Rennin breaks down casein in milk products.
It’s also known as chymosin and is a proteolytic enzyme produced by the chief cells in the stomach. Its purpose is to curdle milk in the stomach. This prevents the milk from flowing through the stomach so that the proteins can be digested. This is very important in children. Rennin is at its highest amount during the first few days after birth, then declines and is replaced by pepsin as the major protease. Chymosin is secreted in an inactive form called prochymosin. Just as pepsinogen is converted to pepsin by exposure to stomach acid it too is converted to the active form by acid.
Chymosin is an important industrial enzyme as it is used in cheese making.