Determination of photostability of monoammonium glycyrrhizinate

In a previous study, it was shown that monoammonium glycyrrhizinate was thermostable in the pH range 7.0–9.0. To establish the best storage conditions of this sweetener, we have determined the photodegradation of 6×10−5 M aqueous solutions of monoammonium glycyrrhizinate (λmax:256 nm, ϵ=10600 M−1 cm−1). The photodegradation appeared to follow first-order kinetics and was found to be pH-dependent. The degradation rate constant was calculated to be 8.85×10−4, 5.38×10−4, 4.33×10−4, 4.66×10−4 and 5.12×10−4 min−1, respectively, at pH 2.0, 4.5, 6.0, 8.0 and 10.0.