CHANGES IN MILK 59 



mation and separation of the calcium phosphate, as 

 discussed below. 



A number of investigations have been conducted to 

 determine whether or not casein, when boiled, undergoes 

 a change in respect to digestibility ; although the results 

 do not wholly agree, such a change does not appear 

 to take place. 



Pasteurization and boiling cause no material change 

 in the fats of milk; the number of the globules is not 

 reduced, there is no fusing of the globules. Possibly 

 the quantity of volatile acids decreases, but no investi- 

 gations have been made on this subject. 



The salts of milk undergo a change upon heating, as 

 the soluble calcium salts become, in part, insoluble phos- 

 phate of lime, especially tricalcium phosphate, Ca 3 P 2 8 . 



As already mentioned, there is much reason to 

 believe that fresh milk contains a peptonizing ferment, 

 galactase; if this is the case, boiling or simply pasteur- 

 izing must, of course, destroy it. This also destroys 

 antitoxins that may be in milk. It is also safe to say 

 that toxic substances which result from diseases of the 

 cow or come from bacterial growth in milk, are made 

 at least partially harmless by continued boiling. 



It is a well-known fact that the taste and odor of 

 milk are changed by boiling; the " boiled taste " ap- 

 pears when it is heated to from 80 to 85 C., but this 

 is less strong than that produced at a higher tempera- 

 ture and is considerably lessened by prompt cooling, 

 immediately after heating. It also appears that the 

 " boiled taste " is less marked when the milk is heated 

 in a closed vessel, so that the absorbed carbonic acid 

 gas may not escape, or when the milk is boiled in the 

 presence of carbonic acid gas. 



The effect that pasteurization and boiling have upon 

 bacterial growth in milk will be taken up later. 



