IMPACT OF FERMENTATION DEGREE ON THE ANTIOXIDANT ACTIVITY OF PU-ERH TEA IN VITRO

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ABSTRACT The consumption of pu-erh tea has been increasing rapidly in recent years. Pu-erh tea is considered to be much more beneficial to human health than other kinds of tea. Antioxidant activity is the main medicinal property of pu-erh tea. The present study compared the antioxidant activities of water extracts of tea (WEOT) and sun-dried green tea with different fermentation degrees in vitro. Antioxidant capacities of the WEOTs were evaluated by testing their total antioxidation capacity. The free radical scavenging capacity was evaluated using 1-1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assays, hydroxyl radical scavenging assays and superoxide anion free radical scavenging assays. Results showed that, of all the WEOTs, the first pile-fermentation tea sample gave the strongest scavenging ability of both DPPH radical and hydroxyl radical, followed by the sun-dried green tea, and DPPH radical scavenging activity was higher than that of hydroxyl radical. DPPH scavenging ability of the sun-dried green tea, the first, the second, the third and the fourth pile-fermentation tea were 87.90%, 89.29%, 85.86%, 82.62% and 80.94%, respectively. The scavenging ability of hydroxyl free radical for the WEOTs of the first pile-fermentation tea is significantly higher (P < 0.05) when compared with other extracts, with a 26.21% inhibition. The first pile-fermentation WEOT exhibited the most potent scavenging activity of superoxide anion free radical and total antioxidation capacity, while the fourth pile-fermentation WEOT had the lowest activity. The superoxide anion free radical scavenging activity and total antioxidation capacity of WEOTs had the most significant difference (P < 0.01) among the five tea samples. The results indicated that proper pile-fermentation process could enhance the antioxidant activity of pu-erh tea, whereas excessive pile-fermentation would provide the opposite effect. PRACTICAL APPLICATIONS Antioxidant activity is the main medicinal property of pu-erh tea. Pile-fermentation process is the key step which has the most important impact on antioxidant activity of pu-erh tea. It is believed that the antioxidant activity of tea depends on their fermentation degree. However, the correlation between pile-fermentation degree of pu-erh tea and its antioxidant activity is unknown. The objective of the present research was to investigate the effects of pile-fermentation of pu-erh tea on the antioxidant activity. The main results support the hypothesis that pu-erh tea with appropriate pile-fermentation degree could enhance the antioxidant activity. The results are very useful to further investigate the antioxidant component in pu-erh tea, and will help control the processing techniques and improve the health-care function of pu-erh tea.