ABSTRACT
Enzymatic browning is a phenomenon that commonly occurs in various fruits and vegetables when they are cut, peeled, exposed to air, undergoes mechanical damage during transportation, or is diseased. Oxidation of phenolic compounds present in fruits and vegetables takes place when these are exposed to air leading to the formation of brown melanins thus causing dark spots on fruits and vegetables. Enzymatic browning is caused by polyphenol oxidases (PPOs) (oxidoreductase enzymes) and peroxidases (POD) (oxidases), which are found in most fruits and vegetables, and in some seafoods. Dark coloration is mainly caused by the oxidation of phenolic compounds to quinones. PODs are thermostable enzymes belonging to a group of oxidases that cause oxidation of phenolic compounds and in this process, H2O2 acts as a catalyst. Enzymatic reactions change the color of fruits and vegetables, which is a serious issue during harvesting, transportation, storage, and processing. Undesirable changes in flavor, texture, color, and the nutritional quality of foods have been related to PODs and such changes make foods unacceptable to the consumers. Various physical and chemical methods are used for the prevention of enzymatic browning. These methods include thermal treatment, prevention of oxygen exposure, use of 362low temperature, irradiation, acidification or reduction using antioxidants, chelating agents, or natural extracts.
