Study On Acylation Modification Of Tea Polyphenols And Changes Of Their Biological Activity

Tea polyphenols are an important classification of active substances in tea,which have the functions of antioxidation,lowering blood fat,lowering blood sugar,antibacterial and other functions.However,natural tea polyphenols have shortcomings such as easy-oxidated instability and poor oil solubility,which seriously limit the application of tea polyphenols in food industry.Improving the physicochemical properties of tea polyphenols through molecular modification is the focus of research in this field.Therefore,it is of great significance to explore a modification method that can not only improve the stability of tea polyphenols but also enhance their activity.In this study,a common Tieguanyin tea was adopted as the raw material to extract tea polyphenols,on which some chemical modification was carried out to figured out the property changes after the modification.The main research contents are as follows:1.Response surface methodology(RSM)was used to optimize the ethanol extraction process of tea polyphenols.Tea polyphenols were extracted from Tieguanyin tea by ethanol-water extraction.The effects of tea powder particle size,ethanol-to-water ratio,material-to-liquid ratio and extraction temperature on the extraction yield were systematically studied.RSM was used to optimize the single factor experimental designs.According to the experiment results,,the optimum conditions were determined as follows: tea powder mesh size greater than 80 meshes,the extraction temperature was 67?,the ethanol concentration was 60% and the ratio of solid-toliquid is 1:30(g:m L).And the content of total phenol in the extract was 14.073%.2.Separation and purification of tea polyphenols.Several kinds of macroporous adsorption resins were used to separate and purify the extracted tea polyphenols.Absorption rate and desorption rate are the indicators to exam the separation and purification effect of several macroporous resins(including LX-8,polyamide,AB-8,D101,HPD-100,X-5)on crude tea polyphenols.The comprehensive adsorption and desorption effect of LX-8 macroporous resin showed the best.At the same time,the effects of eluent concentration,elution volume and sample amount on the extraction rate of tea polyphenols in the dynamic adsorption process were also studied.After a series of single factor orthogonal optimization experiments were done,it was concluded that the optimal process parameters as follows: ethanol concentration of 60%,elution volume of 200 m L,sample loading volume of 100 m L.Under the conditions,the extraction rate of tea polyphenols was86.77%.3.Modification and structural identification of tea polyphenols.The extracted tea polyphenols were acylated modified by cis-butenedioic anhydride,itaconic anhydride and citraconic anhydride.The structure of modified tea polyphenols was identified by infrared spectroscopy,high performance liquid chromatography,electron probe and other methods.The results showed that ester compounds were produced by the modification of tea polyphenols,and the products were mainly mono-substituted.4.Study on biological activity and properties of the modified tea polyphenols.The changes in antioxidant capacity,blood lipid-lowering capacity and stability of tea polyphenols before and after modification were compared.DPPH radical scavenging ability and hydroxyl radical scavenging ability were used to reflect the antioxidant ability.It was found that there was no significant difference in the scavenging levels between modified tea polyphenols and unmodified tea polyphenols.The lowering blood lipids ability of tea polyphenols was measured by cholate adsorption experiment in vitro.It was found that the acid anhydride modification could significantly improve the cholate adsorption ability of tea polyphenols,and the modification by cis-butenedioic anhydride had the strongest improving effect.In a six-week long-term experiment,the modified tea polyphenols showed better stability.