| Summary: | 碩士 === 國立中興大學 === 食品暨應用生物科技學系所 === 97 === “Oolong tea” is one of the important semi-fermented teas of Taiwan. Its outer appearance is dark green and rolled into round shapes. The brewed tea is golden yellow in color, possesses unique aroma and mouth feel, and is widely preferred by Taiwanese. The processing steps of the tea leaves include plucking, withering, mixing, fixation, rolling, preliminary drying, re-rolling, re-drying, etc. “Roasting” is one of the important steps and technologies for processing Oolong tea. This study examines the important influences of the color, aroma, flavor and mouth feel of tea.This study uses the Jinsyuan Oolong tea as the raw materials and examines the effects of different roasting temperatures, time and solid-liquid ratio on Jinsyuan Oolong tea by the Response Surface Method (RSM) model and proceeds to look for the most appropriate processing conditions for processing the tea into drinks. From the research results, it can be seen that the quality of Oolong tea was affected by different roasting temperatures, time and solid-liquid ratio of the tea leaves. The affects of roasting temperatures on the Oolong tea was a lot more than those of the roasting time and solid-liquid ratio. There was a decrease in the pH value along with an increase in the roasting temperatures and time (p<0.05). There was an increasing trend in the acidity of the tea. There was a decrease in the L value (brightness) and an increase in the a value (redness), b value (yellowness), browning index (A420) and total catechin of the tea when the roasting temperature was above 140℃, therefore, there was little differences in the caffeine content of the tea.
The changes in the roasting temperatures and time overlapped with the property curves of soluble solids, pH value, b value, browning, and caffeine and catechin contents. When the overall acceptance was set as 5.2, (out of 7 points), the most appropriate roasting temperature of Jinsyuan Oolong tea was 100-115℃ and the roasting time was between 5.2 - 6.3 hours, the solid-liquid ratio was 1：45 - 1：55, the amount of soluble solid was 0.32 - 0.38 (。Brix), the pH value, b value, browning, catechin content, caffeine content was 6.0 - 6.2, 19 - 23, 0.36 - 0.44, 560 – 670 ppm, 280 - 295ppm, respectively.
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