Hydrolysis and synthesis reactions catalysed by Thermomyces lanuginosa lipase in the AOT/Isooctane reversed micellar system

Abstract

The kinetics of hydrolysis of triolein and tributyrin and of the synthesis of ethyl-laurate by the lipase of Thermomyces lanuginosa, contained in a commercial preparation (Lipolase®), were studied in AOT/Isooctane reverse micelles. Lipolytic activity against triolein depended strongly on the water content in the system ( W 0=[H 2O]/[AOT]), in a bell-shaped manner, with a maximum at a W 0 of 15. The best conditions for enzyme activity were pH 8.0 and 37 °C. The enzyme did not show Michaelis–Menten kinetics for the hydrolysis of either triolein or tributyrin. The enzyme was unstable at temperatures of 37–60 °C, losing approximately 50% of its activity after 30 min. The catalysis of ethyl-laurate synthesis by T. lanuginosa lipase in reverse micelles was studied using factorial designs to optimize the reaction conditions. The most important variables were pH and temperature and their combined effect. The best conditions for ester synthesis were a W 0 of 10, a pH of 5.6, a molar ratio of alcohol to acid of 5.0 and a temperature of 30 °C. The specific enzymatic activity under these conditions was 220 U mg −1 and the ester yield 92% after 60 min of reaction. This high yield, obtained in a relatively short time, justifies further exploration of the potential of this system in biocatalysis.