Degradation kinetics of some phenolic compounds in subcritical water and radical scavenging activity of their degradation products

The degradation of 10 phenolic compounds including 9 phenolic acids (caffeic, chlorogenic, p-coumaric, gallic, gentisic, p-hydroxybenzoic, protocatechuic, syringic and vanillic acids) and one flavanol (catechin) in subcritical water at the initial concentration of 100 mg/L was investigated in a temperature range of 100-250 degrees C for 30-120 min in a batch-type vessel. The degradation process followed the first-order kinetics model. After treatment at 250 degrees C for 30 min, all the compounds completely disappeared. We also demonstrated that the subcritical water treatment of some phenolic compounds, especially, caffeic acid, resulted in products that were quite stable at high temperature and exhibited a high DPPH radical scavenging activity, that is retaining about 50% of the DPPH radical scavenging activity compared to the original caffeic acid solution after the treatment at 250 degrees C for 120 min.