Influence of the solvent system on the composition of phenolic substances and antioxidant capacity of extracts of grape (Vitis vinifera L.) marc

Background and Aims: Grape marc (GM), a byproduct of winemaking, contains significant amounts of substances that are not efficiently used. This study investigated the effect of solvent systems on the extraction of phenolic substances and antioxidant capacity (AC) from the Carignan grape (Vitis viniferaL.) marc, as well as from the peduncle, skin and seed of Carignan. Methods and Results: The solvent systems tested were (v:v): methanol (MeOH):water (6:4, 7:3 and 9:1), MeOH:water:acetone (ACE) (3:3.5:3.5) and ethanol (EtOH):water (6:4, 7:3 and 9:1). The highest extraction of phenolic substances and flavonoids was obtained with EtOH:water (6:4 and 7:3) and MeOH:water:ACE (3:3.5:3.5) followed by MeOH:water (7:3). The highest AC was obtained with MeOH:water:ACE (3:3.5:3.5) followed by EtOH:water (6:4 and 7:3). The concentration of phenolic substances varied from 4.72 to 7.05g catechin equivalents (CE)/kg fresh mass (FM) for seed extracts, 2.72-3.55g CE/kg FM for skin extracts and 2.03-2.11g CE/kg FM for peduncle extracts. Catechin, epicatechin, rutin, myricetin, quercetin, epicatechin gallate, quercetin 3-O-glucuronide, quercetin 3-O-hexoside and malvidin 3-hexoside were found in the marc. Significance of the Study: The best solvent systems for extracting phenolic substances with high AC from Carignan GM were MeOH:water:ACE (3:3.5:3.5) and EtOH:water (6:4 and 7:3). The main phenolic substances that remained in wine marc after fermentation were myricetin, catechin and epicatechin. The results of this study suggest that Carignan GM, considered an industrial waste, is a natural resource of antioxidants.