Samples were also analysed by HPLC to identify individual phenolic selleck inhibitor compounds (Fig. 1). Anthocyanins, flavonol derivatives (quercetin and kaempferol), catechin and epicatechin monomeric flavanols, t-resveratrol and gallic acid were detected and quantified ( Table
2). The data obtained showed differences in the concentration of total anthocyanins for the different varieties, as expected. The values, which ranged from 496.61 to 2917.50 mg/100 g, were 2.1 to 2.7 times greater than those obtained using the pH-differential method described above. This trend has been observed before (Lee, Rennaker, & Wrolstad, 2008), where samples were analysed with the same methods used in this study (pH-differential method and HPLC). As reported by Lee et al. (2008), reversed-phase HPLC coupled with photodiode array detection is the technique which has been most widely used for the identification and quantification of anthocyanins. However, HPLC can result in an underestimation of the amount of anthocyanin present in samples that contain different anthocyanidin glycosides
when using one standard for quantification. Another study, which evaluated anthocyanins and flavonols in grape pomace of different varieties produced in Italy (Ruberto et al., 2007) using HPLC–UV–DAD and HPLC–MS–ESI, found values of total anthocyanins ranging from 375 to 4527 mg/100 g. Regarding the flavonols quantified in the grape pomace extracts, the highest concentrations of rutin, other quercetin derivatives and kaempferol derivatives were observed for the Merlot variety (56.65, A 1210477 41.43 and 15.09 mg/100 g, respectively). The monomeric flavanol catechin was the most abundant non-anthocyanic compound identified in the grape pomace, reaching a value of 150.16 mg/100 g. In general, as described by other authors (Montealegre, Peces, Vozmediano, Gascueña, & Romero, 2006), the phenolic content in the case of grape seeds consists almost exclusively of flavan-3-ols such as catechin, which may explain the significant amounts noted herein. It is GNA12 worth highlighting that some other phenolic compounds, not
quantified due to the lack of standards, were present in the grape pomace, probably mostly proanthocyanidins, commonly present as oligomers and polymers of polyhydroxy flavan-3-ols such as (+)-catechin and (−)-epicatechin, and many in the form of gallate esters or glycosides (Brannan, 2008). The presence of t-resveratrol, chemically known as trans-3,5,4´-trihydroxy-trans-stilbene, was expected. It is a phytoalexin and has been identified in more than 70 plant species including grapes, peanuts, fruits, red wine and mulberries. However, grape skin is a particularly good source of resveratrol as the fresh skin contains around 50–100 μg/g, while in red wine concentrations range from 1.5 to 3.0 mg/L ( Baliga & Katiyar, 2006).