Kinetic and thermodynamic study of the photochemical degradation of patulin.

In a previous work, the UV photodegradation of patulin was concluded to follow a first-order kinetic and to be faster at acidic pH. In this case, the UV photodegradation of aqueous patulin solutions was studied at acidic pH values (3-6) similar to the values of apple juices where patulin has been found, obtaining that the first-order kinetic constant increased when the acidity of the reaction media was also increased (pH decreased). From the parameters obtained by fitting the experimental data to both the Arrhenius and Van't Hoff equations, the existence of kinetic and thermodynamic compensations was studied. Apparent kinetic and thermodynamic compensations were concluded, the isokinetic and isoequilibrium temperatures being -13.4 and -15.4°C, respectively. As the harmonic mean temperature was 34.3°C, applying the statistical criterion, it was concluded that both compensations were real, the reaction mechanism control changing from enthalpic for temperatures lower than the isokinetic-isoequilibrium temperatures (-13.4/-15.4°C) to entropic for higher temperatures. It could also be concluded that the reaction rate depends on the pH value for the acidic range studied.