Chemical Research On Addition Catechins And Theabrownins Of Pu-erh Tea

Pu-erh tea,a well-known tea from ancient times,was originally produced in the Yunnan province of China through a special post-fermentative process,using sun-dried green tea as raw materials,which were prepared from the leaves of(Camellia sinensis(Linn.)var.assamica(Masters)Kitamura).Unlike the black tea fermented by polyphenol oxidase,ripe Pu-erh tea has a unique flavor due to the post-fermentation of microorganisms.The content of catechins such as epicatechin(EC)and epicatechin gallate(EGCg)in ripe Pu-erh tea is drastically decreased compared with green tea.It maybe a series of oxidative polymerization of catechin occur during post-fermentation process.The reaction forms a complex polyphenolic components structure.However,tea pigment such as theaflavins,thearubigins and oolongtheanins were not found in Pu-erh tea.There are some kinds of A ring addition catechins in Pu-erh tea,such as puerin A,B,puerin I-VIII,several carboxymethyl-and carboxyl-catechins.It may be formed by nucleophilic addition or oxidation from of the catechins and other compounds in green tea.These compounds generally have good biological activity,determining them formation mechanism are beneficial to the further utilization of A-ring addition catechins.Theabrownins(TBs)is a kind of water soluble polymeric phenolic compounds,which is formed by various polyphenols,polysaccharides,proteins,lipids,and caffeine via microbial action.TBs is macromolecule polymers with many benzene rings,hydroxyl groups,carboxyl groups,methyl groups,and amino groups,and it hows diverse bioactivities.This kind of components has complex chemical structure and large molecular weight,separation and refining and structural determination are difficult,its physical and chemical properties,structural characteristics and formation mechanism have not been cleared.At present,some fragments of TBs have been obtained by acid hydrolysis reaction,but their structure is still complicated,which can not effectively explain the formation mechanism of TBs.In this study,EGCg was used in the oxidation reaction of theanine or microbial metabolite(such as acetic acid,cinnamaldehyde)to find the most suitable reaction conditions for each reaction.The reaction products were contrasted with the known A ring addition catechins in Pu-erh tea to speculate on the possible formation mechanism of these compounds.The thiol degradation test was used to degrade TBs and determined the degradation products.