In-vitro studies on the effect of polyphenol oxidase and peroxidase on the formation of polyphenolic black tea constituents

Flavanols (catechins and gallocatechins) isolated from green tea leaves (Camellia sinensis) (L) O Kuntze) were treated in vitro with polyphenol oxidase, peroxidase and a combination of both. The flavanol levels and those of the products formed were monitored by reversed-phase high-performance liquid chromatography (HPLC using spectrophotometric detection at 280 and 380 nm. Flavanols and theaflavins were quantified, whilst integrated peak areas are given for the remaining compounds. After fermentation in the presence of polyphenol oxidase higher levels of theaflavins and resolved thearubigins were obtained, whilst peroxidase produced higher amounts of chromatographically unresolved thearubigins of higher molecular weight, observed as a rise in the HPLC baseline, in the presence of peroxidase a significant decrease in the levels of all flavonol glycosides was observed, whilst in the presence of polyphenol oxidase only myricetin glycoside levels decreased.     

Optimisation of withered leaf moisture during the manufacture of black tea based upon theaflavins fractions

A study was conducted to see the effect of different moisture content of withered leaf on the activity of oxidative enzymes polyphenoloxidase (PPO) and peroxidase (PO) and on the formation of theaflavins (TFs) and thearubigins (TRs). Six commercially popular cultivars TV1, TV7, TV9, TV23, TV26 and T.3E/3 of Assam, India, were processed in four different moisture levels (72%, 70%, 68% and 65%). Significant reduction in PPO and PO enzymes, TFs, TRs and theaflavin digallate equivalent was observed with the decrease in moisture content of withered leaf. The TFs (0.83–5.4 mg g^?1) and TRs (23–107 mg g^?1) fractions were lowest at moisture level 65 ± 1%. Of the six cultivars studied, better quality of black tea was obtained for cultivar TV1, TV9 and TV23 at 70 ± 1% moisture content, while for TV7 and TV26, it was 68 ± 1%. Withered leaf moisture content should be carefully chosen to obtain the better quality tea from specific cultivar.