Citric acid especially, but also malic acid, can sequester iron
in a colourless complex, making iron unavailable for the formation
of dark complexes with phenolic acids. Ascorbic acid can furthermore
inhibit the formation of iron-phenolic acid complexes by chelating
Fe2+-ions. The ascorbic acid-iron complex has a light purple
colour and is less stable than the iron-phenolic acid complex
(Muneta & Kaisaki, 1985).