Decomposition of betacyanins and betaxanthins by heat and pH changes

Authors investigated the decomposition of the main beetroot colourings betanin and vulgaxanthin I as a function of temperature and pH value in acetate and citrate buffer solutions, in a temperature-range between 60 °C and 80 °C and pH range of 3.3–6.2. The temperature dependence of betain decomposition is characterized by a Q₁₀ value of 2.23 ± 0.45, and the reaction rate was doubled by reducing the pH value from 6.2 to 3.3 independent from the type of acid used. Also the interaction between temperature and pH value on colour decomposition was verified. Investigations were carried out at low oxygen content, and under this conditions the reaction was exactly described - considering the time interval of 20 min - by a linear function at 60 °C, pH value 3.3–6.2 and by an exponential function at 70 °C and 80 °C and pH 3.3–4.65. Activation energy for betain degradation is 77.5 ± 6.76 kJ/mol.