This document describes the effects of acid, alkali, and prolonged cooking on various plant pigments. It notes that chlorophyll intensifies to an olive green color with acid and remains olive green with alkali, and is slightly soluble in water. Carotene is little affected by acid or alkali unless excessive, which can darken the color, and is slightly soluble in water. Anthocyanin is stable with acid but takes on deeper red, purple or blue hues depending on alkalinity, and is very soluble in water.

5. Pigment Effect of
acid
Effect of
alkali
Effect of
prolonged
cooking
Solubility in
water
Chlorophyll Olive green
Intensifies
green color
Olive green
Slightly
Soluble
Carotene Little effect Little effect
Little effect
unless excessive
way darkens
Slightly
Soluble
Anthocyanin Color is stable
Deeper red
purple or blue
depending on
alkalinity
Little
effect
Very
soluble
Anthoxanthins No effect Yellow
Darken if
excessive in the
presence of iron
Very
soluble