The browning that fruits and certain vegetables experience when they are cut is due to an enzyme called polyphenol oxidase (PPO) that catalyzes the oxidation of different molecules in the presence of oxygen. The process is known as enzymatic browning , it occurs in cut fruits and leaves (apples, potatoes, mushrooms …) and can be avoided by adding lemon juice, which contains ascorbic acid or vitamin C , an antioxidant compound.
Another option to avoid enzymatic browning, used at an industrial level, is the cutting and preparation of these foods in the absence of oxygen, processing the foods in an atmosphere of nitrogen or carbon dioxide.
In humans this same enzyme is responsible for the formation of hair and skin pigments (melanin), and in cephalopods such as squid it produces the pigment of the ink.
