It is generally quite straight forward to locate the sources of enzymes; the natural sources of enzymes are where nature needs them. It comes as no surprise that rennet had traditionally been isolated from the fourth stomach of young calves because digestion by suckling calves is nature’s primary way of processing cow milk
Although rennet is naturally excreted from a calf’s stomach lining, extracting it from its natural source is not economical. Other proteases can also convert casein to para-casein, but their action does not stop there. They further degrade the curd to soluble subunits. Fortunately, large quantities of rennet of consistent quality can now be produced easier and cheaper in a well controlled environment by microbial fermentation. A word of caution is in order here. Enzymes as a class of chemicals are not generally considered as dangerous, toxic, nor poisonous; they do not cause skin irritations or burns as acids or bases. Some exceptions are proteases that catalyze the breakdown of protein molecules to amino acids components. Because meat is mainly protein, protease can digest the soft moist sections of the skin. We can all imagine how that is going to feel.
Lactic acid bacteria (LAB) are widely used in the production of fermented dairy products (FDP) due to their specific metabolic activities. The production of lactic acid is essential for the production of FDP and the development of their typical flavor. Acidification, production of organic acids, and other antimicrobial substances, such as bacteriocins, contribute greatly to the preservation of FDP by inhibiting pathogens and other contaminants.
The transformation of lactose by lactic cultures improves the digestibility of FDP. Various metabolic and enzymatic activites of LAB lead to the production of volatile substances,which contribute to flavor, aroma and texture developments in FDP. The harder the cheese, the more milk is required to produce it. For one kilo of cream cheese, 4- 5 litre milk is required. For hard cheese, it is triple the quantity of milk.