Question

Explain how the enzyme polyphenoloxidase contributes to the discoloration of some fruits and vegetables.

Answer 1

Enzymatic browning is one of the most important reactions that occur in fruits and vegetables, usually resulting in negative effects on color, taste, flavor, and nutritional value. The reaction is a consequence of phenolic compounds' oxidation by polyphenol oxidase (PPO), which triggers the generation of dark pigments. This is particularly relevant for apples, which are rich in polyphenols and highly susceptible to enzymatic browning. Enzymes that create melanins and benzoquinone from natural phenols, resulting in a brown color, in general, enzymatic browning requires exposure to oxygen, for example the browning that occurs when an apple, banana are cut.

So basically polyphenol oxidase produces melanin from naturally occuring phenols in fruits and vegetables in the presence of oxygen which developes the dark colour in them.