Email updates

Keep up to date with the latest news and content from Nutrition Journal and BioMed Central.

Open Access Research

Polyphenolic compounds appear to limit the nutritional benefit of biofortified higher iron black bean (Phaseolus vulgaris L.)

Elad Tako1*, Steve E Beebe2, Spenser Reed1, Jonathan J Hart3 and Raymond P Glahn1

Author Affiliations

1 USDA/ARS, Robert W. Holley Center for Agriculture and Health, Cornell University, Ithaca, NY 14853, USA

2 CIAT- International Center for Tropical Agriculture, Cali, Colombia

3 Department of Plant Biology, Cornell University, Ithaca, NY 14853, USA

For all author emails, please log on.

Nutrition Journal 2014, 13:28  doi:10.1186/1475-2891-13-28

Published: 26 March 2014

Abstract

Background

Our objective was to determine if a biofortified variety of black bean can provide more bioavailable-iron (Fe) than a standard variety. Two lines of black beans (Phaseolus-vulgaris L.), a standard (DOR500; 59μg Fe/g) and biofortified (MIB465; 88μg Fe/g) were used. The DOR500 is a common commercial variety, and the MIB465 is a line developed for higher-Fe content. Given the high prevalence of Fe-deficiency anemia worldwide, it is important to determine if Fe-biofortified black beans can provide more absorbable-Fe.

Methods

Black bean based diets were formulated to meet the nutrient requirements for the broiler (Gallus-gallus) except for Fe (dietary Fe-concentrations were 39.4±0.2 and 52.9±0.9 mg/kg diet, standard vs. biofortified, respectively). Birds (n=14) were fed the diets for 6-weeks. Hemoglobin-(Hb), liver-ferritin and Fe-related transporter/enzyme gene-expression were measured. Hemoglobin-maintenance-efficiency and total-body-Hb-Fe values were used to estimate Fe-bioavailability.

Results

Hemoglobin-maintenance-efficiency values were higher (P<0.05) in the group consuming the standard-Fe beans on days 14, 21 and 28; indicating a compensatory response to lower dietary-Fe. Final total-Hb-Fe body content was higher in the biofortified vs. the standard group (26.6±0.9 and 24.4±0.8 mg, respectively; P<0.05). There were no differences in liver-ferritin or in expression of DMT-1, Dcyt-B, and ferroportin. In-vitro Fe-bioavailability assessment indicated very low Fe-bioavailability from both diets and between the two bean varieties (P>0.05). Such extremely-low in-vitro Fe-bioavailability measurement is indicative of the presence of high levels of polyphenolic-compounds that may inhibit Fe-absorption. High levels of these compounds would be expected in the black bean seed-coats.

Conclusions

The parameters of Fe-status measured in this study indicate that only a minor increase in absorbable-Fe was achieved with the higher-Fe beans. The results also raise the possibility that breeding for increased Fe-concentration elevated the levels of polyphenolic-compounds that can reduce bean Fe-bioavailability, although the higher levels of polyphenolics in the higher-Fe beans may simply be coincidental or an environmental effect. Regardless, Fe-biofortified beans remain a promising vehicle for increasing intakes of bioavailable-Fe in human populations that consume high levels of these beans as a dietary staple, and the bean polyphenol profile must be further evaluated and modified if possible in order to improve the nutritional quality of higher-Fe beans.

Keywords:
Beans; Biofortification; Iron bioavailability; In vitro digestion/Caco- 2 cell model; Broiler chicken; Intestine