Polyphenols can be classified into different categories like anthocyanins, flavonoids, and non-flavonoids. Anthocyanins are pigments present in fruits, flavonoids are occur in catechins, tannins, and beverages, and non-flavonoids are a component of gallic acid in tea leaves.
These polyphenols are unstable and undergo oxidation when exposed to air through a series of biochemical reactions involving conversion of one substrate to a product. The most common chemical reaction taking place is the catalysis of first step of biochemical reactions involving formation of quinones from phenolic compounds, and subsequent polymerization of quinones to insoluble polymers known as melanin. This compound called melanin is responsible for the browning of fruits and vegetables.
Considerable losses occur due to browning of fruits and vegetables. Storage and handling costs also increase, if it gets spoiled during processing steps. Browning reduces the quality of fruits and vegetables. It decreases nutritional value and the flavor of fruits and vegetables.