Assessing biochemical changes during standardization of fermentation time and temperature for manufacturing quality black tea.

In black tea manufacturing, one of the most important steps is fermentation which influences the quality of tea. The macerated tea leaves were fermented at various temperatures (20, 25, 30, 35 °C) for different duration. Changes in polyphenoloxidase and peroxidase activities, depletion patterns of individual catechins, differences in individual theaflavin levels and formation of thearubigins were measured in leaves during fermentation. Higher stability of polyphenoloxidase and peroxidase enzymes was observed at lower temperature (20 °C), and increase in temperature, led to enzyme instability. The rate of degradation of all the catechins was found to be fastest at 35 °C and slowest at 20 °C. The formation and depletion of individual theaflavins varied with temperature and fermentation duration. The time required for the formation of maximum total theaflavins (TF) was highest at lower temperature and this time duration also varied for different theaflavins formation. Maximum amount of thearubigins (TR) content and liquor colour development was observed at 35 °C, and decrease in temperature reduced thearubigins accumulation. However, maximum brightness as well as TF/TR ratio was obtained at 20 °C, which suggests that fermentation at lower temperature is suitable for manufacturing quality black tea.