Improved lateral discrimination in screening the elemental composition of buckwheat grain by micro-PIXE

The elemental composition of specific fractions of cereal and pseudocereal grains can be roughly estimated after milling. Alternatively, the elemental localization of cross-sectioned grains can be quantitatively analyzed by microproton induced X-ray emission (micro-PIXE), taking advantage of high elemental sensitivity and low lateral resolution. We present a micro-PIXE study on buckwheat (Fagopyrum esculentum) grain, with a detailed description of the elemental distributions. Elements such as Mg, P, S, K, Fe, Ni, Cu, and Zn were preferentially localized in the cotyledons and embryonic axis; however, significant amounts of K and Fe were also found in the pericarp. The aleurone layer covering the cotyledons was especially enriched in S and P, while testa, a thin layer above the aleurone did not show any significant element enrichments. The highest concentrations of Al, Si, Cl, Ca, and Ti were found in the pericarp. A detailed element localization study of pericarp layers revealed that the inner layer was enriched in K, Mn, Ca, and Fe, while the outer layer showed enrichments in Na, Mg, P, S, and Al. On the basis of the data obtained, milling techniques can be adapted to obtain milling fractions with targeted nutritional values.