Study On Extraction, Purification And Anti-oxidative Activity Of Ploysaccharides From Longan Fruit

The longan, one of the major subtropical fruits in southern China, is of high nutritional value and healthy value. Modern pharmacological studies have shown that longan fruit have several bioactivities, including anti-aging, reducing blood fat, anti-cancer, anti-oxidation and so on. In this study, the technologies of extraction, separation and purification of the longan polysaccharides(LPS), have been systematically studied, moreover, its structure and antioxidant activity in vitro have been also preliminarily explored.In this study, LPS was obtained by the method of ultrasound-assisted extraction.The extraction process was optimized by the Response Surface Analysis method on the basis of the single-factor experiment. The optimum extraction conditions are as follows: extraction temperature at 60℃for31.111minutes, with the liquid-solid ratio of 19.9697 and supersonic power of 161.414W. The theoretically maximum extraction rate of polysaccharide is 19.96%. The polysaccharide extraction rate by the method of ultrasound-assisted extraction is somewhat high, compared with the method of traditional hot-water extraction. Considering the factors such as time and energy consumption, the method of ultrasound-assisted extraction was optimum to extract polysaccharide.To separate and purify LPS, the protein was removed by Sevag method and TCA method at first and the results of these two methods were compared, and then the decolorization process used by resin, hydrogen peroxide and activated carbon was also studied in this study.The research showed the TCA method was better,and the removal rate of protein was up to79.18%,besides macroporous resin XDA-1 was better than hydrogen peroxide and activated carbon to decolorize polysaccharide.The DEAE-Cellulose column and Sephadex G-100 column were used to furter separate LPS extract and three LPS components were obtained and respectively named LPS-1-A,LPS-1-B and LPS-2. In particular, a smaller protein elution peak was also detected in the range of LPS-2 elution curve, which indicated that LPS-2 may be a sugar-protein complex.The ultraviolet spectroscopy, gel column chromatography and freezing- unfreezing experiments all showed that LPS-2 was a homogeneous polysaccharide. Because of less content of LPS-1-A, LPS-1-B, LPS-2 was only studied in the follow-up test.Infrared spectroscopy analysis showed that the LPS-2 is aβ-heterosaccharides with pyran and acetyl amino group. The monosaccharide standards and derivatives of LPS-2 hydrolysate were analyzed by Gas chromatography, and the results showed that LPS-2 is an acidic heteropolysaccharide, consisting of rhamnose, arabinose, xylose and galactose, and its molar ratio of rhamnose:arabinose:xylose:galactose = 1:2.59:4.43:2.25. Using sulphuric acid–carbazole method detecting uronic acid content of LPS-2, the results showed that the LPS-2 is of lower uronic acid content, only 4.3%.Finally, the antioxidant abilities of the crude longan polysaccharides (CLPS), semi-pure longan polysaccharides product (SLPS) prepared by removing its protein with Sevag method, semi-pure longan polysaccharides product (TLPS) prepared by removing its protein with TCA method, LPS-2 were preliminarily explored from the three aspects of scavenging 1,1-diphenyl-2-picrylhydrazyl radical (DPPH·), hydroxyl radical (? OH) and superoxide anion radical (O-2·). The results showed that LPS have strong scavenging abilities against DPPH·,·OH while has no clear effect on the O-2·. In particular, the higher the purity of polysaccharide, the stronger the scavenging activity against DPPH·. In addition, as for·OH and O-2, the activity of SLPS was the strongest and the LPS-2 was the weakest, which implied that the motley protein inhibited the scavenging activities against·OH and O-2·, nevertheless the protein in glycoprotein promoted the activities.