Grape stems from Sicilian Vitis vinifera cultivars as a source of polyphenol-enriched fractions with enhanced antioxidant activity

From a screening of six different samples of grape stems from Vitis vinifera Sicilian cultivars, 'Nerello Mascalese' as well as 'Nero d'Avola' ethanol extracts showed promising radical scavenging activity and phenol content (DPPH and GAE assays). Aliquots of these three extracts were subjected to two different fractionation protocols on polyamide (PF) and Amberlite XAD-16 (XF). The fractions were examined by DPPH and GAE assays, and subjected to HPLC-DAD analysis for the quantitative determination of the main phenolic compounds. Fractionation of the crude extract NM1E (SC50 = 28.2, GAE = 221.0) through the XF protocol, afforded a polyphenol-enriched fraction (XF1C, GAE = 392.5) with highly enhanced antioxidant activity (SC50 = 7.0), and accounting for only 6.5% in weight of the NM1E extract. Fraction XF1C shows high concentrations of a procyanidin B1 (Pcd) and catechin (Cat). Some considerations on the relationship between antioxidant activity and phenolic HPLC-DAD profiles are also reported.