Stabilization of natural anthocyanin by intercalation into montmorillonite

Because of its non-toxicity, naturally occurring anthocyanin has a potential for the utilization as a harmless coloring material. Its color instability under alkaline condition or light irradiation limits its practical use. Anthocyanin can be stabilized by the intercalation into montmorillonite. The anthocyanin–montmorillonite maintains the original color at basic condition of even pH 11. The intercalated anthocyanin also exhibits enhanced stability against visible light irradiation compared with the anthocyanin simply adsorbed on the external surface of the mineral particles. The stability enhancement is attributed to the electrostatic host–guest interaction and to steric protection from the attack of atmospheric oxygen. The intercalated complex can be a candidate of an environmentally friendly coloring material.