Evolution of flavonols in berry skins of different grape cultivars during ripening and a comparison of two vintages

Abstract

Evolution of flavonols from the onset of ripening to commercial harvest was compared in seven grape cultivars (Vitis vinifera L.) in Qilian region of Gansu Province in northwest China for two consecutive years. The cultivars were three white-skinned (Chardonnay, Semillon, Italian Riesling), one pink-skinned (Gewurztraminer) and three red-skinned (Cabernet Sauvignon, Cabernet Gernischt and Merlot). Isorhamnetin-3-O-glucoside was found in the pink ‘Gewurztraminer’ grape and the three red cultivars, but not in the whites, while myricetin derivatives were found to be specific to the red grapes. Our results indicate that the flavonol synthesis in Gewurztraminer should be similar to that in white cultivars that do not have a flavonoid 3′,5′-hydroxylase-mediated branch pathway. In comparison with the white and pink grapes, the type and level of quercetin and kaempferol derivatives detected in red grapes were relatively variable, which may be attributable to the presence of an additional myricetin branch in flavonol biosynthesis pathway of red grape cultivars, consequently expanding the range of metabolite variation. We also consider that rain during the sampling period may be a major factor causing these changes in the flavonol profile found between the two vintages.