| Summary: | 碩士 === 國立虎尾科技大學 === 生物科技研究所 === 103 === In this study, the effects of fermentation time (0, 3, 6, 9, 12, 18, 21 days) on antioxidative activities (DPPH free radical scavenging activity, reducing power and total phenolic contents) and α-amylase (AA) inhibitory activity of tea (black tea and green tea defined as BT and GT) broths fermented by Acetobacter xylinum isolated from the fermented coconut juice were investigated. The pH values of BT and GT decreased with increasing fermentation time and were 3.28 and3.30, respectively, obtained from the 21st day fermentation. The DPPH radical scavenging activity (defined as DPPH RSA %) of BT and GT broths increased up to certain values with increasing the addition concentrations of the freeze-dried tea broths. There was no significant effect of fermentation time on DPPH RSA% of the fermented broths. The highest Vit. CE (vitamin C equivalent) values for reducing power (RP) of BT and GT obtained at the 21st day and 15th day fermentation, respectively, were 0.499 mg and 0.892 mg Vit. CE/mL, respectively. In addition, the highest GAE (gallic acid equivalent) values for total phenolic contents (TPCs) of BT and GT were 0.395 mg and 0.385 mg GAE/ml, respectively, obtained at the 21st day and 15th day fermentation, respectively. The AA inhibitory activities (AAi%) for BT and GT increased at the first 15 days fermentation, and the highest AAi% for BT and GT were 75.98% and 80.77%, respectively, obtained at the 15th day fermentation. However, the AAi% of only BT was not changed while the AAi% of GT little decreased thereafter. This study demonstrated the optimal fermentation days for BT and GT were 21 and 15 days, respectively. In comparison with BT, GT fermented by A. xylinum showed the better antioxidative activities and α-amylase inhibitory activity.
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