Apples turn brown when the fruit’s phenolic compounds react with oxygen. This oxidation process is driven by polyphenol oxidase (PPO), an enzyme. When an apple’s cells are ruptured – for example, by bruising, biting or cutting – the browning reaction begins when PPO found in one part of the cell is able to react with phenolic compounds found elsewhere in the cell.
Recent mapping of apple’s genome revealed that PPO is genetically encoded in a diverse, multi-gene family. Apples have at least eight PPO genes, in three main PPO gene families. To breed a truly nonbrowning apple, all of the active PPO genes must be silenced. Arctic® apples have been genetically engineered to produce little or no PPO enzyme, so cell disruption doesn’t lead to browning.
