Sodium iron EDTA and ascorbic acid, but not polyphenol oxidase treatment, counteract the strong inhibitory effect of polyphenols from brown sorghum on the absorption of fortification iron in young women

Abstract

In addition to phytate, polyphenols (PP) might contribute to low Fe bioavailability from sorghum-based foods. To investigate the inhibitory effects of sorghum PP on Fe absorption and the potential enhancing effects of ascorbic acid (AA), NaFeEDTA and the PP oxidase enzyme laccase, we carried out three Fe absorption studies in fifty young women consuming dephytinised Fe-fortified test meals based on white and brown sorghum varieties with different PP concentrations. Fe absorption was measured as the incorporation of stable Fe isotopes into erythrocytes. In study 1, Fe absorption from meals with 17 mg PP (8·5 %) was higher than that from meals with 73 mg PP (3·2 %) and 167 mg PP (2·7 %;P< 0·001). Fe absorption from meals containing 73 and 167 mg PP did not differ (P= 0·9). In study 2, Fe absorption from NaFeEDTA-fortified meals (167 mg PP) was higher than that from the same meals fortified with FeSO4(4·6v.2·7 %;P< 0·001), but still it was lower than that from FeSO4-fortified meals with 17 mg PP (10·7 %;P< 0·001). In study 3, laccase treatment decreased the levels of PP from 167 to 42 mg, but it did not improve absorption compared with that from meals with 167 mg PP (4·8v.4·6 %;P= 0·4), whereas adding AA increased absorption to 13·6 % (P< 0·001). These findings suggest that PP from brown sorghum contribute to low Fe bioavailability from sorghum foods and that AA and, to a lesser extent, NaFeEDTA, but not laccase, have the potential to overcome the inhibitory effect of PP and improve Fe absorption from sorghum foods.