Thermal Kinetics of Gamma–Aminobutyric Acid and Antioxidant Activity in Germinated Red Jasmine Rice Milk using Arrhenius, Eyring-Polanyi and Ball Models

The thermal kinetics of changes of –aminobutyric acid (GABA) and antioxidant activity (DPPH assay) in germinated red jasmine rice milk (GRJM) at heating temperatures of 80, 90, 100 and 121C using Arrhenius, Eyring–Polanyi and Ball models was examined in this study. Under isothermal conditions, the increasing of heating temperature from 80C to 121C resulted in the decreasing of GABA. However, DPPH radical scavenging activity increased under temperature range of 80–100C, but decreased at 121C. The highest residue of GABA was 94% after heating at 80C for 30 min, while the highest increasing of DPPH radical scavenging activity was 230% at 90C for 30 min. Thermal degradation of GABA followed a second–order reaction kinetic, while the increasing of antioxidant activity (80–100C) followed a first–order kinetic as well as the degradation of antioxidant activity (121C). The heating temperature dependence of rate constant for degradation of GABA and increasing of antioxidant activity were described by Arrhenius, Eyring–Polanyi and Ball models. Following the Arrhenius law, activation energies were 59.62 kJ/mol and 30.31 kJ/mol, respectively for degradation of GABA (80–121C) and increasing of antioxidant activity in GRJM (80–100C). Arrhenius, Eyring–Polanyi and Ball models could be used to predict accurately GABA content and antioxidant activity in GRJM during isothermal heat treatment.