Extraction, isolation, characterization and antioxidant activity of polysaccharides from Astragalus membranaceus

In this study, optimization of combined enzyme extraction (CEE), isolation, characterizationand antioxidant activities of polysaccharides (APs) from Astragalus membranaceus (AM) were investigated. Response surface methodology (RSM) and orthogonal experiments were used to optimizethe CEE conditions, which are as follows: combined enzyme concentration of 1.5%, 1% and 0.5% of cellulase, pectase and papain, extraction time of 94.5 min, extraction temperature of 49.9 degrees C and pH of5.1. The APs were further fractionated using DEAE Sepharose Fast Flow and Sephadex G-200 column to afford three purified fractions of APs-1-1, APs-2-1 and APs-3-1. Their physicochemical properties were investigated by gas chromatography (GC), high-performance gel-permeation chromatography (HPGPC) and Fourier-transform infrared spectroscopy (FT-IR). The results indicated that their total sugar, uronic acid content, molecular weight and monosaccharide composition were significantly different. Antioxidant activities were evaluated by various antioxidant assays in vitro. The results showed that all the three polysaccharides possessed good antioxidant properties in a concentration-dependent manner, especially APs-3-1 with the highest uronic acid content and the lowest molecular weight had the strongest antioxidant capacity and free radicals scavenging activity. The present results suggested that APs-3-1 might be exploited as effective natural antioxidant for medical and food industries. (C) 2015 Elsevier B.V. All rights reserved.