Heat stability of milk

Abstract

Fresh milk at its natural pH can be heated at 140 °C for more than 10 min before coagulation occurs, but when the pH is changed or milk is concentrated, heat stability can be reduced. Heat-induced coagulation of milk is the result of aggregation of the milk proteins. Heat-induced dissociation of ê-casein from the micelles and the acid-induced collapse of the ê-casein brush on the micelle surface, as a result of heat-induced acidifi cation, destabilize the micelles, making them susceptible to aggregation. Heatinduced denaturation of whey proteins and association with the casein micelles can stabilize against heat-induced coagulation. However, in concentrated milk, heat-induced whey protein aggregation can be a strong destabilizing factor, particularly at high pH. Controlled pre-denaturation of whey proteins prior to sterilization is an adequate manner of improving heat stability. Addition or removal of minerals like calcium and phosphate strongly infl uences the heat stability of milk, as does the amount or urea naturally present in milk and the heat-induced degradation of lactose. Improving and controlling the heat stability of milk therefore requires control of a wide variety of intricate relationships between constituents and physicochemical properties of milk.