90 



PRELIMINARY COLD STORAGE STUDIES. 



in milk kept at —1.6° C. have been observed by Pennington. a In 

 these experiments the acidity of the milk, which is due to bacterial 

 activity, increased enormously. There was also observed a very pro- 

 nounced hydrolysis of the casein, but such a degradation might be 

 ascribed either to the natural enzymes of the milk or to those produced 

 by bacteria or to a combination of the two factors. 



That enzymic activity is not stopped at 0° C. or even below it seems 

 to be generally accepted, and neither are the enzymes destroyed by 

 cold. Macfayden a found that Buchner's zymase withstood for 

 24 hours the temperature of liquid air. Very recently KovehofP found 

 that freezing for 24 hours did not destroy the proteolytic enzyme in 

 wheat, peas, and the tissue of Viciafaba. After thawing, the enzyme 

 caused a decrease in protein nitrogen, the nonprotein nitrogen in 

 one experiment reaching 48.7 per cent. 



Though able to survive low temperatures, the common enzymes 

 are greatly hindered, and the usual course of action of some of them is 

 so altered that their characteristic expression of it is quite lost. For 

 instance, Muller, a experimenting with the action of rennin on milk, 

 found that curding did not take place at 0° C, but, on the other hand, 

 the enzyme still functioned to some extent, because, when brought to 

 40° C, the curding time was greatly accelerated. The following table 

 illustrates this point: 





5 cc milk at 0° C + 1 ec of rennin, kept at 0° C for — 



Coagulation at 40° 

 C after- 





Minutes. 



Seconds. 





2 

 1 

 1 

 1 



00 



75 minutes 



50 



90 minutes 



45 





10 



120 minutes 



55 



150 minutes 





45 



24 hours 





45 







45 



96 hours 





50 









After 96 hours, at 0° C, the coagulation occurred as a fine flocking 

 which made its recognition difficult. If other enzymes behave simi- 

 larly it would tend to throw light on many obscure flesh decomposi- 

 tions which take place after cold storage has been maintained for long 

 periods. 



Some milk enzymes, however, are not only partly but wholly 

 able to function, as is indicated by the fact that galactase acts in the 

 ripening of cheese at low temperatures, and also Jansen's statement, 

 that this enzyme does not act more rapidly at 40° C. than at ordinary 

 temperatures. 



The optimum temperature for the action of the common enzymes 

 lies not far from 40° C. However, it is not yet definitely proven that, 



«Loc. cit. 



&Ber. d. botan. Ges., 25: 473. 



