Extraction And Purification Of Tea Polyphenols By An Aqueous Two-phase System Combined With Microwave-ultrasoni

In China,there are a lot of tea resources,but amount of tea wastes are also produced during the process of making tea,which can't be effectively developed and ultilized.In the tea wastes,there is about 15%-30% of tea polyphenols.Tea polyphenols have many functions,such as lipid lowering,anticancer,preservation,antibacterial and so on,which is also a food additive approved by the National Health Security.In this study,a new technology of an aqueous twophase system combined with microwave-ultrasoni is used to extract tea polyphenols from the tea wastes as raw materials,and then a two-step resins purification process of tea polyphenols extracted is discussed in detail as followed:(1)For the new technology of an aqueous two-phase system combined with microwaveultrasoni,the system of aqueous two-phase extraction was established based on the partition coefficient theory.According to a single factor experiment,the most suitable system was obtained,such as the ethanol of 40 vol.%,the ammonium sulfate content of 0.32 g/mL,and the corresponding distribution coefficient was gotten 11.6.With the response surface method,the operated conditions were optimized,and the optimum condition was the ratio of solid to liquid of 1:60 g/mL,extraction temperature of 63°C,microwave time of 4 min,microwave power of 400 W,ultrasonic time of 7 min,and ultrasonic power of 400 W.Under the condition,the extraction ratio of polyphenols reached 17.43%,which was 17% higher than that with the traditional method.(2)For the two-step resins purification process of tea polyphenols extracted,the comparative experiments of adsorption-elution performances of eight resins for tea polyphenols was studied at a certain operated condition.The results obtained showed that HPD-722 and AB-8 were selected as the adsorbents for caffeine and tea polyphenols,respectively.For HPD-722,the caffeine could be effectively adsorbed at 30° C and pH 8 for 4 h,at which the adsorption ratio of caffeine reached about 77.5%.For AB-8,the experiments of adsorption-elution for tea polyphenols were conducted by a single factor experiment method coupled with design expert software.The optimum adsorption ratio was gained as 83.21% at 29 °C and pH of 6 for 6 h,and the optimum elution ratio was 79.20% at 40°C and pH of 6 for 2 h and with a solution contained ethanol of 80 wt.% as an eluent.(3)According to adsorption kinetics and thermodynamics of tea polyphenols for AB-8,it's found that the kinetic adsorption process accorded with intraparticle diffusion model,which suggested that the adsorption process is controlled by internal diffusion.The adsorption isotherms were conformed to the Langmuir equation,which indicated that the adsorption of tea polyphenols was monolayer adsorption.To confirm whether the sample extracted from tea wastes was tea polyphenols or not,several tests were applied to compare with the characteristics of the sample extracted and the standard sample of tea polyphenols,which included appearance direct comparison method(color and smell),Uv spectrum at 270 nm,infrared spectrum and high performance liquid chromatography.The results obtained proved that the sample extracted was mainly consisted of tea polyphenols,and the purity of tea polyphenols was about 67.09 wt.%.