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Protein Nutritional Value of Opaque-2 Corn Grain for Human Adults¹

Department of Food and Nutrition, Agricultural Experiment Station and College of Home Economics, University of Nebraska, Lincoln, Nebraska 68503

The protein nutritive value of degermed opaque-2 corn for human adults has been investigated in three separate studies. The objective of the first study was to determine the effect of total dietary nitrogen on protein nutriture of nine adult subjects when degermed opaque-2 corn was used as the near sole source of dietary protein. Mean nitrogen balances of the subjects fed 4.0 g N per day from ground opaque-2 corn plus 0.0, 4.0, or 8.0 g N/day from urea were – 0.36, + 0.27, and – 1.49. These results suggest that total nitrogen intake as well as favorable amino acid proportionality patterns are important in determining the protein value of a dietary protein source. The objective of the second study was to determine the first limiting amino acid in degermed ground opaque-2 corn for maintenance of nitrogen equilibrium in human adults. Mean nitrogen balances of subjects maintained on 4.0 g N/day from opaque-2 corn plus L-lysine, L-tryptophan, L-methionine, a combination of these amino acids, or no essential amino acids were – 0.11, – 0.84, – 0.77, – 0.18, and – 0.81 g N/day, respectively. The change in nitrogen balance obtained with supplements of L-lysine suggest lysine still to be the first limiting amino acid in degermed opaque-2 corn for maintenance of N equilibrium in the human adult. The objective of the third study was to compare the protein nutritive value of two corn grains (degermed or whole ground) reputedly carrying the opaque-2 gene with an environmentally altered whole ground Nebraska field corn (single-cross hybrid B₁₄ x N₆) for humans under conditions of equal intake of corn protein and under conditions of equal intake of corn grain. Nitrogen balance data indicated that the two opaque-2 corn line materials were of superior protein value to the Nebraska field corn as measured both at equal levels of protein intake and at equal intakes of grain.

KEY WORDS: • corn • protein • human adult

¹ Supported in part by Public Health Grant no. R01AM08846. Published with the approval of the Director as paper no. 3005, Journal Series, Nebraska Agricultural Experiment Station.

Manuscript received 3 December 1971.