A novel method for the decrease of phenolic content in commercial canola meal using an enzyme preparation secreted by the white-rot fungus Trametes versicolor.

Abstract

This research project was focused on the development of a novel enzymatic method for upgrading commercial canola meal by decreasing its phenolic content. The new method is based on the enzymatic transformations of sinapic acid esters (SAE) and free sinapic acid (SA), the two main constituents of the phenolic fraction of canola meal (CM), using an enzyme preparation secreted by the white-rot fungi Trametes versicolor ATCC 42530. The study was divided into three parts: (1) enzyme production; (2) characterization of the enzyme produced--a model enzymatic system; (3) enzymatic upgrading of commercial canola meal--a canola meal system. The enzyme preparation produced was characterized in the model enzymatic system using sinapic acid (SA), sinapine (SIN) and sinapaldehyde (SALD). The results showed that the enzyme is inhibited by high concentrations of SIN and SA. Depending on the substrate, the optima temperatures and pH are in the range of 50$\sp\circ$C-60$\sp\circ$C and 3.3-4.5, respectively. The enzyme was very thermostable; the maximum thermal stability was noticed at pH values between 4.5 and 6.5. Sodium azide was a strong inhibitor of this enzyme while its activity was not affected by EDTA. Based upon the results obtained, the enzyme was characterized as a polyphenol oxidase. The overall transformation of SA was described by a mathematical model based on the Theorell-Chance Bi-Bi mechanism with oxygen as the first substrate, and the second substrate being one of the alternate phenolic compounds: SA, DAD and the unknown compound formed via the thermolysis of DAD. The modeling of sinapine transformation was also considered in this work. A mechanistic model, based on the Theorell-Chance Bi-Bi mechanism, that simultaneously predicted the effects of the concentrations of the enzyme, SIN and oxygen, for any given pH and temperature level, on the rates of the enzymatic reaction was formulated. The model parameters were estimated following the new procedure developed in this work for analyzing data concerning the effects of pH and temperature on enzyme activity. The formula relating the optimum pH of the reaction with the temperature was proposed. The enzyme preparation produced and subsequently characterized was used in the novel method to decrease the phenolic content in commercial CM, which was based on the addition of the enzyme to the meal-buffer slurry. It was found that: (1) the natural buffering capacity of CM resulted in the negligible effect of the pH of the buffer, which was used as the continuous phase in the process, on the extent of SAE decrease; (2) the system was saturated with the enzyme when the enzyme concentration was 4 nkat per mL of the continuous phase; (3) the optimum temperature was 50$\sp\circ$C. (Abstract shortened by UMI.)