Reactions Involved in the Processing of Tea

During rolling, the tea leaf is macerated and the substrate and enz3unes are brought together a prerequisite for fermentation. The subsequent enzymatic oxidative reactions are designated as 

The enzymatic oxidation of flavanols via the corresponding o-quinones gives theaflavins (Formula 21.6, IX-XIt bright ted color, good solubility), bisflavanols (XIH-XV colorless), and epitheaflavic acids (XVI, XVII bright red color, excellent solubility). The theaflavins and epitheaflavic acids are important ben-zotropolone derivatives that impart color to black tea. 

Aroma development during fermentation is accompanied by an increase in the volatile compounds typical of black tea. They are produced by Strecker degradation reactions of amino acids with oxidized flavanols (Formula 21.7) and by oxidation of unsaturated fatty acids and the caroti-noid neoxanthin. 

During the firing step of tea processing, there is an initial rise in enzyme activity (10-15% of the theaflavins are formed during the first 10 min), then aU the enzymes are inactivated. Conversion of chlorophyll into pheophytin is involved in reactions leading to the black color of tea. A prerequisite for these reactions is high temperature 

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