Casein micelle formation

In summary, intact milk proteins have their specific functions such as casein micelle formation and regulation of lactose synthesis. Milk proteins exhibit various biological activities when they are partially digested as described before. They are finally a source of essential amino acids. This means milk proteins are highly functional substances. 

Yoshikawa, M., Sasakai, R., and Chiba, H. 1981. Effect of chemical phosphorylation of bovine casein components on the properties related to casein micelle formation. Agric. Biol. Chem. 45,... 

The Golgi complex is also the locus of casein micelle formation. In association with calcium, which is actively accumulated by Golgi vesicles, the polypeptide chains associate to form submicelles, and then micelles, prior to secretion. 

Home, D.S. (2003). Casein micelles as hard spheres limitations of the model in acidified gel formation. Colloids and Surfaces A Physicochemical and Engineering Aspects, 213,255-263. 

This description of micelle formation is also called the two-state model. Thus, the solution contains p-casein micelles of about 38—40 monomer... 

Rollema, H.S. (1992). Casein association and micelle formation. In Fox, P.F. (Ed.). Advanced Dairy Chemistry, Vol. 1 Proteins, London Elsevier Applied Science, pp. 111-140. 

The major caseins interact with each other and, in the presence of Ca2+, these associations lead to the formation of casein micelles. 

Although the gelation properties of whey proteins are of great importance in many foods (Mulvihill, 1992) and it is possible to form a weak gel in creams by the formation of a continuous network of fat globules, most important milk gels are those involving casein micelles which can be made to form a gel matrix either by isoelectric precipitation (acid-induced gel) or by the action of a proteolytic enzyme (rennet-induced gel). Both gel types... 

The association that occurs between the monomers of the same milk protein as influenced by their environment has been discussed in the section Structure and Conformation of Milk Proteins. However, in addition to this type of association, the milk proteins are known to form complexes with small ions and molecules, to bind water, and to form complexes with other macromolecules and with each other. The most important example of the last phenomenon is the formation of casein micelles, which is discussed in Chapter 9. 

Waugh, D. F. 1971. Formation and structure of casein micelles. In Milk Proteins, Vol. 

Raw milk is standardized to the proper fat and total milk solids content to produce a final product with a minimum of 50% fat on a solids basis and <39% moisture (CFR 1982 Packard 1975). Cheese is made from pasteurized or raw milk, but raw milk cheese must be aged a minimum of 60 days at >1.7°C (CFR, 1982). Minimum temperature and time combinations are normally used for pasteurization of milk for cheese manufacture in order not to interfere with casein micelle coagulation and curd formation. Milk is sometimes heated only to subpasteurization temperatures to dispel dissolved gases, reduce bacterial populations, and kill certain pathogens, thus resulting in a cheese product with improved flavor (Babel 1976). 

Keenan, 1975 Neville et al., 1981 Watters, 1984 Virk et al., 1985), the presumption is that the formation of casein micelles is orchestrated with the transport of ions, the phosphorylation and glycosy-lation of the caseins, and lactose synthesis, such that the intravesicular ionic environment and casein concentration change continuously during the 20 min or so required for micelle assembly. Patton and Jensen (1975) observed, in electron micrographs, the same density of micellar particles in the alveolus as in mature vesicles, suggesting that, by this stage, the vesicular concentrations are virtually identical to those in the aqueous phase of milk. 

It is argued here that the formation of casein micelles is a highly controlled process, producing a macromolecular complex with a specific structure and function. This point needs to be stressed because of a long-standing view of caseins as random coil-type proteins which associate to produce a largely random coil complex having only a nutritional function. 

The most thorough study of the formation of artificial casein micelles is that of Schmidt and co-workers (1977 1979 Schmidt and Koops, 1977 Schmidt and Both, 1982 Schmidt and Poll, 1989), who not only studied the properties of the casein aggregates but also attempted to relate them to the solution conditions under which they were formed. In the precipitation of calcium phosphate from solution, the means by which solutions are mixed together is of crucial importance Schmidt et al. (1977) described a method in which four solutions were pumped simultaneously into a reaction vessel while keeping the pH constant. As a result of careful, slow mixing, the reproducibility of the size distributions of particles, measured by electron microscopy on freeze-fractured and freeze-etched specimens, was very good. In the first series of experiments, the objective was to produce milk like concentrations of the most important ions while... 

The primary (enzymatic) phase of renneting overlaps somewhat with the secondary phase of aggregation. The gel subsequently undergoes syneresis to produce curds and whey while a slow but more general proteolysis of the caseins begins, which eventually contributes substantially to the distinctive flavor and texture of cheese. The enzymatic coagulation of milk and formation of the curd has been reviewed by Dalgleish (1987). Here, attention will be confined to parts of the subject that most clearly relate to the structure and stability of bovine casein micelles. 

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