Enzymatic browning

Enzymatic browning is the discoloration of cut fruits and other foods when enzymes oxidize phenolic compounds, producing colored pigments.

Polyphenol oxidase: An enzyme that oxidizes phenolic compounds using molecular oxygen. It catalyzes the oxidation that initiates most enzymatic browning.
Ascorbic acid: A water-soluble antioxidant vitamin that can reduce oxidized compounds and react with oxygen. It delays browning by reducing quinones back to colorless phenolic compounds.
Apple: A fruit of the tree Malus domestica, eaten fresh and used in cooking. Cut apple flesh is a familiar example of rapid enzymatic browning.
Maillard reaction: A set of reactions between reducing sugars and amino compounds that produces brown pigments and many cooked-food aromas. It browns foods through heat-driven chemistry, not oxidation by fruit enzymes.
Phenolic compounds: A broad class of molecules characterized by one or more hydroxyl groups attached to aromatic rings. These molecules supply the substrates that browning enzymes oxidize.
Citric acid: A weak organic acid found in citrus fruits and widely used as a food acidulant. Its acidity and metal binding can slow polyphenol oxidase activity.
Banana: An elongated edible fruit produced by several large herbaceous plants in the genus Musa. Bruised or cut banana tissue darkens through enzymatic oxidation.
Caramelization: The thermal decomposition of sugars that produces brown pigments and characteristic flavors. It requires heating sugars, unlike enzymatic browning in exposed raw tissue.
Quinone: An oxidized aromatic compound containing two carbonyl groups in a conjugated ring. Polyphenol oxidase converts phenolic substrates into reactive quinones.
Blanching: Brief heating of food in hot water or steam, often followed by rapid cooling. Heat inactivates browning enzymes before freezing or other processing.

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