Immobilization of Thermomyces lanuginosus lipase on mesoporous poly-hydroxybutyrate particles and application in alkyl esters synthesis: Isotherm, thermodynamic and mass transfer studies

Abstract

• Thermomyces lanuginosus lipase was immobilized on poly-hydroxybutyrate particles. • The optimization of alkyl oleate synthesis was performed by experimental design. • Under optimal conditions, maximum conversion was around 90% at 15 min of reaction. • The biocatalyst retained around 70% of its activity after five cycles of esterification. The aim of this work was to immobilize Thermomyces lanuginosus lipase (TLL) by physical adsorption on mesoporous poly-hydroxybutyrate particles (PHB) to catalyze alkyl esters synthesis by direct esterification of oleic acid and short-chain alcohols (methanol and ethanol) in organic medium. The catalytic properties of the biocatalysts prepared were assayed on the olive oil emulsion hydrolysis. The adsorption of TLL on PHB particles obeyed the Langmuir isotherm model and maximum adsorption capacity was 26.5 ± 1.8 mg protein/g and hydrolytic activity of 1300 IU/g of support. The enzyme adsorption was a favorable process. The biocatalyst prepared was slightly more thermal-stable than crude lipase extract in aqueous medium. This slight increase on the thermal-stability was confirmed by the determination of thermodynamic parameters. The biocatalyst prepared by offering 40 mg protein/g of support, which presented immobilized protein amount of 24.7 ± 1.1 mg/g and hydrolytic activity around 1240 IU/g of support, was selected for the production of alkyl esters. Under optimal conditions, ester conversion around 90% was reached after 15 min of reaction performed at equimolar ratio alcohol:oleic acid at 2500 mM of each reactant in heptane medium for methyl oleate and in a solvent-free system for ethyl oleate synthesis. The esterification reactions were not affected by external mass transfer and internal diffusion effects. After five successive cycles of esterification reactions, the biocatalyst retained around 70% of its initial activity.