Measurement of Tea Fermentation Degree and the Activity of Immobilized Tannase
Date Issued
2008
Date
2008
Author(s)
Chang, Fu-Shiang
Abstract
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.
Subjects
tea
fermentation
redox potential
stopped-flow
enzyme
conductometric
Type
thesis
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