Volume 4, Issue 1

A novel Dye-decolorizing peroxidase from the basidiomycete Pleurotus sapidus was screened for dyedecolorizing peroxidase activity with 2,2‘-azino-bis(3- ethylbenzothiazoline-6-sulfonic acid), Remazol Brilliant Blue R and Guaiacol. Additionally, the catalytic efficiency on degrading β-carotene into volatile products, and the catalyst storage stability with three different additives were also studied. The apparent inhibition constant (KS) was 51.7 μM. Optimal reaction rates (Vmax) and affinity constants (Km) towards the reducing substrates were obtained using Michaelis-Menten kinetic theory. The trend in the calculated Km’s was found to be 7.0 mM > 0.524 mM > 0.051 mM for Guaiacol, 2,2‘-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) and Remazol Brilliant Blue R. The storage stability of the catalyst was evaluated with 7.0% w/v PEG400, 7.0% w/v PEG1450 and 0.1% w/v Tween®80 at 5°C over a period of 45 days. The study revealed the longest activity conservation with PEG1450, where rDyP had lost 30% of initial activity. The enzyme solution presented similar pH and temperature dependence to known fungal dye-decolorizing peroxidases with most prolific enzymatic activities registered at pH 4.0 and temperatures below 30°C. An interesting property of the catalyst was oxidation observed in the absence of hydrogen peroxide.

The present paper demonstrates application of biocatalysis to the synthesis of ethyl hexanoate, i.e. pineapple flavour ester, in a solvent free system. In order to evaluate the effect of various process parameters on reaction conversion, response surface methodology (RSM) complemented by central composite design (CCD) was employed. A maximum conversion of 88.57% was obtained while changing one factor at a time, at optimum conditions of temperature (50 °C), enzyme dose (2%), molar ratio acid to alcohol (1:3), speed of agitation 250 rpm and reaction time of 120 min. Based on this RSM study, the optimum predicted conditions were: 1:3.39 alcohol to acid ratio, 2.35% enzyme loading and 48.83 oC, for a predicted conversion of 90.99%. The activation energy for the enzymatic esterification was determined and calculated to be 25.76 kJ/mol. The positive values of Gibbs-free energy (ΔG), enthalpy (ΔH) and negative value of entropy (ΔS) revealed that the esterification reaction was non-spontaneous and an endothermic reaction. The reaction seems to follow bi-substrate Ping Pong Bi Bi mechanism with inhibition by both substrates.