Regarding the flavonols quantified, rutin and the other quercetin
derivatives were detected in the skin of all the grape varieties. Highest
concentrations of flavonols in the skin were observed for the varieties
Sangiovese and Negro Amaro in the case of quercetin (39.05 and
40.03 mg/100 g dw, respectively) and kaempferol (14.10 and
14.89 mg/100 g dw, respectively), and for Sangiovese in the case of
rutin (57.04 mg/100 g dw). Minor quantities of flavonols were found
in some of the seed extracts, these compounds not being present in all
grape varieties. The catechin was the most abundant monomeric
flavanol compound identified in the seeds of the grape varieties
analyzed (24.12–117.00 mg/100 g dw), with the exception of Pinot
Noir in which the epicatechin was the most abundant monomeric
flavanol compound (47.50 mg/100 g dw). Radovanović, Radovanović,
and Souquet (2010) analyzed the phenolic profile of Cabernet
Sauvignon wines from 8 different Balkan regions and showed that
the contents of phenolic compounds varied depending on the
agroclimatic factors and enological practices of the vineyard region.
Based the results the authors proposed that the concentrations of the
main components catechin and quercetin can be used as biochemical
markers for the authentication of red grape cultivars.