Study On Extraction And Purification Of Tea Polyphenols From Fresh Green Tea

Taking fresh green tea produced in Nanchang as the research object, the studies on the extraction and purification of tea polyphenols (TP) from the fresh green tea were carried out in this experiment.Ethanol aqueous solution was used to extract TP from fresh green tea. First, through single factor experiment method, the effects of liquid/solid ratio, mass percentage of ethanol solution, extraction time and extraction temperature on the TP extraction rate were investigated and the suitable technical conditions were determined as6,70%,30min and70℃respectively, under which the TP extraction rate was2.90%. Then the further optimization of the technical conditions and the effect accuracy of the factors were studied through orthogonal test method. The results showed that the optimized parameters were close to those by single factor method and all the factors had no obvious effects on the target. Finaly, the response surface method and Design-Expert7.0software system were applied to further optimize the technical conditions and to establish the quadratic multinomial regression equation. The optimized operation parameters were liquid/solid ratio of6.6, ethanol solution mass percentage of74%, extraction time of30min and extraction temperature of71℃,under which the TP extraction rate reached2.97%. The established model has a good agreement of experiment value with calculated value.The composite metal ion precipitation(Al3++Zn2+) method was employed to precipitate TP from the extract liqior.First, the effects of precipitant dosage, pH of the extract liquor, precipitation placing time and precipitation temperature on the TP precipitation rate were investigated and the suitable conditions were obtained to be0.2g(relative to lOg fresh green tea),6,0min and20℃respectively,which gave the TP precipitation rate of98.20%.After that, the response surface method and Design-Expert7.0software system were applied to further optimize the technical conditions and to establish the quadratic multinomial regression equation. The optimized operation parameters were precipitant dosage of0.22g, pH5.8, precipitation placing time of0min and and precipitation temperature of22.4℃,under which a high TP precipitation rate of98.98%was aquired. The test values were very close to the model values, meaning that the model was highly credible and can predict the TP precipitation rate at various different conditions.