SCHVED, F., Department of Food Science, Agricultural Research Organization, The Volcani Center, P. O. Box 6, Bet Dagan, Israel
KAHN, V., Department of Food Science, Agricultural Research Organization, The Volcani Center, P. O. Box 6, Bet Dagan, Israel

When 2, 3‐dihydroxybenzoic acid (2, 3‐DBA) is acted upon by mushroom tyrosinase, a yellow intermediate, 2, 3‐DBA‐o‐quinone, characterized by a peak at 415 nm, is the first product detected. 2, 3‐DBA‐o‐quinone gives rise to a “final blue product” (λmax = 230, 410, 620 nm), and to “soluble oxidation product(s)” (λmax = 275–280, 350–360 nm). Kinetic data (assayed spectrophotometrically and polarographically) obtained when different concentrations of 2, 3‐DBA were oxidized by a fixed amount of mushroom tyrosinase, deviated from classic Michaelis‐Menten kinetics. Reduction of the “final blue product” with ascorbate resulted in the loss of the blue chromophore at 620 nm and the concomitant appearance of a “yellowish reduced final product.” The “yellowish reduced final product” could be reoxidized with either mushroom tyrosinase or with NaIO4 to the “final blue product,” indicating that the latter has carbonylic quinonoid groups in ortho position to each other. Copyright © 1991, Wiley Blackwell. All rights reserved