198 Report of the Chemical Department of the 



enzyme in cheese-ripening is dependent upon the presence of 

 acid, 



ACTION OF RENNET-EXTRACTS OF DIFFERENT AGES AND OF 

 COMMERCIAL PEPSIN ON MILK-CASEIN. 



In considering the results obtained in cheese-ripening by the 

 use of rennet-extract, the question may arise as to whether the 

 observed proteolytic changes were due to rennet-enzyme alone 

 or whether the rennet may not have contained some proteolytic 

 bacterial enzymes produced in the rennet-extract previous to its 

 use. In order to answer this question, we tried the effect of two 

 samples of rennet-extract upon milk-casein, using one extract 

 known to be in good condition and one known to be old and 

 apparently in the first stages of putrefaction. These experiments 

 were carried out in the following manner: We heated 8.6 liters 

 of milk for 15 minutes at 85° C. (185° F.), and after cooling 

 added 2 per ct. of chloroform by volume. Of this milk, we 

 placed in each of several bottles 100 cc. In one case, we added 

 to the neutral milk 0.22 cc. of Hansen's fresh rennet-extract, and 

 in another the same amount of old rennet-extract. In other 

 bottles, we added, in addition to the rennet-extract, 0.5 cc. of pure 

 concentrated lactic acid. For comparison, we placed in other 

 bottles, with and without acid, the same amount of milk and 

 0.06 gram of Parke, Davis & Co.'s aseptic scale pepsin for each 

 7 grams of proteid contained in the milk. Duplicates were used 

 in all cases. The contents of these bottles were kept at 15.5° C. 

 (60° F.) and were examined at intervals both chemically and 

 bacteriologically. With the exception of a single determination 

 in the case of one bottle, the germ content was below 50 per cc, 

 which undoubtedly represented spore forms. 



The results of chemical analysis are given in the subjoined 

 table. 



The determinations of nitrogen in the form of amides were 

 made by the use of phosphotungstic acid, since it has been 

 shown 3 that, in the case of peptic digestion, phosphotungstic 

 acid is a more satisfactory reagent than, tannic acid, especially in 

 solutions having an acid reaction. The amount of nitrogen 

 originally in the milk was 0.561 per ct. 



3 New York Agr. Exp. Sta. Bui. No. 215, pp. 90 and 98 (1902) 



