Effects of Chemical Phosphorylation of Bovine Casein Components on the Properties Related to Casein Micelle Formation

Abstract

Bovine casein components (α_s1, β-, and κ-caseins) were chemically phosphorylated and the properties of the modified components were compared with those of the native to clarify the function of the intrinsic phosphate groups of casein components in casein micelle formation. The calcium binding ability of casein components increased after chemical phosphorylation. The concentrations of calcium chloride required to precipitate modified α_s1- and β-caseins were higher than those for native components. However, phosphorylation of α_s1- and β-caseins did not affect their properties of forming micelles through interaction with κ-casein. The stabilizing ability of κ-casein for α_s1- and β-caseins was impaired by its phosphorylation, but the stability was recovered by treating phosphorylated κ-casein with phosphoprotein phosphatase. The results show that the phosphate content of κ-casein mustbe low to form a stable casein micelle. The results also explain why the specific phosphorylation of casein components in the mammary gland is required.