A STUDY OF ENZYMES IN CHEESE.* 

L. L. VAN SLYKE, H. A. HARDING AND B. B. HART. 
SUMMARY. 
I. 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. 
II. 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. 
III. Methods of chemical analysis used.—Outlines are given to 
show methods used in determining total nitrogen, water-solubie 
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 adl nitro- 
gen-compounds except casein and albumin; in cheese, it includes 
all the nitrogen soluble in water under the conditions indicated. 
IV. Ejfect of chloroform, ether and formalin on the action of 
enzymes.—(1) The effect of quantities of chloroform, varying from 
24 to 30 per ct. in milk, covering a period of 192 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 
