CHANGES PRODUCED IN MILK BY HEAT 



229 



off of the phosphorus from the caseinogen as the result of alkalies 

 and digestive enzymes is of interest in this connection. 



The Effect of Heat on Albumin. The albumin of both human 

 and cows' milk is affected by heating and coagulates at temperatures 

 below that of boiling-point. 



Solomin stated that albumin begins to be coagulated and hence 

 precipitated at 60 C., but that it does not coagulate completely 

 until the temperature reaches I3o-I40 C. 



Jensen and Plattner carried out elaborate investigations upon 

 the temperature of the coagulation of albumin and the extent 

 to which this occurred. The general trend of their investigations 

 is shown in the following table : 



Cows' Milk, showing Percentage Distribution of Nitrogen on Heating 



The method employed was to heat the milk to the temperature 

 required and subsequently collect the casein by the addition of 

 acetic acid. The precipitate thus obtained consisted of all the 

 casein plus the coagulated albumin. This gave the figure for the 

 casein plus albumin. The figure for the remaining albumin in 

 solution was obtained by estimating the protein in the filtrate, 

 and the figure for nitrogen in the filtrate shows the residual 

 nitrogen after the albumin had been removed. 



In the experiments where the milk was not heated the caseinogen 

 was precipitated alone in the cold and the albumin subsequently 

 precipitated by heating. The degree of precipitation of albumin 

 as a result of heating is shown to some extent in the preceding 

 table, but in addition the authors show that the soluble albumin 

 was 



Completely precipitated by 5 minutes at 90 C., 

 or 30 minutes at 80 C, 

 or 60 minutes at 77'5 C. 



When the temperature was raised above 100 C. the nitrogen in 

 the filtrate was found to be increased. This effect was produced 

 by heating either at 110 C. for half an hour or to 120 C. for from 

 five to fifteen minutes. 



It has already been mentioned that the coagulation of caseinogen 



