Studies On The Preparation?Characterization?Activirties And Stability Of Tea Polyphenol-Zinc Complexes

Based on the theory of coordination chemistry of traditional Chinese medicine,the development of tea polyphenols(TP)as tea polyphenol-metal complexes has a very broad application prospect.In order to objectively understand and scientifically evaluate the structure and function of tea polyphenol-zinc complexes,and to make good use of the medicinal value of tea polyphenol-metal complexes,as well as to provide new ways for the utilization of tea and its by-products,this work aims to analyze the preparation,structure,antioxidant activities,antibacterial activities and stability of tea polyphenol-zinc complexes.The results are as follows:1.Research on the extraction of TP by inner ebullition.Results showed that a maximum extraction yield of TP of 22.45%was obtained under the optimized conditions:concentration of desorption agent,50%ethanol solution;the time of desorption at room temperature,10 min;solid-liquid ratio of desorbent,1:6;the dosage of the extract,1:110;the extraction temperature,100?;extractant,water;extraction time,10 min.Compared with water bath extraction,the extraction rate of TP was increased by 11.53%,and the extraction time was reduced effectively.Also,the contents of catechins and antioxidant activities of TP were strengthened significantly.2.Analysis on the preparation and structure of tea polyphenol-zinc complexes.According to the preferred preparation process(the molar ratio of TP to Zn²⁺,1:2;the reaction p H,6.5 and the reaction time,20 min),three complexes of TP-Zn,TTP-Zn and EGCG-Zn were prepared by using TP,TP extracted from fresh leaves and epigallocatechin gallate(EGCG).The structures of three complexes and ligands were characterized:UV-visible spectroscopy revealed that the characteristic absorption peaks of the complexes showed red shift;Fourier transform infrared spectroscopy analysis showed that Zn²⁺reacted with phenolic hydroxyl groups;Scanning electric microscope showed that the complexes were nano-sized viscous particles;Proton nuclear magnetic resonance indicated that the reaction occurred on the ortho-phenolic hydroxyl groups of ring B and ring D;Thermogravimetric analysis indicated that the complexes had better thermal stability,and the molecular formula of EGCG-Zn was speculated to[Zn₂C₂₂H₁₄O₁₁]·2H₂O.3.Investigation on the activities of tea polyphenol-zinc complexes.The antioxidant results presented that the scavenging abilities of radicals(DPPH free radicals,hydroxyl radicals and superoxide anion radicals)of complexes were significant stronger than that of ligands.The antioxidant capacities were in order:EGCG-Zn>EGCG>TP-Zn>TP>TTP-Zn.The bacteriostatic tests showed that the tea polyphenol-zinc complexes could significantly inhibit the growth of Escherichia coli and Staphylococcus aureus and had stronger antibacterial abilities than the ligands.4.Studies on the stability of tea polyphenol-zinc complexes.The results indicated that the p H value had significant effects on the spectral properties of the complexes.With the temperature rises and the storage time increases,the contents of the complexes decreased gradually.The stability of the complexes was affected by the light.Therefore,the aqueous solution of the complexes should be preserved at slightly alkaline condition,low temperature without light and in the short time.In summary,tea polyphenol-zinc complexes could be used as a good antioxidant or bacteriostatic drug.TTP-Zn could not only reduces production cost,but also shows superiority physiological activities than tea polyphenol,which has a promising application prospect.