NUTKITIVE VALUE OF FISH AND SHELLFISH 529 



ANALYSES OF THE PROTEINS 

 FORM OF NITROGEN 



Upon extraction of fresh fish muscle with water the following 

 substances are obtained: Histidine, hypoxantliine, carnosine, tyro- 

 sine, creatine, and creatinine. Of these, histidine and tyrosine are 

 especially valuable in nutrition. 



A study of the proteins of fish by the Hausmann method of analysis 

 gives some information concerning their nutritive value. According 

 to tliis procedure the amounts of ammonia nitrogen, monoamino 

 nitrogen, diamino nitrogen, and humin nitrogen are determined. 

 Since humin nitrogen is found chiefly by the decomposition of the 

 amino acid tryptophane, which is essential for proper nutrition, the 

 percentage of humin nitrogen found may be taken as an index of the 

 quantity of tryptophane in the protein. The diamino nitrogen 

 includes the nitrogen in the form of the diamino acids, arginine, 

 histidine, and lysine. Since any diet must contain an ample amount 

 of lysine and either arginine or histidine, or both, it is interesting to 

 note whether or not the fish that have been analyzed are deficient in 

 diamino nitrogen. From the data given in Table 19 it is seen that 

 the proteins of halibut, cod, herring and scallops compare very favor- 

 ably with those of beef and cliicken in then- content of diamino and 

 humin nitrogen. 



Table 19. — Analyses showing form of nitrogen in certain fish, meats, etc} 



[Total nitrogen =100] 



1 Compiled from papers published by Drummond (1918-1919), and Osborne and Heyl (1908). 



The Hausmann method does not give much information concern- 

 ing proteins that is of value from a nutrition viewpoint, but as 

 it is comparatively rapid and does not require a high degree of 

 skill it has been used in the examination of a very large number of 

 proteins. Physiological experimentation and the deteraiination of 

 the individual amino acids are required to obtain much information 

 conc'erning the nutritive value of protiens. No two physiological 

 chemists agree entirely as to the procedure that should be followed in 

 feeding experiments in determining the nutritive value of a given 

 protein. On this account there is some disagi'eement between 

 chemists as to the exact value of many proteins in the diet. The 

 increase in our knowledge concerning the amino acid content of 

 proteins is aiding in the proper evaluation of proteins from a nutritive 

 standpoint. 



