Synchrotron X-ray Fluorescence Microscopy study of the diffusion of iron, manganese, potassium and zinc in parboiled rice kernels

• Spatial distribution of micronutrients in intact rice kernel was studied by using Synchrotron XFM.
• The germ contained highest concentration of micronutrients followed by bran layer.
• Hydrothermal treatment caused the inwards diffusion of minerals from germ and bran layer.
• Higher hydration temperature for longer time facilitated inward diffusion of minerals.
• The extent of mineral diffusion differed between the different mineral species.

Parboiled rice is known to contain higher levels of nutrients than its non-parboiled counterpart. In order to study the diffusion of micronutrients into the starchy endosperm of the parboiled rice kernel, the parboiled paddy samples were prepared by combining different hydrothermal treatments (hydrated only, steamed-only, hydrated then steamed) employing two hydration temperatures (60 °C and 90 °C). The rice kernels were sectioned longitudinally into 90 μm thick sections after hydrothermal treatment, drying and milling. These rice kernels sections were analysed by Synchrotron X-Ray Fluorescence Microscopy (S-XFM) to determine the distribution of iron (Fe), manganese (Mn), potassium (K) and zinc (Zn). The S-XFM results showed that the bran and germ were rich in these minerals whereas the endosperm had a low concentration. Hydrothermal treatment of kernels increased the mineral diffusion into the endosperm from the bran layer and germ. The highest diffusion of Fe, Zn and Mn was observed in the sample treated with high temperature hydration for a longer time followed by steaming. However, K did not appear to diffuse into the endosperm as much as other the minerals.