DISTRIBUTION, LOCATION AND INHIBITORS OF POLYPHENOL OXIDASES IN FRUITS AND VEGETABLES USED AS FOOD

Abstract

Polyphenol oxidases (PPOs) are ubiquitous enzymes that catalyze the oxygen-dependent reaction that transforms o- diphenols to o-quinones. These quinones are reactive and capable of covalently modifying a wide variety of nucleophilic species into cells leading to the formation of brown polymers, known as enzymatic browning. The phenomenon of browning during growth, collection, storage and processing of fruits and vegetables, is a major problem in the food industry and is recognized as one of the leading causes of commercial value and quality loss, since it produces important changes in the appearance and organoleptic properties of edible fruits and vegetables, and it is often associated to the release of odors and negative effects on nutritional value. Although PPOs have been described in various plant tissues such as roots, sedes, leaves and fruits, the control of this phenomenon requires biochemical knowledge of the type of phenolic substrates present in each plant, the level of reducing compounds, the level of O₂ accessibility, of the nature of the various oxidizable compounds and, finally, o-quinones polymerization and degradation. This paper present a review of the biochemical effect, distribution, location and potential inhitors of PPOs in fruits used for food.