O20] Entropy

Abstract

The initial step in the manufacture of most cheese varieties involves enzymatic hydrolysis of one of the milk proteins, κ-casein. The enzyme involved is called rennet. During the primary stage, κ-casein is cleaved by rennet at the Phe105–Met106 bond, resulting in a reduction in both the net negative charge and steric repulsion, such that rennet-altered micelles become susceptible to aggregation and, after a lag phase, a three-dimensional gel network is formed. Historically, rennet was extracted from the fourth stomach of young calves, but today various other forms are available including recombinant chymosin, which is produced by several genetically modified organisms. The coagulation reaction involves two phases: the primary enzymatic phase involving hydrolysis of κ-casein and the secondary aggregation reaction that involves the association of micelles that have most of their κ-casein peptides hydrolyzed by rennet. The rennet coagulation of milk is greatly impacted by environmental conditions such as temperature, pH, and calcium content, and by genetic differences that affects the overall composition of the milk.