268 



PHYSIOLOGY OF THE FUNGI 



Table 46. Approximate Amino-acid Composition (in Per Cent) of Some Plant 

 AND Animal Proteins Calculated to 16 Per Cent Nitrogen 

 (Block and Boiling, Arch. Biochem. 7, 1945. Published by permission of Academic 

 Press, Inc.) 



Amino acid 



Arginine 



Histidine 



Lysine 



Tyrosine 



Tryptophane . 

 Phenylalanine 



Cystine 



Methionine . . . 

 Threonine. . . . 



Leucine 



Isoleucine .... 

 Valine 



Polished 

 rice 



7.2 

 1.5 

 3.2 

 5.6 

 1.3 

 6.7 

 1.4 

 3.4 

 4.1 

 9.0 

 5.3 

 6.3 



* Eight strains analyzed. 



The value of fungus protein in nutrition can be assessed only in relation 

 to the amino-acid composition of the remainder of the diet. If the 

 dietary proteins are low in certain essential amino acids, the supplemen- 

 tary value of yeast (or other) protein may be great. The cereal grains, 

 which furnish the bulk of protein for the population of the world, are 

 generally low in one or more essential amino acids. Usually cereal 

 protein is low in lysine or tryptophane or both. Sure (1946, 1947) studied 

 the effect on the growth of rats of adding 1, 3, and 5 per cent of dried 

 yeast to diets which contained cereals as the sole source of protein. The 

 most marked effect of yeast occurred on a maize diet. At the end of a 

 10-week experimental period the rats receiving only cereal weighed 

 27.3 g., while the rats which received an additional 1 per cent yeast 

 weighed 50.5 g. Rats which received the cereal plus 3 and 5 per cent 

 yeast weighed 91.8 and 109.9 g., respectively. The effect of yeast was 

 not so great when wheat or rice supplied the protein in the diet. In 

 general, the most promising use of yeast protein in human nutrition is 

 as a supplement rather than as a sole source of protein. 



Yeasts are efficient in absorbing and concentrating the vitamins present 

 in the media in which they grow (Gorcica and Levine, 1942). The 

 relative value of yeast as a source of vitamins depends upon the vitamin 

 content of the other constituents of the diet. The prevalence of vitamin 

 deficiency diseases (beriberi, pellagra, and others) is evidence that the 

 vitamin content of many diets is inadequate. 



