CHANGES IX MILK 5i) 



Illation and separation of the calcium phosphate, as 

 discussed below. 



A number of investigations have been conducted to 

 iletermine 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 iilace. 



Pasteurization and boiling cause no material change 

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

 reduced, there is no fusing of the globules. Possibly 

 the quantity of volatile acids deci-cascs, but no investi- 

 gations have lieen 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, ( 'a PJ )^. 



As already mentioned, there is much reason to 

 believe that fresh milk contains a peiitonizing fennent, 

 (/((hichisf; if this is the case, boiling or simply i)asteur- 

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

 antitoxins that ma>- 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 l)y continued l)oiling. 



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 SO"' to S.'i-' ('., but this 

 is less strong than that produced at a higher tempera- 

 ture and is considerably lessened liy prompt cooling, 

 immediately after heating. It also apjiears 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 

 l)resence of carbonic acid gas. 



The action that pasteurization and boiling have upon 

 bactei'ial growtli in milk will be taken up later. 



