5. COMPARATIVE RATES OF OXIDATION OF DIFFERENT POLYPHENOLIC SUBSTRATES BY TEA-OXIDIZING ENZYMES BY H. B. SREERANGACHAR, Tea Research

The oxidizing-enzyme preparation employed in previous work was obtained from tea by grinding fresh leaf under acetone until the residue was almost completely free of all colouring constituents of the leaf. Among the differences that exist between the in vitro action of this acetone-prepared tea enzyme and the in vivo reaction in the minced leaf are the rates of oxidation of different polyphenolic substrates. Thus, acetone-prepared enzyme oxidizes catechol about two or three times as rapidly as it does tea tannin [Lamb & Sreerangachar, 1940], whereas in the fermenting leaf-mince to which the polyphenolic substrates are introduced after completion of its initial fermentation, tea tannin is oxidized at about three times the rate of catechol oxidation [Harrison & Roberts, 1939]. There is obviously one main difference between the conditions that exist in the minced-leaf sy6tem prior to the addition of the polyphenolic stibstrates, and those obtaining in the acetone-prepared enzyme reaction system. In the former, the leaf polyphenols are, as a result of initial reactions, in various stages of oxidation and condensation, whereas in the latter such oxidized products of tea taanin are absent at the commencement of the reaction. The object of the present investigation is to find out the exact influence of these oxidized polyphenols on subsequent oxidation reactions, and to arrive at a clear distinction between the direct reactions of the enzyme and the possible indirect action of other substances present.