部分發酵茶茶菁、製程及成茶中可溶性化學成分與揮發性有機化合物之研究

Abstract

部分發酵茶是臺灣重要的茶葉種類，以豐富的滋味及香氣著稱，包括包種茶、烏龍茶及白毫烏龍茶 (東方美人茶)，依據製造過程的發酵程度差異，成茶的香氣與茶湯滋味各具特色。部分發酵茶是一種非常需要製造經驗的茶葉種類，製造過程充滿氣味的轉變，以實際製茶時的嗅覺感受作為取樣依據，捕捉部分發酵茶製造過程中揮發性化合物及茶湯內容物動態變化。青草味化合物在製程中穩定存在，而萜類及酯類化合物在每次攪拌過後會合成並提高相對含量，呈現連續性的波動上升，至結束發酵的階段。在發酵後期香氣表現較明顯時，表型酯類兒茶素變化與揮發性化合物變化有相似模式。白毫烏龍茶是臺灣部分發酵茶中，屬於重發酵的特色茶，主產區為桃園、新竹、苗栗地區，以‘青心大冇’製成的白毫烏龍茶風味最佳。感官品評是一種根據訓練的感官評比科學，是目前比賽茶分級的主要方式。分析不同產區、品種及比賽等級的白毫烏龍茶在揮發性有機化合物的差異，結果顯示可將揮發性化合物區分為熟果香因子、重發酵因子及小綠葉蟬吸食因子來辨別產區，且品種鑑別時，可做為親緣關係的化學指紋，而白毫烏龍茶中相對含量比例較高的芳樟醇氧化物 (linalool oxides)、苯乙醇 (phenethyl alcohol)、吲哚 (indole)、反式-β-紫羅蘭酮 (trans-β-ionone) 及α-法尼烯 (α-farnesene) 等化合物，以正向逐步迴歸分析結果認為與感官品評的比賽等級有顯著正相關。製作白毫烏龍茶的茶菁必須使用小綠葉蟬吸食過的嫩芽葉，嘗試以人為模擬處理茶菁，激發茶菁的植物防禦機制，包括葉施益收溶液、水楊酸溶液及高速噴灑石英砂，分析茶菁內可溶性內容物、揮發性有機化合物的變化與調查茶芽農藝性狀。試驗進行三個年度 (2009、2010及2011年)，年度間茶菁表現無法達到再現性，但以水楊酸溶液葉施的茶菁表型兒茶素含量較高、茶芽表現較健壯，益收溶液葉施的處理揮發性化合物種類較多，石英砂噴灑會造成茶菁葉面傷痕，使茶菁外觀受損。人為模擬處理仍無法使茶菁生成與小綠葉蟬吸食相同的二次代謝產物。

Semi-fermented tea is a typical kind of Taiwan tea. It is famous for its enriched flavor and elegant fragrance. Different degree of fermentation makes the partial fermentation unique and distinctive. The famous semi-fermented teas are including pouchung tea, don-ding oolong tea and bai-hau oolong tea. When manufacturing semi-fermented tea, aroma was appearance in all way and it was the discipline of fermentation. We sampled the tea samples by aroma changing in partial fermentation. Dynamic volatiles organic compounds (VOCs) and chemical components were evaluated during manufacturing process. We found the green leaf odor was constant through all manufacturing, but terpenes and ester compounds were increased alternatively until stopping the fermentation. During the late stages of fermentation, the pattern of epi-catehcins increment was also fluctuation. Bai-hau oolong tea has the strongest partial fermentation. The famous producing areas in Taiwan are Taoyuan county, Hsinchu county and Miaoli county. The best choice of cultivar in good quality of bai-hau oolong tea was ‘Chin-hsin-da-pan’. The quality could be ranking by sensory evaluation. We analyzed the volatile organic compounds of the bai-hau oolong tea from different producing areas, different cultivars, and different ranking in contest. After principle component analysis by the VOCs, our results suggest that the fragrance of ripen fruits, the fragrance of strong fermentation, and the VOCs synthesis because of wounded by leafhopper were the three principle factors which could distinguish the producing areas in bai-hau oolong tea. The VOCs also could be the effective chemical fingerprints in phylogenetic relation in analysis of cultivar’s differences. Linalool oxidative, phenethyl alcohol, indole, trans-β-ionone, and α-farnensene are the positive correlation in forward stepwise regression by the VOCs and contest ranking. Because tea materials made for bai-hau oolong tea is needed wounding by leafhopper, we tried to simulate the triggers to tea leaves and shoots. Spraying ethrel R and salicylic acid in different concentrations and the mechanical injured by high-speed spraying quartz sand. We investigated the chemical components, the VOCs and the characters of tea shoots in 3 years. There is no good reproducibility in results among 3 yeara. However, the stronger tea shoots and more epi-catechins were observed in spring salicylic acid solution treatments. There were more VOCs in ethrelR-spraying treatments. The mechanical injured by quartz sand leaved the scars on the tea shoots. Artificial simulating treatments still can not make tea shoots synthesize the same secondary metabolites as green leafhoppers did.