Classification of Food Colours

Anthocyanins are water-soluble flavonoid pigments responsible for the red, purple, and blue colors of many fruits, vegetables, and flowers. Their color depends mainly on the pH of the surrounding medium because changes in pH alter the chemical structure of the anthocyanin molecule.

• Acidic medium (pH 1–3): Anthocyanins exist mainly as the flavylium cation, which gives a bright red color.
• Slightly acidic to neutral (pH 4–6): The red pigment gradually changes to purple as different molecular forms are produced.
• Alkaline medium (pH 7–9 or higher): Anthocyanins convert to the quinonoidal base, producing a blue color.
• Strongly alkaline conditions: The pigment becomes unstable and eventually degrades, resulting in a loss of color or formation of brown compounds.