Skim Milk Acidification
Skim milk was acidified slowly using glucono-delta-lactone and HCl. On lowering the pH the steric stabilization of the casein micelles diminishes and as a result the micelles exhibit attractive interactions. These interactions can be quantitatively described using an adhesive hard sphere (AHS) model. The strength of the attraction is found to be proportional to 1/(pH - pC); it is suggested that pC may be related to an effective dissociation constant of the carboxylic acid groups along the kappa-casein backbone. If pH approaches pC, the polyelectrolyte-like kappa-casein brush collapses onto the surface of the micelles. The AHS model is quantitatively tested using viscosity and dynamic light scattering measurements.
de Kruif CG
Netherlands Institute for Dairy Research (NIZO), Kernhemseweg 2, Ede, 6710 BA, The Netherlands