Supplementation of Cereal Proteins with Amino Acids: V. Effect of Supplementing Lime-Treated Corn with Different Levels of Lysine, Tryptophan and Isoleucine on the Nitrogen Retention of Young Children

Abstract

A lime-treated corn diet was supplemented with two levels each of lysine and of tryptophan, as well as two levels of isoleucine with a constant lysine and tryptophan supplement. Comparison of corn protein with the FAO reference protein indicates tryptophan to be the first limiting amino acid and lysine the second. In 18 3-day balance periods in two children lysine supplementation alone somewhat improved nitrogen balance, but tryptophan addition had no effect. Analysis of 12 3-day balance periods in 4 children indicated that the addition of lysine to give 180 mg/g N in the diet (0.30% l-lysine·HCl) and of tryptophan to a total of 75 mg/ g N (0.28% dl-tryptophan) approximately doubled the percentage of nitrogen retention compared with the results when the basal diet was fed. Increasing the lysine to 270 mg/g N (0.56% l-lysine·HCl) or the tryptophan to 90 mg/g N (0.35% dl-tryptophan) either singly or together, did not improve significantly the nitrogen balance compared with that obtained with these amino acids at the lower levels of supplementation. The addition of isoleucine to 270 mg/g N (0.45% dl-isoleucine) to the 270 mg lysine/g N plus 25 mg tryptophan/g N resulted in a slightly higher nitrogen balance. The addition of isoleucine to a level of 225 mg/g N gave an intermediate value for nitrogen retention. None of the amino acid combinations used to supplement corn-masa resulted in as high nitrogen retention as those obtained from feeding isonitrogenous levels of milk. The variable results with supplementation of different cereals with essential amino acids to the level in the FAO reference protein provide further evidence that reference amino acid patterns should include both upper and lower limits for the amount of each amino acid per gram of nitrogen and specify the range of protein intake over which they apply.