Separation，Purification And Antioxidant Activity On The Polysaccharide From Purple Sweet Potato

This thesis mainly focused on the raw material of purple sweet potato, the crudepolysaccharide was extracted from it by the method of ultrasonic aided hot waterextraction. The crude polysaccharide was pre-separated by removing protein, coloringmatter, inorganic salt and other impurities of it, then was isolated through ionexchange column again, the better polysaccharide components were selected andcollected. The collected polysaccharide component was purified again by Sephadexcolumn, selected several typical molecular weight polysaccharide components tocollect and lyophilize. At last, the antioxidant properties of the polysaccharide isolatedby the ion exchange column was researched, the simple structure of the polysaccharidepurified by the Sephadex column was knew simply.First, the crude polysaccharide was extracted from the purple sweet potato by themethod of ultrasonic aided hot water extraction. During the test, the influences of thecrude extraction factors on the yield of the polysaccharide extraction were studied. Bythe method of orthogonal experiment, the optimum extraction process of thepolysaccharide from purple sweet potato as the following: the extraction temperatureof hot water was80℃, the ratio of liquid to solid was11mL.g-1, the extraction timewas30min, the ultrasonic power was720W, and under this optimum process the rateof crude polysaccharide was about34.47%, then the crude polysaccharide extracted bythe above optimum process was pre-separated by removing protein, coloring matterand others. The results of the single factor experiment method showed when thecontent of trichloroacetic acid (TCA) in the polysaccharide solution was3%, the rateof deproteinization was about95.54%, while, the loss rate of polysaccharide was leastabout52.60%in this test.Second, the crude polysaccharide pre-separated was isolated by the ion exchangecolumn (DEAE-Cellulose52). During the test, the influence of elution fractionsproduced by the different pH conditions and the different ion strength eluents was studied, whether the components eluted with different ionic strength eluents incorresponding pH environment during the elution process had the hybrid phenomenonwas also studied. The results showed that the elution effect of NaCl solution in neutralenvironment was better, the low ionic strength eluent of NaCl could get the betterelution effect, in this test the concentration of NaCl was11.7g.L-1, the purity ofpolysaccharide was about94%, while, the elution rate was about3%. Thepolysaccharide component eluted with high ionic strength eluent of NaCl after loadingwith sample once could contain the component eluted with low ionic strength eluent ofNaCl after loading with sample once, this explained the component eluted first withhigh ionic strength eluent of NaCl could have the hybrid phenomenon.Third, the polysaccharide component eluted with the solution of11.7g.L-1NaClwas purified by Sephadex G-100column again. The eluent, the sampling amount, thecollection amount in each tube and other elution condition were studied in this test.The results showed that that the purification effect of Sephadex G-100was best wheneluted with5.85g.L-1NaCl after loading with1mL sample then collected2mL eluatesin each tube. The molecular weights of polysaccharide components under the first peak,the second peak and the third peak were calculated roughly by the method of gelchromatography and they were about129,909Da,107,354Da and88,715Darespectively. The low, middle and high molecular weight polysaccharide componentsgot by the eluent of5.85g.L-1NaCl were scanned by infrared spectroscopy, the infraredspectrogram showed that the two different molecular weight components were allpolysaccharides, and their ring structures were both furanoid type, it also showed thatthe configurations of the end group anomeric carbon in this two different molecularweight polysaccharides were both α-type.Finally, the polysaccharide isolated by DEAE-Cellulose52column was studiedthe antioxidant properties to the oil. The results of thiobarbituric acid (TBA) methodshowed that the polysaccharide isolated by DEAE-Cellulose52column had theantioxidant effect on the sesame oil, the antioxidant effect of0.15%polysaccharidewas the same as the0.1%Vc on the sesame oil and they both had the bidirectionalmodulatory effects on antioxidant properties to oil.