| Summary: | 碩士 === 國立屏東科技大學 === 食品科學系 === 95 === Abstract
The present study analyzes and compares the theanine contents in various kinds of teas. Five pan-fried green teas made from major Taiwan tea cultural cultivars are chosen as the experimental materials, which include Chin-Shin Oolong, TTES No.12, Chin-Shin Da Pan, Si-Ji-Chun, and TTES No.13, harvested in spring, summer, fall and winter respectively. The amount of theanine contained in these experimental materials was examined. From the experimental data, it is found that the contents of theanine are between 110.74~32.56ppm(extracted with 90℃ for 20minutes). The Chin-Shin Oolong contains the highest amount of theanine among the fore-mentioned experimental materials, and the Si-Ji-Chun follows. Theanine in spring tea is much higher than that in other seasons’ teas.
The effects of processing technologies on theanine of tea drinks are examined afterwards. Three highest contents of theanine tea cultural cultivars (the Chin-Shin Oolong spring tea, the Chin-Shin Oolong summer tea, and the Si-Ji-Chun spring tea) are prepared using normal tea drink processing technologies. The results show that extracting with 95℃ for 25 minutes can get the best extraction of theanine, there is no obvious influence on theanine concentration for adding additives, even though the pH values of tea drinks have been changed during the processes. The centrifugal procedure is however large influence on tea drink theanine concentrations, the higher the rotating speed used in the centrifugal procedure , the lower the theanine concentration is obtained, so, it should avoid using high speed on centrifugal processes. As for the sterilization process, the Chin-Shin Oolong spring tea is sterilized at 100℃ for 15 minutes. The theanine content is about 128.60ppm, which is similar to that before sterilization, however, the theanine content drops obviously to 117.14ppm at 131℃sterilization condition.
The best processed tea drinks are then canned and stored for storage tests. Three different types of cans, 340mL iron can, 600mL PET, and 300mL aseptic package are used in the test, these cans are stored at 4℃, 30℃, and 55℃ for 60 days, the theanine content, Lab values, total catechins, caffeine and clarity are recorded. The results showed that the content of theanine is higher when stored at 4℃, the theanine decreased when the tea drinks are stored more than 30 days, aseptic package tea drinks preserve much higher theanine contents. As for the hues, the L values decrease after 15 days’ storage, it means the tea drinks become darker. The iron can tea drinks give worse brightness. There are no significant variations in a value for different kinds of storage processes. Considering the b values, higher b values mean the tea drinks tend to be more yellow, the aseptic package tea drinks show the highest yellow color trends. The longer the storage time, the more decrement of the catechins contents. The aseptic package tea drinks preserve the highest contents of catechins among the three different types of canned tea drinks.
The acceptance of high theanine content tea drinks is examined using hedonic scale test, the tastes of the Chin-Shin Oolong spring tea is less astringent and less bitter, and the aftertaste in flavor of this tea drink is the best among the rest of the samples. Overall, the Chin-Shin Oolong spring tea (the highest theanine content tea) is close to leaning mouth feeling, and the acceptance is obviously higher than other samples used in the present study.
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