230 MILK AND ITS HYGIENIC RELATIONS 



does not occur at temperatures below boiling-point, but Jensen 

 and Plattner considered that such coagulation does occur when the 

 milk is heated for half an hour at 130 C. or for five minutes at 

 140 C., and they believe that the brown colour which appears 

 in milk when heated to these temperatures is due to a com- 

 mencing disintegration of caseinogen. 



Grosser estimated the total nitrogen content of both cows' 

 milk and human milk at different temperatures. He removed 

 the protein from the milk used by him by passing it through a 

 Bechhold filter under pressure of six atmospheres of nitrogen. 1 



It seems certain that when milk is boiled some of the 

 albumin is precipitated, but where the same vessel is used for 

 storage and feeding purposes, there is no difficulty in maintaining 

 the same amount of nitrogen in the food. There is no indication 

 that there is any difficulty in the digestion of the coagulated 

 albumin ; in fact it is probably more readily digested than in the 

 raw state. 



Caseinogen is not coagulated, and such evidence as is avail- 

 able tends to show that it is more readily digested after heating than 

 before. There would not appear, therefore, to be any disadvantage 

 in the heating of milk in relation to the protein portion of this 

 food. 



Lactose. There is abundant evidence to show that no altera- 

 tion occurs in lactose unless the temperature be raised considerably 

 above 100 C., or unless the boiling be carried out for a very prolonged 

 period. 1 



Fat. Changes in the fat as a result of heating have been investi- 

 gated by several observers. 



Jensen and Plattner showed that the fat does not undergo any 

 hydrolysis as a result of boiling. 



Woll heated the milk he was investigating in a steriliser for 

 several successive days for a period of thirty to thirty-five minutes, 

 and found practically no change in the size of the fat globules. 

 He obtained, however, some slight decrease in the viscosity in the 

 first period of sterilisation and also with pasteurisation for twenty 

 minutes at 67 C. When the sterilisation was repeated more than 

 once, a slight rise in the viscosity was found to occur. 



Purvis, Brihaut and McHattie found that there was some 

 decrease in the fat content when milk was boiled, which amounted 

 to approximately 60 per cent, of the total fat, which loss was 

 replaced by a gain of 13 per cent, when the milk was sterilised at 

 a temperature of no-i30 C. They found that less loss occurred 

 when the milk was boiled in closed vessels, but the figures obtained 

 in the different experiments gave somewhat unequal results. 



Calcium. The calcium content of milk in its raw condition 

 has already been considered in Chap. IV, and it is not proposed 



1 See table on p.- 232. 



* Cp. Splittgerber, Jensen and Plattner, and others. 



