Discoloration Kinetics of Carthamus Red in Aqueous Ethanol

Abstract

The solubility of carthamus red, red pigment from safflower, in aqueous ethanol largely depended on the ethanol concentration, and it was the highest near 60 and 70% (v/v) ethanol. Discoloration of carthamus red in aqueous ethanol was monitored under temperature-programmed heating conditions where the temperature of test solution raised linearly with time to evaluate the activation energy and frequency factor. The activation energy and frequency factor did not depend on the ethanol concentration, suggesting that ethanol does not affect the discoloration mechanism. The activation energy was 78 ± 5 kJ/mol. The increase in absorbance at 390 nm during discoloration of carthamus red correlated with the decrease in absorbance at 520 nm. This fact also suggests no effect of ethanol on discoloration mechanism of carthamus red.