Sedimentation Property of Casein Micelles from Milk Destabilized by Frozen Storage

Abstract

Casein micelles destabilized in milk under frozen storage was compared with stable casein micelles before frozen storage by means of analytical ultracentrifugation.

The stable micelles disaggregated with urea-containing buffer showed a single homogeneous peak of ~0.9S, while a fast sedimenting subpeak, in addition to the major peak of ~0.9 S, appeared in the destabilized micelles. However, any difference was not found between the stable and destabilized caseins when they were analyzed after removal of calcium. It is suggested that a new type of association is formed, possibly through salt linkages, in the casein system destabilized under frozen storage. Sedimentation pattern of calcium paracaseinate phosphate complex in urea-containing buffer suggests that the destabilization of the micelles by rennin does not involve the change of salt linkages.