White tepary bean shows higher in vitro iron bioavailability than brown tepary or common bean

Abstract

Iron deficiency anemia is the most prevalent global micronutrient disorder, especially in populations who consume mainly plant‐based diets. Although beans contain a greater amount of iron in comparison to wheat, corn or other staple crops, the bioavailability is often low due to inhibitory factors like polyphenols and phytic acid. Tepary beans (Phaseolus acutifolius) thrive better in arid climates than other beans, making them a suitable crop for expansion into marginal ecological zones with climate change. Iron bioavailability is unknown for many tepary varieties, but proximate analysis shows higher iron content than in most common bean (Phaseolus vulgaris) varieties. The study purpose was to determine in vitro iron bioavailability, proximate analysis, polyphenol, and phytic acid content of tepary and common bean varieties. Increased iron bioavailability in a bean with arid climate resiliency can offer a sustainable solution towards reducing iron deficiency anemia in developing countries. Whole seeds of 5 tepary white, 3 tepary brown, 4 black, and 2 pinto bean varieties were analyzed. Polyphenol (PP) and phytic acid (PA) extractions were assessed colorimetrically. Iron concentrations were determined using ICP‐mass spectrometry following a microwave digestion. Iron solubility analysis was completed through in vitro digestion of the cooked beans. Supernatants from the in vitro digestion were used in determining the iron bioavailability through a CaCo‐2 cell culture model. For statistical analysis, results were pooled by tepary white, tepary brown, black bean, and pinto bean. Both tepary white and tepary brown groups showed significant differences in PP content in comparison to the black and pinto (p≤0.05), whereas PA, amongst all groups, showed no significant differences (p>0.05). Iron content ranged from 29.8 μg/g to 78.47 μg/g, with pinto beans having significantly lower iron concentration (mean = 33.64 μg/g). Significant differences in percent solubility were found between the pinto bean and tepary varieties (p≤0.05), but not the black. Iron bioavailability of the tepary white showed a negative correlation with PP content (high iron, low PP). The tepary white showed significantly higher iron bioavailability (p≤0.02) in comparison to both pinto and black beans. Our data suggests that the low PP and PA contributes to higher iron bioavailability in the white varieties of Phaseolus acutifolius. Further studies to replicate these findings are needed, followed by clinical testing of tepary white iron bioavailability in humans.