Differential latency toward (–)-epicatechin and catechol mediated by avocado mesocarp polyphenol oxidase (PPO)

• Avocado fruit PPO requires activation to metabolize (–)-epicatechin.
• Activity toward catechol, an exogenous substrate, does not require activation.
• Specific free fatty acids can activate avocado fruit PPO.
• PPO activity declines during avocado ripening.
• The population of PPO isoforms changes during fruit ripening.

The polyphenol oxidase (PPO) metabolism of the endogenous substrate (–)-epicatechin has been correlated with browning in avocados and other fruit. Although total PPO activity declined during ripening in the avocado mesocarp, a selective retention of high electrophoretic mobility isoforms was observed during ripening. Avocado PPO was virtually inactive toward (–)-epicatechin without the addition of an activator such as sodium dodecyl sulfate. In contrast, PPO was active toward catechol, an exogenous substrate, in the absence of an activator. Low concentrations of the free fatty acids oleic acid, linoleic acid, and arachidonic acid were effective activators of (–)-epicatechin oxidation in vitro. The data suggest that these endogenous free fatty acids may play a role in the PPO-mediated browning of avocado fruit in vivo.