A Comparative Study of Iron and Zinc Concentration, Localization, Speciation and Bioavailability in Two Wheat Cultivars

Iron (Fe) and Zinc (Zn) deficiency remains a prevalent nutritional disorder worldwide, disproportionally affecting people of low and middle income countries due to the reliance on non-meat sources in the diet. Cereals, a relatively poor Fe and Zn source, account for over 50% of the energy intake in developing countries, and are a potentially important target for biofortification strategies aimed at improving dietary Fe and Zn content and utilisation. The effectiveness of a crop in combating Fe and Zn deficiency is largely dependent on Fe and Zn speciation, as different forms vary in their bioavailability. Size exclusion chromatography, coupled with inductively coupled plasma-mass spectrometry is a valuable approach to identify and quantify different forms of Fe and Zn in the grain. Adaptations of the method to quantify and identify nutritionally relevant forms of Fe and Zn (ferritin, Fe-phytate, mono-ferric phytate and Fe-nicotianamine, Zn-nicotainamine) are described, together with the assessment of bioavailability of Fe in wheat using an in vitro Caco-2 cell model system. Speciation of Fe and Zn varied between milling fractions with low molecular weight (LMW) complexes likely to be Fe-deoxymugenic acid/nicotianamine and Zn-nictainamine being the predominant extractable Fe and Zn species in the purest white flour fraction. During in vitro digestion the speciation of Fe differed between white and wholemeal bread. Overall, the bioavailability of Fe assessed using a Caco-2 cell model system appeared to be much higher in white bread than in wholemeal bread. Addition of ferrous sulphate was a more effective fortificant in white bread compared to wholemeal bread. The quantity of total or soluble Fe did not appear to be related to predicted bioavailability from the Caco-2 cell model, indicating that the effects of Fe speciation and the presence of absorption inhibitors are of greater importance than total or soluble iron when determining Fe bioavailability

Iron bioavailability in two commercial cultivars of wheat: a comparison between wholegrain and white flour and the effects of nicotianamine and 2'-deoxymugineic acid on iron uptake into Caco-2 cells

Iron bioavailability in unleavened white and wholegrain bread made from two commercial wheat varieties was assessed by measuring ferritin production in Caco-2 cells. The breads were subjected to simulated gastrointestinal digestion and the digests applied to the Caco-2 cells. Although Riband grain contained a lower iron concentration than Rialto, iron bioavailability was higher. No iron was taken up by the cells from white bread made from Rialto flour or from wholegrain bread from either variety, but Riband white bread produced a small ferritin response. The results probably relate to differences in phytate content of the breads, although iron in soluble monoferric phytate was demonstrated to be bioavailable in the cell model. Nicotianamine, an iron chelator in plants involved in iron transport, was a more potent enhancer of iron uptake into Caco-2 cells than ascorbic acid or 2'-deoxymugineic acid, another metal chelator present in plants

Distribution and Speciation of Iron and Zinc in Grain of Two Wheat Genotypes

This study aimed to determine differences among wheat cultivars in the distribution and speciation of Fe and Zn in grain milling fractions. Cultivars with higher Fe and Zn concentrations in the wholemeal flour were found to contain higher concentrations in the white flour. Soluble Fe and Zn were extracted and analyzed by size exclusion-inductively coupled plasma mass spectrometry. Fe speciation varied between milling fractions with a low molecular weight (LMW) complex likely to be Fe-deoxymugenic acid/nicotianamine being the predominant extractable Fe species in white flour, accounting for approximately 85% of the extractable Fe. Bran fractions had a lower amount of LMW-Fe form but more as soluble Fe-phytate and an unidentified high molecular weight peak. In the white flour fraction soluble Zn was found to be present mainly as a LMW peak likely to be Zn-nicotianamine complex. Soluble Fe-phytate was found in the white flour fraction of a high-Fe cultivar but not in a low-Fe cultivar

Distribution and Speciation of Iron and Zinc in Grain of Two Wheat Genotypes

This study aimed to determine differences among wheat cultivars in the distribution and speciation of Fe and Zn in grain milling fractions. Cultivars with higher Fe and Zn concentrations in the wholemeal flour were found to contain higher concentrations in the white flour. Soluble Fe and Zn were extracted and analyzed by size exclusion–inductively coupled plasma mass spectrometry. Fe speciation varied between milling fractions with a low molecular weight (LMW) complex likely to be Fe–deoxymugenic acid/nicotianamine being the predominant extractable Fe species in white flour, accounting for approximately 85% of the extractable Fe. Bran fractions had a lower amount of LMW-Fe form but more as soluble Fe–phytate and an unidentified high molecular weight peak. In the white flour fraction soluble Zn was found to be present mainly as a LMW peak likely to be Zn–nicotianamine complex. Soluble Fe–phytate was found in the white flour fraction of a high-Fe cultivar but not in a low-Fe cultivar

Effects of Nitrogen on the Distribution and Chemical Speciation of Iron and Zinc in Pearling Fractions of Wheat Grain

Increasing nitrogen supply can increase Fe and Zn concentrations in wheat grain, but the underlying mechanisms remain unclear. Size-exclusion chromatography coupled with inductively coupled plasma mass spectrometry was used to determine Fe and Zn speciation in the soluble extracts of grain pearling fractions of two wheat cultivars grown at two N rates (100 and 350 kg of N ha^–1). Increasing N supply increased the concentrations of total Fe and Zn and the portions of Fe and Zn unextractable with a Tris–HCl buffer and decreased the concentrations of Tris–HCl-extractable (soluble) Fe and Zn. Within the soluble fraction, Fe and Zn bound to low molecular weight compounds, likely to be Fe–nicotianamine and Fe–deoxymugineic acid or Zn–nicotianamine, were decreased by 5–12% and 4–37%, respectively, by the high N treatment, whereas Fe and Zn bound to soluble high molecular weight or soluble phytate fractions were less affected. The positive effect of N on grain Fe and Zn concentrations was attributed to an increased sink in the grain, probably in the form of water-insoluble proteins