Micellar calcium phosphate-cross-linkage in buffalo casein micelles.

The composition of yak casein micelles and the physico-chemical properties of micellar calcium phosphate (MCP)-cross-linked casein in yak casein micelle were investigated. Furthermore, the formation of micelles and MCP-cross-linkage of yak casein were examined using artificial micelles. Micellar casein content was 3.27% in yak milk, which was 1.39 times higher than that of bovine milk. The total calcium, micellar calcium, and inorganic phosphorus (Pi) contents were also higher in yak milk than in bovine milk. Micellar calcium and Pi contents were 1.21 and 1.45 times higher in yak casein than in Holstein cow milk, respectively. The MCP-cross-linked casein in yak casein micelles, which was separated from yak casein micelles by high-performance gel chromatography on a TSK-GEL G4000SWxL column using 6 M urea-simulated milk ultrafiltrate as the eluent, was 25.7% of total casein content, which was about half of the corresponding casein micelles of Holstein cow milk. The serum casein content increased when yak milk was cooled at 4 □ for 24 h. Contents of MCP-cross-linked casein were 15.3 and 38.0% for the artificial yak micelles formed at 20 mM calcium and 17 mM Pi, and 30 mM calcium and 22 mM Pi, respectively, which were much lower than those of corresponding bovine casein micelles. The organic phosphorus content of yak casein used was 0.72%, which was lower than that of bovine casein. The lower organic phosphorus content of yak casein was considered to be the reason why less yak casein was cross-linked by MCP than bovine casein.