Subcritical (carbon dioxide + ethanol) extraction of polyphenols from apple and peach pomaces, and determination of the antioxidant activities of the extracts

The effects of pressure (20–60 MPa), temperature (40–60 °C), ethanol concentration (14–20 wt.%) and extraction time (10–40 min) on subcritical (CO2 + ethanol) extraction of polyphenols from apple and peach pomaces (moisture content ≅ 14%, particle size = 0.638 mm) were determined. All variables increased total phenolic contents (TPC) and antiradical efficiencies (AE) of the extracts significantly (p ≤ 0.05). The optimum pressure and temperature were 54.6–57 MPa and 55.7–58.4 °C for apple pomace, and 50.6–51 MPa and 50.9–52.3 °C for peach pomace. The optimum ethanol concentration and extraction time were 20% ethanol and 40 min for both pomaces. TPC of the extracts were 0.47 and 0.26 mg gallic acid equiv./g sample and AE of the extracts were 3.30 and 1.5 mg DPPH/mg sample for apple and peach pomaces, respectively. Low TPC and AE of the extracts from peach pomace could be contributed to low concentrations of ferulic and p-coumeric acids, epicatechin, and presence of anthocyanins in peach.