Hordatine A β-D-glucopyranoside was isolated from ungerminated barley grains for the first time and identified by MS spectrometry and one- and two-dimensional NMR spectroscopy. This compound was observed 20 days after flowering (DAF) and most abundant at 35 DAF when the dry weight of grains reached a maximum. The contents of the compound markedly decreased when grains were pearled from 85% to 70% yield, suggesting that the compound is localized in the aleurone layer. The compound was commonly observed in ungerminated mature grains among 10 cultivars, and its contents ranged from 103 to 254 nmol/g dry weight. Because hordatines have been reported to have antifungal activities, the compound may act as an antifungal component in the latter half of the maturing stages and in mature barley grains.
In red wheat, reddish-brown pigments accumulate in testa of mature seeds. Half-cut wheat seeds were immersed in p-dimethylaminocinnamaldehyde (DMACA) reagent that stains flavanol structures blue. Testa of 10-40 days after flowering (DAF) in red wheat ("Norin 61" and "Satonosora") seeds were stained blue and the reagent color changed to blue with 10-25 DAF seeds. No blue staining was observed in white wheat ("Tamaizumi") seeds during maturation. "Norin 61" seed coats at 10 DAF contained dihydroquercetin, dihydromyricetin, (+)-catechin, procyanidin B3, and prodelphinidin B3, which were identified by HPLC-diode array detector and LC-MS/MS analyses. These five components began accumulating 7 DAF, reached maxima at 10 or 15 DAF, and then decreased in red wheat seeds, but were not detected in white wheat seeds. These results suggest that flavanol and proanthocyanidins are possible precursors of the reddish-brown pigments of red wheat seeds, and are converted to insoluble compounds as the seeds mature.
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