Study On Method Of Separation And Purification Of Rebaudioside A

Steviosides extracted from stevia leaves is a new sweetener widely used in the foodindustry. It has the characteristics of high sweetness, low calorie, no fermentation and toxicity,internationally known as “the third sucrose of the world”. Rebaudioside A (RA) has thehighest sweetness and the taste quality of all the components in steviosides. Long-termconsumption will not increase blood glucose concentration. Rebaudioside A can be effectivein preventing obesity, diabetes, hypertension, phenylketonuria and other symptoms, but itscontent accounts for only about25%of the total mass. The chemical structure and polarity arevery similar between Rebaudioside A and stevioside, which with the highest content, so thatthe work of extracting Rebaudioside A has become very difficult.In this paper, solubilities of Rebaudioside A in acetone, ethanol and ethanol volumefraction of95%and90%in the temperature range from273.15K to318.15K were measuredby laser monitoring method. The experimental data was related by the apelblat equation, idealsolution equation and polynomial empirical equation, the maximum average relative errors ofcorrelation results are1.75%,3.85%,0.96%respectively. The metastable zone properties ofRebaudioside A in solvents of ethanol and ethanol volume fraction of95%and90%were alsoinvestigated in the experiment. The experimental results have provided the theoretical basisand data support for determination of crystallization scheme and optimization ofcrystallization conditions.Steviosides was separated by cooling crystallization method. The effect on crystallizationseparation in different concentration solution has been studied, the result showed thatRebaudioside A can be isolated in high purity, which can reach a maximum of92.82%. Usingsolventing-out crystallization method to separate steviosides, according to the optimalexperiment scheme, the separation effect from the factors of solution concentration andtemperature has been investigated synthetically. The result showed that when the selectionswere experimental concentration of0.30g/mL and temperature of25℃, the productivity ofcrystallization was73.33%. From analysis on the crystallization products with electronmicroscope, morphology of crystal product was evaluated that products of solventing-outcrystallization were better than those of cooling crystallization, and the products were idealwith uniform distribution and morphological rules.Steviosides was separated by macroporous adsorption resin. The DM18macroporousresin was selected as the most suitable resin for the separation of steviosides, its separationperformance was investigated by the static and dynamic experiments. The thermodynamicand kinetic behaviors of DM18macroporous resin were studied by the static experiments. Theadsorption isotherm of25℃and kinetic curve were achieved, the result showed that theadsorption of DM18macroporous resin was the first-order reaction and the rate constant k of adsorption equilibrium was1.76×10-4s-1. The dynamic adsorption leakage curves anddynamic desorption curves of steviosides and its main components (Rebaudioside A andstevioside) were achieved, which showed that DM18macroporous resin had excellentadsorption selectivity to Rebaudioside A, its separation effect was satisfactory, it had a goodapplication prospect.