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United States Department of Agriculture

Agricultural Research Service

Research Project: Bioavailability of Iron, Zinc and Select Phytochemicals for Improved Health

Location: Plant, Soil and Nutrition Research

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

Authors
item Tako, Elad
item Beebe, Steve -
item Hart, Jon -
item Reed, Spenser -
item Glahn, Raymond

Submitted to: Nutrition Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 24, 2014
Publication Date: March 26, 2014
Repository URL: http://DOI: 10.1007/s10886-013-0258-3
Citation: Tako, E.N., Beebe, S.E., Hart, J.J., Reed, S.M., Glahn, R.P. 2014. Polyphenolic compounds appear to limit the nutritional benefit of biofortified higher iron black bean (phaseolus vulgaris L.). Nutrition Journal. 13:28.

Interpretive Summary: The objective of the current study was to compare the capacities of biofortified (increased iron) and standard black beans to deliver iron (Fe) for blood hemoglobin (Hb) synthesis. Two lines of black beans (Phaseolus vulgaris L.), a standard ("Low Fe") and biofortified ("High Fe") in Fe (59 and 88 ug Fe/g, respectively) were used. The black beans based diets were formulated to meet the nutrient requirements for the chicken broiler (Gallus gallus) except for Fe (dietary Fe concentrations were 39.4+/-0.2 and 52.9+/-0.9 mg/kg). For 6 weeks, Hb, feed-consumption and body weights were measured (14 birds per treatment). Results showed that Hemoglobin Maintenance Efficiency (indicator for dietary Fe availability) values differ between groups on days 14, 21 and 28 (P<0.05). Final total Hb-Fe (indicator for Fe availability) contents differ between the standard and high-Fe (24.4+/-0.8 and 26.6+/-0.9 mg, respectively) bean groups (P<0.05). The gene expression of iron absorption related transporters and enzyme (DMT-1, Dcyt-B, and ferroportin) were higher and liver ferritin was lower (P>0.05) in the standard group vs. the biofortified group. In vitro comparisons showed no difference between the beans, and indicate the presence of high levels of polyphenolic compounds that inhibit Fe absorption. The beans polyphenols profile indicated that certain polyphenolic compounds may have an inhibitory effect on Fe bioavailability and are present in relatively high levels in black beans. We concluded that the “High Fe” bean diet appeared to deliver more absorbable Fe as evident by Hb and Hb-Fe. Also, results suggested that breeding for increased Fe concentration in black beans also elevates the polyphenolics concentrations, which reduce bean Fe-bioavailability. Our observations are important as these polyphenols compounds represent potential targets to manipulate and thus improve the Fe-bioavailability in beans. Biofortified beans seem to be a promising vehicle for increasing intakes of bioavailable-Fe in human populations that consume these beans as a dietary staple. However, the bean polyphenols profile must be further evaluated in order to improve the nutritional benefit of beans. This justifies further work on black beans which are the staple of a large-region of South America where Fe-deficiency anemia is a primary cause of infant death and poor health status.

Technical Abstract: Background: Our objective was to compare the capacities of biofortified and standard black beans to deliver Fe for Hb synthesis. Two isolines of black beans (Phaseolus vulgaris L.), a standard (DOR500, "Low Fe") and biofortified (MIB465, "High Fe") in Fe (59 and 88 ug Fe/g, respectively) were used. The DOR 500, is a commercial variety in several countries. Therefore it is important to know the affect of biofortification of these beans on diets that simulate human feeding studies. Methods: Black beans 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). For 6 weeks, Hb, feed-consumption and BW were measured (n=14). Results: HME values differ between groups on days 14, 21 and 28 (P<0.05). Final total Hb-Fe contents differ between the standard and high-Fe (24.4+/-0.8 and 26.6+/-0.9 mg, respectively) bean groups (P<0.05). DMT-1, Dcyt-B, and ferroportin expressions were higher and liver ferritin was lower (P>0.05) in the standard group vs. the biofortified group. In vitro comparisons showed no difference between the beans, and indicate the presence of high levels of polyphenolic compounds that inhibit Fe absorption. The beans polyphenols profile indicated that the compounds myricetin and salicylic-acid may have an inhibitory effect on Fe bioavailability and are present in relatively high levels in black beans. Conclusions: The “High Fe” bean diet appeared to deliver more absorbable Fe as evident by Hb and Hb-Fe. Also, results suggested that breeding for increased Fe concentration in black beans also elevates the polyphenolics concentrations, which reduce bean Fe-bioavailability. Our observations are important as these polyphenols compounds represent potential targets to manipulate and thus improve Fe-bioavailability. Biofortified beans seem to be a promising vehicle for increasing intakes of bioavailable-Fe in human populations that consume these beans as a dietary staple. However, the bean polyphenols profile must be further evaluated in order to improve the nutritional benefit of beans. This justifies further work on black beans which are the staple of a large-region of South America where Fe-deficiency anemia is a primary cause of infant death and poor health status.

Last Modified: 9/20/2014
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