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, ‘NerelloMascalese’ as well as ‘Nero d’Avola’ ethanol extracts showed promising radical scavenging activity andphenol content (DPPH and GAE assays). Aliquots of these three extracts were subjected to two differentfractionation protocols on polyamide (PF) and Amberlite XAD-16 (XF). The fractions were examined byDPPH and GAE assays, and subjected to HPLC-DAD analysis for the quantitative determination of themain phenolic compounds. Fractionation of the crude extract NM1E (SC50 ¼ 28.2, GAE ¼ 221.0) throughthe XF protocol, afforded a polyphenol-enriched fraction (XF1C, GAE ¼ 392.5) with highly enhancedantioxidant activity (SC50 ¼ 7.0), and accounting for only 6.5% in weight of the NM1E extract. FractionXF1C shows high concentrations of a procyanidin B1 (Pcd) and catechin (Cat). Some considerations onthe relationship between antioxidant activity and phenolic HPLC-DAD profiles are also reported