Rate-controlling mechanisms in the photo-degradation of ochratoxin A

Abstract

This work studies the rate-controlling mechanisms of the UV photo-degradation of OTA by applying kinetic and thermodynamic compensations. The study tries to go in depth into a previous study where the UV photo-degradation of OTA was concluded to take place following first-order kinetics. For this purpose, aqueous solutions of 100 mg L−1 of OTA were irradiated at acidic pH values usually found in fruit juices at the same temperatures than the previous study, using the same mid-pressure mercury lamp with emission wavelengths between 250 and 740 nm. The new photo-degradation data also fitted well to the first-order kinetic model, with the new parameters matching the old ones. The kinetic constants were used to study whether the kinetic and thermodynamic compensation could be applied. Applying the Leffler’s criterion, the OTA photo-degradation was concluded to be enthalpically controlled and isokinetic temperatures of 388.0 K and 382.9 K were obtained for the kinetic and thermodynamic compensations, respectively. As the harmonic mean temperature (302.8 K) is clearly different lower than both isokinetic temperatures, it can be concluded that the compensation is not caused by the propagation of the experimental errors and that the reaction is controlled by enthalpy.