Fermentation of tea in aqueous suspension. Influence of tea peroxidase

Abstract

The natural peroxidase and catalase of tea leaf were shown to be active under the conditions employed for the fermentation of minced tea leaf in aqueous suspension. Fermentations carried out under nitrogen with ethyl hydrogen peroxide, which is not decomposed by catalase, yielded predominantly thearubigins, a high proportion of which were polymeric in nature. Fermentations using an excess of hydrogen peroxide gave similar results. Fermentations under conditions of controlled dissolved oxygen using both air and hydrogen peroxide resulted in a pigment distribution intermediate between those observed using air alone and using ethyl hydroperoxide under nitrogen. Adjustment of the amount of hydrogen peroxide used to around 120 pmol 8-1 leaf resulted in a pigment distribution closely similar to that of a good quality black tea. A mixture of theaflavins was stable in the presence of air and tea polyphenoloxidase but decomposed rapidly to yield polymeric materials under the action of hydrogen peroxide and peroxidase derived from tea or horseradish. Kinetic measurements suggest that tea flavanols are generally poorer substrates for peroxidase than for catechol oxidase. However, the level of peroxidase is high and, furthermore, in view of the respective pH optima of the two enzymes, its action would be favoured as the pH falls during fermentation. It is postulated that the nature and distribution of the pigments formed during the fermentation of tea is governed in part by the relative actions of catechol oxidase and peroxidase. These actions are, in turn, influenced by the availability of oxygen and the action of catalase.

Cocoa tea (Camellia ptilophylla Chang), a natural decaffeinated species of tea – Recommendations on the proper way of preparation for consumption

“…Some of PO were oxidized into tea pigments or other substances during fermentation. GA increased because of the hydrolysis of ester-catechins such as GCG and EGCG (Dix, Fairley, Millin, & Swaine, 1981). Theobromine did not change upon fermentation.…”

Orthodox tea (Camellia sinensis L .) oxidation under the influence of compressed air: Process optimization

“…The increasing trend of TR may be due to the activity of the two oxidizing enzyme. While PPO is more active in the early phase, POD plays a major role in the later part of the oxidation process (Dix, Fairly, Millen, & Swame, 1981). POD inhibits PPO resulting in the loss of TF and produce TR as a secondary product (Baruah & Mahanta, 2003), hence in over oxidized leaves, PPO declines linearly but POD remains active.…”

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

“…The thermostability of PODS and even a partial recovery of their activity are responsible for the quality deterioration of a variety of foods (Robinson 1991) including part of the decrease in tea quality during storage (Millin 1987). The most extensive study on peroxidase effects during tea fermentation was carried out by Dix et al (1981) who concentrated on the use of peroxidase during tea fermentation in aqueous suspension, eg for the production of instant tea. They monitored the products formed in a model fermentation system using gel chromatography on Sephadex LH-20.…”