The hairy casein micelle: evolution of the concept and its implications for dairy technology

Abstract

Physico-chemical measurements on the native bovine casein micelle have indicated that the outermost region comprises a diffuse layer of flexible hydrophilic polypeptide chains from the C-terminal half of κ-casein. By analogy with the steric stabilization theory devised for hydrophobic colloids, 'the hairy layer' presents a virtually impregnable barrier against aggregation unless the hairs are removed enzymically (e. g. renneting) or if the solvent quality is reduced (e. g. ethanol stability). In acid gelation, the disruption of the core structure of the casein micelles caused by the dissolution of the colloidal calcium phosphate is undoubtedly implicated in the loss of stability, rather than gelation being caused by some simple neutralisation of charges at the iso-electric point. In the other technologically important processes such as acid gelation and heat coagulation of milk, the mechanism by which the steric barrier is breached, bridged, or otherwise rendered ineffective is largely unknown.