

2.2 Thermisation 16

2.3 Pasteurisation 17

2.3.1 Introduction 17

2.3.2 Historical Background 18

2.3.3 Pasteurisation Equipment 21

2.3.4 Process Characterisation 24

2.3.5 Processing Conditions 27

2.3.6 Changes During Pasteurisation 28

2.3.7 Changes During Storage 32

2.3.8 Pasteurisation of Other Milk–Based Products 34

References 36

3 Heat Treatments of Milk – ESL, UHT and in–Container Sterilisation 41

3.1 Introduction 41

3.2 Some Important Definitions 41

3.2.1 Q10 41

3.2.2 Bacterial Indices, B* and F0 42

3.2.3 Chemical Index, C* 43

3.3 Extended Shelf–Life (ESL) Milk Processing 44

3.3.1 ESL Milk by Thermal Treatment 44

3.3.2 ESL Milk by Microfiltration Plus HTST Heat Treatment 49

3.3.3 ESL Milk by Thermal Treatment Plus Bactofugation 50

3.3.4 ESL Milk by Thermal Treatment Plus an Antibacterial Agent 50

3.3.5 ESL Milk by Thermal Treatment Plus a Non–Thermal Technology Treatment 50

3.3.6 ESL Milk by Multiple Thermal Treatments 51

3.4 Sterilisation 52

3.4.1 Introduction 52

3.4.2 UHT Processing 54

3.4.3 In–Container Sterilisation 58

References 61

4 Microbiological Aspects 65

4.1 Introduction 65

4.2 Bacteria in Raw Milk 65

4.2.1 Non–Spore–Forming Psychrotrophic Bacteria and their Heat–Resistant Enzymes 68

4.2.2 Spore–Forming Bacteria 69

4.3 Heat Inactivation of Bacteria 78

4.4 Microflora in Processed Milks 80

4.4.1 Pasteurised Milk 80

4.4.2 ESL Milk 83

4.4.3 UHT Milk 85

4.4.4 In–Container Sterilised Milk 90

4.5 Sterilisation of Equipment and Packaging to Prevent Microbial Contamination of UHT Products 90

References 91

5 UHT Processing and Equipment 103

5.1 The UHT Process 103

5.2 Heating 104

5.2.1 Steam–/Hot–WaterBased Heating Systems 104

5.2.2 Electrically Based Heating Systems 146

5.3 Homogenisation 150

5.4 Deaeration 154

5.5 Aseptic Packaging 155

5.5.1 Types of Packaging 155

5.5.2 Sterilisation of Packaging 158

5.5.3 Establishing and Maintaining a Sterile Environment 158

5.5.4 Aseptic Package Integrity 159

5.5.5 Validation of Aseptic Packaging Operations 159

5.6 Plant Cleaning and Sanitisation 161

5.6.1 Introduction 161

5.6.2 Rinsing 161

5.6.3 Water−Product Changeover 162

5.6.4 Cleaning 162

5.6.5 Methods of Measuring Cleaning Effectiveness 164

5.6.6 Kinetics of Cleaning 166

5.6.7 Disinfecting and Sterilising 167

6 Changes During Heat Treatment of Milk 177

6.1 Chemical 177

6.1.1 pH and Ionic Calcium 177

6.1.2 Mineral Salts 182

6.1.3 Proteins 184

6.1.4 Lactose 195

6.1.5 Vitamins 200

6.1.6 Flavour 201

6.1.7 Chemical Heat Indices 208

6.2 Physical Changes 212

6.2.1 Heat Stability 212

6.2.2 Fouling 222

6.3 Kinetics and Computer Modelling 240

References 242

7 Changes During Storage of UHT Milk 261

7.1 Chemical Changes 263

7.1.1 pH 263

7.1.2 Dissolved Oxygen Content 264

7.1.3 Flavour 266

7.1.4 Proteolysis 273

7.1.5 Protein Cross–Linking 275

7.1.6 Deamidation 276

7.1.7 Lactosylation 277

7.1.8 Formation of Monosaccharides 278

7.1.9 Reactivation of Alkaline Phosphatase 278

7.1.10 Vitamins 279

7.1.11 Light–Induced Changes 280

7.2 Physical 282

7.2.1 Sedimentation 282

7.2.2 Age Gelation 283

7.2.3 Thinning 289

7.2.4 Fat separation 290

7.2.5 Maillard Browning 292

7.3 Changes to Some UHT Products Other than Single–Strength Fresh White Cow’s Milk 299

7.4 Accelerated Storage Testing 300

7.5 Chemical and Physical Changes During Storage Trials of UHT Milk 301

7.5.1 Storage Trial 1 (DIAL, 2014) 301

7.5.2 Storage Trial 2 (UCC, 2015) 304

7.5.3 Other Storage Trials 307

References 307

8 Quality Control and Assurance 321

8.1 Introduction 321

8.2 Safety and Quality Considerations 321

8.2.1 Safety Issues 321

8.2.2 Quality Issues 323

8.3 Heat Treatment Regulations 323

8.4 Quality Assurance/Commercial Sterility: The Current Approach 327

8.4.1 Introduction 327

8.4.2 Commercially Sterile Products 329

8.4.3 Sampling Theories and Probabilities 329

8.4.4 Characteristic Curves 330

8.4.5 Sampling for Process Verification 333

8.4.6 Sampling Plans for Refrigerated Products 334

8.5 Important Quality Considerations for UHT Processing 335

8.5.1 Raw Material Quality 336

8.5.2 Processing Aspects 338

8.5.3 Other Factors 339

8.6 Some Practical Aspects 340

8.7 Microbiological Examination of Heat–Treated Foods 343

8.7.1 Introduction 343

8.7.2 Sample Pre–Incubation 344

8.7.3 Testing for Microbial Activity 345

8.7.4 Plate Counting and Microscopy 345

8.7.5 Rapid Instrumental Methods for Total Bacteria 347

8.7.6 Analyses of Specific Bacteria 350

8.7.7 Indirect Methods Based on the Metabolic Activity of Microorganisms 354

8.8 Non–Invasive Methods 354

8.9 The Milk Microbiome 355

8.10 Use of Modelling Procedures 356

8.11 UHT Product Alerts and Recalls 357

8.12 Time−Temperature Indicators 358

8.13 Conclusions 358

References 359

9 Other Shelf–Stable Products 365

9.1 Introduction 365

9.2 Reconstituted and Recombined Milk 365

9.3 Concentrated Milk Products 367

9.3.1 UHT Evaporated Milk 371

9.3.2 Concentration by Membrane Filtration 372

9.4 Lactose–Reduced Milk (LRM) 373

9.5 Mineral–Fortified Milk 374

9.5.1 Calcium 374

9.5.2 Other Minerals 376

9.6 Flavoured Milk 377

9.6.1 Fruit–Flavoured Milk 378

9.6.2 Chocolate and Other Confectionery Milk 379

9.7 High–Protein Milk Drinks 383

9.8 Breakfast Milk Products 384

9.9 Starch–Based and Thickened Desserts 385

9.10 UHT Cream 386

9.11 UHT Ice Cream Mix 387

9.12 Infant Formulae 390

9.13 UF Permeate 391

9.14 Whey Proteins 392

9.15 Yogurt and Cheese 392

9.15.1 Yogurt 392

9.15.2 Cheese made from UHT Milk 395

9.16 Milk from Species other than Cows 396

9.16.1 Buffalo’s Milk 397

9.16.2 Goat’s Milk 398

9.16.3 Camel’s Milk 400

9.17 Non–Dairy Products 401

9.17.1 Soy Milk 404

9.17.2 Peanut Milk 408

9.17.3 Coconut Milk 410

9.17.4 Almond Milk 411

9.18 Other Non–Dairy Beverages 411

9.18.1 Tea and Coffee 411

9.18.2 Fruit Juices, Purees and Drinks 412

References 415

10 Non–Thermal Technologies 427

10.1 Introduction 427

10.2 Microfiltration 427

10.3 High]Pressure Processing 433

10.3.1 Effect on Bacteria and Potential for Producing ESL and Shelf–Stable Milk 433

10.3.2 Effect on Milk Components 434

10.4 Pulsed Electric Field (PEF) Technology 435

10.4.1 Effect on Bacteria and Potential for Producing ESL and Shelf–Stable Milk 436

10.4.2 Effect on Milk Components 437

10.5 High–Pressure Homogenisation 438

10.5.1 Effect on Microorganisms and Potential for Producing ESL and Shelf–Stable Milk 440

10.5.2 Effect on Milk Components 442

10.6 Bactofugation 443

10.7 UV Irradiation 444

10.8 Gamma Irradiation 446

10.9 Carbon Dioxide 447

10.9.1 High Pressure Carbon Dioxide 449

References 450

11 Analytical Methods 461

11.1 Introduction 461

11.2 Commonly Used Analytical Methods 461

11.2.1 Amylase 461

11.2.2 Browning 462

11.2.3 Density/Specific Gravity 463

11.2.4 Dissolved Oxygen 463

11.2.5 Fat Separation and Fat Particle Size 464

11.2.6 Flavour Volatiles 467

11.2.7 Fouling of Heat Exchangers 469

11.2.8 Freezing Point Depression (FPD) 470

11.2.9 Furosine 471

11.2.10 Hydrogen Peroxide 471

11.2.11 Hydroxymethyl Furfural (HMF) 472

11.2.12 Lactulose 472

11.2.13 Lysinoalanine (LAL) 473

11.2.14 Lipase 473

11.2.15 Lipolysis (Free Fatty Acids) 475

11.2.16 Lysine – Blocked and Reactive 475

11.2.17 Minerals and Salts 477

11.2.18 pH and Titratable Acidity 484

11.2.19 Protease 486

11.2.20 Protein 487

11.2.21 Proteolysis (Peptides) 488

11.2.22 Sediment 492

11.2.23 Sensory Characteristics 493

11.2.24 Separation Methods 496

11.2.25 Stability Tests 499

11.2.26 Viscosity 502

11.2.27 Vitamins 503

11.2.28 Whey Protein Denaturation 503

11.3 Advanced Analytical Techniques 505

11.3.1 Chemometrics 505

11.3.2 Nuclear Magnetic Resonance (NMR) 506

11.3.3 Proteomics 508

11.3.4 Ultrasonic Techniques 509

References 510

12 Concluding Comments 527

12.1 Spore–Forming Bacteria 527

12.1.1 Highly Heat–Resistant Spores 527

12.1.2 Enzymes Produced by Spores 527

12.1.3 Sources of Spores 527

12.1.4 Identification of Spores 528

12.1.5 Spore Counts in Raw Milk 528

12.1.6 Conditions of Activation and Germination of Spores 528

12.1.7 Psychrotrophic Spore–Formers 529

12.2 Biofilms 529

12.3 Age Gelation 530

12.3.1 Mechanism 530

12.3.2 Early Prediction of a Milk’s Susceptibility 530

12.4 Predictive Modelling 530

12.5 The Shelf–Life of UHT Milk 531

12.6 The Shelf–Life of ESL Milk 532

12.7 Non–Thermal Technologies 533

12.8 Analytical Methods 533

12.9 Using the Literature 533

12.10 Further Reading 534

References 534

Further Reading: References to Books, Book Chapters and Reviews Arranged Alphabetically within Publication Type 536

Index 541

About the Authors
Hilton C. Deeth, Emeritus Professor, School of Agriculture and Food Sciences, University of Queensland, Australia, and consultant to the dairy industry

Michael J. Lewis, Honorary Fellow, Department of Food and Nutritional Sciences, Taught and researched at The University of Reading, Whiteknights, UK, for 38 years and now working as an adviser on milk and milk products