| Longan polysaccharides (LP) is one of the most important bioactive compounds in longan pulp. In recent years, it has been drawing close attention because of its bioactive function in immunoregulation, anti-tumor and antioxidant activities. In this research, the longan polysaccharides of 7 Guangdong main cultivars were studied and the high polysaccharide cultivar was chosen; the extraction and preparation of longan polysaccharide were optimized; the antioxidant activities of longan polysaccharide were evaluated. Main conclusions were summarized as follows:Chuliang longan contained 6.37±0.16 mg polysaccharide per 10.0 gram pulp weight, which was significantly higher than that of the other 6 longan cultivars (p<0.05). Longan polysaccharide was heteropolysaccharides which were composed of monosaccharides including fructose, rhamnose, mannose, glucose, galactose, xylose and arabonose. Glucose, galactose, xylose and arabonose were the main monosaccharide components of longan polysaccharide in the 7 cultivars. The monosaccharide components of Chuliang longan polysaccharide were fructose, rhamnose, glucose, galactose, xylose and arabonose, and the ratio of percentage composition were 3.88%:5.27%:74.96%:6.06%:2.81%:6.99%. After comprehensive consideration, Chuliang longan was selected as the high polysaccharide content cultivar and was studied in the following research.Single factor analysis and response surface methodology (RSM) were used to optimize the enzyme and microwave-ultrasonic extraction. The analysis result showed that, using enzymatic extraction method, the optimal conditions to obtain the highest yield were enzyme concentration 1.2%, water to raw material 6.0(mL/g), extraction temperature 45.0℃and extraction time 187.0min. Using microwave-ultrasonic extraction method, the optimal conditions to obtain the highest yield were microwave power 640W, microwave time 60s, ultrasonic power 590W, ratio of water to material 9.5(mL/g), ultrasonic time 8.5min. The actual yields of EELP and MUELP were 12.23±0.15mg/g and11.03±0.38mg/g, respectively.The preparations of EELP and MUELP were optimized, the fruit residue was determined to be washed twice; the trichloroacetic acid (TCA) processing to remove protein were determined to be with the concentration of 2% and the time of 2h; the alcohol precipitation processing were determined to be with the concentration of 65% and the time of 12h in the EELP and the concentration of 75% and the time of 18h in the MUELP. Under these preparations, the final yields of EELP and MUELP were 9.17±0.32mg/g and 8.11±0.28mg/g, and the polysaccharides contents were 71.26±2.41% and 70.53±3.53%, respectively.The acute toxicity and antioxidant activities of longan polysaccharide were evaluated. The result of acute toxicological study in mice showed that the longan polysaccharide is of actual non-toxic. The result of antioxidant activities showed that longan polysaccharides had good free radical scavenging abilities in removing hydroxyl radicals, 1,1-dipheny1-2-picrylhydrazyl(DPPH) radicals, 2,2'-azinobis-3-ethyl-benzothiazoline-6-sulphonic acid (ABTS) radicals. The IC50 value of MUELP were 8.204±0.239, 0.667±0.053 and 0.481±0.038mg/mL respectively; and the IC50 value of EELP were 9.601±0.223, 1.710±0.068 and 0.604±0.031mg/mL respectively. With the polysaccharides concentration of 50mg/mL, the superoxide anion radicals IC50 value of MUELP and EELP were 36.10% and 18.94% respectively. With the polysaccharides concentration of 25mg/mL, the OD value at 700nm of MUELP and EELP were 1.119±0.041 and 0.641±0.024, respectively. Therefore, MUELP had antioxidant activities better than EELP.
|
PDF Full Text Request