- 學位論文
紫外線對茶樹葉片中兒茶素含量之影響
Effect of Ultraviolet Radiation on Catechins Content of Tea Fresh Leaves.
摘要
茶葉中的化學成分含量，因茶樹品種、栽培環境、採摘部位及製茶加工而不同。環境因子中的紫外線，為光照下高能量之射線。當植物在紫外線逆境下，可以累積對紫外線波長有高吸收能力的二級代謝物，做為一過濾保護，避免紫外線破壞光合作用的穩定性。 多元酚類為茶葉中含量最多的可溶性物質，約佔乾重的30%，其中又以兒茶素含量最多。近年來保健食品風行，學者對兒茶素的生物性作用備感興趣，有許多有關兒茶素之抗氧化、預防心血管疾病及癌症等相關試驗。因此，本研究以紫外線照射試驗，欲達到使茶葉中兒茶素含量增加之效果。 第一部分以‘臺茶十二號’與‘青心烏龍’茶苗為材料，栽培於溫控生長箱中，加照UV-A與UV-B之試驗，處理時間有一天、五天、一週與兩週。試驗結果發現，栽培環境下施予紫外線，確使茶葉鮮葉中兒茶素含量改變。以UV-A處理一天後，‘臺茶十二號’與‘青心烏龍’兩品種茶苗鮮葉，其兒茶素類中epicatechin(EC)之含量均增加，但其餘兒茶素含量變化趨勢並非完全一致。在UV-B處理下，除處理一天後，‘青心烏龍’ 茶葉鮮葉中EC之含量顯著增加，無論處理時間長短，以UV-B處理兩品種茶樹，鮮葉中其餘兒茶素類含量均有減少趨勢。 若要在茶園田間處理紫外線，實為不便，故第二部分試驗，以採收後茶菁為材料，看葉片離體後兒茶素含量是否也會因紫外線有所影響。分別以UV-A、UV-B及UV-C，三種不同波長之紫外線處理。‘臺茶十二號’茶菁，在UV-B照射下，於10、20、30、60、90及120分鐘後取樣，其兒茶素含量均低於對照組。在UV-A與UV-C處理下，處理前期兒茶素含量會有減少情況，但後期含量會略高於對照組。此現象可能與兒茶素最高吸收峰為280 nm有關，故對UV-B的反應較其他兩波長之紫外線不同。 試驗結果未如預期，經紫外線處理後茶葉兒茶素含量多為下降趨勢。但採收後茶菁以UV-B處理後，兒茶素含量明顯減少的結果，或可利用於綠茶製茶產業。因綠茶屬未發酵茶，若茶菁中兒茶素含量過高，會增加成茶之苦、澀味。應可發展為一加工過程，在茶菁殺菁前，以UV-B照射一段時間，即可減少兒茶素含量，提升其品質。
並列摘要
The chemical composition of tea leaves may be effected by cultivars, geographical and climatic conditions, agronomic practice, and manufacture process. Ultraviolet radiation, a high energy radiation of light rays, is one of many environmental factors. When plants are put under ultraviolet stress, they are subject to UV radiation response, increasing plants’ UV-absorption secondary metabolites, which act as a filter, protect against UV damage. Polyphenols are the most soluble substances in tea, accounting for 30% of dry weight. Catechins are the most abundant group of polyphenols. Since health foods have become popular in recent years, scholars are interestied in the biological effects of catechin. There are many papers proving that catechins have antioxidants, and prevent cardiovascular disease and cancer. Therefore, this study used ultraviolet radiation treatment on tea, to increase the catechins content in tea. In the first part, ‘TTES No. 12’ and ‘Ching Shin Oolong’ tea trees were used as material. Samples of each were placed in three separate temperature-controlled chambers. The first chamber was treated with UV-A, the second with UV-B, and the last was the control. The treatment time was one day, five days, one week and two weeks. The results found that the UV treatment affected the catechins content of tea leaves. After one day of UV-A treatment, epicatechin content increased both in ‘TTES No. 12’ and ‘Ching Shin Oolong’ tea leaves. However, the trend of other catechins content was not consistent. In the UV-B treatment, the epicatechin (EC) content increased in only the ‘Ching Shin Oolong’ tea leaves after one day. Regardless of the length of treatment time, the catechins content has a decreasing trend in both varieties of tea leaves after UV-B treatment. Using UV radiation in the field is inconvenient. In the second part of this study, fresh tea leaves were used as treatment material, to see whether the catechins content of tea leaves will change by UV radiation after harvest. Three different wavelengths of UV radiation, UV-A, UV-B and UV-C, were used in this postharvest treatment. Fresh ‘TTES No. 12’ leaves’ catechins content was lower than control after 10, 20, 30, 60, 90 and 120 minutes of treatment by UV-B. But in the UV-A and UV-C experiment, the catechins content was reduced in the beginning, and then increased after a longer treatment time. This result may occur because of the absorption peak of catechins, so the response to UV-B was more obvious than to UV-A and UV-C. The result was not as expected. After UV treatment, catechins content of tea was reduced. However, the content of catechins in fresh tea leaves was significantly reduced by treating them with UV-B after harvest. This may be used in the green tea industry. Green tea is unfermented tea, so catechins will increase the bitter and astringent taste in tea. Before blanching, treating fresh tea leaves with UV-B may reduce the content of catechins in tea leaves and improve its quality. If this strategy works, it should be developed into a green tea process.