Why Apples Turn Brown: The Chemistry of Oxidation

Cutting an apple breaks cell walls, releasing enzymes called polyphenol oxidases.
These enzymes react with oxygen in the air, triggering oxidation.
Oxidation forms melanin-like pigments, which make the apple flesh look brown.
The browning isn’t harmful—it just changes the fruit’s color and flavor slightly.
Acidic juices like lemon slow browning by lowering pH and deactivating enzymes.
Cold storage reduces enzyme activity, delaying the browning reaction.
Salt water soaks work by blocking oxygen contact with the apple’s surface.
Plastic wrap or airtight containers limit oxygen exposure, keeping slices fresh longer.
Different apple varieties brown at different speeds due to varying enzyme levels.
Genetically modified apples have been developed with reduced enzyme activity to resist browning.