Enhancing Beans (Phaseolus Vulgaris L.) as Sources of Bioavailable Iron through Genetic Selection

Abstract

Iron (Fe) deficiency is the most prevalent nutrient deficiency in humans. Globally, this disorder adversely affecting the health, well being, and livelihood of over 2 billion people, especially those living in developing countries. Significantly increasing the bioavailable amount of Fe in staple plant foods could contribute greatly to reducing the incidence of Fe deficiency, particularly among those at greatest risk (i.e., poor women, infants and children). Fe-enriched genotypes of beans could be selected for in plant breeding programs to improve human nutrition and thereby enhance nutritional health in a sustainable manner.

Studies were conducted to determine the effects of Fe, phytate (myo-inositolhexaphosphate), and tannin concentrations in 24 select genotypes of bean seeds on iron bioavailability to rats. Beans selected from field trials in Cali, Columbia for their variations in Fe, phytate and tannin seed concentrations were grown in a green house in nutrient solutions radiolabeled with ⁵⁹Fe. Samples of radiolabeled mature seeds were autoclaved and lyophilized The dried bean homogenate was used to prepare test meals fed to rats. Test meals contained 1 g of dried bean, 0.5 g sucrose and 1 g of basal Fe-deficient rat diet. The meals were fed to marginally Fe-deficient weanling rats over a 3-h period. The rats were radioassayed in a “whole body” gamma spectrometer immediately after feeding the test meals and daily thereafter for the next 10 d. “Whole body” radioiron retention data were used to calculate percent Fe absorption (i.e., Fe bioavailability) from the meals.

Concentrations of Fe in mature bean seeds harvested from the 24 accessions grown at the same time in a greenhouse varied with genotype and ranged from 51 to 157 µg g⁻¹ dry weight. The bioavailability to rats of Fe in the bean seeds depended on the genotype and varied from 53% to 76% of the Fe in the seed. There was no correlation between Fe concentration in the seeds and Fe bioavailability to rats fed the seeds even though the “antinutrients”, phytate and tannins, varied widely in seeds of the different genotypes studied. Our results support the contention that breeding for enhanced concentrations of Fe in bean seeds can result in significant increases in bioavailable Fe for humans eating the beans as staple food. Results of the effects of phytate and tannin levels on Fe bioavailability are also presented.