ENZYMS IN MILK 237 



Based on the presence of some enzyms found in milk several 

 tests have been devised for the purpose of detecting whether milk 

 has been heated to a certain temperature to control pasteuriza- 

 tion, or to simulate raw milk. Some of these tests depend upon 

 color production from colorless compounds by oxidation by a 

 peroxydase or superoxydase in presence of hydrogen peroxid. 

 Other tests depend upon the reduction of colored compounds 

 by reductases. When the temperature applied has been high 

 enough to destroy the enzyms there is no reaction, but the tempera- 

 ture required by different enzyms is not the same, and therefore 

 it was expected that the tests would be of considerable value. 



However, no reliable test depending upon destruction of en- 

 zyms has been devised that can be applied to milk pasteurized at 

 low temperature. Whether such a test is possible can only be 

 determined by patient research among the enzyms usually found 

 in milk. 



The reducing power of milk has also been used for a rough 

 estimation of bacterial pollution, since bacteria have the property 

 of decolorizing methylene-blue. The following method is prac- 

 tised for this purpose: A methylene-blue solution is prepared by 

 dissolving 2 grams methylene-blue in 100 c.c. 50 per cent, alcohol. 

 The test is then carried out in this manner: Place in test-tubes 

 falling amounts of milk from 1 to 0.05 c.c., add to each tube 3 

 drops of the methylene-blue solution, and fill with boiled milk 

 to a volume of 10 c.c. As control fill a tube with 10 c:c. of the 

 same boiled milk and 3 drops of methylene-blue solution. Then 

 cover the surface of the mixtures of milk and methylene-blue with 

 melted paraffin .or paraffin oil and incubate all tubes at 37 C. 

 One c.c. of fresh raw milk will be decolorized in one to two hours. 

 Old milk or heavily contaminated milk is decolorized in a shorter 

 time. Heated milk is decolorized slowly. If heated to 60 C. 

 for twenty minutes the milk is decolorized after about six hours, 

 while boiled milk takes a much longer time for decolorization. 



The following test for catalase according to Koning is used to 

 detect the presence of milk from diseased udders: Place in a 

 graduated fermentation tube 5 c.c. of a 1 per cent, solution of 

 hydrogen peroxid and 15 c.c. of the milk to be tested. The 

 amount of oxygen liberated after two hours' incubation at room 

 temperature should not exceed 2.5 c.c. Abnormal milk produces 

 more oxygen. Van Slyke states that if milk is more than six 

 hours old and more than 4 c.c. oxygen are in the closed arm, the 

 milk has been derived from a diseased udder. 



The catalase test is also indicative of heated milk. The test 

 may be carried out as follows: 25 c.c. of the milk and 0.5 c.c. of 

 Merck's perhydrol are placed in a fermentation tube, which is 



