Degradation kinetics of (-)-epigallocatechin gallate as a function of pH and dissolved oxygen in a liquid model system

The degradation kinetics of (-)-epigallocatechin gallate (EGCG) as a function of pH (4 to 7) and dissolved oxygen concentration (0 to 7.59 mg/L) in citrate buffer solutions were determined. EGCG degradation followed a pseudo- first order kinetic model, regardless of the conditions when the fractional conversion technique was applied for data reductions. The rate constant increased log-linearly with respect to both pH and dissolved oxygen concentration. The temperature dependence of the rate constant was adequately modeled by the Arrhenius equation with an average activation energy of 18.7 +/- 1 kcal/mol. A mathematical model that relates the rate constant to temperature, pH, and dissolved oxygen concentration was developed and validated. These results can help predict losses of EGCG during processing and/or storage.