Colloidal Calcium Phosphate-cross-linkage in Casein Micelles.

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It is recognized that colloidal calcium phosphate (CCP) participates in characteristics of casein micelles in milk processing such as heating, cooling and freezing. However, the state and role of CCP has not yet been elucidated sufficiently. In the present study, the effects of heating on CCP-cross-linkage and the relation between CCP-cross-linkage and the release of serum casein on cooling were examined.It was confirmed that CCP content was increased on heating casein micelle dispersion (CMD) and concentrated CMD at 60-90 ﾟC for 10 min or 135-140ﾟC for 15-75 sec. The content of casein aggregates cross-linked by CCP was decreased from 51.9 to 46.1% in CMD and 52.5 to 43.6% in concentrated CMD on heating at 135-140 C for 75 sec, indicating the cleavage of the CCP-cross-linkage.CCP-increased CMD was prepared by addition of calcium and phosphate. The content of casein aggregates cross-linked by CCP was increased from 49.3 to 68.3%. The amount of serum casein released from casein micelles was decreased with increasing CCP content. When the CCP content was increased to a large extent, beta-casein released on cooling was decreased from 31.8 to 2.1% of the total casein while beta-casein cross-linked by CCP and beta-casein which is not cross-linked and not released on cooling were increased from 46.2 to 69.9% and from 22.0 to 28.0% of the total beta-casein, respectively. The increase in beta-casein cross-linked by CCP and strengthening of interaction between beta-casein and other casein constituents were considered to be reasons for the decrease of beta-casein release on cooling.