STRUCTURE AND STABILITY OF BOVINE CASEIN MICELLES

The casein micelle is an important and characteristic macromolecular assembly of mammalian biology, occurring in all milks that are examined. They form a coagulum in the stomach of the nursling, allowing the slow release of nutrients down the digestive tract, and to act as a means of transporting calcium and phosphate in a readily assimilable form from mother to young. This chapter discusses the structure and stability of bovine casein micelles. Casein micelles are spherical particles; their appearance in electron micrographs is not smooth but is likened to the surface of a raspberry. A substructure is seen in unstained thin sections of casein micelles, with regions of greater electron density dispersed evenly in a less dense matrix. When casein micelles are dissociated, spherical particles are observed with a size similar to the scale of the substructure. Casein micelles are remarkably stable structures. The appearance, substructure, size distribution, voluminosity, and dissociation of casein micelles are discussed in the chapter. The forces involved in coagulation, steric stabilization of micelles, and action of chymosin on casein micelles are also emphasized. © 1992 Academic Press, Inc.