Casein micelles: the colloid-chemical approach

The colloidal properties of micellar casein are reviewed. It is shown that behaviour of intact micelles is much at variance with the predictions from the Schulze-Hardy rule, and that therefore their stability cannot be explained by the principles of the DLVO theory. Towards electrolyte, micelles behave as a protein rather than a lyophobic colloid. Casein is a strong protective colloid. In the micelle, however, it does not completely cover the inorganic constituent which remains sensitive to changes in the ionic environment. The rate theory of the enzyme-induced clotting of casein micelles is summarized. It is shown that the lag phase in the clotting is due to the second order of the co-agulation reaction. Flocculation rate constants of micelles have been deduced from clotting times. Their relatively low values can be attributed to an orientational constraint. Practical consequences of the theory with respect to clot structure, gelation of sterilized products and cheese manufacture are discussed.