Localization and distribution of Zn and Fe in grains of biofortified bread wheat lines through micro- and triaxial-X-ray fluorescence spectrometry

Highlights: • 10 Normal and Zn-biofortified wheat varieties were grown under normal and high Zn conditions. • 5 High-yield high-Zn biofortified varieties were grown in Zn-rich fields. • A robust statistical analysis was made to obtain a genotypic ranking for Zn-Fe content. • Zinc elemental maps of the wheat grains were obtained with micro-XRF. X-ray fluorescence analysis has been performed in wheat grains from a field trial where some biofortified and non-biofortified wheat varieties were subjected to Zn biofortification through soil fertilizer application. A set of ten biofortified and non-biofortified wheat varieties developed at the International Maize and Wheat Improvement Center, Mexico, were used for this study. Two analytical methods were employed to investigate the contents and localization of the trace metals Zn and Fe within the grains, one with polarized monochromatic X-rays for lower limits of detection, and another featuring polycapillary lenses for micrometric beam size (μ-EDXRF). Elemental maps were obtained with μ-EDXRF allowing for the study of Zn and Fe localization in plants grown in normal and Zn-enriched soil. It is acknowledged that the biofortification procedures result in around 30% average increase in overall Zn concentration when compared to other high Zn genotypes grown in normal soil. A genotypic ranking was performed taking into account the influence of the measurement methods and field conditions and the obtained results show that two of the top three varieties regarding zinc contents also rank among the top three in terms of Fe concentration. Elemental mapping analysis seems to favor the use of integral flour for the manufacture of bread and pasta products, as the bran retains most of the minerals.