Superior activities of lipase immobilized on pure and hydrophobic clay supports: Characterization and catalytic activity studies

Lipase from Candida rugosa was immobilized on 3-aminopropyltriethoxysilane-modified montmorillonite K-10 (Mt–S) support via glutaraldehyde spacer (Mt–G). Simple physical adsorption technique was also employed to immobilize lipase on Mt. The supports as well as the novel immobilized biocatalysts were characterized by a combination of techniques, namely X-ray diffraction (XRD), nitrogen adsorption studies and Scanning Electron Microscopy (SEM). Using the hydrolysis reaction of p-nitrophenyl palmitate in aqueous and organic media, the properties of the immobilized lipases were assayed and compared with those of the free enzyme. The effects of reaction temperature, pH, thermal and storage stabilities of the immobilized lipases were evaluated. The optimum reaction temperature rose from 35 °C to 50 °C for Mt–I and to 55 °C for Mt–G. The covalently immobilized conjugate, Mt–G retained almost 90% activity at 50 °C, while the free enzyme retained only 20% activity after 120 min heat treatment. Immobilized lipases exhibited enhanced storage stability than the native lipase (up to 40 days). The kinetic parameters of the free and immobilized lipases, Km and Vmax were also assayed. The activity of the free lipase in heptane (0.213 U/mg) was 0.51% of that in the aqueous medium (41.6 U/mg). The Km value for the free lipase was nearly 50-fold higher in organic media. The free lipase was 195-fold more active in water compared to that in organic solvent.