Behavior of Calcium and Phosphate in Artificial Casein Micelles

¹ United Chair of Applied Resource Chemistry, Course of Bioresource Science for Processing, United Graduate School of Agricultural Sciences, Kagoshima University, Kagoshima 890, Japan
² Department of Biochemical Science and Technology, Faculty of Agriculture, Kagoshima University, Kagoshima 890, Japan

This study investigated the behavior of Ca and phosphate in artificial casein micelles using ⁴⁵Ca and ³²P by means of UF, equilibrium dialysis, and gel permeation HPLC in the presence of 6 M urea. Artificial casein micelles were prepared at a casein concentration of 2.5% with 30 to 40 mM Ca, 22 to 27 mM phosphate, and 10 mM citrate using ⁴⁵Ca or ³²P. About 75 and 65% of colloidal ⁴⁵Ca and ³²P, respectively, in artificial casein micelles that were formed in the presence of 30 mM Ca and 22 mM phosphate were exchanged after dialysis of artificial casein micelles against a simulated milk ultrafiltrate at 4°C for 72 h. The percentages of ⁴⁵Ca and ³²P in the fraction of casein aggregates that were crosslinked by micellar Ca phosphate were 26.9 and 27.6%, which decreased to about 10% after equilibrium dialysis against a simulated milk ultrafiltrate at 4°C for 72 h. The proportion of exchanged colloidal ⁴⁵Ca and ³²P in artificial casein micelles during dialysis for 72 h were higher at 25°C than at 4°C, suggesting that the exchange of Ca and phosphate between the diffusible and colloidal phases depended on temperature. The results suggest that the exchange of Ca and phosphate between diffusible and colloidal phases proceeds slowly, and a portion of the Ca and phosphate in the artificial casein micelles is difficult to exchange.

Key Words: casein micelles • calcium • phosphate • radioisotope

Submitted on October 20, 1995
Accepted on April 22, 1996