High performance liquid chromatographic and digital fluorescence imaging studies of germ flavonoids in wheat milling fractions and FT-IR microspectroscopic examination of germ

In wheat, flavonoid pigments occur predominantly in the embryonic axis of germ as C-glycosyl flavones based on apigenin. Specifically, flavonoids are localized in the coleorhiza and root cap of the primary root, the outer cell layers of the lateral roots and in the epiblast. There are lesser amounts of flavonoids in the plumule (primary leaves) and scutellum. The flavonoid content of the bran is considerably lower than in the germ and the endosperm is nearly free of flavonoids.; The localization of flavonoids in germ tissue has formed the basis for the development of a sensitive, selective HPLC procedure for tracking the germ content in wheat milling fractions. The germ flavonoid content in the 23 intermediate flour streams from six different milling experiments conducted in the Kansas State University pilot mill were measured to develop a distribution pattern for the fate of the germ in the milling process. The germ content increases from the head to the tail of the mill. There are several intermediate streams at the front end of the mill, including 1st and 2 nd break, 1st and 2nd middlings and sizings that have a low level of germ contamination. There are certain other pivotal streams, such as 3rd middlings and 1st tailings that can make a considerable contribution to the germ content of the final flour product.; There is a good relationship between the quantitative HPLC germ flavonoid data and fluorescent pixel ratio data obtained by automated digital fluorescence image analysis. Select flour streams were treated with diphenylborinic acid ethanolamine ester re agent, which induces fluorescence in flavonoids.; FT-IR microspectroscopy was utilized to examine in situ chemical differences in the morphological structures of the embryonic axis, scutellum and the junction between the scutellum and endosperm. The compositional changes that occur in the germ structure can be visualized with contour absorbance maps for select functional groups. The chemical differences in the embryonic axis and scutellum as determined by FT-IR microspectroscopy parallel the chemical differences determined by proximate analysis of the dissected tissues.