Fe (III)-polyphenol complex

Ingredients

Gallic acid (GA), Quercetin (QC), iron (II) sulfate heptahydrate (FeSO4.7H2O)

Evidence

"the color of the mixture turned intense blue-black indicating formation of Fe (III)-polyphenol complex."

Remarks

The primary chromogenic agents in Mahġ are complexes formed between iron and polyphenols, specifically gallic acid (GA) and quercetin (QC) (p. 2, 5). The complex with GA forms at pH 7.0 with a 1:1 metal-ligand stoichiometry ([Fe (GA)]), appearing as a black colored complex with an absorption maximum at 550 nm (p. 5). The complex with QC has a 1:2 stoichiometry ([Fe (QC)2]) and changes color from colorless to dark blackish brown, with an absorption band at 438 nm (p. 5). The addition of iron to the plant extracts containing these polyphenols results in an instant chelation at neutral pH, producing the characteristic intense blue-black ink color (p. 2, 5).