Re: please tell me about rennin, its effects on Casein, and its optimum pH+temp

Hannah –
	Rennin is also known as an enzyme called chymosin. As you may well 
know, enzymes are proteins that catalyze a reaction. In the case of 
chymosin, the reaction involves the breakdown of casein in milk resulting 
in clot formation in the presence of calcium ions – this is the basis for 
the production of many varieties of cheeses.  Chymosin belongs to a family 
of enzymes called the aspartic proteinases. The reason that it belongs to 
this family is because it possesses an aspartic acid residue at the active 
site of the enzyme.
	Calf chymosin is secreted from the fourth stomach of the calf and 
while its exact function is not known, there are currently some ideas 
about what function it does serve for the calf.  As stated earlier, 
chymosin breaks down casein resulting in clot formation (in the presence 
of calcium ions).  More specifically, chymosin preferentially cleaves one 
"type" of casein, kappa-casein; again, the reason for this is unknown.  
One hypothesis states that the clot formation may retard the passage of 
food from the stomach to the intestine allowing the calf to extract 
nutrients from the clot. Also, clot formation may also stimulate further 
digestive reactions that will be essential as the calf matures.  Since 
chymosin is a gastic enzyme, the pH, which it is most active, is quite 
low; its optimum pH is approximately 3.5.  The optimum temperature is 
around 37 degrees C – which is the approximate body temperature of the 
calf.  
	The demand for calf chymosin for use in cheesemaking is greater 
that the supply of the enzyme; therefore, alternative milk clotting 
enzymes have been sought out for use.  These include bovine chymosin, 
porcine (pig) chymosin, fungal extracts, bacterial extracts, and 
recombinant chymosin (that is, the gene encoding calf chymosin has been 
genetically engineered into E. coli to produce chymosin).
	I hope that this has provided some more insight about rennin 
(chymosin).  Best of luck 
:-)                                               
A couple of references that may be of use:  

Foltmann, B. 1970.  Prochymosin and chymosin.  Methods Enzymol. 19:421-436.

Foltmann, B. 1987. General and molecular aspects of rennets. In: Fox, P. 
(ed.) Cheese: Chemistry, Physics and Microbiology, vol. 1. Elsevier 
Applied Science Publishers. pg. 33-61.

	Glynis K. 
	Rutgers University, Food Science