12 THE BOOK OF BUTTER 



A study of the curd is essential in ascertaining some 

 of the possible causes of certain flavors and other 

 changes in butter. Van Slyke 1 says that the average 

 percentages of elements found in the uncombined protein 

 are as follows : 



Carbon 53.00% 



Oxygen 22.70% 



Nitrogen 15.70% 



Hydrogen 7.00% 



Phosphorus 0.85% 



Sulfur 0.75% 



It is generally considered that casein is present in milk 

 as the compound calcium casein, containing in combina- 

 tion about 1.5 per cent calcium oxide. Osborne and 

 Guest, as quoted by Van Slyke, say : " Our present 

 knowledge of the structure of any protein is stated by 

 giving the percentages of the different amino-acids formed 

 by hydrolysis of the protein. The products of the hy- 

 drolysis of casein have been extensively studied, and the 

 following summary may be regarded as the most reliable 

 up to the present time " (formulae quoted) : 



PER CENT 



Glycocoll or glycine (amino-acetic acid) CH 2 . NH 2 COOH 0.00 

 Alanine (a-amino-propionic acid) CH 3 CHCNH 2 . COOH 1.50 

 Valine (a-amino-isovaleric acid) 



(CH 3 ) 2 CH.CH(NH 2 ).COOH .... 7.20 

 Leucine (a-amino-caproic acid) 



(CH 3 ) 2 CH.CH 2 .CH(NH 2 ).COOH . . 9.35 

 H 2 C - CH 2 



I I 

 Proline (pyrrolidine-carboxylic acid) H 2 C CH . COOH . 6.70 



NH 

 Phenylalanine (phenyl-a-amino propionic acid) 



C 6 H 5 CH 2 .CH(NH 2 ).COOH 3.20 



1 Van Slyke, L. L., Proteins of Milk, Allen's Commercial 

 Organic Analysis, p. 119, 1913. 



