316 



CASEIN 



generally admitted, while one or two others are possibly present in very 

 small proportion. 



Casein or, according to modern nomenclature, caseinogen, is a 

 white amorphous body, devoid of taste or smell, insoluble in water, 

 alcohol, or ether, soluble in dilute alkalies or solutions of alkaline carbon- 

 ates or phosphates. It is insoluble in dilute, but dissolves in strong, acids. 



It is capable of uniting with calcium salts, particularly the phos- 

 phate, with which it is associated in milk and from which it is freed 

 with difficulty. 



According to Halliburton's nomenclature, casein is the name given 

 to the curd formed by the action of rennet upon milk. In the milk 

 caseinogen exists and can be precipitated by acids. 



Various analyses of casein have been published. The following,, 

 by Chittenden and Painter, may be taken as typical : 



Per cent. 

 Carbon 53-30 



Hydrogen 



Oxygen 



Nitrogen 



Phosphorus 



Sulphur 



7-07 

 22-03 

 15-91 



0-87 

 0-82 



Caseinogen is capable of coagulation in two ways by the action of 

 an acid, less acid being required at high than at low temperatures ; or 

 by the action of the enzyme contained in rennet, known as rennin, lab, 

 chymosin, or pixine. This ferment is found in the stomachs of a large 

 number of animals, being generally more abundant in young than in 

 adult individuals. It, or a ferment possessed of similar powers, is 

 found in birds, fishes and in many plants ; also as a product of the 

 action of certain bacteria. 



In the case of acid coagulation, the curd formed consists of the 

 unaltered caseinogen and is almost free from calcium compounds. 



With rennet the effect is very different ; the caseinogen is changed 

 into two proteids, one of which only is readily coagulated, the other 

 with difficulty. The former is at once coagulated by the calcium salts 

 (mainly phosphate) present in cows' milk, and forms, with the en- 

 tangled fat, the curd ; the latter goes into the whey and can be coagu- 

 lated by heating to 95 or 100. The curdling of milk by rennet is. 

 thus dependent upon the presence of calcium phosphate in the milk. 



