DECOMPOSITION OF CARTHAMIN IN AQUEOUS-SOLUTIONS - INFLUENCE OF TEMPERATURE, PH, LIGHT, BUFFER SYSTEMS, EXTERNAL GAS PHASES, METAL-IONS, AND CERTAIN CHEMICALS

External factors suspecting to influence the chemical nature of carthamin in aqueous media were assessed under experimentally designed model systems. The pigment was more readily decomposed to orange-yellow or yellow compounds at higher temperature. The stability of carthamin was evidently pH-dependent, with increased degradation occurring above and below the pH range in which the red pigmentation is most stable (pH 1.5-5.5). On exposure to visible and ultraviolet light, the red colour in aqueous solutions decreased with half-lives of approximately 1 and 40 min, respectively. Loss of carthamin red coloration also occurred without perceptible dependence on the buffer systems, external gas phases or certain chemicals. Metal ions at a level of 0.03-3.0 mmol concentration caused an increase in the degradation rate compared to that of the control with no metal cations. Fe2+ had the greatest effect, reducing the rate of degradation approximately 47-fold compared to the control. The reaction systems were surveyed spectrophotometrically to check carthamin composition patterns. © 1990 Springer-Verlag.