Why does increasing the concentration of Rennin, increase the rate at which it coagulates with milk?

Question

scientific answers please

Answer 1

Milk is an emulsion of fat and water. This means that that there are two 'phases' in the milk that do not naturally mix; the way the fat and the water stays mixed is by proteins. The proteins in milk, mainly one type called 'casein,' coat the little blobs of fat and allow them to stay soluble in the water 'phase,' called 'whey' for milk. The type of casein that is on the outside of the fat blobs is called kappa-casein. Kappa-casein is what is called a 'phospho-protein,' a protein that has phosphate molecules on it. Phosphates are naturally negativley charged, and like charges repel, so the fat globs naturally repel eachother and don't stick together. But when an acid is introduced, like lemon juice, the proteins' charges are reduced, and the globs stick together. Rennin does the same thing. Rennin is a protein, and protein that degrades other proteins, that makes it a 'proteolytic enzyme,' or just a 'protease.' Rennin cleaves the kappa-casein molecules' repulsive sections, this make the blobs able to stick together and form a solid, in milk it is called 'curds.' Hope this helps.
-But why does an increase in rennin increase the rate? Rate is measured by units of product per unit time- or let's say milliliters of milk clotted per minute. Each molecule of rennin can only destroy so much milk at a time. The more rennin added to the milk, the more clotting activity will take place, therefore the more rate you will have. There is a point at which there will be more rennin then kappa-casein and at this point the rate will no longer go up with the addition of more rennin; this is called saturation. I doubt you could added too much rennin to milk to the point of sturation, or at least it would be way too expensive to do it.