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.