Kinetic analysis of thermal degradation of betanin at various pH values using deconvolution method

Abstract

Although betanin is commonly used as a water-soluble red colorant in foods, it is unstable when heated. In this study, the discoloration of betanin in a buffer solution was kinetically studied in the pH range of 2.6 to 7.6 at 40 °C to 80 °C. The absorption spectrum of betanin was deconvoluted into the spectra of betanin and its degradation product, betalamic acid. Subsequently, a reversible consecutive reaction, in which betanin was reversibly degraded to betalamic acid, and betalamic acid was further degraded, was assumed to calculate the first-order rate constant of each step. The apparent reaction mechanism varied depending on the pH values. Based on these rate constants, the activation energy of each process, as well as the equilibrium constant and enthalpy change for the reversible reaction between betanin and betalamic acid were evaluated.