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. Ywi Slyke ^ says that the average 

 percentages of elements found in the uncombined protein 

 are as follows : 



Carbon . 



Oxygen 

 Nitrogen . 

 Hydrogen 

 Phosphorus 

 Sulfur . . 



53.00% 



22.70% 



15.70% 



7.00% 



0.85% 



0.75% 



It is generally considered tliat 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-aoetic afid) CH2 . NHjCOOH 0.00 

 Alanine (a-amino-propionic acid) CH3CHCNH2 . COOH 1.50 

 Valine (a-amino-isovaleric acid) 



(CH3)2CH.CH(NH2).COOH . . . 7.20 



Leucine (a-amino-caproic acid) 



(CH3)2CH.CH2.CH(NH2).COOH . 9.35 



H2C - CH2 



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



\/ 



NH 

 Phenylalanine (phenyl-a-amino propionic acid) 



C6H5CH2.CH(NH2).COOH . . 3.20 



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

 Organic Analysis, p. 119, 1913. 



