title: Polyphenolic compounds appear to limit the nutritional benefit of biofortified higher iron black bean (Phaseolus vulgaris L.).
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.
authors.affiliation: USDA/ARS, Robert W, Holley Center for Agriculture and Health, Cornell University, Ithaca, NY 14853, USA. et79@cornell.edu.
authors.forename: Elad
authors.initials: E
authors.lastname: Tako
authors.forename: Steve E
authors.initials: SE
authors.lastname: Beebe
authors.forename: Spenser
authors.initials: S
authors.lastname: Reed
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Hart
authors.forename: Raymond P
authors.initials: RP
authors.lastname: Glahn
mesh_terms: D000818:Animals; D001682:Biological Availability; D001947:Breeding; D018938:Caco-2 Cells; D002645:Chickens; D005293:Ferritins / Q000096:biosynthesis; D006454:Hemoglobins / Q000096:biosynthesis; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects; D007501:Iron / Q000008:administration & dosage* / Q000378:metabolism*; D027805:Phaseolus / Q000235:genetics / Q000378:metabolism*; D059808:Polyphenols / Q000494:pharmacology*
chemical_list: D006454:Hemoglobins; D059808:Polyphenols; D005293:Ferritins; D007501:Iron