Antioxidant Properties And Identification Of Active Components Of Pu-erh Tea

During the past decade numerous studies have suggested the possible effects of teas and their polyphenolic constituents as antioxidants on the models of risk of cancer and cardiovascular disease or makers of lipid metabolism in vitro and in vivo. While these properties of green tea and black tea have been extensively studied, the less attention has been given to these properties of pu-erh tea. Pu-erh tea, a kind of post-fermented tea, produced mainly in Yunnan province of China, is consumed widely in Southeast Asia. Some studies have implied that pu-erh tea has a wide range of biological effects. In the present study, compared with green tea and black tea, the antioxidant activity of pu-er tea as special post-fermented tea was investigated. The bioactivities of compounds from different fermented process were discussed. Furthermore, the antioxidant activity of pu-erh tea was evaluated from a view of its active components and their chemical structures.1. The polyphenols of green, black and pu-erh teas and their role in scavenging free radicals and effect on the antioxidant function of rats were compared. The results were as follows: a) The content of polyphenols (including catechins) in green tea was the higher than that of black and pu-erh tea, but flavones in green tea was the lower than that of black and pu-erh tea. Black and pu-erh tea had the equivalent amount of gallic acid and caffeine, which were higher than those of green tea. b) The order of 2, 2-diphenyl-1-picrylhydrazyl (DPPH) scavenging ability of these teas was green tea > black tea > pu-erh tea. c) The activity of antioxidant enzyme SOD were increased in green and black tea groups as compared to the control group significantly (P<0.01) , but SOD activity was decreased in pu-erh tea group(P<0.01) . The activity of GSH-PX was increased in all tea-treatment groups significantly (P<0.05 or P<0.01) . The MDA content in pu-erh tea group was decreased significantly (P<0.05) .2. The water-extracted pu-erh tea and black tea were separated by the order of chloroform, ethyl acetate, and n-butanol. The antioxidant activity of these teas and their fractions were investigated by the hydroxyl radical-induced luminol chemiluminescence assy and visible spectrophotometric method. The results revealed that black tea had slightly stronger antioxidant activity than pu-erh tea in water phase. The two types of tea had considerable antioxidant effect on some lipid. The ethyl acetate fraction was the most contributions to the antioxidant activity of the two types of tea in water phase which antioxidant activity was a little stronger from black tea than that from pu-erh tea, and had scarcely any antioxidant activities in oil phase.3. The antioxidant activity of pu-erh tea extracts was investigated by the DPPH free radical-scavenging assay. The result pointed pu-erh tea ethyl acetate extract (PEAF) had the strongest DPPH scavenging activity. High performance liquid chromatography combined with diode array and electrospray-ion trap- mass spectra detection was used to separate and identify the compounds present in PEAF. There are three phenolic acids, i.e., 4-hydroxy- benzoic acid, dihydroxy- benzoic acid and gallic acid, seven catechins, i.e., catechin, epicatechin (EC), gallocatechin, epigallocatechin (EGC), epicatechin gallate, epigallocatechin gallate and epiafzelechin-3-O-gallate, nine catechins derivatives, i.e., procyanidins dimmer, puerin A, puerin B, EC- [8, 7-e]-4α-(4-hydroxyphenyl)-dihydro-2 (3H)-pyranone, EC- [8, 7-e]-4β-(4-hydroxyphenyl)-dihydro-2 (3H)-pyranone, Cinchonain Ib (αandβ), EGC-[8, 7-e]-4α-( 3, 4-dihydroxyphenyl)-dihydro-2 (3H)-pyranone and EGC-[8, 7-e]-4β-( 3, 4-dihydroxyphenyl)-dihydro-2 (3H)-pyranone, and six flavonol glycosides, i.e., quercetin, quercetin-glucoside, quercetin- rhamnoside, quercetin-rutin, quercetin-glucoside-rhamnoside-rhamnoside and kaempferol-rutin.In summary, there were remarkable effects of polyphenols in different fermented processes on the antioxidant ability of tea. It suggested that some unidentified new polyphenols may play the same role with catechins in the post-fermented tea, the pu-erh tea, and their antioxidant activity may be even stronger than catechins in vivo. Some catechins derivatives were identified, which maybe prove the occurrence of specific polyphenols in pu-erh tea. There is need for more detailed studies to improve our understanding of the role of these catechins derivatives in the bioactivity of pu-erh tea.