以擴散模式探討茶葉短時間浸泡溶出的動力學

Kinetics of Short-time Tea Infusion Using a Diffusion Model

本研究以簡單的單葉擴散模式探討茶葉中主要成份：咖啡因、兒茶素與沒食子酸的溶出動力學。我們以高效能液相層析儀（HPLC）定量由台茶12號製成的綠茶與紅茶其溶出的咖啡因（CA），表沒食子兒茶素（EGC），表兒茶素（EC），表沒食子兒茶素沒食子酸酯（EGCg），表兒茶素沒食子酸酯（ECg），與沒食子酸（GA）之濃度，透過短時間濃度的數據擬合，我們可以以外插擴散方程式而得到其平衡濃度。從平衡濃度我們可以進一步計算一階溶出速率常數（k_(obs)）與活化能。結果顯示，當高溫浸泡時，等效遲滯時間約15~17秒，低溫時則超過22秒。對綠茶與紅茶的成份萃出率則分別為85.5%~93.8%及86.6%~98.3%。而綠茶與紅茶的等效活化能則分別為8~27kJ/mol與7~39kJ/mol。此結果主要是因為這些化合物的分子量差異與製茶過程的不同所引起的。

This study was to explore the infusion kinetics of the major compounds in tea, caffeine, catechins and gallic acid, using a simple one-leaf diffusion model. The concentrations of caffeine (CA), (-)-epigallocatechin (EGC), (-)-epicatechin (EC), (-)-epigallocatechin gallate (EGCg), (-)-epicatechin gallate (ECg) and gallic acid (GA) in Taiwanese green and black teas manufactured from TTE 12 cultivar were analyzed by HPLC. By fitting the short time infusive concentration, we extrapolated the equilibrium concentration C from the diffusion equation. This equilibrium concentration was to calculate the first order infusion rate constant (k_(obs)) to obtain the activation energy. The results showed that effective delay time was about 15~17 seconds for high temperature infusion (85 and 100 °C) and above 22 seconds for 70 °C steeping. The extractive efficiencies of these compounds from tea leaf were 85.5%~93.8% and 86.6%~98.3% for green and black teas, respectively. The effective activation energies of green tea were 18~27 kJ/mol and black tea were 7~39 kJ/mol. These results were conducted by the molecular weight and the differences in the manufacturing techniques between black and green teas.