Book review: Milk Proteins: From Expression to Food

The contributors to this volume have truly done a superb job in describing at length every aspect of milk. The order of chapters is organized in a very logical sequence to provide an uninterrupted flow of knowledge describing milk protein’s compositional differences. Such differences include: species, factors affecting milk proteins, use of milk proteins in industry, biological and physiological effects of milk proteins, and the future of milk proteins in industrial use. A brief review of these chapters is given below. Chapter 1 serves as introduction to this book and provides an excellent overview about milk, its components, and its physical, chemical, biological, and physiological properties. The author details the history of milk used for about 8,000 years. It is a very flexible raw material, from which a range of different products are produced, including about 1,400 varieties of cheese. Microconstituents (minerals, vitamins, etc) are mostly derived from blood, whereas the macroconstituents (lipids, sugars, proteins) are synthesized in the mammary gland and are milk-specific. He further discusses differences that exist in milk secretion and composition among different species, thus setting the stage for the rest of the book. Chapter 2 describes the comparative biology of milk using genomics, proteomics, and bioinformatics data in species with extreme lactation adaptations. The two animal models discussed in this chapter are tammar wallaby (Macropus eugenii) and the Cape fur seal (Arctocephalus pisillus). The tammar wallaby has a short gestation and a long lactation that is asynchronous. The Cape fur seal has a repeated cycle of lactation. The authors rightly point out that milk components with unique functions resulting from adaptations to extreme selective pressures are likely to have commercial potential either as nutraceuticals in functional foods or pharmaceuticals. The dairy industry focuses on milk proteins which are rich in bioactive properties and are particularly valuable to dairy processors and suppliers. Chapters 3–5 discuss milk protein composition. Chapter 3 is mostly focused on bovine milk protein and the authors compare the composition, structure, and function of bovine milk proteins to milk proteins from other species. There may be as many as 300 different proteins in milk. Important milk proteins include caseins and its isoforms, b-lactoglobulin (b-LG), a-lactalbumin (a-LA), immunoglobulins (Ig), glycomacropeptide, lactoferrin (LF), lactoperoxidase, lysozyme, and bovine serum albumin (BSA). In Chapter 4, the authors explain how caseins exhibit a high degree of heterogeneity as a result of post-translational modifications. Phosphorylation of aand b-caseins and glycosylation of j-casein are the best-known modification which are critical for the formation and stability of casein micelles. Absence of j-casein causes a failure of lactation, which results from aggregated caseins clogging the lumina of the mammary gland. Micellar structure of milk proteins is most important factor in regulating its properties, which is elegantly described within Chapter 5. Casein makes milk supersaturated with calcium phosphate, which transports calcium phosphate safely through the mammary gland for the development of bones and teeth in the suckling infant. Three models for casein–calcium interaction are described: the submicelle model, the nanocluster model, and the dual-binding model. Kappa-casein is the most important of the caseins in the dual-binding model of micellar assembly and structure. The other important set of milk proteins are whey proteins and include b-LG, a-LA, Ig, glycomacropeptide, lactoferrin, lactoperoxidase, lysozyme, and serum albumin. The secondary and quaternary structure of the whey proteins under stable and destabilizing conditions (change in pH, temperature, pressure, etc) are described in Chapter 6. Whey proteins are widely used as nutritional and functional ingredients by the food industry. Processing treatments such as heat and high pressure are applied to kill microbes and to extend the shelf-life of products. Chapter 7 describes the effects of high-pressure processing (HPP) on whey protein and their interactions with other proteins. High pressures cause proteins to lose their native three-dimensional structures leading to denaturation and aggregation and/or their interactions with each other. Sensitivities of each of the whey proteins to heat treatment (Ig>LF>BSA>b-LG B>b-LG A>a-LA) and pressure treatment (b-LG B>b-LG A>IgG>LF>BSA> a-LA) are considerably different because the heat treatment also affects both covalent bonds and noncovalent bonds. Milk can be subjected to high temperatures and pressures, high shear, and variation in concentration without causing appreciable damage to the casein micelle system but denaturation of whey proteins can modify the functional behavior of dairy products. Chapter 8 describes whey protein denaturation in detail. The interactions of denatured whey proteins with other proteins (including those of the casein micelles) and casein micelle dissociation reactions are discussed at length. Studies on these interactions may provide insights into the functional properties of heated-milk products. Most milk proteins are used in a dehydrated form, the focus of Chapter 9. Dairy products are usually dehydrated by spray drying. Whole milk powder (WMP), skim milk powder (SMP), whey products, casein, and other dairy ingredients are discussed. The native properties of milk components are substantially unaffected by moderate drying conditions. The industrial requirement for protein powders with specific properties is expanding. Powder is the easiest way to carry and store milk derivatives and increasing in importance is the need to understand rehydration behavior of dairy powders. The next issue for the dairy industry is the storage of the dried milk components. Chapter 10 describes the chemical changes that milk proteins undergo even as dried powders. The dried proteins not only undergo microbiological degradation but also chemical change occurs during long-term storage. A range of reactions can occur in the dry powders, which can affect powder functionality and nutritional value. Milk proteins are widely used as ingredients in many manufactured foods, e.g., dairy desserts, spreads, confectionery, and baked goods, and the authors provide coverage of how components in milk interact with other ingredients in Chapters 11, 12, and 13. Chapter 11 deals mainly with the properties and functionalities of food emulsions formed with milk protein products, and how AMERICAN JOURNAL OF HUMAN BIOLOGY 21:852–860 (2009)