Polyphenoloxidase are enzymes found abundantly in fruits and vegetables. Polyphenoloxidase catalyses the o-hydroxylation of monophenols to o- diphenols. They can further catalyze the oxidation of o-diphenols to produce o-quinones. It is the rapid polymerization of o-quinones to produce black, brown or red pigments, that is the cause of fruit browning. Hence, many vegetables and fruits become discolored during storage. These highly reactive quinines polymerize with other quinines, amino acids and proteins to produce colored compounds, and nutrient quality and attractiveness is reduced. PPO is synthesized early in tissue developments and is stored in chloroplasts.