Final answer:
Rennin, or chymosin, curdles milk by acting on the protein casein to make cheese. However, hard boiling milk denatures its proteins, including casein, which prevents rennin from working properly and makes it impossible to produce cheese from such milk.
Step-by-step explanation:
Rennin, also known as chymosin, is an enzyme crucial for cheese production. It works by curdling or coagulating the milk, separating it into solid curds and liquid whey.
Chymosin is particularly effective at coagulating milk because of its action on casein, the main protein present in milk. The use of rennin is a key factor in making cheese, as it allows the curds to be separated and processed into cheese.
However, when milk is hard boiled, it undergoes a physical change which denatures the proteins, including casein, making them unable to form the proper structures for cheese.
Enzymes like rennin are highly specific and work under certain conditions. Heat alters the structure of casein to a point where rennin can no longer bind to it and perform its function, thus rendering it useless in the cheese-making process after milk has been hard-boiled.
Modern cheese production often uses genetically engineered chymosin which is created using microbial cells such as E. coli to maximize efficiency and cost-effectiveness. Despite this technological advancement, the basic principle of enzyme action remains unchanged, meaning hard-boiled milk still cannot be used for making cheese.