Genetic selection for enhanced bioavailable levels of iron in bean (Phaseolus vulgaris L.) seeds

The bioavailability of Fe from 24 select genotypes of bean (Phaseolus vulga ris L.) seeds containing a range of concentrations of Fe, myo-inositol pent aphosphate plus phytic acid (IP5+IP6), and tannins was studied using a rat model. Bean accessions, selected from field trials for their variations in Fe, phytate, and tannin seed concentrations, were grown in a greenhouse in nutrient solutions radiolabeled with Fe-59. Mature seeds were autoclaved an d lyophilized. Test meals (containing 1 g of dried bean, 0.5 g of sucrose, and 1 g of basal Fe-deficient diet) were fed to marginally Fe-depleted wean ling rats over a 3-h period; rats were radioassayed in a gamma-spectrometer immediately after feeding and daily thereafter for the next 10 d. Radioiro n retention data were used to calculate percent Fe absorption (i.e., Fe bio availability) from the meals. Seed Fe concentrations ranged from 52 to 157 mu g g(-1) dry weight. There was a tendency to also select for higher Zn co ncentrations in the beans when selecting for high Fe concentrations. The Fe bioavailability to rats from test meals depended on the genotype and varie d from 53% to 76% of the total Fe. Bean genotypes with higher seed Fe conce ntrations resulted in increased amounts of bioavailable Fe to rats. There w as no significant correlation between the Fe concentration in different bea n genotypes and Fe bioavailability to rats attributable to variations in IP 5+IP6 or tannins, even though these antinutrients varied widely (i.e., from 19.6 to 29.2 mu mol of IP5+IP6 g(-1) and from 0.35 to 2.65 mg of tannins g (-1)) in the test meals. Other unknown seed factors (i.e., antinutrients or promoter substances) may be contributing factors affecting Fe bioavailabil ity from bean seeds.