Co-Authors:
Kahn, V., The Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan, Israel
Abstract:
Hydrogen peroxide (H2O2) affects polyphenol oxidase (PPO) of avocado mesocarp in several ways. In the absence of an exogenous hydrogen donor (AH2), H2O2-at different concentrations (3.6-364 mM)-shortens the lag period of tyrosine hydroxylation and this effect was abolished when catalase was included in the reaction mixture. DOPA oxidation by avocado PPO is slightly increased by a relatively low concentration of H2O2 (3.3-30 mM), while higher concentrations of H2O2 decrease both the rate and the final level of dopachrome formed. Dopachrome and melanins were bleached in the presence of relatively high concentrations of H2O2 (50-500 mM). Preincubation of avocado PPO with H2O2 in the absence of a substrate resulted in the gradual loss of enzymatic activity, with the rate of loss of monophenolase activity being faster than that of o-dihydroxyphenolase activity. The possibility that relatively low in situ concentrations of H2O2 contribute indirectly to the low or high browning potential of avocado mesocarp is discussed. © 1983.
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