A STUDY OF ENZYMES IN CHEESE * 



L. L, VAX SLYKE, H. A. HARDING AND B. B. HART. 



SUMMARY. 



7. Introduction.— Cheddar cheese contains enzymes coming 

 from (1) bacteria, (2) milk glands of cows and (3) rennet. These 

 enzymes, or chemical ferments, change insoluble cheese-casein 

 into soluble nitrogen-compounds. The investigation has aimed 

 to exclude bacterial action in cheese and limit the action to 

 results produced by enzymes present in milk when made into 

 cheese. 



//. Historical outline. — Early work done to show whether 

 enzymes were active in cheese ripening gave negative results, 

 owing to faulty methods of investigation, Babcock and Russell 

 furnished the first positive evidence in 1897 in the discovery of 

 the enzyme galactase in milk. They and others have also shown 

 the power of rennet-enzymes to render cheese-casein soluble. 



///. Methods of chemical analysis used. — Outlines are given to 

 show methods used in determining total nitrogen, water-soluble 

 nitrogen and nitrogen in forms such as albumoses, peptones, 

 amides and ammonia; also method of determining chloroform in 

 cheese. In milk, the term soluble nitrogen includes aJl nitro- 

 gen-compounds except casein and albumin; in cheese, it includes 

 all the nitrogen soluble in water under the conditions indicated. 



IV. Effect of chloroform, ether and formalin on the action' of 

 enzymes. — (1) The effect of quantities of chloroform, varying from 

 2^ to 30 per ct. in milk, covering a period of 102 days, is shown 

 to be apparently small in respect to restraining enzyme action. 

 (2) It is shown that increase of fat in a mixture has little or no 



*A reprint of Bulletin No. 203, 



165 



