196 Report of the Chemical Department of the 



the absence of acid, does little or no work in the formation of 

 soluble nitrogen compounds in the process of cheese-ripening. 



In passing, it may be well to speak of the sources of the 

 soluble nitrogen compounds found in fresh cheese, that is, cheese 

 about 24 hours old. The milk-albumin is a fairly constant 

 source of soluble nitrogen. This is retained in cheese as a con- 

 stituent of the whey, and the quantity retained depends largely 

 upon the amount of whey held in the cheese. In ordinary normal 

 cheese, the amount varies from 1.2 to 1.5 per ct. of the nitrogen 

 in the cheese, but in extreme cases may exceed 2 per ct. In 

 addition to milk-albumin, we have, as a source of soluble 

 nitrogen compounds in fresh cheese, slight amounts of proteolytic 

 products formed from casein and paracasein during the operation 

 of cheese-making. The amount from this source varies with 

 the conditions of manufacture. It is probable that paracasein and 

 paracasein monolactate are slightly soluble in water and may 

 contribute small amounts to the soluble nitrogen compounds of 

 the fresh cheese. 



In the cheeses used in most of the experiments described in 

 this bulletin, excessive amounts of whey were unavoidably 

 retained in the cheese, and the soluble nitrogen compounds found 

 in the fresh cheese are therefore larger than in cheese holding less 

 moisture. 



ACTION OF RENNET-ENZYME IN THE PRESENCE OF ACIDS IN 

 CHEESE-RIPENING. 



In experiments 45, 46, 48 and 51, we added to the milk enough 

 lactic acid to equal about 0.2 per ct. of the milk by weight. 

 We thus had only two factors that could act as proteolytic agents 

 in the cheese, the rennet-enzyme and the acid. The results of 

 these experiments are given in Table II. 



