Protein quality of two varieties of high-lysine maize fed alone and with black beans or milk to normal and depleted weanling rats.

Opaque-2 corn, modified high-lysine corn with vitreous endosperm, and common corn were compared in rat growth studies. Corn alone supplied 8.6% protein; and at both 8.6 and 11.4% protein, corn furnished 60% of the protein and either milk or black beans supplied 40%. The modified corn, which also was high in both lysine and tryptophan, did not differ significantly from Opaque-2 corn in its ability to stimulate growth and nitrogen deposition in both well-nourished and partially protein-depleted rats; and both were significantly superior to common corn when fed alone. Milk was a more effective supplement for corn than black beans, especially when high-lysine varieties were fed, whereas beans exerted a similar effect on all varieties of corn. The depleted rats deposited more nitrogen as a result of eating most diets than did well nourished rats. Implications of these findings for preschool children are discussed.