茶品發酵度與固定化單寧水解酶活性量測

Abstract

品質是目前台灣茶產業的關鍵，特別是烏龍茶，介於未發酵的綠茶與全發酵的紅茶間，烏龍茶是一種部分發酵茶，而其品質大大地取決於發酵程度。然而，由於技術上的困難與限制，對於茶的發酵度至今仍沒有提出官方甚至是具體可行的量測方法。因為茶的發酵是好氧過程，本研究開發了一個茶湯氧化還原電位的量測工具，發現氧化還原電位確實隨著發酵度提高而上升。氧化還原電位可於十秒內高再現性(CV < 3%)，以白金電極與Ag/AgCl參考電極間的開路電壓取得。此電位已成功地用來觀測茶品發酵過程並估計市售樣品的發酵度。 另一方面，近年台灣冰紅茶的市場持續增加。而茶乳卻容易形成於冷卻的高濃度發酵茶，這將會影響口味及賣相。在目前茶品工業中，茶乳通常是採用單寧酸水解酶(EC 3.1.1.20)將造成問題的酯型多酚(即水解型單寧)水解以抑制其形成。此酵素通常被固定化而成生物反應器，但固定化酵素的活性需不斷地監控以確保品質。本論文的第二部份探討斷流方式直接觀測酵素活性的電導度裝置。本裝置亦可為一便利的單寧感測器，其工作濃度範圍為0.1~1 mg/ml。本研究亦使用此便利的裝置量測固定化單寧酸水解酶(由Aspergillus oryzae取得)對一些基質的動力學參數。

Quality has become the major concerns of the tea industry in Taiwan, especially for its famous oolong tea. Between unfermented Japanese green tea and fully fermented western black tea, oolong is a partial fermented tea and the degree of tea fermentation is very critical for the quality. However, due to some technical difficulties and limits, no official or even practical methods have been proposed for the measurement. Since tea fermentation is an aerobic bioprocess, this study developed a tool to measure the redox potential of tea infusion and found that the redox potential did rise as the degree of fermentation. The redox potential was measured as the open circuit voltage between an indicating platinum electrode and an Ag/AgCl relectrode for the reference in ten seconds with high reproducibility (CV < 3%). The potential was successfully used to monitor the tea fermentation process and to estimate the fermentation degree. On the other hand, the market of ice black tea is rapidly increasing these years in Taiwan. Tea cream was known to form in a concentrated chilled fermented tea which may influence taste and appearance. In instant tea industry, tea cream formation is generally inhibited by enzymatic treatment using tannase (EC 3.1.1.20) to hydrolyze the problematic hydrolysable tannins (most of them are galloyl esters). The enzyme is usually immobilized as a bioreactor but the activity should be constantly monitored to assure the quality. In the second approach of this dissertation, a conductometric device was developed to directly monitor the enzyme activity by a stopped-flow manner. The device can also serve as a convenient tannin sensor with the dynamic range of 0.1~1 mg/ml. With the convenient device, the kinetic parameters of several substrates for the immobilized tannase (from Aspergillus oryzae) were investigated.