Kinetic and Thermodynamic Characteristics of Thermal Degradation of Anthocyanins from Strawberry and Blueberry Commercial Juices

Thermal stabilities of anthocyanins in strawberry and blueberry commercial juices were studied over the temperatures 75, 85 and 95 oC. Results indicated that the thermal degradation of anthocyanins followed the first-order reaction kinetics. The temperature-dependent degradation was adequately modeled on the Arrhenius equation. During heating, anthocyanins in the strawberry juice degraded faster than in blueberry juice, with the activation energies of 74.16 kJ/mol and 65.75 kJ/mol, respectively. Cyanidin-3-glucoside (cyd-3-glu) was more susceptible to the thermal treatment than pelargonidin glycosides in strawberry juice. Delphinidin glycosides were more susceptible to the thermal treatment than cyanidin glycosides in blueberry juice. However, cyd-3-glu in strawberry juice was more sensitive to the thermal treatment than in blueberry juice. Obtained results for activation enthalpies indicated that the degradation process was endothermic and Gibbs free energy of activation indicated that they were not spontaneous.