Catechol oxidase (; CAS number: 9002-10-2) is an enzyme that catalyses the oxidation of phenols such as catechol. Catechol oxidase is a copper-containing enzyme whose activity is similar to tyrosinase, a related class of copper oxidases.

Catechol oxidase carries out the oxidation of phenols such as catechol using dioxygen (O₂). In the presence of catechol, benzoquinone is formed (see reaction below). Hydrogens removed from catechol combine with oxygen to form water.

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enzymes | Copper compounds | EC 1.10.3

Browning in Fruit

Fruits and vegetables, can be kept fresh by storage at coldish temperatures, because the cold slows down all cellular mechanisms. Similar to hibernation - the cells are still alive, but do not need a high turnover of oxygen and nutrients. However, one of the banes of apples and bananas, from a consumer point of view, is browning. The browning is caused by a reaction between catechol and oxygen, catalyzed by the above enzyme "catechol oxidase" resulting in benzoquinone. This compound is brownish in color and is toxic to bacteria. When the peal is damaged, oxygen can then react with the catechol, protecting the fruit. Nitrogen is sometimes used to insulte the fruit - extending shelf life by not allowing ogygen to come in contact with the fruit.