Extraction Optimization, Purification and Physicochemical Properties of Polysaccharides from Gynura medica
Extraction of polysaccharides from Gynura medica (GMPs) was optimized by response surface methodology (RSM). A central composition design including three parameters, namely extraction temperature (X 1 ), ratio of water to raw material (X 2 ) and extraction time (X 3 ), was used. The best conditions were extraction temperature of 91.7˝C, extraction time of 4.06 h and ratio of water to raw material of 29.1 mL/g. Under the optimized conditions, the yield of GMPs was 5.56%, which was similar to the
... was similar to the predicted polysaccharides yield of 5.66%. A fraction named GMP-1 was obtained after isolation and purification by DEAE-52 and Sephadex G-100 gel chromatography, respectively. GMP-1, with a molecular weight of 401 kDa, mainly consisted of galacturonic acid (GalA), xylose (Xyl), glucose (Glu). Infrared spectroscopy was used to characterize the major functional groups of GMP-1 and the results indicated that it was an acidic polysaccharide. The antioxidant and α-glucosidase inhibitory activities of GMPs and GMP-1 were determined in vitro. The results indicated that GMPs and GMP-1 show potential for use in functional foods or medicines. RSM is an effective statistical technique for optimizing complex processes  . The RSM technique has advantages over other statistical techniques in that it is less laborious and time-consuming, and produces more precise and statistically significant results for trials using small data sets [9,10]. Many researchers have successfully used this technique to optimize polysaccharide extraction processes [11, 12] , but to the best of our knowledge, there are no reports examining the extraction of polysaccharides from Gynura medica. In the present study, RSM was used to optimize the extraction of polysaccharides from Gynura medica for maximum yield. The extraction parameters were temperature, time and ratio of water to raw material. GMP-1 was then purified and preliminary characterization carried out. The antioxidant and α-glucosidase inhibitory activities of the Gynura medica polysaccharides were evaluated too. Results and Discussion Single-Factor Experimental Analysis Extraction temperature is one of the most important variables affecting the extraction yield of GMPs. To study the effect of different temperatures on the yield of GMPs, the extraction process was carried out using different temperatures between 60 and 100˝C. The extraction time was fixed at 3 h, and the ratio of water to the raw material was fixed at 30:1 (mL/g). As shown in Figure 1a , the maximum yield of GMPs was 4.95% when the extraction temperature was 90˝C, and at the highest temperature tested (100˝C) the yield decreased. One explanation for this is that increasing the temperature accelerates solvent diffusion velocity and enhances the solubility of the active ingredients [13, 14] . When temperature was 100˝C, however, the extraction yield of GMPs decreased which is probably because the higher temperature destroys the structure of the polysaccharides [15, 16] . Considering the extraction yield of GMPs, the results indicate that the high temperature needed to maximize the extract will increase the cost for the extraction process , so from and an industrial point of view, temperature ranges from 85 to 95˝C were selected as the optimal conditions in this work.