The fermentation process in tea manufacture

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Abstract
II. There is a marked seasonal variation in the peroxidase content of tea leaf, plucked at weekly intervals, from the same plot. The curve falls into 3 well-defined periods, each of which is associated with a particular type of manufactured tea. Generally there is no correlation between peroxidase activity and rate of oxidation of tea tannin in fermentation. The amt. of peroxidase in the leaf is apparently in excess of requirements. The controlling factor is the rate of production of H2O2 which is formed by the aerobic dehydrogenation of the non-tan oxidizable matter. The increase in peroxidase content during the withering process is accelerated by loss of moisture from the leaf. When the moisture falls below a critical-level (72%), peroxidase activity again declines. Protein-N decreases during withering and, as bruised withered leaf undergoes fermentation (tannin oxidation) at the same rate as bruised fresh leaf, the increase in the amount of protein degradation products has no protective effect against the inactivation of the enzymes by tea tannin.[long dash]III. A complete reaction scheme for the fermentation process is deduced from the exptl. data. The H2O2 necessary for the oxidation of tea tannin by peroxidase originates in the aerobic oxidation of ascorbic acid, and this reaction controls the rate of the whole process. A shortage of ascorbic acid oxidase, as in the case of the Kharikatia leaf, retards fermentation. The oxidizable non-tan, which decreases during fermentation, is identified with glucose. Dehydroascorbic acid functions as the H-acceptor in the oxidative breakdown of the latter. One atom of O only is taken up per molecule of tea tannin during fermentation. The oxidation product then undergoes an irreversible change into condensation products. The relation of the fermentation process to normal respiration is discussed.

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