Investigation of processes in black tea manufacture through model fermentation (oxidation) experiments

Flavanol depleted whole fresh green tea leaf powder, as reported in the literature, was used as matrix for a systematic study of the endogenous oxidative enzymatic conversion of selected flavanol combinations to theaflavins and thearubigins. The activity of the two crucial enzymes polyphenol oxidase (PPO) and peroxidase (POD) was controlled individually through addition of H2O2 and/or O2. Using the endogenous peroxidase only it was shown that (-)-epicatechin alone did not react with POD. According to these results it is possible that theaflavin formation occurs via reaction of a flavanol quinone with a nonquinone flavanol. It was confirmed that only a dihydroxy-B-ring flavanol with a trihydroxy-B-ring flavanol gave a theaflavin upon enzymatic oxidation. Use of horseradish peroxidase in the presence of a flavanol depleted tea leaf matrix led to significantly higher kinetics on theaflavin 3-gallate degradation compared to the absence of leaf matrix, suggesting a catalytic effect of the leaf matrix not reported before.