Extraction And Purification Of Tea Polyphenols And Its Properties

Tea polyphenols(TP), with variety of physiological activities and functionalproperties, is the most important effective ingredient in tea. It has been widely used inmany fields recent years, such as medicine, food and daily chemical industry. In thisthesis, extraction and purification of TP were studied and optimized, with itsproperties investigated as well. Besides, TP was treated with PPL lipase. TP was alsoapplied to investigate the interaction with papain and preparation of microcapsules.Finally, an effectively comprehensive extraction process was developed to extract TPand other functional ingredients. Main conclusions of this thesis were summarized asfollows:The optimization of extraction conditions to prepare TP: Taking extractionyield of TP as index, the optimal extraction conditions for sing-factor tests weredetermined (extraction time45min, solid-to-liquid ratio1:30, extraction temperature70°C, extraction3times, pH5~6, stirring rate100r/min). According to the results ofsing-factor tests, orthogonal tests were carried out. The extraction yield (95.04%) andpurity (50.41%) of tea polyphenols, were achieved at the following optimal extractionconditions: extraction temperature60°C, solid-to-liquid ratio1:30, pH5~6, extractiontime50min, extracting4times.The research of stability of TP: Stability of TP under various pH and temperaturewere studied. The results showed that in an acid environment especially pH3~5, TPand its individual monomers were relatively stable, with small amplitude degradation.While pH was above6, EC and ECG exhibited greater stability than EGCG and EGC.Meanwhile, TP was very unstable in alkaline environment. Besides, though hightemperature led to degradation of TP, it could also bring about isomerization of EGCGand ECG.Hydrolysis study of TP with PPL lipase: In aqueous system, EGCG and ECGwere hardly hydrolyzed by PPL. On the contrary, PPL showed ideally hydrolyzedresults in water saturated ethyl acetate, in which90.58%of EGCG and51.28%ofECG were hydrolyzed. Besides, more effective components such as EGC, EC and GAwere obtained.Interaction between TP and papain: Fluorescence and UV-Vis spectroscopy wereemployed to reveal the mechanism of binding between TP and papain. The bindingconstant and thermodynamic parameters for TP-papain interactions were calculated by fluorescence quenching method. The results indicated that the quenchingmechanism of TP-papain interaction was statistic quenching, and the binding processwas spontaneous, in which hydrophobic forces might play a major role. Afterwards,properties of tea-polyphenols-complexed-papain(TPC-P) were investigated as well.Experimental results demonstrated that TPC-P had greater activity and a widertemperature range than that of free papain. Moreover, thermal stability of TPC-P wasimproved significantly due to the effective antioxidant activity of TP.Preparation of TP microcapsules and sustained release: The uniform TPmicrocapsules with average diameter2.23mm were prepared. With mixtures ofchitosan, sodium alginate and KGM as wall material, the embedding rate could reach97.67%. The concentration of KGM and CaCl2had great effect on the embedding rateand sustained release of TP.Purification of TP and development of comprehensive extraction process: Thefinal purity of TP could reach85.56%by using three-step purified method. Thecomprehensive extraction technology of other functional ingredients of tea wasdeveloped. Finally, tea proteins (163.26mg·g-1), caffeine (1.36mg·g-1, purity93.28%),tea polysaccharides(14.46mg·g-1, contents of total sugar above65%) and theanine(1.36mg·g-1, purity65.2%) were also isolated from tea by fractional extracting.