Abstract
The ability of partially purified pear tyrosinase (PPO) to catalyse the oxidation of l-ascorbic acid (AA) has been reported here for the first time. The ascorbate oxidase activity of PPO was studied by oxymetric assays. The activity was linearly related to the enzyme concentration with a Michaelis constant (Km) for AA of 0.55±0.03 mM at pH 7. The stoichiometry was found to be 1:2 (O2:AA). The action of the PPO inhibitors tropolone and sodium chloride was studied to exclude a possible interference of endogenous pear ascorbate oxidase in the oxidation of AA. A possible role of the ‘AA/PPO’ system in the browning of pears is proposed.
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