What causes browning when fresh fruits and vegetables are cut?

Browning in cut fruits and vegetables is primarily caused by a chemical reaction called enzymatic browning. Here's a breakdown of the process:

1. Enzymes: Fruits and vegetables contain enzymes called polyphenol oxidases (PPO). These enzymes are naturally present and play a role in plant defense mechanisms.

2. Exposure to Oxygen: When fruits and vegetables are cut, their cells are exposed to oxygen in the air. This oxygen comes into contact with the PPO enzymes.

3. Oxidation: The PPO enzymes react with oxygen and certain compounds called phenols found in the fruits and vegetables. This reaction leads to the formation of quinone molecules.

4. Quinone Polymerization: Quinones are highly reactive and quickly polymerize, forming melanin. Melanin is a dark brown pigment that causes the browning effect.

Factors that influence browning:

* Type of fruit or vegetable: Some fruits and vegetables have higher levels of PPO and phenols, making them more prone to browning (e.g., apples, bananas, potatoes).

* pH: Acidity inhibits the activity of PPO. Fruits like citrus have lower pH levels, which can slow down browning.

* Temperature: Warmer temperatures accelerate enzymatic browning.

* Exposure to light: Light can also stimulate browning.

Ways to prevent browning:

* Acid treatment: Using acidic ingredients like lemon juice, vinegar, or ascorbic acid (vitamin C) can lower the pH and slow down browning.

* Blanching: Heating fruits and vegetables briefly in boiling water or steam can deactivate the PPO enzymes.

* Storage: Storing cut fruits and vegetables in airtight containers or wrapping them in plastic wrap can minimize contact with oxygen.

* Cold temperatures: Refrigerating or freezing fruits and vegetables can slow down enzymatic browning.

It's important to note that browning doesn't necessarily mean that the food is unsafe to eat. However, it can affect the taste, texture, and appearance of the food.