Effect of enzymatic dephosphorylation on caprine casein micelle structure

Abstract

The effect of enzymatic dephosphorylation, using intestinal alkaline phosphatase, on the structure of casein micelles in caprine micellar casein concentrate (MCC) was studied. An optimal condition, involving preheating the MCC dispersion, pH 6.4, 2.5 mg casein/mL and 0.4 U phosphatase/mL, was established and used to prepare MCC with 0–49% dephosphorylation by incubation at 37 °C for 0–180 min. β-Casein showed marked dephosphorylation and formed multi-phosphorylated isoforms depending on dephosphorylation degree, whereas αs- and κ-caseins showed limited and fast dephosphorylation, respectively. With increasing dephosphorylation, both the colloidal calcium and the calcium sensitive micellar caseins, especially β-casein, were gradually dissociated, and the calcium insensitive serum κ-casein was gradually associated with the micelles. The dissociated β-casein fraction was predominated by isoforms with lower number of phosphate groups. For micelles with increasing dephosphorylation, the molar mass decreased, the gyration and hydrodynamic radii decreased, the ratio of gyration to hydrodynamic radii and micellar hydration increased, the spherical morphology was generally retained, and the internal protein inhomogeneity disappeared progressively. These results suggest that after dephosphorylation, the caprine micelle framework underwent an intra-micellar mass redistribution, and become more loose and homogeneous.