A METHOD OF DETECTING RENNET PRODUCTION 



BY BACTERIA 



H. J. CONN 



New York Agricultural Experimtnt Station, Geneva, New York 



Received for publication January 19, 1922 



The usual method for determining whether bacteria produce 

 rennet or rennet-Uke enzymes is to inoculate the organisms under 

 investigation into tubes of sterilized milk and then to notice 

 whether or not the milk curdles without the production of acid. 

 This method has several weaknesses. Heated milk is not as 

 readily curdled by enzymes as unheated milk and the curd 

 produced is often so soft that it can scarcely be detected; when 

 an organism produces peptonizing enzymes as well, the presence 

 of curd before peptonization is often difficult to demonstrate; 

 certain organisms curdle the milk through the action of enzymes 

 and subsequently bring about an acid reaction, so that it is 

 difficult to tell whether the milk has been coagulated by the 

 acid or by an enzj^me. 



It is possible by the following very simple method to avoid 

 these weaknesses of the usual technic. Inoculate the culture 

 under investigation into the milk in the usual manner,' then 

 incubate for twentj'-four hours or such time as is necessary to 

 allow the organism in question to produce vigorous action in 

 the milk with at least 0.5 cc. of whey on the surface. At the 

 end of this incubation period obtain fresh milk and place 10 cc. 

 of it in a test tube, but do not sterihze it. Warm this milk to 

 about 37°C. Then add to the milk a measured quantity, say 

 0.5 CO., of whey from the incubated culture and place in a 37° 

 incubator. Examine every five minutes for the first half hour 

 and, if not curdled then, at less frequent intervals for a few hours 

 longer. If rennet is present in any abundance, the milk is or- 

 dinarily curdled inside of half an hour. By varying the quantity 



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