MILK AND MILK PRODUCTS 



MILK 



Milk, the nutritive secretion of nursing mammals, consists 

 of water, fat, proteids, sugar, and mineral matters. Cow's 

 milk is meant in all cases, unless otherwise stated. 



Fat. — This occurs in globules varying from 0.0015 ™i^- to 

 0.005 ™i^' in^ diameter, in a condition which prevents spon- 

 taneous coalescence. It is peculiar among animal fats in con- 

 taining a notable proportion of acid radicles with a small num- 

 ber of carbon atoms. 



Proteids. — ^The nature of the proteids of milk has been 

 much discussed, but it is now generally conceded that there are 

 at least three forms, casein, albumin, and globulin, the casein 

 being present in by far the greatest amount, and the globulin as 

 traces only. 



Casein. — Casein is, probably in part, in combination with 

 phosphates. It is precipitated by many substances, among 

 which are acids, rennet, and magnesium sulfate, but not by 

 heat. Acids precipitate it by breaking up the combination 

 with phosphates. The action of rennet is complex and probably 

 partly hydrolytic, splitting the casein into several proteids, some 

 of which are precipitated in the curd. Films of proteid matter 

 occur abundantly in milk, for which reason it is distinctly 

 opaque, even when nearly all the fat has been removed by 

 centrifugal action. 



The albumin of milk appears to be a distinct form, and is 

 called lactalbumin. It is not precipitated by dilute acids, but 

 is coagulated by heating to 70° — 75°. The proportion in cow's 

 milk is usually from 0.35 to 0.50 per cent., but colostrum may 

 contain much larger proportions. 



Globulin is present only in minute amounts in normal milk, 



