Apples turn brown primarily due to a natural process called enzymatic browning.
The Science Behind Apple Browning
This unappetizing phenomenon is actually due to a chain of biochemical reactions known as “enzymatic browning.” When an apple is injured (or cut into pieces), the plant tissue is exposed to oxygen. This triggers an enzyme known as polyphenol oxidase (PPO) to—wait for it—oxidize polyphenols in the apple's flesh.
In simpler terms, when the internal parts of an apple come into contact with air, an enzyme within the apple reacts with compounds present in the apple's cells. This reaction produces new compounds that cause the brown discoloration.
Here's a breakdown of the key players:
| Component | Role in Browning |
|---|---|
| Oxygen | Triggers the reaction when present. |
| Polyphenol Oxidase (PPO) | The enzyme that initiates browning. |
| Polyphenols | Compounds oxidized by PPO. |
| Brown Pigments | The result of the oxidation reaction. |
Preventing Apple Browning
While browning is a natural process, you can slow it down or prevent it using a few simple methods:
- Limit Oxygen Exposure:
- Place cut apples in an airtight container.
- Submerge apple slices in water or a weak saltwater solution.
- Lower the pH:
- Coat apple slices with acidic liquids like lemon juice, lime juice, or pineapple juice. The acidity inhibits the activity of the PPO enzyme.
- Apply Heat:
- Briefly blanching or cooking apple slices deactivates the PPO enzyme, preventing browning.
Understanding enzymatic browning helps explain why keeping apples whole until you're ready to eat them is the best way to maintain their fresh appearance.
