Casein micelle interactions

Native casein micelles are considered as an association colloid, sterically stabilized by a layer of Ic-casein hairs. This hairy or furry layer, as it is traditionally called, is considered as a polyelectrolyte brush. Its sta bility or extension is related to the brush density (renneting), charge den sity (pH) along the chain, concentration of (divalent) salt ions and polari zability of the solvent (ethanol content). At lowered brush density, lowere d charge density, lowered polarizability of the solvent and increased calci um level, the brush will more readily collapse on the surface of the micell e. It is then assumed that, as a result, the casein micelle loses its collo idal stability and flocculates, allowing brush collapse to be easily monito red. This simple unifying picture was checked by testing theoretical scalin g relations, e.g. the relation between renneting level and pH. Results show that there is a quantitatively and qualitatively correct relation between the influence of the various parameters. A simple picture of the stability of casein micelles is presented which allows a good estimate of the influen ce of technological treatments on the stability of skim milk. (C) 1999 Else vier Science Ltd. All rights reserved.