Function of Rennin Enzymes

Enzymes are special type of protein produced by living cells. They act as organic catalysts that speed up the rate of biochemical reactions in any living organism. Enzymes are found from the smallest virus up to the largest oak tree in the planet. Enzymes are needed to carry out many body activities such as digestion, reproduction, respiration, coagulation (blood clotting), energy production, growth, and development. Life is unimaginable without enzymes. Each enzyme has a specific function to do. For example, the function of the rennin enzyme is to coagulate milk (curdling) into a form that can be easily digested.

Rennin (also known as chymosin) is an important proteolytic enzyme for milk digestion in young mammals (e.g. man, goat, cow, lamb, horse, etc.). It is produced by cells in the inner linings of the stomach. Immediately after birth, the stomach cells of young mammals produce plenty of rennin in preparation for milk digestion.

The function of rennin is to coagulate milk (milk curdling) so that the milk can stay longer to the stomach for proper digestion. If there is no milk curdling occur, the milk will not be digested and just pass to the intestine unabsorbed. If this happens, the young mammal could not survive since milk is its primary food after birth. Rennin production in the stomach declines as the organism grow; it would then be replaced by the protease enzyme pepsin.
How does Rennin Cause Milk Curdling?

Rennin is produced in the stomach in its inactive form: prorennin. It is only activated by hydrochloric acid produced in the stomach immediately after consuming milk. Milk contains the protein caseinogen, which is composed of four molecules: alpha-s1, alpha-s2, beta-casein, and kappa-casein. The first three molecules mentioned can be precipitated by calcium, but not the last one which is kappa-casein. Kappa-casein prevents the precipitation of alpha- and beta-caseins. The function of rennin is then to deactivate kappa-casein to allow milk coagulation.

How the Function of Rennin is Affected by Temperature?

Just like any other enzyme, rennin is affected by an increase and decrease of temperature beyond the “normal” temperature to which rennin works best. The ideal temperature that permits optimum rennin activity is 37 degress Celsius. Higher temperature can break the hydrogen and ionic bonds that gives the enzyme (a protein) its active structure. If the enzyme is destroyed as a consequence of higher temperature, it would no longer perform its function.

Lower temperature (below 37 deg. Celsius) is not also favorable because it slows down the rate of reaction. The reason why temperature affects the activity of an enzyme like rennin can be explained by the Molecular Kinetic Theory.

What are the Industrial Applications of Rennin?

Among the industrial applications of rennin is cheese production. Milk curdling by rennin is a crucial step in cheese making. Rennin from the stomach of calves and other mammals is used to make cheese. It is the common practice for centuries. However, industrial production of cheese cannot just rely on collecting rennin to calves; there should be an abundant supply of rennin to sustain large production. Certain species of bacteria are now genetically engineered to produce rennin for use in cheese making and food production.

Cheese Factory In the Netherlands (Image from Wikimedia Commons)

Cheese Factory In the Netherlands