Flavonol profiles of Vitis vinifera white grape cultivars

The flavonol profiles of a wide set of Vitis vinifera white grape cultivars were determined by HPLC–DAD–ESI-MSn in order to confirm the presence of isorhamnetin-type flavonols and also to evaluate their ability for cultivar authenticity and differentiation. Only 3-O-glycoside derivatives of kaempferol, quercetin and isorhamnetin were identified as grape flavonols. The 3-O-glucosides and 3-O-galactosides of kaempferol, quercetin, and isorhamnetin, and also the 3-O-glucuronides of kaempferol and quercetin, were detected in all the grape varieties. In addition, traces of isorhamnetin 3-O-glucuronide and rutin (quercetin 3-O-(6″-rhamnosyl)-glucoside) were detected in some cases. Flavonol profiles of white grapes are dominated by quercetin-type flavonols. However, the preliminary results have shown remarkable differences (Principal Component Analysis) in the contribution of kaempferol-type flavonols to the characteristic white grape flavonol profiles, which could suggest their use for cultivar authenticity and differentiation purposes. In addition, some white grape cultivars (e.g., Pedro Ximénez, Gewürztraminer, Verdejo, Albillo, and Riesling) were characterised by relatively high and significantly different proportions of the newly reported, usually very minor, isorhamnetin-type flavonols.