Spectrophotometric investigation on betanin degradation induced by copper cations

Betanin pigment structurally belong to red-violet betacyanins which represent a class of N-heterocyclic water soluble plant pigments providing the colours in a wide variety of fl owers and fruits [1, 2]. Most of betacyanins, such as betanin, are 5-O-glucosides of betanidin (the basic chromophoric aglycone unit). Betanin colorant (E-162) is produced from red beet roots (Beta vulgaris L.) and is available in concentrates produced by evaporating beet juice under vacuum or as powders made by spray--drying the concentrate. In this study, an eff ect of copper cations on betanin stability was investigated in aqueous and organic-aqueous solutions. The presence of organic solvents (methanol, ethanol and acetonitrile) increased substantially the decomposition of the pigment induced by metal cations in acidic media, for which generally much lower degradation in aqueous solutions was observed. A possibility of a complex formation between betanin and Cu2+ was also stated at pH 7–8 and its relatively high stability in aqueous samples was observed. A presence of numerous products of betanin decomposition was noticed at the wavelength range of 380–500 nm in spectra obtained for the investigated metal cations, especially in the organic-aqueous solutions.