Heat-Induced Changes in Milk

Abstract

In modern dairy technology, milk is almost always subjected to a heat treatment; typical examples are: thermization (65 ˚C × 15 sec), low temperature – long time pasteurization (65 ˚C × 30 min), high temperature – short time (72 ˚C × 15 sec) pasteurization, ultra-high temperature sterilization (140 ˚C × 5 sec), in-container sterilization (112 ˚C × 15 min). The objectives of heat treatment, include: killing heat-sensitive spoilage bacteria (therminization), killing pathogenic bacteria (pasteurization), killing all bacteria, including spores (sterilization), inactivation of enzymes and increasing heat stability. Milk is a very heat – stable system but some chemical and physico-chemical changes do occur in milk on heating. These changes include: damage to the creaming properties, non-enzymatic (Maillard) browning, degradation of lactose to lactulose and acids, denaturation of whey proteins and after severe heat treatment, dephosphorylation and hydrolysis of the caseins and eventually heat-induced coagulation. The principal heat-induced changes in milk are described in this chapter.