| Summary: | 碩士 === 國立臺灣海洋大學 === 食品科學系 === 103 === The main purpose of this study is to explore how different partially-fermented process condition affects tea leaves, tea powder’s color and its yield so as to obtain the requirement condition of fresh green color and high yield. Si-Ji-Chuen is the major cultivar sample used in the experiment for this study. The mechanically-plucked tea leaves will be under partially ferment process (including solar-withering, indoor-withering, panning, rolling and drying), and detect the difference of its color value and weight. Moreover, comparing 20 types of green tea power from the market with that in this study aims to understand the color difference by examining the color value and hue(b/a).
According to the study, compared to leaves with 20 minutes solar withering and 20 minutes one with leaves turnover, 10 minutes solar withering remains fresher green. The leaves with the first hour of 10-hour indoor withering only had significantly decreased on adaxial leaves L value and abaxial leaves hue(b/a). The experimental data was close to leaves with solar withering. Leaves separately with 10 minutes and 20 minutes solar withering had no distinct difference on the color value and hue(b/a) after 10 hours indoor withering. However, leaves with 20 minutes solar withering (the first 10- minute turnover) obviously decreased on abaxial leaves hue(b/a) after the 5 hours during 10 hours indoor withering. Meanwhile, different temperature leads to various outcomes. Leaves with 300℃ panning process can retain their fresh green color by comparison with 230℃ and 150 ℃ ones. Leaves with 80℃ drying process had a brighter green than that with 100℃ and 120 ℃; Adding rolling treatment to tea powder process condition apparently decreased on the color value of leaves and tea powder. Based on different partially-fermented process condition, 600g tea leaves can approximately produce 151.9 to 163.2g tea powder; higher temperature panning and lower temperature drying bring high yield with tea powder, but required higher cost of gas and electricity. According to experimental data, the color a value range of the commercial green tea-powder in Taiwan will be at -3.96 tol2.64, and its hue (b/a) range will be -9.81 to -3.49; the a value range of the tea powder made in this experiment will be -8.52 to -12.08 and it hue(b/a) range will be -5.08 to -3.74.
Based on the above results, if partially fermented leaves aims to make better fresh green color tea powder, leaves with either solar withering or indoor withering should avoid turnover, leaves with high-temperature panning for short time are preferable, and tea power made from leaves with low-temperature drying can maintain fresh color. Rolling treatment is considered dispensable to lower the cost. The purpose of study aims to aid tea growers to solve the dead stock problems in the season of summer and fall.
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