Casein micelle structure and stability

Abstract

The physicochemical properties of the casein proteins are reviewed, highlighting the factors controlling the strength of those interactions most important to the assembly and structure of the casein micelle, namely, electrostatic repulsion and hydrophobic attraction, with particular emphasis on their magnitude and range. The various strands are drawn together step-by-step to develop the dual-binding model of casein micelle assembly and structure. A biomineralization mechanism is developed for the synthesis of micellar calcium phosphate nanoclusters. The linkage into these by the phosphoserine groups of the caseins forms one polymerization pathway in the dual-binding model. This model is then used to predict the behavioral properties of the micelle in fluid milk, where, by considering the rheology of high-concentration milks, the hard sphere colloidal approach is shown to be a special case limited to milk of normal concentration and pH. The necessity for a dual-binding approach is then forcefully demonstrated in its ability to provide full mechanistic explanations of observed behavior in the renneting, acid gelation, and alcohol-induced destabilization of skim milk. It is emphasized that the dual-binding model is only a tool and that the most important features are the interactions of the caseins with themselves and mineral calcium phosphate.