Combined effect of pH and high temperature on the stability and antioxidant capacity of two anthocyanins in aqueous solution

Abstract

The stability of two cyanidin-based anthocyanins from black rice in an aqueous system containing them with a pH range of 2.2-6.0 was investigated at temperatures ranging from 100 to 165°C. Within these pH and temperature ranges, the stability of the two anthocyanins was found to decrease gradually with increasing pH. The lowest (8.99×10(-4)s(-1)) and highest (0.120s(-1)) degradation rate constants for cyanidin-3-glucoside were obtained at pH 2.2 & 100°C and pH 6.0 & 165°C, respectively, whereas those for cyanidin-3-rutinoside were 5.33×10(-4)s(-1) at pH 2.2 & 100°C and 7.39×10(-2)s(-1) at pH 5.0 & 165°C, respectively. Antioxidant capacity analysis was conducted on thermally processed anthocyanin solutions to further evaluate the effects of pH and thermal treatment on the anthocyanins. The total antioxidant capacity of samples after thermal treatments under various pHs was found to remain at a similar level.

Keywords: Anthocyanins; Antioxidant capacity; Black rice; Kinetic modelling; Thermal degradation; pH.