The Percentage of Protein in Corn and its Nutritional Properties

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Abstract
Rats grew slowly on both a high-protein and a low-protein corn diet and an attempt was made to identify the limiting factors in each. The high-protein corn diet contained 15% of protein and the animals which consumed it gave a slight response to tryptophan. They gave responses that were larger, and approximately equal, when the supplement was either nicotinic acid or lysine. In each of these trials the response fell short of statistical significance. When nicotinic acid and lysine were added simultaneously to the high-protein corn diet the response was increased again, but the combination of tryptophan and lysine gave a still larger increase. The response to each of these combinations was statistically significant. The rats did not grow more rapidly on a combination of nicotinic acid and tryptophan than on nicotinic acid alone. The low-protein corn diet contained 7% of protein, and the rats which consumed it grew more slowly than did those on the high-protein corn diet. They gave no response to single additions of either tryptophan or nicotinic acid, or to the combination of tryptophan and nicotinic acid. The response to lysine alone did not reach statistical significance. The response to lysine and nicotinic acid was not more marked than to lysine alone. The response when both lysine and tryptophan were added to the low-protein corn diet was highly significant. In the samples of corn studied, lysine was the first limiting factor, and tryptophan was the second. Under our experimental conditions threonine was not a limiting factor in the high-protein corn. This point was not investigated in low-protein corn. The biological value of the protein in low-protein corn was superior to that of the protein in high-protein corn. However, per unit of weight, the high-protein corn was superior to low-protein corn. As a source of protein for the rat, casein is superior to the protein mixture in corn, even though it is supplemented with lysine and tryptophan.