Rennin is a historically significant enzyme, a biological catalyst that accelerates biochemical reactions. It plays an important role in digestion and has been used in human traditions for centuries. Its unique properties have made it a subject of scientific interest and practical application.
Understanding Rennin’s Identity
Rennin, also known as chymosin, is a proteolytic enzyme. It is primarily found in the stomach of young mammals, particularly newborn calves, in the abomasum. While “rennin” is traditional, “chymosin” is preferred in scientific and industrial contexts. Humans, chimpanzees, and horses do not naturally produce rennin due to inactivating mutations in their chymosin gene, relying on other enzymes like pepsin for milk protein digestion.
The Mechanism of Milk Coagulation
Rennin’s primary function is milk coagulation, a process central to its biological and industrial roles. Milk proteins, mainly caseins, form complex structures called micelles. Kappa-casein stabilizes these micelles by forming a protective, hydrophilic layer on their surface, preventing clumping.
When rennin is introduced, it acts as a highly selective molecular scissor, precisely cleaving a bond within the kappa-casein molecule. This removes the hydrophilic portion, known as the macropeptide, from the micelle surface. With the stabilizing layer compromised, the remaining para-kappa-casein loses its ability to keep micelles dispersed. In the presence of abundant calcium ions, these destabilized micelles aggregate and precipitate, forming a solid curd and separating from liquid whey. This rapid transformation turns liquid milk into a semi-solid mass.
Rennin’s Natural and Industrial Significance
Rennin plays an important role in the natural digestive processes of young mammals. It causes milk to curdle in the stomach, transforming it into a semi-solid. This coagulation slows the passage of milk through the digestive system, allowing more time for other enzymes to act on proteins and for efficient nutrient absorption. This process is especially important in newborn calves, where rennin secretion is maximal shortly after birth.
Beyond its natural biological function, rennin is widely used in the food industry, particularly in cheesemaking. Its ability to separate milk solids (curds) from liquid (whey) is fundamental for cheese production. Traditionally, rennin was extracted from the stomachs of young calves to produce rennet. As cheese demand grew, alternatives emerged, including microbial sources and fermentation-produced chymosin (FPC), which is genetically engineered. Today, FPC accounts for a large portion of the rennet market, offering a consistent and often purer product than animal-derived rennet.
Differentiating Rennin from Renin
The similar-sounding names “rennin” and “renin” often cause confusion, but they are distinct biological molecules. Rennin is a proteolytic enzyme primarily involved in milk digestion and coagulation in the stomach of young mammals. Its action is localized to the digestive system.
In contrast, renin is a hormone and enzyme produced by the kidneys. It plays a role in the body’s renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure and fluid balance. Renin acts on angiotensinogen, converting it into angiotensin I, which influences blood vessel constriction and fluid retention. Thus, rennin is a digestive enzyme for milk proteins, while renin is part of a hormonal system regulating cardiovascular function. They are separate entities with different spellings, sources, and physiological roles.