Figure 3.

a Mineral fluorescence in transverse (left) and longitudinal (right) sections of wheat grain under x-ray illumination. In both sections, the crease region is at the top of the image and the embryo (germ) at the bottom. It is clearly evident that the central part of the grain (the endosperm) contains little to no mineral content. The minerals, here represented as iron (green), zinc (red) and manganese (blue) are distributed particularly in the phytate inclusions of the aleurone (53–56). The embryo here shows zinc and manganese whose concentration is higher in the germ (64), however due to the germ’s smaller mass w/w, the bran still contributes more zinc and manganese overall in a whole grain diet. These images were produced at the Diamond Light Source synchrotron facility on the microfocus spectroscopy beamiline I18 using 10 keV excitation.

b Native fluorescence associated with the pericarp and aleurone layers observed in sectioned wheat grain. When excited with 359 nm wavelength light, aleurone cells emit fluorescence in the 460 nm (blue) region of the spectrum due to high concentrations of hydroxycinnamic acids, particularly ferulic acid. In a similar manner, when viewed under 492 nm light, the grain coverings emit fluorescence in the 520 nm (green) region of the spectrum of uncertain origin (59–61).