Chemical and Laccase catalysed oxidation of gallic acid: determination of kinetic parameters.

During grape crushing, the release in the liquid phase of oxidizing enzymes can reduce the concentration of phenols which are natural antioxidants important for human health. On the contrary, in the following phases, related to the aging of wine, it is the slower chemical oxidation that causes the unwished degradation of the phenolic compounds. In spite of the wide literature on the field, kinetic evaluations which allow to quantify the extent of the phenomenon with temperature (30 and 45 degrees C) are not yet available. To evaluate the phenol degradation kinetics, a model solution containing gallic acid which was subjected to both chemical and enzymatic oxidation was used. After determination of the kinetic equation able to describe the time reduction of the gallic acid concentration in the solution, the kinetic parameters related to the degradation curves and the oxidative process involved were calculated. In both the chemical and enzymatic oxidation experiments, an increase in the temperature of 15 degrees C induced a reduction of the gallic acid oxidation rate, evidencing an influence of temperature on the oxygen amount dissolved in the liquid phase. In the presence of laccase, the oxidative kinetics was three orders of magnitude higher than that recorded without the enzyme.