DIETARY METHIONINE STATUS AND ITS RELATION TO THE BIOAVAILABILITY TO RATS OF ZINC IN CORN KERNELS WITH VARYING METHIONINE CONTENT

A whole-body radioassay method was used to assess effects of supplemen tal dietary methionine (Met) on absorption by rats of zinc (Zn) provid ed in test meals labeled either extrinsically or intrinsically with Zn -65. Intrinsically labeled meals contained kernels harvested from two genotypes of corn (Zea mays L.) grown in Zn-65-labeled nutrient soluti ons. One genotype had kernels with normal Met content (Nor-Met corn) ( 2.0 g Met per kg) and the other had Met-rich kernels (High-Met corn) ( 3.2 g Met per kg). Rats fed extrinsically labeled meals absorbed about 57, 67, 73 and 71% of the Zn-65 dose when a soy-based diet contained either 0, 1, 2 or 3 g of Met added per kg diet, respectively. Absorpti on of extrinsic Zn-65 from test meals was not affected by additional M et when dietary protein was provided by egg whites. Supplemental Met e nhanced absorption by rats of intrinsic Zn-65 in kernels of both the N or-Met and High-Met corn genotypes. As indicated by absorption of Zn-6 5, the bioavailability to rats of intrinsic Zn in the kernels was simi lar regardless of the Met content of the corn. However, the Zn concent ration in High-Met kernels (30 mu g/g) was greater than that in the No r-Met corn (22 mu g/g) so that rats fed High-Met corn ingested and abs orbed more Zn from the test meals than did rats fed the Nor-Met corn. Zinc absorption was depressed in rats fed a soy-based diet without add ed Met, and these rats;were marginally deficient in Met. The Met statu s of experimental animals may be an important consideration in studies conducted to assess Zn bioavailability. Selection of seeds and grains with increased amounts of Met may enhance Zn bioavailability and ther eby increase the nutritional value of plant foods. Copyright (C) 1996 Elsevier Science Inc.