Optimization of the extraction of phenolic compounds from red grape marc (Vitis vinifera L.) using response surface methodology

Optimization of the extraction of total polyphenols (TPC), flavanols (FL), total anthocyanins (TA) and total tannins (TT) from grape marc by the response surface methodology is important to improve the recovery of these high-value phytochemicals. The independent variables studied were ethanol concentration (% EtOH), extraction time (h) and liquid-to-solvent ratio (L/S). TPC, FL, TT and TA showed different patterns of extractability, with significant variation in the linear, quadratic and interaction effects of the independent variables. The optimal extraction conditions were determined and the quadratic response surfaces were drawn from the mathematical models. The optimal extraction conditions were: 57% EtOH, 17 h, 50:1 L/S for TPC; 57% EtOH, 13 h, 50:1 L/S for FL; 62% EtOH, 16 h, 50:1 L/S for TT and 52% EtOH, 6 h, 10:1 L/S for TA. These optimum conditions yielded: 24 mg GAE/g DM of TPC; 1.5 mg quercetin/g DM of FL; 18 mg catechin/g DM of TT and 6 mg malvidin/g DM of TA.