Stabilization of Natural Dyes by High Levels of Antioxidants
Natural dyes are normally unstable to photooxidation by UV light. We have measured the stability of a number of natural dyes in combination with high concentrations of antioxidants, excited state quenchers, and UV absorbers. We find that certain combinations, including indigo/BHT, methylene blue/p-benzoquinone, and methylene blue/triethylamine show enhanced stability in solution and/or in thin polymer films. By comparing solutions and films of the mixed components with solutions and films of the antioxidant placed between the dye and UV source, we can show that the effect is not UV screening but is due to some form of intermolecular chemistry. We believe that this effect may account for the high stability of natural dyes in plant tissues, such as the skins of fruit, and may be usable to stabilize natural dyes in foods or textiles, especially if suitable nanoparticle structures can be developed.
Jianzhong Shao and Qinguo Fan
D. P. Li et al., "Stabilization of Natural Dyes by High Levels of Antioxidants", Advanced Materials Research, Vol. 441, pp. 192-199, 2012