Kaempferol and Quercitrin Effect on Iron Bioavailability in White and Colored Bean Seeds ( Phaseolus vulgaris L.) Using an In Vitro Digestion/Human Caco‐2 Cell Model

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Four different colored commercial beans (white, red, pinto and black beans) were investigated for factors affecting iron bioavailability. An in vitro digestion/human Caco-2 cell model was used to study the polyphenols from whole beans, de-hulled beans and their hulls and assess iron bioavailability. The results show that white beans contained higher levels of bioavailable iron compared to colored beans. These differences in bioavailable iron were not due to bean-iron and bean-phytate levels. Flavonoids in the colored bean hulls were found to be contributing to the low bioavailability of iron in the colored beans. White bean hulls contained no detectible flavonoids. The flavonoids, kaempferol and quercitrin, were identified in red and pinto bean hulls via HPLC. Some unidentified anthocyanins were also detected in the black bean hulls but not in the other colored bean hulls. Kaempferol and quercitrin were shown to inhibit iron bioavailability, with quercitrin being more inhibitory than kaempferol. Treatment of in vitro digestates with kaempferol and quercitrin inhibited iron bioavailability in a concentration dependent fashion. Thus, these flavonoids were found to be the main inhibitory factors affecting iron bioavailability in the red and pinto beans studied.