GENERAL CHEMISTRY OF MILK 89 



AMOUNTS OF ACIDS REQUIRED TO COAGULATE BOILING MILK 



Amount required in normal cubic centi- 

 Kind of acid. meters per liter of milk. 



Hydrochloric acid 



Sulphuric acid 



Acetic acid . 



Lactic acid 



Citric acid 



Oxalic acid. . 



9 to 10 

 9.7 

 13.5 



28.5 



Phosphoric acid 34 to 35 



The quantity of acid required for complete coagulation of 

 casein depends upon the amount necessary to transform diphos- 

 phates into monophosphates. 



When casein is desiccated at a temperature above 90 C. it 

 splits into three bodies, namely, one which is soluble in dilute 

 alkali isocasein; one which forms a jelly in dilute alkali caseid; 

 and phosphoric acid. Isocasein is insoluble in water; neutral 

 solutions in alkali are not opalescent and are not coagulated by 

 rennet. Caseid is closely related to casein. 



Freshly precipitated casein is decomposed by water, but the 

 split products have not been studied. Neutral alkaline or alkali 

 earth solutions of casein decompose rapidly at body temperature. 



When a suspension of casein in water is boiled it splits into 

 several products. One substance is formed which does not com- 

 bine with alkalies as readily as casein; another one forms a soft 

 mass which adheres to the walls of the vessel and is insoluble in 

 alkalies. The filtrate from the boiled suspension of casein contains 

 2.27 per cent, of albumin and becomes opalescent when heated. 



Heating casein in water under pressure decomposes it into 

 products which are similar to those obtained by hydrolysis with 

 acids or from digestion with proteolytic enzyms. 



Hydrolysis of casein with pepsin yields different caseones. 

 Hydrolysis with tryspin yields caseone, amino-acids, and ammonia. 

 Erepsin also splits casein, although it does not attack native pro- 

 teins. Trypsin produces more profound breaking up of casein 

 than pepsin. The following products of trypsin digestion of casein 

 and lactalbumin are given by Raudnitz : 



SPLIT PRODUCTS OF TRYPTIC DIGESTION OF CASEIN AND LACTALBUMIN 



Casein, Lactalbumin, 



Split product. per cent. per cent. 



Ammonia 1.8 



Alanin 0.9 2.5 



Leucin 10.5 19.4 



Isoleucin trace 



Asparagin 1.2 1.0 



Glutamicacid 10.77 10.1 



Serin 0.43 



Cystin 0.065 



Lysin 5.8 



Diaminotrioxydodecanacid trace 



Histidin 2.6 



Arginin 5.38 



Phenylalanin 3.2 2.4 



Tyrosin 4.5 0.85 



Alpha-pyrrolidin carboxylic acid 3.1 4.0 



Oxy-alpha-pyrrolidin carboxylic acid 0.25 



Tryptophan 1.5 



