CONTROLLING OF ENZYMATIC BROWNING IN PROCESSING OF FRUITS AND VEGETABLES

摘要

Browning reactions in food are of widespread occurrence and become evident when, for instance, food material is subjected to processing or to mechanical injury. Such reactions are important in terms of alteration of appearance, flavor and nutritive value. Browning is desirable when it enhances the appearance and flavor of food products such as coffee, maple syrup, and toasting of bread. In fruits, vegetables, frozen and dehydrated foods, however, browning is undesirable as it results in off-flavor and poor appearance. Browning of raw fruits and vegetables due to mechanical injury during postharvest handling and processing is an important cause of quality and value loss in affected commodities. Polyphenoloxidase (PPO), responsible for enzymatic browning, occurs universally in fruits and vegetables. This darkening reaction results from the PPO catalyzed oxidation of phenolic compounds to O-quinones. These quinones may condense and react nonenzymatically with other phenolic compounds, amino acids, proteins, and other cellular constituents to produce colored polymers and pigments. Such browning reactions have an important bearing on food quality and marketability and are therefore of great importance to the fruit and vegetable processing industry.