Subcritical (carbon dioxide plus 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 degrees 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 congruent to 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 degrees C for apple pomace, and 50.6-51 MPa and 50.9-52.3 degrees 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 center dot/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. (C) 2007 Elsevier B.V. All rights reserved.