RENNET-ENZYME AS A FACTOR IN 

 CHEESE-RIPENING.* 



L. L. VAN SLYKE, H. A. HARDING and E. B. HART. 



SUMMARY. 



I. The object of the work described in this bulletin was to ascer- 

 tain to what extent the formation of soluble nitrogen compounds in 

 cheese-ripening is due to the rennet-extract used in cheese-making. 

 In the case of the work previously done here and elsewhere, the 

 effect of rennet-enzyme has not been studied apart from the action 

 of other factors that are present in cheese-ripening. It was our pur- 

 pose to study its action by itself, apart from other proteolytic agents. 



II. The action of rennet-extract was first studied in cheese con- 

 taining rennet-enzyme as the only ])roteolytic factor, with and with- 

 out acid, and also with and without salt. In these experiments (44 

 to 51), all milk-enzymes were destroyed by heating the milk at 95"C. 

 to 98°C. (203°F. to 2o8°F.), the coagulable property of the milk- 

 casein was restored by the addition of either calcium chloride or 

 carbon dioxide gas, and all organisms were rendered inactive by 

 chloroform. Acid, when present, was furnished by addition of pure 

 lactic acid. 



III. The action of fresh rennet-extract on casein in milk, with 

 and without acid, was studied in comparison with old rennet-extract, 

 and also in comparison with commercial pepsin. In these experi- 

 ments, the milk-enzymes were destroyed by heat and all organisms 

 were rendered inactive bv chloroform. 



^\ reprint of Bulletin No. 233. 



