FORMATION OF GAMMA-CASEINS DURING COOLING OF RAW-MILK

It has been shown that there is a time-dependent transfer B-casein and the milk serine proteinase system from micelles to milk serum with change of temperature from 38 to 4 C. It has been established that the y-caseins can be formed by proteolytic degradation of β-casein. By a simple extraction technique, the very hydrophobic y-casein fraction was separated from stored milks (26 and 4 C) and estimated quantitatively. The results showed that the proteolytic degradation of β-casein is faster at 4 C than at room temperature and this can be explained by the immobilization of enzyme and substrate at the micelle surface at higher temperatures (26 C). The results indicate that irreversible changes during cooling for short periods do not cause problems in milk processing, but the formation of y-caseins and phosphopeptides may influence the technological properties of raw milk stored for more than 48 h. © 1979, Proprietors of Journal of Dairy Research. All rights reserved.