The enzyme is located in the plastids of plant cells and the phenolic substrates are
stored in the vacuoles. This physical separation prevents any oxidation of the phenolics in
the undamaged living tissues. The separation can be lost as a result of damage to the cell
during harvesting (unintentional) and processing (intentional). Oxidation of the phenolics by
polyphenol oxidase (PPO) then begins.