Coagulating agents, coagulum formation and cutting of the coagulum

COAGULATING AGENTS

The coagulating agent used in the dairy industry may be classified in to

1. Animal (calf, lamb, cow, kid, pig)
2. Microbial (Mucor meihei, Mucor pusillus, Endothia parasitica and Bacillus subtilis)
3. Plant (Carica papaya and Ficus carica)
4. Genetically engineered or recombinant chymosin (Kluyveromyces marxianus var lactis, Escherichia coli K-12, Lactobacillus delbrueckii subspecies lactis).

The above said enzymes are referred to as peptide hydrolases because they act mainly on the casein micelle during the coagulation process of the milk.

Rennet which consists of chymosin (80%) and pepsin (20%) is extracted from the fourth stomach of a young calf, and this preparation finds extensive use in cheese industry. The ratio of pepsin to chymosin in coagulants increases as the donor animal ages and practically 100% pepsin preparations are obtained from the stomachs of cows and pigs. Rennet coagulants from other sources may also be used but due to broad specific proteolytic activity of these enzymes, there may be faults in the texture of the finished cheese.

The hydrolytic activity of chymosin on the casein micelle can be divided in to three phases. The primary phase is the destabilization of kappa casein by the enzymatic hydrolysis of the susceptible amino acid bond at the phenyl alanine methionine linkage resulting in formation of two components namely para kappa casein and casinomacropeptide.