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 stability or extension is related to the brush density (renneting), charge density (pH) along the chain, concentration of (divalent) salt ions and polarizability of the solvent (ethanol content). At lowered brush density, lowered charge density, lowered polarizability of the solvent and increased calcium level, the brush will more readily collapse on the surface of the micelle. It is then assumed that, as a result, the casein micelle loses its colloidal stability and flocculates, allowing brush collapse to be easily monitored. This simple unifying picture was checked by testing theoretical scaling 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 influence of technological treatments on the stability of skim milk. (C) 1999 Elsevier Science Ltd. All rights reserved.