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 333.15 K to analyze their influence upon total phenols of the extracts. The overall extraction curves were determined and suggested 10 MPa and 313.15 K 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-CO2 + 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 α-tocopherol/100 g DM). SC-CO2 methods were compared with methanol extraction.