SYMPOSIUM: GENETIC PERSPECTIVES ON MILK PROTEINS: COMPARATIVE STUD1 ES AND NOMENCLATURE Review and Update of Casein ChemIstryl,*

Of all food proteins, bovine milk proteins are probably the most well characterized chemically, physically, and genetically. The primary structures are known for most genetic variants of a s l , as2-, 0-. and K-caseins, &lactoglobulin, and a-lactalbumin. Secondary and tertiary structures of the whey proteins have been determined, and secondary structures of the caseins have been predicted from spectral studies. The caseins, although less ordered in structure and more flexible than the typical globular whey proteins, have significant amounts of secondary and, probably, tertiary structure. The amphipathic structure of the caseins is especially noteworthy; thus, these proteins most likely are divided into polar and hydrophobic domains. The presence of anionic phosphoseryl residue clusters in the calciumsensitive casein polar domains is particularly significant because of their interaction with calcium ions, or calcium salts, or both, and the formation of micelles. Flexibility of casein structures is reflected by their susceptibilities to limited proteolysis, which dramatically changes functionality. Received August 24, 1992. Accepted December 16, 1992. 'Paper Number FSR92-27 of the Journal Series of the Department of Food Science, Noah Carolina State University, Raleigh 27695-7624. The use of trade names in this publication does not imply endorsement by the North Carolina Research Service of products named or criticism of similar ones not mentioned. 2Support for the presentation of this symposium papcr was paaially provided by che California Dairy Foods Research Center. (