Optimization extraction, preliminary characterization and antioxidant activity in vitro of polysaccharides from Stachys sieboldii Miq. tubers

Response surface methodology was used to optimize the extraction conditions of water-soluble polysaccharides from Stachys sieboldii Miq. tubers. A central composite design was used to optimize the extraction processing parameters. The optimum extraction conditions are as follows: extraction temperature, 95 °C; extraction time, 2.5 h; water to raw material ratio, 16; and extraction frequency, 3. Under the optimized conditions, an experimental yield of 9.21 ± 0.18%, which is in good agreement with the predicted yield, was obtained. Purified polysaccharide SSP II-a was successfully obtained using diethylaminoethanol-Sepharose and Sepharose CL-6B column chromatography. SSP II-a was found to be an acidic polysaccharide fraction with an average molecular weight of 168 kDa and composed of rhamnose, glucuronic acid, galacturonic acid, glucose, galactose and arabinose. In vitro antioxidant activity assays suggested that SSP II-a presents high scavenging activity toward superoxide anion, hydroxyl, and 2,2′-azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid) radicals but relatively lower scavenging activity toward 1,1-diphenyl-2-picrylhydrazyl radicals. The results indicated that response surface methodology is an effective method for the extraction of polysaccharides from S. sieboldii Miq. tubers and the polysaccharides could be explored as a potential antioxidant agent for use in medicine or functional food.