446 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



THE COAGULABLE PROTEINS OF MILK. 



In addition to the protein caseinogen (p. 460), milk contains small 

 quantities of coagulable proteins, lactoglobulin and lactalbumin, which 

 closely resemble those of blood. 



Lactoglobulin. 



Milk is saturated with finely powdered sodium chloride to remove the 

 caseinogen. The nitrate is saturated with magnesium sulphate. The pre- 

 cipitate is dissolved in water and again precipitated and the process is repeated. 

 The precipitate is dissolved in water and dialysed to remove salts, or coagu- 

 lated by heat in acid solution. 



Lactoglobulin closely resembles serum globulin. Crowther and Raistrick's 

 analysis of lactoglobulin points to its identity with serum globulin. 



Lactalbumin. 



Milk is saturated at 30 with magnesium sulphate which precipitates the 

 caseinogen and lactoglobulin. The nitrate is acidified with acetic acid so 

 that the content of acid is about i per cent. The precipitate is filtered off, 

 pressed out and dissolved in water ; the solution is neutralised and dialysed ; 

 the lactalbumin is obtained on evaporation in vacuo, or as coagulated protein 

 by heat coagulation or by precipitation with alcohol. 



Lactalbumin is very similar to serum albumin but differs in rotation and 

 percentage composition. It has been obtained in a crystalline state in the 

 'same way as serum albumin. It behaves like serum albumin in other 

 respects. 



