CHANGES PRODUCED IN MILK BY HEAT 227 



milk when compared with human milk. It may therefore be 

 reasonably assumed that, in relation to infant feeding, boiling pro- 

 duces no detrimental effect upon the ash of milk. Moreover, it 

 may be mentioned that these substances only pass from the soluble 

 to the insoluble state, and there is no reason for supposing that 

 they are incapable of being assimilated by the infant in this latter 

 form. 



Generally speaking, the changes which occur on heating milk 

 to a temperature of about 100 C. for a short period cannot be 

 regarded as having any detrimental influence from the nutritional 

 standpoint. Above this temperature changes undoubtedly occur, 

 but for the most part high temperatures are not employed to any 

 extent in connection with the feeding of infants. 



CHAPTER XIV 



CHANGES OCCURRING IN MILK AS A RESULT OF THE 

 APPLICATION OF HEAT 



IT would not appear necessary to enter at any length into a dis- 

 cussion of the literature concerned with the chemical changes 

 produced by the heating of milk. The evidence which has been 

 brought forward in the preceding chapters, provides sufficient 

 testimony to the value of heated milk as a food for infants. Any 

 additional consideration of the chemical changes taking place on 

 heating is therefore a matter of interest, rather than directly con- 

 nected with the hygienic aspect of the milk question. 



In view of the great discussion which has taken place during 

 this century, and earlier, upon the changes due to heating, it 

 is proposed to consider briefly the more important papers dealing 

 with various aspects of this subject. There can be no question 

 that changes do occur in connection with the heating of milk, but 

 the degree of change is dependent upon the temperature and the 

 length of time over which that temperature is maintained. The 

 changes in the more important constituents alone will be con- 

 sidered here. 



Changes occurring in the Protein Constituents of Milk as a 

 Result of Heating. The proteins of milk have been considered 

 already in Chap. Ill, where reference was made to the different 

 proteins occurring in milk and to their relative proportions in 

 both human and cows' milk. It was there stated that caseinogen 

 forms the major part of the protein of cows' milk, while in human 

 milk the proportion of caseinogen to albumin is more equal. 



Effect of Heat on Caseinogen. Caseinogen is not coagulated 



