Dietary methionine status and its relation to the bioavailability to rats of zinc in corn kernels with varying methionine content
1997
House, W.A. | Van Campen, D.R. | Welch, R.M.
A whole-body radioassay method was used to assess effects of supplemental dietary methionine (Met) on absorption by rats of zinc (Zn) provided in test meals labeled either extrinsically or intrinsically with 65Zn. Intrinsically labeled meals contained kernels harvested from two genotypes of corn (Zea mays L.) grown in 65Zn-labeled nutrient solutions. 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 65Zn dose when a soy-based diet contained either 0, 1, 2 or 3 g of Met added per kg diet, respectively. Absorption of extrinsic 65Zn from test meals was not affected by additional Met when dietary protein was provided by egg whites. Supplemental Met enhanced absorption by rats of intrinsic 65Zn in kernels of both the Nor-Met and High-Met corn genotypes. As indicated by absorption of 65Zn, the bioavailability to rats of intrinsic Zn in the kernels was similar regardless of the Met content of the corn. However, the Zn concentration in High-Met kernels (30 micrograms/g) was greater than that in the Nor-Met corn (22 micrograms/g) so that rats fed High-Met corn ingested and absorbed 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 added Met, and these rats were marginally deficient in Met. The Met status 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 thereby increase the nutritional value of plant foods.
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