Plant Polyphenol Oxidase: Biochemical Properties and Browning of Fruits and Vegetables

Polyphenol oxidase, a copper-containing metalloprotein, catalyzes the oxidation of phenolic compounds to quinones, which produce brown pigments in wounded tissues. This enzymatic mechanism causes post-harvest losses and mainly affects tropical fruits and vegetables. The enzymes purified form different plant sources showed dif ferences in the biochemical properties. The PPO protein structure has been elucidated and reported in few plants. The active site of the enzyme undergoes transitions among met-, oxy-, and deoxy-forms in a cyclic manner for catalysis. In this article, biochemical characteristics of polyphenol oxidase from different plants are reviewed. Biochemical and molecular characterization of the polyphenol oxidase could help to develop or to choose more effective methods for controlling browning of fruits, vegetables and its products.