713. The relation between the chemical composition of milk and the stability of the caseinate complex: II. Coagulation by ethanol

Abstract

1. The variation in the stability of milk protein to ethanol and the relationship between milk composition and ethanol stability were examined. 2. Samples of herd bulk milk were very similar in stability to ethanol; the range of aqueous ethanol solutions required to coagulate the caseinate complex in an equal volume of milk was only 80–84% (v/v) ethanol. Samples from individual cows showed a wide variation in stability; coagulation was caused by ethanol solutions ranging in strength from 66 to 90% (v/v) ethanol. 3. Colostrum was very unstable to ethanol but stability rapidly increased during the post-colostrum period to higher levels in mid-lactation. Late lactation and subclinical mastitis milk showed no definite bias towards stability or instability. 4. The strength of ethanol required to coagulate the caseinate complex in an equal volume of milk was inversely related to the concentration of ionized calcium in the milk. The correlation coefficient was –0·76 (significant at 0·001 level) indicating that approximately 60% of the variation in stability was accounted for by the variation in the concentration of ionized calcium. 5. The relationships between the concentrations of other milk constituents and stability to ethanol could be attributed to the interrelations of the concentrations of these constituents and the concentration of ionized calcium.