Supplemental Value of Certain Amino Acids for Beef Protein

Abstract

The supplemental values of the amino acids cystine, methionine, phenylalanine, leucine, isoleucine, valine, and tryptophane for beef protein were determined by feeding tests with young male albino rats. When protein constituted 10% of the diet, beef protein was deficient only in cystine or methionine. When beef protein was supplemented with 0.2% to 0.4% of either cystine or methionine, the growth-promoting value of the protein was equal to that of egg protein. When the diet contained 12.5% protein, beef protein was somewhat deficient in cystine, but when this amino acid was added, the growth-promoting value was increased to that of egg protein. When protein constituted 15% of the diet, beef protein was not deficient in cystine and the growth-promoting value was equal to that of egg protein. The ratio of methionine to cystine in a diet containing 10% egg protein was 1.7 : 1; in a diet containing 10% beef protein the ratio was 2.5 : 1; and in a diet containing 10% beef protein + 0.2% cystine the ratio was 1 : 1.