Preliminary Study On Ultrasonic Extraction Of Green Tea Polyphenols And Its Activity And Structure

Tea is Chinese traditional drink and the 21st century green drinks,it was used as medicine firstly,drink later,and now back to the drugs,attribute to the modern biological technology and modern medical technology.In China,there are many types of tea.According to the differences of manufacturing technology and quality,generally it can be divided into green tea,red tea,oolong tea,white tea,black tea and cyan tea etc.Tea polyphenols is one of the most important biologically active components and the polyhydroxy mixture of phenolic compounds which tea contains.It is soluble in water,methanol,ethanol,acetone,ethyl acetate etc and insoluble in organic solvents such as chloroform and benzene.It is a kind of powder,the colour of which ranges between pale yellow and dark brown.At present,there have been papers about the effect of ultrasound on extraction rate of tea polyphenols from the green tea,but there have been few papers about the systematic research of effect of ultrasonic enhanced extraction on extraction rate and the structure.Direct observation of microstructure of tea polyphenols has not been found by atomic force microscopy.Accordingly,this paper used Shaanxi Green Tea as materials,a water bath method and ultrasonic method for tea polyphenols extraction had been used respectively.The effect of both extracts were compared,the activity,structure and morphology of tea polyphenols which were extracted by the two methods were preliminarily studied,which provided necessary basic data and experimental evidence of tea polyphenols structure and oxidative effects by ultrasonic method.The main research contents and corresponding results reported in the papers were summarized as follows:(1) When study on the extraction of tea polyphenols,the water bath and ultrasound were used.The best extraction conditions were determined through single-factor experiments and response surface method.the optimum condition of the water bath method was as follows:extraction temperature was 79.9℃,extraction time was 60.5min,liquid ratio was 30.9mL/g,Under these conditions the yield of Shaanxi Green Tea polyphenols was 10.273%,the optimum condition of ultrasonic method was as follows:liquid ratio was 40.2mL/g,ultrasonic power was 476W,extraction time was 15.1min,the TP rate was 10.312%.So ultrasonic extraction compared with water extraction of tea polyphenols significantly reduced oxidation time in the high temperature,improved product quality and extraction rates,reduced energy loss and the production costs.(2) To the activity of tea polyphenols,the ability to remove of hydroxyl radical(·OH),superoxide anion radical(O^-₂·),as well as the free radicals DPPH in vitro has been reserached. The results showed that green tea polyphenols have a certain amount of free radical scavenging,and increased with the concentration clearance rate in a certain narrow range of concentration of the three radicals.(3)To qualitative analysis of tea polyphenols with the high-performance liquid chromatography, Agilent HC-C₁₈(5μm,4.6×250mm)column,using gradient elution:0min(20%A+80%B),9min(70%A +30%B),12min(85%A+15%B),mobile phase A was methanol and mobile phase B was 1%(volume ratio) aqueous acetic acid,injection volume was 10μL,flow speed was 1mL/min,detection wavelength was 275nm and column temperature was 30℃.This method could separate the five kinds of tea polyphcnols effectively,short analysis time(12min) and it is easy to operate,have good reproducibility.(4)To analysis of tea polyphenols with the infrared spectral,the standard sample of tea polyphenols,the tea polyphenols extraction of ultrasonic and water bath method were scanned and qualitatively analysised,the frequency and co-frequency of corresponding absorption peak such as:the O-H stretching vibration,C-O stretching vibration,C=C vibration contraction,C-C vibration contraction were found respectively,benzene ring in the fingerprint area of infrared spectroscopy was valuable to study Shaanxi Green tea polyphenols initial structure.(5) To the morphology structure of tea polyphenols,the atomic force microscope was used to observe surface morphology of the standard tea polyphenols.We could clearly see that the surface was the same as fishing net which evenly distributed on the mica surface.The atomic force microscopy was a very useful tool to study high tea polyphenols structure,however,the molecular structure of tea polyphenols morphology can not be observed in the scope of the observation in this experiment,therefore,we need to be further studied.