| Summary: | 碩士 === 國立中興大學 === 食品暨應用生物科技學系所 === 105 === There are more than 600 volatile tea aroma compounds available, which are generated from four main precursors such as carotenoids, lipids, glycosides, and maillard reaction. Glycoside precursors can be hydrolyzed by endogenous enzyme such as β-D-glycosidase to release the free aroma compounds. However, tea plant glycosidases are often destroyed by thermal deactivation during tea manufacturing process, thus there are many bound aroma compounds left in tea product. Additional β-glucosidase has been widely used in aroma enhancement due to its roles in releasing the aroma compounds. Hence, this study focus on the aroma enhancing capabilities by β-glucosidase from Aureobasidium pullulan NCH-218 in green tea. The study starts with production of the enzyme under optimal condition based on the previous study: 5% wheat bran (w/v), 2.5% lactose (w/v), initial pH at 6.25-6.27, after that 1% (v/v) A. pullulans NCH-218 was inoculated and cultured at 30°C and 150 rpm for 4 days. Moreover, the produced crude enzyme was centrifuged and filtered then proceed further by using ultrafiltration which could obtain 136.8 U/ml of enzyme activity. At first, preliminary study was conducted to decide which beverage is the most suitable for the enzyme application. The result demonstrated that enzymatic treatment was resulted in higher amount of glucose content in all of the beverages, especially in green tea with the highest increasing rate for about 14% and also highest preference score (aroma profile) for the sensory evaluation test compare to other beverages. Furthermore, GC-MS chromatogram of enzyme-treated green tea indicated the highest increase of methyl salicylate (glycoside-based) and another increase was also detected in the amount of linalool. The highest amount methyl salicylate and linalool was obtained after mixing 10% of 350 U/ mL of β-glucosidase to 20% (w/v) cold-brewed green tea and was reacted for 3 hours at 50°C. The enzymatic treatment was resulted in the highest concentration of 16.23 ppm methyl salicylate and 1.14 ppm linalool, respectively. Some antioxidant activity assays as well as catechin and caffeine content determination was also conducted in order to examine the enzymatic treatment effect towards the composition and antioxidant properties of the green tea. Overall, there wasn’t any remarkable changes in the antioxidant properties and the composition of catechin and caffeine after the enzymatic treatment with β-glucosidase. Therefore, this enzymatic treatment by β-glucosidase from A. pullulans NCH-218 was proved to not only offer a promising aroma enhancement effect but also did not give any negative impact on the antioxidant properties as well as the composition of the green tea.
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