INFLUENCE OF DIETARY SULFUR-CONTAINING AMINO-ACIDS ON THE BIOAVAILABILITY TO RATS OF ZINC IN CORN KERNELS

A whole-body radioassay method was used to assess effects of supplemen tal dietary amino acids on absorption by rats of zinc in two varieties of corn kernels labeled either intrinsically or extrinsically with Zn -65. Corn genotypes were a normal type (Nor-corn) with one row of cell s in the aleurone layer of the kernel and a variety (Mal-corn) that ha d multiple rows of cells in the aleurone. In experiment 1, rats fed a basal diet containing 15% soy protein absorbed 64% of the Zn-65 provid ed extrinsically in test meals. When provided test meals that containe d intrinsically labeled Nor-corn or Mal-corn kernels, the rats absorbe d 64 and 57% of the intrinsic Zn-65, respectively. In rats fed diets t hat contained supplemental lysine, methionine, or both lysine and meth ionine, absorption of extrinsic Zn-65 averaged 69, 82 and 86% of the d ose, respectively. In experiment 2, rats fed the basal diet absorbed 5 7 and 53% of the intrinsic Zn-65 in Nor-corn and Mal-corn kernels, res pectively, but rats fed supplemental methionine or cysteine absorbed 7 3% of the intrinsic Zn-65 in either the Nor-corn or Mal-corn kernels. Supplemental methionine or cysteine fed to rats that were marginally z inc deficient enhanced the absorption of Zn-65 provided in test meals in the form of either intrinsically labeled corn kernels or as Zn-65-l abeled zinc sulfate.