Effect of different extraction conditions on compositions of oolong tea infusion

• Main Authors: Shu-Ching Li, 李淑靜
• Other Authors: Lang-Bang Hung
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/55568228530837074225

碩士 === 國立臺灣海洋大學 === 食品科學系 === 94 === The study focus on commercial oolong tea to investigate the content of its bitter-stringent components such as catechin and caffeine, the sweet components such as amino acids and theanine, and the fragrance components in tea. We attempted to infuse the tea leaves in water at different temperatures (70, 80 and 90℃) and infusion time (1, 2 and 3 min) to extract the oolong tea and investigated the effects of brewing conditions on dissolution of bitter, stringent, fragrant and sweet components in the tea infusions. Furthermore, the effects of various extraction conditions on content variations of tea infusions regarding catechin, caffeine, total amino acids, theanine, and tea color were examined. Based on the experimental results, the better brewing conditions were selected in order to obtain higher catechin content, greater sweet components, greater fragrance, and least caffeine content. We also examined number of oolong tea brewing using 90℃ water on the components of tea infusions. The brewing conditions for the 1st to 5th brewing were 1, 1.5, 2, 2.5 and 3 min, respectively; and from 6th to 10th brewing, 3 min intervals were applied. The fragrant components from the tea infusions were extracted and analyzed qualitatively and quantitatively using GC-MS. The catechin, caffeine, total amino acids, and theanine content variations could serve as criteria for preparing most healthful tea and beverage teas. The results of the study are summarized below: 1. Based on the results of analysis, various components of the tea infusions obtained using different brewing temperatures and times tend to increase with brewing times. The total catechin content for teas brewed at 70℃ for 1~3 min was 4.35 to 7.31 mg/g; those brewed at 80℃ was 5.03 to 7.92 mg/g; and those brewed at 90℃ was 6.04 to 10.27 mg/g. The total amino acids content for teas brewed at 70℃ was 0.79 to 1.20 mg/g; those brewed at 80℃ was 1.17 to 3.15 mg/g; and those brewed at 90℃ was 1.17 to 3.15 mg/g. For caffeine content, teas brewed at 70℃ had 0.41 to 0.94 mg/L; those at 80℃had 0.60 gto 1.13 mg/g; and those at 90℃ had 0.80 to 1.70 mg/g. 2. Ten consecutive brewing at 90℃ gave tea liquid catechin content of 5.88, 9.84, 12.13, 10.74, 12.31, 12.59, 11.73, 10.19 and 9.35 mg/g, respectively. The cumulative catechin content of the 10 brewing accounted for 88% of all catechin in the tea leaves. 3. The sweet component, amino acids were relatively low in the 1st and 2nd infusions, containing 1.0 to 1.2 mg/g, respectively. In the 3rd to 5th infusion, they reached 2.9, 3.5 and 3.0 mg/g, respectively. In the 6th to 10th infusions, there were still ca. 1.0 mg/g content. Thus the 3rd to 5th infusions were particularly sweet. 4. There was the least caffeine content in the 1st infusion of the oolong tea, ca. 0.7 mg/g; in the 2nd to 10th infusions, caffeine content varied, but maintained a level of 1.5 to 2.0 mg/g. 5. Thrity-six compounds were identified by GC-MS for the fragrance of the tea infusions. These included phenylethyl alcohol, metyl jasmonate, linalool and indole etc. The main component was indole with fragrance akin to grapefruit and mild flora scent. The fragrances were at the maximum in the 2nd infusion reaching a content of 2898 μg/mL. These decreased to 1296 μg/mL in the 5th infusion and 186.5 μg/mL in the 10th. 6. In the tea infusions, the free radical scavenging capacity determined by DPPH assay showed a positive correlation with the catechin content. 7. In the study, we established the methods of analysis various components in tea infusions which could be used as a reference for model evaluations.