Microwave-assisted polyethylene glycol-based aqueous two-phase extraction of gallic acid and ellagic acid from Euonymus alatus: Process optimization, quantification analysis and antioxidant activity

Abstract

A novel method of extraction and separation of gallic acid and ellagic acid from Euonymus alatus was developed by microwave-assisted extraction (MAE) coupled with aqueous surfactant two-phase extraction (ASTPE). Using PEG-400/(NH4)2SO4 system as the extractant, the effects of key factors on the extraction yields of the phenolic acids were investigated by response surface methodology. The optimized extraction conditions were as follows: (NH4)2SO4 concentration 17.74% (w/w), PEG-400 concentration 25.94% (w/w), extraction temperature 95.40 °C and liquid-to-material ratio of 59.99:1. The results of validation experiments were close to the predictedvalues of the model. The extraction yields of the phenolic acids for MAE-ASTPE were superior to that of conventional methods. The proposed approach coupled to high-performance liquid chromatography was successfully applied for extraction and determination of the phenolic acids in three batches of Euonymus alatus. The extraction yields of gallic acid and ellagic acid were 0.4532 ± 0.0031, 0.5864 ± 0.0061, 0.4966 ± 0.0056 mg/g and 0.1713 ± 0.0043, 0.3072 ± 0.0030, 0.1374 ± 0.0015 mg/g, respectively. The extract obtained by MAE-ASTPE had stronger antioxidant activity, and EC50 values of scavenging DPPH (2,2-diphenyl-1-picrylhydrazyl), hydroxyl, superoxide and ABTS (2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid) radicals were respectively 198.5 ± 1.2, 358.0 ± 2.8, 776.3 ± 3.3 and 333.6 ± 1.8 μg/mL. MAE integrated with ASTPE could improve not only extraction efficiency but also extraction selectivity, and facilitated to develop natural antioxidant from Euonymus alatus.