Biocatalytic esterification of citronellol with lauric acid by immobilized lipase on aminopropyl-grafted mesoporous SBA-15

Mesoporous SBA-15 was synthesized under acidic condition at 40 °C with a non-ionic triblock copolymer (P123) as the template. The synthesis gel composition used was 1 SiO₂:0.017 P123:2.9 HCl:202.6 H₂O. Functionalization of SBA-15 with 3-aminopropyltriethoxysilane (APTES) by post-synthesis method was performed under reflux for 2 h. The mesoporous samples were characterized using Fourier transform infrared (FT-IR), nitrogen adsorption, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). They were then utilized as supports for the immobilization of lipase to be subsequently used for the esterification of citronellol and lauric acid. Leaching and reusability tests were also conducted on the immobilized enzymes. Functionalization resulted in about 10% improvement in enzyme loading, leading to higher activity. The immobilized enzyme was also more stable to low pH and high temperature while showing better retention (up to 95%) of enzyme molecules. Immobilized lipase maintained 90% of its esterification activity in non-aqueous system even after 4 cycles of use. The improvements were associated with enhanced surface hydrophobicity, changes in pore shapes and stronger enzyme–support interactions with minimal effects to the enzymatic activity.