, 2009 and García-Falcón et al., 2007). In this study, we found that among all 12 phenolic

compounds evaluated, gallic acid, myricetin, and quercetin were the compounds responsible for differences in the antioxidant activity among clusters, corroborating the results reported in previous studies (Alén-Ruiz et al., 2009, Arnous et al., 2001, Brenna and Pagliarini, 2001, Cimino et al., 2007, Di Majo et al., 2008 and Lotito et al., 2002). As mentioned before, the total content of monomeric anthocyanins did not significantly correlate to any antioxidant activity assay, corroborating GSK1120212 the findings of Granato et al. (2010) and Giovanelli (2005). However, it is important to note that when individual anthocyanins and proanthocyanidins (dimers, trimers and polymers) are quantified, a significant correlation between these compounds and the antioxidant

activity is http://www.selleckchem.com/products/chir-99021-ct99021-hcl.html attained (Salaha, Kallithraka, Marmaras, Koussissi, & Tzourou, 2008). Therefore, it is possible to assume that quercetin, gallic acid, and myricetin, along with other phenolics compounds such as proanthocyanidins, contribute significantly to the in vitro antioxidant activity of red wines. The antioxidant activity of phenolic compounds, especially flavonoids, is due on one hand to the number and acidity of their phenolic hydroxyl groups, and on the other hand to the resonance between the free electron pair on the phenolic oxygen and the benzene ring, which increases electron delocalisation and confers a partial negative charge and thus a nucleophilic character upon the substitution position adjacent to the hydroxyl group (Cheynier, 2006). The A-ring shared by all wine flavonoids possesses two nucleophilic sites, in the C8 and C6 positions, due to the hydroxyl groups’ activation of its phloroglucinol (1,3,5-trihydroxy)-type

structure (Mira, Silva, Santos, Caroço, & Justino, 2002). Quercetin and (+)-catechin (Fig. 2) have 5 hydroxyl groups in the same positions, but quercetin also contains the 2,3-double bond in the C ring and the 4-oxo function (Cheynier, 2006). This structure enhances quercetin’s total antioxidant activity towards free radicals by allowing electron else delocalisation across the molecule. In our study, both (+)-catechin (r = 0.33, p < 0.01) and quercetin (r = 0.37, p < 0.01) correlated with the antioxidant activity measured by ORAC, but only the quercetin content was significantly different among clusters. These results imply that the 2,3-double bond in the C-ring and the 4-oxo function may be responsible for the higher antioxidant activity of flavonols compared with flavan-3-ols. Another observation was that the flavonols kaempferol (4 –OH groups) and myricetin (6 –OH groups) (Fig. 2) correlated (p < 0.01) to ORAC (r = 0.37, r = 0.32, respectively), and both contain the 2,3-double bond in the C-ring and the 4-oxo function.