Casein Micelles as Colloids: Surface Structures and Stabilities

Abstract

The interactive behavior of bovine casein micelles during processing depends on the structure of the micellar surface. Although some gross features are known, such as that the surface is covered by "hairs" of the macropeptide of κ-casein, the details of the surface topology are lacking because of the apparent complexity of the micellar structure or a general lack of understanding of it. It is instructive to attempt to understand the micellar surface by comparing it with some better characterized colloidal systems, such as emulsion droplets or polystyrene latex particles, the surfaces of which are covered by monolayers of adsorbed proteins, either single types or as mixtures. This paper describes such a comparison, combining information from micellar studies and models. The comparison suggests that the surface of the casein micelle is only partly similar to the colloidal systems because of the different structures of the interiors of the particles and the manner in which the surface caseins interact with the interior of the micelle. The κ-casein molecules on the micellar surface are probably distributed unevenly and have spaces between them that may permit the passage of other molecules, which might have some important consequences for understanding the behavior of the micelle.