Identification of Black Bean (Phaseolus vulgaris L.) Polyphenols That Inhibit and Promote Iron Uptake by Caco-2 Cells

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. This study 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 3-fold higher total concentration than the promoters (143 ± 7.2 vs 43.6 ± 4.4 μM), 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 suggest a potential for breeding bean lines with improved iron nutritional qualities.

Genetics and Biochemistry of Zero-Tannin Lentils

“…Phenolic acids, flavones, and flavonols show anti-oxidative [2–4], anti-cardiovascular disease [3], anti-cancer [3–6], anti-diabetic [3, 6], and anti-HIV [3, 6] effects. They may also increase the bioavailability of iron [8]. Our new knowledge of the underlying basis of the genotypes and phenotypes of zero-tannin lentil seed coats will be useful for designing future lentil cultivars with improved nutritional profiles.…”

“…Phenolics are associated with health benefits including antioxidant activity and protection against diseases such as cardiovascular disorders, cancer, HIV, and diabetes [2–6]. Physical removal of the seed coat of lentils leads to improved iron bioavailability [7], probably due to the removal of phenolic compounds and the implication that these compounds interfere with iron nutrition [8]. …”

The Combined Application of the Caco-2 Cell Bioassay Coupled with In Vivo (Gallus gallus) Feeding Trial Represents an Effective Approach to Predicting Fe Bioavailability in Humans

“…Developing staple food crops for enhanced nutritional quality often requires high throughput methods capable of examining hundreds and sometimes thousands of samples [11,12,13,14]. In general, for Zn and provitamin A, the content of these micronutrients has been more positively correlated with enhanced nutritional quality; whereas for Fe, enhanced content does not always equate to improved nutritional quality [15,16,17,18,19]. Understanding the factors related to the bioavailability of Fe may therefore be the key to developing sustainable Fe-biofortified crops, hence, the development of the appropriate screening tools is vital to properly guide the crop breeding process.…”

“…Such results indicate that breeding for higher Fe could concomitantly increase the levels of inhibitory polyphenols and thereby negate the benefit of higher Fe content. In addition, recent research indicates that not all of the polyphenols in bean seed coats are inhibitory, and that some may actually be promoters of [18,19]. For example, in bean seed coats the compounds myricetin, quercetin and quercetin 3-glucoside are definite inhibitors, whereas catechin, kaempferol and kaempferol 3-glucoside are promoters of Fe bioavailability.…”

In Vitro Bioaccessibility and Bioavailability of Iron from Potatoes with Varying Vitamin C, Carotenoid, and Phenolic Concentrations

“…21 A recent study showed however that some phenolic compounds may promote iron absorption, stressing the complexity of the interactions of this large family of compounds. 22 Given the time and expense required for in vivo trials, in vitro models have been developed to estimate iron bioavailability from food. 23 In combination with simulated human gastrointestinal digestion, the Caco-2 cell model has been demonstrated to be effective in comparing iron bioavailability from diverse bean, rice, and maize genotypes.…”