Immobilization of Candida rugosa lipase on ZnO nanowires/macroporous silica composites for biocatalytic synthesis of phytosterol esters

ZnO nanowires were successfully introduced into a macroporous SiO 2 by in-situ hydrothermal growth in 3D pores. The obtained composites were characterized by SEM and XRD, and used as supports to immobilize Candida rugosa lipase (CRL) through adsorption. The high specific surface area (233   m 2 /g) and strong electrostatic interaction resulted that the average loading amount of the composite supports reached 287.2   mg/g. Both adsorption capacity and the activity of the CRL immobilized on the composite supports almost kept unchanged as the samples were soaked in buffer solution for 48   h. The immobilized CRL exhibited better thermal stability, reusability and pH adaptability in comparison to free CRL. The immobilized CRL was used as biocatalyst for the preparation of phytosterol esters by the esterification of phytosterol and oleic acid. A maximum molar conversion of 96.5% was achieved under the optimal condition. After twelve recycles the immobilized lipase could retain 89.9% of its initial activity.