Enzymatic transformation of sinapine using polyphenol oxidase from Trametes versicolor. Effect of pH and temperature and model development

Sinapine, a choline ester of sinapic acid and a main component of the phenolic fraction of rapeseed meals, was enzymatically transformed by an enzyme secreted by a white rot fungus Trametes versicolor. A model based on the Theorell-Chance Bi-Bi mechanism that describes the effect of pH, temperature, substrates and enzyme concentrations on the initial reaction rate was developed. The model parameters were estimated from the data regarding the effect of pH and temperature on initial reaction rates using a two-step estimation procedure that was developed in this work. The model predicts experimental data fairly well, and is valid for any pH and temperatures ranges. The optimum pH and temperature of reaction determined experimentally and confirmed by the model are 4.24 and 50 °C, respectively. However, when the effect of temperature on the oxygen solubility is not considered, i.e. oxygen is not the limiting substrate, the model shows that the optimum temperature of reaction is 60 °C. A relation between the temperature and the optimum pH of reaction was proposed. The developed model was used to predict the dynamics of sinapine transformation. The results showed that the investigated enzymatic system includes additional enzymatic reactions between oxygen and the products of sinapine transformation.