Studies on human casein preparations from single milk samples

Abstract

Specimens of human casein representing all stages of lactation have been prepared by a standard procedure from 80 milk samples given by 47 mothers. Electrophoresis of human casein on starch gel at pH 8.6 gives a 6-band pattern. Three casein types (A, B and C) have been characterized, which differ in the relative strengths of the bands within this main pattern. The results suggest that for any one individual the type does not change during the course of a lactation. The sialic acid content of casein preparations fell during lactation from about 1.0 to 0.2%; it showed a positive correlation with the amount of sialic acid present in the skim milk after casein had been removed. About 1/2 the casein sialic acid was sensitive to the action of rennin. It is concluded that the nature and properties of human casein may be influenced by the relative activity of certain enzymes in the mammary alveolar cell, and by the composition of the milk from which it is derived.