Water and ethanol as co-solvent in supercritical fluid extraction of proanthocyanidins from grape marc: A comparison and a proposal

Supercritical carbon dioxide (SC-CO2) extraction of grape marc was studied using water (W) and ethanol (EtOH) as co-solvent at 15% (w/w), 100 and 200 MPa, and 313.15, 323.15 and 333.15K to analyze their influence upon total phenols of the extracts. The overall extraction curves were determined and suggested 10 MPa and 313.15K as the best operating conditions for SC-CO2 +15%W extraction, and 10 MPa and 333.15 K for SC-CO2 + 15% EtOH. The phenolic yields obtained were 63.4 g/kg of extract for SC-CO2 + 15%W and 38.8 g/kg of extract for SC-CO2 + 15% EtOH. An alternative method combining Sc-CO2 + 15% W extraction, followed by SC-O-2 + 15% EtOH was tested. This procedure provided the best results allowing to obtain the highest phenolic yield (68.0 g/kg of extract), phenol content (733.6 mg GAE/100 g DM), proanthocyanidins concentration (572.8 mg catechin/100 g DM) and antioxidant activity (2649.6 mg alpha- tocophero1/100g DM). SC-CO2 methods were compared with methanol extraction.