Immobilization of lipase Lk2 and Lk3 on NiSiO3 microspheres and the application in the synthesis of methyl esters and β-sitosteryl esters
Titin Haryati, Made Puspasari Widhiastuty, Fida Madayanti Warganegara, Akhmaloka Akhmaloka
Abstract
Bacterial lipase is widely used in industrial applications due to its stability and availability. In order to meet the commercial demands of industrial lipases, research on the characterization of novel bacterial lipases is crucial. We successfully characterized the soluble Lk2 and Lk3 from metagenomic approach in a previous investigation. In this study, we immobilized lipases Lk2 and Lk3 to NiSiO3 matrices, and we carried out characterization based on the transesterification activity using methyl ester substrates with different carbon lengths (C12–C18, C18:1, C18:2). We also investigated the utilization of immobilized Lk2 and Lk3 as catalysts in the synthesis of methyl esters and β-sitosteryl esters. The substrates for methyl esters are crude palm oil and methanol, whereas the substrates for β-sitosteryl esters are β-sitosterol and para-nitrophenyl esters of various lengths (pNP4, pNP8, pNP10, pNP12, pNP14, pNP16, and pNP18). Substrate preference for immobilized lipase was C16, different from free lipase was C18:1 for Lk2 and C18:2 for Lk3, respectively. In the temperature range of 40–60 °C, immobilized lipase had higher activity than free lipase. The immobilized Lk2 and Lk3 maintained 100% activity at the 6th and 5th cycles, respectively, and maintained 70% of their initial activity at the 10th cycle. After 6 h of reaction, Lk2 and Lk3 had optimal methyl esters conversion percentages of 49.8% and 62.7%, respectively, while β-sitosteryl ester conversion percentage was 72%. The computational analysis of the sterol-binding residues in Lk2 and Lk3 structures verified those lipase's abilities to synthesize β-sitosteryl esters. Immobilized Lk2 and Lk3 are appropriate for industrial applications.