Milk Quality

Milk has played a major contribution to the human diet in many different countries across the world since the dawn of time. The dairy cow was domesticated over 6000 years ago, she was the object of worship in the Middle East 2000 years before Christ, and milk and milk products are mentioned more than 50 times in the Bible. Milk and dairy products have become a major part of the human diet in many countries. It is not surprising therefore, that over many years considerable attention has been paid to improving the quality of milk. We have worked to improve the yield, the compositional quality and the hygienic quality, and have striven to minimise the level of contaminants which can find access to this, perhaps our most natural, unrefined and highly nutritious foodstuff. The chain of people involved in the milk industry extends from milk production-farmers, veterinarians and farm advisors-through transport to processing-quality controllers, manufacturers-and on to retailers, legislators, nutritionists, dairy educators and consumers. All will be interested in the quality parameters of milk which are reg­ ularly measured for commercial reasons, for trade, for legal requirements and for reasons of nutrition.

1 World milk production.- 2 Milk production: Factors affecting milk composition.- 2.1 Introductio.- 2.2 Synthetic and secretory tissues of the mamary gland.- 2.2.1 Functional anatomy.- 2.2.2 Role of the milk-producing cell.- 2.2.3 Milk flow within the udder.- 2.3 The initiation and establishment of lactation.- 2.4 The milk ejection reflex.- 2.5 Effect of breed on milk composition and yield.- 2.6 Role of genetics in milk production.- 2.7 Effect of environment on milk composition and yield.- 2.7.1 Effects of season.- 2.7.2 Effects of thermal stress.- 2.8 Dairy cattle nutrition and its influence on milk yield and composition.- 2.8.1 Dietary effects on milk fat.- 2.8.2 Influence of ration on milk protein.- 2.9 The effects of milking management practices on milk quality.- 2.9.1 Milking interval.- 2.9.2 Milking rate.- 2.9.3 Frequency of milking.- 2.9.4 Milking routine.- 2.9.5 Cow preparation and residual milk.- 2.10 Influence of age and stage of lactation on milk component yield 22 References and further reading.- 3 Mastitis and milk quality.- 3.1 Introduction.- 3.2 Causative organisms.- 3.3 Contagious and environmental pathogens.- 3.4 Inflammation.- 3.5 Compositional changes.- 3.6 Milk losses.- 3.7 Impact on dairy products.- 3.8 Control of mastitis.- 3.9 Measurement.- 3.10 Summary 37 Further reading.- 4 Hygienic quality.- 4.1 Milk production, plant cleaning, on-farm storage and collection of milk.- 4.1.1 Milk production.- 4.1.2 Plant cleaning and sterilisation.- 4.1.3 Effect of storage time and temperature on bacterial count.- 4.2 Types of bacteria.- 4.3 Cooling and storage of milk on the farm.- 4.4 Collection, delivery and reception of milk.- 4.4.1 Churn collection.- 4.4.2 Bulk collection.- 4.5 Delivery and storage prior to processing 47 4.5.1 Storage of milk prior to processing.- 4.6 Importance of hygienic quality of milk.- 4.7 Measurement of the hygienic quality of milk.- 4.7.1 Simple, rapid tests for mesophiles.- 4.7.2 Tests for cooled milk.- 4.7.3 Staining and counting bacteria.- 4.7.4 Measurement of metabolic products of microbial cells.- 4.7.5 Measurement of metabolic activity.- 4.8 The future.- 4.9 Sampling, storage, preservation and transportation of samples 55 4.9.1 Sample transport and preservation.- References and further reading.- 5 Adulteration of milk.- 5.1 Introduction.- 5.2 Extraneous water.- 5.2.1 Vieth ratio.- 5.2.2 Nitrates as an indication of extraneous water.- 5.3 Freezing point test for detecting adulteration.- 5.3.1 Basis of the test.- 5.3.2 Freezing point depression and how it is controlled.- 5.3.3 Measurement units.- 5.3.4 How constant is the freezing point of milk?.- 5.3.5 Freezing point of goat’s, buffalo’sand ewe’s milk.- 5.3.6 Factors affecting freezing point of milk.- 5.3.7 Test method.- 5.3.8 Calculation of amount of extraneous water in milk.- 5.4 Sources of contamination by extraneous water.- 5.5 How to avoid getting water into milk at the farm.- 5.6 Control of extraneous water through payment schemes.- 5.7 Other sources of adulteration.- 5.7.1 Salt.- 5.7.2 Sugar.- 5.7.3 Skim-milk powder.- 5.7.4 Detergent sterilants.- 5.7.5 Preservatives.- 5.7.6 Colostrum.- 5.7.7 Blood.- 5.7.8 Taints.- References and further reading.- 6 Compositional quality.- 6.1 Composition of milk.- 6.2 Measurement of total solids in milk.- 6.3 Measurement of the solids-not-fat (SNF) of milk.- 6.4 Major constituents.- 6.4.1 Fat.- 6.4.2 Proteins.- 6.4.3 Lactose.- 6.5 The use of instruments in assessing compositional quality.- 6.5.1 Assessing compositional quality using infrared.- 6.6 Dairy herd improvement (DHI) and quality payment laboratories.- 6.7 Quality payment systems for milk.- 6.7.1 Compositional quality.- References and further reading.- 7 Milk from sheep and goats.- 7.1 Introduction.- 7.2 Milking practices.- 7.3 Compositional quality.- 7.4 Measuring cow’s milk in sheep’s or goat’s milk products.- 7.4.1 Differences in lipids.- 7.4.2 Differences in protein.- 7.4.3 Immunological techniques.- 7.4.4 General differences.- 7.5 Instrumental methods of analysis.- References and further reading.- 8 The impact of raw milk quality on product quality.- 8.1 Introduction.- 8.2 Compositional quality.- 8.3 Opportunities for manipulation of compositional quality.- 8.3.1 Fat.- 8.3.2 Protein.- 8.4 The effect of raw milk hygienic quality on product quality.- 8.5 Animal health.- 8.5.1 Mastitis.- 8.6 Physical handling of milk.- 8.7 Taints and contaminants.- 8.8 Pasteurised milk and cream.- 8.8.1 Summary of action to limit problems in pasteurised products.- 8.9 UHT products.- 8.10 Cheese.- 8.10.1 Impact of milk quality.- Further reading.- 9 Processed milk.- 9.1 Introduction.- 9.1.1 Raw milk.- 9.1.2 Frozen milk.- 9.1.3 Concentrated milks.- 9.1.4 Homogenised milk.- 9.1.5 Immune milk.- 9.2 Heat treatments.- 9.2.1 Pasteurisation.- 9.2.2 Sterilisation.- 9.2.3 UHT treatment.- 9.2.4 Factors affecting the shelf-life of heat-treated milk.- 9.3 Quality control of heat-treated milks.- 9.3.1 Pasteurised milk.- 9.3.2 UHT milk.- 9.3.3. Sterilised milk.- 9.4 Milks of modified compositional quality.- 9.4.1 Fat-reduced milks.- 9.4.2 Lactose-reduced milks.- 9.5 Compositional quality of fluid milk products.- References and further reading.- 10 Contaminants.- 10.1 Introduction.- 10.2 Veterinary drugs.- 10.2.1 Importance of drugs.- 10.2.2 Test methods.- 10.3 Keeping antibiotics out of milk.- 10.3.1 Correct and clear identification of treated cows.- 10.3.2 Record all treatments.- 10.3.3 Withholding time.- 10.3.4 Dry cow therapy.- 10.3.5 Other treatments.- 10.3.6 Milking plant contamination.- 10.4 Hormones (BST).- 10.5 Disinfectants.- 10.6 Nitrates, nitrites and nitrosamines.- 10.7 Pesticides.- 10.7.1 Incidence.- 10.7.2 Significance of residues.- 10.7.3 Limiting residues in milk.- 10.8 PCBs.- 10.9 Motoxins.- 10.10 Toxic metals.- 10.10.1 Lead.- 10.10.2 Cadmium.- 10.10.3 Mercury.- 10.11 Dioxins.- 10.12 Radionuclides in milk.- 10.12.1 What is radioactivity?.- 10.12.2 Radioactive decay.- 10.12.3 Our exposure to radiation.- 10.12.4 How do we measure radiation levels?.- 10.12.5 Access to milk.- 10.12.6 The risk in perspective.- 10.12.7 Partition of radionuclides in dairy products.- 10.13 Irradiation.- Further reading.- 11 Nutritional aspects.- 11.1 Introduction.- 11.2 Milk fat.- 11.3 Dietary cholesterol.- 11.4 Proteins.- 11.5 Milk allergy and intolerance.- 11.5.1 Lactose intolerance.- 11.5.2 Milk allergy.- 11.6 Cultured or fermented milks.- 11.7 Immune milk.- 11.8 Minerals.- 11.8.1 Calcium.- 11.8.2 Trace elements.- 11.9 Vitamins.- Further reading.