| Summary: | 碩士 === 國立臺灣海洋大學 === 食品科學系 === 106 === Green tea beverages are commonly liked by people in Taiwan. Green tea is rich in catechins. These antioxidants also have a function of regulating blood lipids, which is accordingly used to obtain health food certification. In this study, green tea infusion was prepared by using Songbailing tea made from Taiwan. Vitamin C or vitamin C/sodium bicarbonate was added before and after extraction of tea infusions. After being autoclaved at 121°C for 5 minutes, samples were stored at 7°C, 12°C, and 25°C for 30 days. Catechins, Brix, pH, caffeine, and color were analyzed and compared. In the extracted infusions, level of total catechins was: Group C (vitamin C before extraction; 38.59 ppm) > Group B (vitamin C/Sodium bicarbonate before extraction; 34.60 ppm) > Control (33.96 ppm) > Group D (vitamin C/sodium bicarbonate after extraction; 32.80 ppm) > Group E (vitamin C after extraction; 31.22 ppm). After sterilization, the total catechins content was in the following order: Group C (36.71 ppm) > Group B (35.39 ppm) > Group D (31.93 ppm) > Control group (31.09pm) > Group E (30.61ppm). Obviously, adding vitamin C before extraction reduced the isomerization reaction of catechins due to heating. For example, the cis-structured EGCG remained 1.2 times as much as that of control. When stored at 7°C, 12°C, and 25°C for 30 days, the total catechins was the highest (31.61 ppm) in Group B stored at 7°C, while the lowest (17.41 ppm) was found in Group E stored at 25°C. Overall, degradation of cathchins was sgnificantly lower at 7°C than at 12°C and 25°C storages. During storage, the changes in pH, Brix, and caffeine in samples were not apparent, indicating not suitable as an indicator for the determination of catechins in advance. Neverless, higher storage temperature induced a darker color of infusions, in which adding vitamin C/sodium bicarbonate considerably effectively retarded the color change. Consequently, when the retention of catechins in green tea beverage with a shelf-life of 30 days is concerned, the best practice during manufacture and market circulation is to add vitamin C/sodium bicarbonate before extraction and to keep it at 7°C.
|
|---|
