Rennin is a protease enzyme that plays a role in biological and industrial processes. Its primary function is to coagulate or curdle casein, a major protein found in milk. This action transforms liquid milk into a more solid form, with implications for both digestion and food production.
The Role of Rennin in Digestion
Rennin, also known as chymosin, is produced in the stomachs of infant ruminant mammals, such as calves, goats, and camels. It is found in the lining of their abomasum, known as the fourth stomach. The enzyme’s main purpose is to curdle milk ingested by these young animals.
This curdling action slows the passage of milk through the digestive system, converting it from a liquid into a semi-solid, cheese-like consistency. This allows for a more prolonged and complete absorption of nutrients before the milk moves further down the intestine. While human infants also digest milk, this function is primarily carried out by other enzymes like pepsin, as humans do not produce rennin.
Rennin in Cheesemaking
Rennin is a valued ingredient in the cheesemaking industry, serving as the primary active component in traditional rennet. It initiates the process of milk coagulation, which separates milk solids from liquids. This activity forms the solid curds that become cheese.
The enzyme works by targeting and cleaving a protein called kappa-casein, located on the surface of casein micelles in milk. Rennin breaks a peptide bond within the kappa-casein molecule. This cleavage removes the protective, negatively charged “hairy” layer that normally keeps the casein micelles suspended. Once destabilized, in the presence of calcium ions, the casein micelles aggregate and form a three-dimensional protein network, creating the solid curds and releasing the liquid whey.
Distinguishing Rennin from Similar Terms
Understanding rennin involves differentiating it from two similarly named terms: rennet and renin. Rennin is the enzyme, also known as chymosin, responsible for coagulating milk proteins.
Rennet, in contrast, refers to the commercial preparation or mixture that contains rennin as its active ingredient. Traditionally, rennet was extracted from the stomachs of young calves, but modern cheesemaking also utilizes rennet derived from microbial or plant sources. This commercial product contains other enzymes, such as pepsin, alongside rennin.
Another term, renin (spelled with a single ‘n’), is distinct from rennin. Renin is an enzyme produced by the kidneys in mammals, including humans. Its primary function is to regulate blood pressure and maintain fluid balance within the body. Renin accomplishes this by initiating reactions that impact blood vessel constriction and fluid retention.