SUMMARY OF CHAPTER XIV 



CHANGES OCCURRING IN MILK AS A RESULT OF THE 

 APPLICATION OF HEAT 



WHEN the use of boiled milk first became at all general, certain 

 observers believed that they noticed a detrimental influence upon 

 the children who were fed with milk which had been subjected to 

 heat. The chemical changes which undoubtedly occur as a result 

 of heating at temperatures not exceeding 100 C. were investigated 

 by a considerable number of observers. Many of these investigators 

 at once attributed the detrimental effects said to have been noticed, 

 to the changes which they discovered in the milk, very frequently 

 without any attempt to connect the statement with fact. 



It was found that the application of heat produced a lowering 

 of the calcium content of milk by throwing the calcium out of 

 solution. The amount of calcium precipitated was found to be 

 different by the different authors who investigated the subject. 

 In any case only a portion of the calcium falls out, and the total 

 calcium content of cows' milk appears, even after boiling, to be 

 equal to, or higher than, that of human milk. The changes in 

 acidity and the delay in clotting with rennet, which were found 

 to occur as a result of heating, were studied in detail. It is probable 

 that both these phenomena are connected either directly or indirectly 

 with the calcium content of the milk, and the changes occurring 

 therein as a result of heating. 



Changes also occur in the protein on heating, but unless the 

 temperature is allowed to reach considerably above 100 C. these 

 changes appear to be confined to the albumin fraction. Different 

 observers have given different temperatures for the commencement 

 of precipitation of the albumin. It seems probable that compara- 

 tively little change, if any, occurs below the temperature of 65 C., 

 but that after this temperature has been reached an increasing 

 amount of albumin is precipitated, the amount depending not 

 only upon the absolute temperature reached, but also upon the 

 length of time of heating. 



Changes of a more radical character do not take place in the 

 milk unless the temperature is raised above 100 C. In the process 



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