Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2015
Publication Date: 6/16/2015
Citation: Hart, J.J., Tako, E.N., Kochian, L.V., Glahn, R.P. 2015. Identification of black bean (Phaseolus vulgaris L.) polyphenols that inhibit and promote iron uptake by caco-2 cells. Journal of Agricultural and Food Chemistry. DOI: 10.1021/acs.jafc.5b00531.
Interpretive Summary: Iron-deficiency anemia is the most common human micronutrient deficiency in the world. Natural chemical compounds present in staple plant foods can worsen iron deficiency by binding iron and making it unavailable for absorption in the intestinal tract. This paper focused on polyphenols, a group of plant-produced chemicals known to inhibit iron uptake. Specifically, we examined the effects of the eight most abundant polyphenols present in black beans. Iron uptake was measured in Caco-2 cells, which are laboratory-cultured human intestinal cells that closely approximate the iron uptake process of the human intestinal tract. In contrast to most previous investigations that examined the combined effects of total polyphenols, this study measured the iron uptake effects of individual polyphenols. The results showed that, as expected, some (four) polyphenols strongly inhibited iron uptake; however, the other four clearly promoted iron uptake. The ability of some polyphenols to promote iron uptake and the identification of specific polyphenols that inhibit iron uptake suggests a potential way to develop bean lines with improved iron nutritional qualities.
Technical Abstract: In nutritional studies, polyphenolic compounds are considered to be inhibitors of Fe bioavailability. Because they are presumed to act in a similar manner, total polyphenols are commonly measured via the Folin-Ciocalteu colorimetric assay. In this study, we measured the content of polyphenolic compounds in white and black beans and examined the effect of individual polyphenols on iron uptake by Caco-2 cells. Analysis of seed coat extracts by LC-MS revealed the presence of a range of polyphenols in black bean, but no detectable polyphenols in white bean. Extracts from black bean seed coats strongly inhibited iron uptake. Examination of the eight most abundant black bean seed coat, non-anthocyanin polyphenols via Caco-2 cell assays showed that four (catechin, 3,4-dihydroxybenzoic acid, kaempferol and kaempferol 3-glucoside) clearly promoted iron uptake and four (myricetin, myricetin 3-glucoside, quercetin and quercetin 3-glucoside) inhibited iron uptake. The four inhibitors were present in three-fold higher total concentration than the promoters (143 +/- 7.2 uM vs. 43.6 +/- 4.4 uM), consistent with the net inhibitory effect observed for black bean seed coats. The ability of some polyphenols to promote iron uptake and the identification of specific polyphenols that inhibit Fe uptake suggests a potential for breeding bean lines with improved iron nutritional qualities.