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.

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

High Temperature Processing of Milk and Milk Products covers many aspects of thermal processing of milk and milk products with particular focus on UHT processing. The book begins 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. A unique feature is a chapter on analytical methodologies applicable to thermally processed dairy products. There are also chapters on high-temperature processed products other than white cows' milk, including products based on plant materials, and on non-thermal technologies which may be used in place of or as adjuncts to thermal processing. The book concludes with a chapter outlining some of the challenges with the technologies and treated products, and a compendium of relevant reviews, chapters and books.