The phenolic substances of manufactured tea. VIII.—Enzymic oxidations of polyphenolic mixtures

When a mixture of substrates is acted upon by the tea oxidase the substrate of lower rH is oxidised preferentially. In tea fermentation, therefore, oxidations are largely limited to those affecting the gallocatechins. When a mixture of two substrates is oxidised mixed dimers are not produced unless both have similar rH values. In tea fermentation there is only a limited coupled oxidation of gallic acid and theogallin. The trace substances Q (now confirmed to be a mixture) are produced by coupled oxidation of gallic acid; oxidation of theogallin probably results in the formation of substances chromatographically similar to the thearubigins. The catechins function as carriers for coupled oxidations of theaflavins, bisflavanols and thearubigins. Such coupled oxidations probably form part of the fermentation process and it is possible that such oxidations of theaflavins and bisflavanols yield thearubigins.