The main flavonols found in seven widespread Vitis vinifera red grape cultivars include the 3-glucosides and 3-glucuronides of myricetin and quercetin and the 3-glucosides of kaempferol and isorhamnetin. In addition, the methoxylated trisubstituted flavonols, laricitrin and syringetin, were predominantly found as 3-glucosides. As minority flavonols, the results suggest the detection of the 3-galactosides of kaempferol and laricitrin, the 3-glucuronide of kaempferol, and the 3-(6' '-acetyl)glucosides of quercetin and syringetin. The flavonol profiles based on the eight above-mentioned flavonols allowed the cultivar differentiation of the grape samples. With regard to flavonol biosynthesis in the berry skin, quercetin 3-glucuronide predominated at véraison, followed by quercetin 3-glucoside, and only trace amounts of trisubstituted flavonols were detected. The proportion of quercetin 3-glucoside remained almost constant during berry ripening, whereas the proportion of quercetin 3-glucuronide decreased and the other flavonols, especially myricetin 3-glucoside, increased their importance. In wines, flavonol 3-glycosides coexisted with their corresponding free aglycones released by hydrolysis. The presence of laricitrin, syringetin, and laricitrin 3-glucoside in red wines is reported here for the first time. The extent of hydrolysis was widely variable among wines made from the same grape cultivar, and the results suggest the influence of the type of aglycone and glycoside on the rate of hydrolysis. Due to hydrolysis, the differentiation of single-cultivar wines gave acceptable results only when aglycone-type flavonol profiles were used.

Garnacha Tintorera (also known as Alicante Bouschet) is one of the few V. vinifera grape cultivars with red-colored berry flesh. The study of the phenolic composition of both berry flesh and skin of Garnacha Tintorera grapes shows interesting findings. Anthocyanins were asymmetrically distributed within grape flesh and skins. Malvidin derivatives dominated in skin, followed by peonidin-type anthocyanins; in contrast, the flesh almost exclusively contained peonidin 3-glucoside. In addition, LC-UV-vis and LC-MS evidence suggest the presence of small amounts of peonidin 3,5-diglucoside and a second peonidin dihexoside derivative, and, very likely, the first report of the occurrence of pelargonidin 3-glucoside and its acetyl and p-coumaroyl derivatives in V. vinifera grapes. Flavonols also occurred in the flesh of Garnacha Tintorera grapes, but its flavonol profile showed lower contribution of trisubstituted flavonoid structures (myricetin, laricitrin, and syringetin) when compared to that of skin. The skin of Garnacha Tintorera grapes contained hydroxycinnamic acids in higher amounts than in flesh, caftaric acid being the main derivative found, and coutaric acid accounting for its highest proportion in the skin. The phenolic composition of the whole grape berries reflected the average of the differences described for the two aforementioned berry parts, and subsequently, the red wines made from these grapes had a phenolic composition closer to that shown by the whole berries. The formation of anthocyanin-derived pigments in Garnacha Tintorera red wines makes necessary the use of LC-MS for detecting the minor pelargonidin-based anthocyanins and peonidin dihexoside, which could be suggested as chemical markers for cultivar authentication of this grape cultivar and its wines.

Petit Verdot grape skins by solid-phase extraction using a combination of reverse-phase and ion-exchanging materials. This procedure allowed us to separate a fraction of anthocyanin-free flavonol 3-O-glycosides that was further split into neutral and acidic subfractions, thus facilitating flavonol identification. By means of semipreparative reverse-phase high-performance liquid chromatography, we isolated several of these flavonol 3-O-glycosides for structural elucidation. The identification of different flavonol 3-O-glycosides was based on liquid chromatography-diode array detection-electrospray ionization-tandem mass spectrometry and NMR data when available. The results suggest that red grape flavonol 3-O-glycosides comprise three different complete series, according to the nature of the sugar moiety linked to the C-3 position. The 3-O-glucosides were the main derivative of the six possible flavonol aglycones (kaempferol, quercetin, isorhamnetin, myricetin, laricitrin, and syringetin), whereas the 3-O-galactoside derivatives were found as minor compounds for all of the flavonol aglycones. The 3-O-glucuronides are the third kind of red grape flavonol derivatives and normally account as minor compounds for all of the flavonol aglycones, with the exception of quercetin 3-O-glucuronide, which was as abundant as quercetin 3-O-glucoside. In addition, the presence of quercetin 3-O-(6"-rhamnosyl)-glucoside (rutin) was also detected as a trace compound in the skins of Petit Verdot grapes.

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