Comprehensive Study of Sustainable Pressurized Liquid Extractions to Obtain Bioavailable Antioxidant Phenolic Compounds from Grape Seed By-Products

Few investigations have been conducted to evaluate pressurized liquid extraction (PLE) technology as a sustainable method for the recovery of phenolic compounds of grape seed by-products. In this study, PLE combined with an experimental design was evaluated for optimizing the sustainable extraction of phenolic compounds from grape seed by-products. The solvent ethanol content (X1, 0-100%), temperature (X2, 20-100 degrees C) and time (X3, 1-11 min) were studied as independent experimental factors. Yield, TPC, antioxidant activity and phenolic composition were analyzed as optimized dependent variables. Two optimal extraction conditions at different temperatures (20 degrees C and 100 degrees C) were found, but thermal degradations at 100 degrees C allowed for selecting the optimal condition as 75% ethanol, 11 min and 20 degrees C. The optimal extracts showed high phenolic content (TPC = 350.80 +/- 3.97 mg GAE/g extract) and antioxidant activity (ABTS, 9.31 +/- 0.33 mmol Trolox/g extract), mainly composed of polymeric and mono-oligomeric flavan-3-ols. The digestion process reduced the TPC and antioxidant activity due to the low bioaccessibility of the flavan-3-ols, mainly as catechin, epicatechin and polymeric proanthocyanidin losses during the digestion process. However, increases in the antioxidant activity of the basolateral side (DDPH, 0.061 +/- 0.000 mmol Trolox/g extract) were determined after in vitro transepithelial transport, which is a consequence of bioavailable catechin and epicatechin and reduced amounts of dimer B2, dimer B1, epicatechin gallate and gallic acid. Consequently, PLE combined with hydroalcoholic solvents at a low temperature resulted in a valuable methodology to obtain sustainable extracts from grape seed by-products (contributing to the circular economy), containing bioavailable phenolic compounds, which are able to increase the antioxidant status.