| Steviol glycosides isolated from the leaves of Stevia rebaudiana Bertoni have been regarded as a promising natural sweetener because of their high sweetness and lower calorific value. Steviol glycosides have many biological effects without side effects, they have caused great interest of some researchers and have been regarded as the substitute of sucrose. Nowadays, Steviol glycosides have been widely used in many fields including cosmetic, food and medicine industry.In this dissertation, the Steviol glycosides were chosen as the research object. The methods of extraction, impurity removal, purification, fine purification and decolorization of Steviol glycosides from Stevia rebaudiana Bertoni were studied. extraction rate, loss rate and purity of Steviol glycosides chosen as the evaluation indexes. The contents of this dissertation are the following:1.The study on extraction technic of Steviol glycosides in Stevia rebaudiana Bertoni.the extractrd technology of Steviol glycosides from Stevia rebaudiana Bertoni by reflux extraction, immersion extraction, enzymatic extraction, countercurrent extraction and reflux set extraction were studied. The five methods were compared by their results of extraction rate of Steviol glycosides. The extraction yields of the optimum process for above five methods were 98.08 %, 80.17 %, 86.01 %, 79.98 % and 94.54 %, respectively. The result indicated that reflux set extraction had the advantages of higher extraction rate of Steviol glycosides, shorter extraction time and saving - water. Therefore, the reflux set extraction have their unique superiority over other method.2.The study on impurity removal of Steviol glycosides in Stevia rebaudiana BertoniThe impurity removing rate and loss rate of Stevioside were choosen as the assessment index and then three impurity removal process of water extracts of Stevia rebaudiana Bertoni were compared. The results showed that ethanol subsiding method was better than flocculation and modified attapulgite adsorption technology. The best conditions of ethanol subsiding method were as follows: adding 95% ethanol(speed is 10 mL/min)to obtain 80% ethanol concentration in solution, and standing for 1 h, then centrifuging to obtain the supernant, in this optimum process, the loss rate of Stevioside is 6.13 % and impurity removal rate is 16.47 %.3. The study on purification and fine purification of Steviol glycosides in Stevia rebaudiana Bertoni.(1)Dynamic adsorption and characteristic of L macroporous resin to Steviol glycosides in Stevia rebaudiana Bertoni were researched. The results showed its best dynamic adsorption and desorption conditions as follow: sample volume is 1400 mL; sample concentration is 0.025 g/ml; adsorption velocity is 40 BV/h; the number of water is 800 mL(10BV), desorption velocity is 7.2 BV/h; temperature of dynamic adsorption and desorption is 40℃; desorption agent is mixed solvent; desorption velocity is 40 BV/h the number of collected tubes is 600 mL(8BV).(2)choice of four kinds of macroporous resin by comparing the results of static adsorption of Steviol glycosides in Stevia rebaudiana Bertoni, and selected a suitable macroporous resin to Steviol glycosides in Stevia rebaudiana Bertoni, and the study of adsorption of Steviol glycosides in Stevia rebaudiana Bertoni by dynamic adsorption. the results showed that the better adsorption performance to Steviol glycosides in Stevia rebaudiana Bertoni is D-1macroporous resin, and the best adsorption conditions is that: sample concentration is 0.1 g/mL; adsorption velocity is12 BV/h; sample volume is 40 mL; desorption agent is 70 % ethanol; the number of collected tubes is 100 mL. the puity of Steviol glycosides in Stevia rebaudiana Bertoni by purification and fine purification is 75.30 %.4.The study on decoloration of Steviol glycosides in Stevia rebaudiana Bertoni.The result of active aluminum oxide -column chromatography-app lied in decolorization of Steviol glycosides revealed that it had some influences not only on decolorization, but also on the purity and quality. The optimal conditions were as follows: desorption agent is water; temperature of decolorization 35℃, time 30 min; the mass ratio of Steviol glycosides to active aluminum oxide 1:0.8. then, Used column chromatography to purify Steviol glycosides, desorption agent is 70 % ethanol. the puity of Steviol glycosides in Stevia rebaudiana Bertoni by Decolorization is 91.76 %.
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