Preparation and characterization of micellar calcium phosphate-casein phosphopeptide complex

Micellar calcium phosphate (MCP) in bovine milk was separated as the complex with casein phosphopeptide (CPP) by the following procedures. Rennet curd obtained from skim milk was suspended in water, the pH was adjusted to 4.6, and the suspension was centrifuged at 1,000 x g. CPP was separated from the precipitated casein by tryptic hydrolysis and ethanol precipitation. The supernatant, which contained calcium and inorganic phosphate liberated from casein micelles by acidification, and CPP were mixed; the pH was adjusted to 6.7; and then the solution was lyophilized. From 1 L of skim milk, 3.16 g of the MCP-CPP complex was obtained. The dried MCP-CPP complex was easily dissolved in water and contained 12.7% calcium, 0.3% magnesium, 3.4% inorganic phosphorous, and 2.2% organic phosphorous. No crystal structure of hydroxyapatite was shown in the MCP-CPP complex by the X-ray diffraction analysis, although the pattern of NaCl crystal was observed. The X-ray diffraction pattern of commercial whey mineral, which was prepared by precipitation at alkaline pH from rennet whey, was similar to that of hydroxyapatite. It was confirmed by high-performance gel chromatographic analysis that the form of calcium phosphate in the MCP-CPP complex was similar to that of casein micelles. The MCP-CPP complex was also separated from commercial rennet casein. The method for the separation of MCP-CPP complex described above can be applied to the large-scale preparation.