Not available – first paragraph follows: Fresh fruit tissues turn brown when bruised, cut, or otherwise damaged during harvesting and postharvest handling. This browning detracts from the appearance of fruits marketed fresh or used for processing. The extent of the discoloration depends not only on the severity of bruising, but also on the inherent browning potential of the fruits. Browning potential depends upon the total amount of phenolic compounds and level of activity of the poly-phenol oxidase (PPO) enzyme, which catalyzes enzymic browning in fresh fruits. Normally, phenolic compounds are separated from PPO enzyme in the intact tissue. Once the fruit tissue is damaged, PPO gets access to the phenolic compounds, and reactions leading to browning occur. These reactions involve the oxidation of phenolic compounds to form quinones, which are tightly unstable and polymerize quickly to form brown-colored products.

Photographs were taken by Don Edwards, Department of Pomology, UC Davis.