Sedimentation Analysis of Bovine Milk Casein Micelle at pH 6.8 and pH 5.8

Abstract

The sedimentation analysis was based on the opacity transfer velocity of micelle under ultracentrifugal field and photograms were taken with a schlieren optical system on the plate. The sedimentation coefficients determined at 30°C in milk serum were 440 S at pH 6.8 and 570 S at pH 5-8, respectively, at the maxima of the concentration gradient curves. The distribution of sedimentation coefficient at pH 6.8 ranged from 250 to 1500 S. The distribution of micelle size calculated from these results ranged from 850 to 2100 Å in diameter with a most probable value of 1200 Å. The size distribution was calculated also at pH 5.8. The micelle size at pH 5.8 was smaller in diameter by about 10% than at pH 6.8, indicating the shrinkage of micelles with decreasing pH.