Optimization of Withering Time and Fermentation Conditions During the Manufacture of Black Tea Using a Response Surface Methodology

The Central Composite Design (CCD) technique, a Response Surface Methodology (RSM), was used to study the effect of the withering time and fermentation conditions of tea leaves on black tea quality parameters. A three level, three variable, design was adopted. The three independent variables investigated in this experiment, each at three levels, were; withering time, fermentation duration and fermentation temperature. Responses were represented mathematically by a second-order quadratic equation and assessed, using a polynomial multiple regression model. The highest level of the theaflavins (TFs) formation (>= 1.25%) was with the withering time at about 19-20 hrs, while the fermentation duration was about 25-30 min (fermentation temperature = 25 degrees C). The gradual increase in the thearubigins (TRs), as the function of the withering time and the fermentation temperature, was noticeable. The increase in TR content at > 11.5% was minor and related to the narrower ranges of the two parameters studied (x(1) and x(3)). The predicted dependence of the TLC evaluation (%) (spectrophotometric measurement) on the fermentation duration (x(2)) and on the fermentation temperature (x(3)) was statistically significant. The results of this study suggest that the CCD and RSM can be efficiently used in the fermentation process in the manufacture of black tea.