GENETIC SELECTION FOR ENHANCED BIOAVAILABLE LEVELS OF IRON IN BEAN (PHASEOLUS VULGARIS L.) SEEDS

Authors: Welch, Ross; House, William; BEEBE, STEVEN - CENTRO INT'L AGR TROPICAL; CHENG, ZHIQIANG - CORNELL UNIVERSITY

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Dry beans do not contribute very much of the iron available in the US food supply, but these foods may become more important sources of iron as people alter their dietary habits to comply with recent dietary recommendations calling for increased consumption of plant foods and decreased intake of animal products. Failure to consume adequate amounts of iron may cause health problems. For example, iron deficiency anemia is a common debilitating disorder in many children and premenopausal women. This nutritional disorder may result either from failure to consume adequate amounts of iron or from excessive consumption of dietary compounds, such as phytate and some tannins, that interfere with iron uptake. Phytate is the major storage form of phosphorus in seeds and tannins are complex substances occurring in various foods of plant origin, including some seeds. Because plant foods are generally considered to be poor sources of dietary iron, increasing the amount and improving the bioavailability of iron in bean seeds is important to nutritional health. In the present study, rats were fed 24 distinct varieties of bean seeds that contained different amounts of iron, tannin and phytate. As indicated by absorption of radioactive iron, the bioavailability of iron ranged from 53 to 76% of the iron in the seeds; the amount of iron absorbed increased as the concentration of iron in the seeds increased. There was no apparent relationship between the amount of iron absorbed and the concentration of phyate or tannin in the seeds. These results indicate that plant breeding techniques can be used to increase the amount and bioavailability of iron in dry bean seeds and thereby increase the nutritional value of these foods.

Technical Abstract: A whole-body radioassay procedure was used to assess the absorption by rats of iron (Fe) in 24 genotypes of bean seeds containing varying amounts of Fe, tannin, and myo-inositolpentaphosphate plus phytic acid (IP5+IP6). Test meals fed to male rats contained mature seeds harvested from plants grown in nutrient solutions that contained 59Fe. The rats were marginally anemic; hemoglobin concentration averaged 10.6 g/dL. Iron concentrations in the beans varied with genotype and ranged from 52 to 157 ug/g dry weight. Selection of beans for enriched seed-Fe concentration tended to also select for higher Zn concentrations in the beans. As indicated by absorption of 59Fe, bioavailability to rats of Fe in the bean seeds depended on the genotype and varied from 53% to 76% of the total Fe. Increasing the concentration of Fe in bean seeds via genetic selection resulted in increased bioavailable Fe to rats. There was no apparent correlation between the Fe concentration in different bean genotypes and F bioavailability to rats attributable to variations in seed IP5+IP6 or tannins, even though IP5+IP6 varied from 19.6 to 29.2 umol/g and tannin ranged from 0.35 to 2.65 mg/g. White-colored beans had the highest percent of bioavailable Fe although tannin levels in other bean lines tested could not account for differences in bioavailable Fe between genotypes. Other unknown seed factors (i.e., antinutrients or promoter substances) may be contributing factors in affecting Fe bioavailability from bean seeds. 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.