Classification of Food Colours

Chlorophyll is the green pigment in vegetables like spinach, peas, and green beans. Its green color mainly comes from a central magnesium (Mg²⁺) ion held inside its porphyrin ring structure.

What happens in acidic conditions?

When vegetables are exposed to acids (low pH conditions)—for example during cooking with acidic ingredients like tomatoes, lemon juice, or vinegar—the structure of chlorophyll changes:

1. Magnesium is replaced

• Hydrogen ions (H⁺) from acids enter the chlorophyll molecule.
• These H⁺ ions displace the central magnesium (Mg²⁺).

2. Formation of pheophytin

• Once magnesium is removed, chlorophyll is converted into a compound called pheophytin.
• Pheophytin has an olive-green or dull brown color, instead of bright green.

3. Loss of bright green color

• This chemical change breaks the original light-reflecting structure responsible for vibrant green color.
• As a result, vegetables look dull, olive, or brownish-green after cooking in acidic conditions.