Estimation of optimum supplements of essential amino acids to a wheat and barley-based diet in rats using a nitrogen balance technique

Abstract

Nitrogen balance experiments were conducted on growing rats to study the possibility of improving protein quality of a cereal-based diet by amino acid supplementation. A complete supplement of all essential amino acids to a basal diet containing wheat and barley (1.4:1) and fortified with lysine and threonine significantly increased nitrogen balance (NB) and the biological value of the protein (BV). The removal of individual amino acids from the complete supplement resulted in a significant decrease in NB in the case of lysine + threonine, sulphur amino acids and isoleucine. In the case of valine, the decrease was near the limits of significance. The addition of arginine or non-essential amino acid mixture to the diet which was fortified with limiting amino acids had no positive effect on NB or BV. Based on the differences in NB between diets with complete and incomplete supplement, and on the efficiency of utilization of amino acids for growth, the following optimum supplements of limiting amino acids were calculated (% of diet): lysine, 0.123; threonine, 0.091; sulphur amino acids, 0.083; isoleucine, 0.035; valine, 0.040. The NB and BV of the diet with optimized supplements were similar to those obtained on the diet supplemented with all essential amino acids.