Apples turn brown after being cut due to a chemical reaction called enzymatic browning. This process is initiated when the apple's cells are exposed to oxygen.
The Science Behind Browning
When you cut an apple, you break open its cells, exposing the inner tissues to oxygen in the air. Apples contain an enzyme called polyphenol oxidase (PPO) and compounds called polyphenols. When PPO comes into contact with oxygen, it catalyzes a reaction with the polyphenols, resulting in the production of melanin, a brown pigment. This is the same process responsible for the browning of hair and skin in humans. Britannica, Scientific American
This is an oxidation reaction – a chemical reaction involving the addition of oxygen to a compound. The browning is a natural process and doesn't necessarily indicate spoilage, though it can affect the taste and texture. Glad® , Mass Farm to School
Factors Affecting Browning
Several factors influence the rate of browning:
- Variety of apple: Different apple varieties contain varying levels of PPO and polyphenols, affecting browning speed.
- Exposure to air: More oxygen exposure leads to faster browning.
- Temperature: Higher temperatures generally accelerate enzymatic browning.
Preventing Browning
Several methods can slow or prevent browning:
- Adding acid: Acids like lemon juice or citric acid react with oxygen, preventing the oxidation reaction that causes browning. Mass Farm to School
- Refrigeration: Lowering the temperature slows down enzymatic activity, reducing browning.
- Preventing oxygen exposure: Submerging in water or covering slices with plastic wrap minimizes oxygen contact.
- Commercial treatments: Pre-sliced apples sold commercially often undergo treatments with chemicals such as calcium ascorbate or citric acid to inhibit browning. Reddit
