Separation And Purification Of Stevia Glycosides From Stevia Rebaudiana (Bertoni) Leaves

Stevioside（STV）and Rebaudioside A（RA）are two main components of Stevia glycosides in Stevia rebaudiana（Bertoni）.They are sweeteners with high sweetness and low calorie（zero calorie）extracted from Stevia rebaudiana leaves.How to obtain high purity stevioside is the key to develop the active ingredients in Stevia rebaudiana.In this study,STV and RA were taken as the research objects,and a simple and efficient extraction process was established.The separation and purification of STV and RA were studied by macroporous resin and membrane separation technology.Specific research is as follows:Study on the extraction process of stevioside.High-speed shear homogenization extraction（HSHE）was used to study the extraction process of STV and RA.Based on the single factor experiment,the response surface method was used to further optimize the extraction conditions.The optimized extraction conditions were:59%ethanol aqueous solution,extraction time was 8min,the extraction temperature was 68℃,and the yields of STV and RA obtained under the optimal conditions were 5.37%and 8.68%,respectively.The content of impurity components such as pigment,protein,pectin and inorganic salt ions in the crude extract of HSHE extraction method was compared with extraction method（SE）,ultrasonic method（UAE）and microwave method（MAE）,and the results showed that HSHE the impurity content in the crude extract is lower than the other three methods.The purity of STV obtained by the above extraction conditions was8.05%,and the purity of RA was 17.17%.Study on the separation and purification of stevioside by macroporous resin.Using water as the sample solution,70%ethanol is the best solution.The adsorption and desorption of STV and RA by different polar resins were studied.It is known that the weakly polar resin CD-60 has the best adsorption and desorption effect on STV and RA.The adsorption and desorption rates of STV are 40.42 mg/g and 85.79%,respectively.The adsorption and desorption rates were 70.64 mg/g and 87.85%,respectively.It is known from the adsorption kinetics study that the adsorption of STV and RA on CD-60 resin reaches the adsorption equilibrium after 13 h.The adsorption thermodynamics of STV and RA is consistent with the Langmuir model.The optimum adsorption temperature is 40℃,the adsorption pH is 8-9,and the cleaning solvent is 20%ethanol.The adsorption and desorption of CD-60 resin can increase the purity of STV from 8.05%to 18.3%,the yield is 95.84%;the purity of RA is increased from 17.17%to 43.73%,and the yield is91.00%.Separation and purification of stevioside by microfiltration-ultrafiltration-nanofiltration membrane coupling technique.The effects of polyethersulfone（PES）microfiltration membranes with different pore sizes,PES ultrafiltration membranes with different molecular weight cutoff and 400 molecular weight cut-off polyamide（PA）nanofiltration membranes on the separation performance of stevioside were studied.The effect of nanofiltration membrane on the separation performance of stevioside showed that the microfiltration process selected microfiltration membrane with pore diameter of 0.10μm and the flux under steady state was 109.79 L/（m²·h）.The ultrafiltration process selects a PES ultrafiltration membrane with a molecular weight cutoff of 10,000,and the flux at steady state is 95.15 L/（m²·h）.The flux of the nanofiltration membrane at steady state during the nanofiltration concentration process is 85.39 L/（m²·h）.The decolorization rate of the microfiltration-ultrafiltration-nanofiltration membrane coupling process was 97.32%,and the salt rejection rates(Ca²⁺,Fe³⁺,K⁺,Mg²⁺,Na⁺)were:60.54%,97.92%,60.41%,72.93%,47.05%,STV,respectively.The purity of RA and RA were 33.66%and 53.76%,respectively,and the yields were 82.84%and 80.53%,respectively,which were higher than the macroporous resin pretreatment process.In the production process of stevioside,the microfiltration-ultrafiltration-nanofiltration membrane coupling process is stable,reliable,simple,and green,safe,and has guiding significance for industrial production and promotion.