Entrapment of Geobacillus kaustophilus lipase in ZIF-8 and cross-linking with genipin for biodiesel production from vegetable oils

Abstract

Lipases are widely employed in biodiesel production through green synthesis approaches. However, enhancing the performance of these enzymes is crucial for efficient biodiesel synthesis. In this study, a recombinant lipase (Gklip) derived from a thermophilic bacterium was immobilized in a metal-organic framework (Gklip@ZIF-8). Additionally, to improve stability, cross-linking with genipin was performed (Gklip@ZIF-8-genipin). The immobilization process was validated through instrumental analyses including SEM, SEM-EDS, FTIR and TGA/DTG. Biochemical analyses determined that the optimum pH for Gklip and Gklip@ZIF-8 was 8.0, while Gklip@ZIF-8-genipin form had an optimum pH of 7.5. The optimum temperatures were 50 °C for the free enzyme and 60 °C for the both immobilized samples. Thermal stability tests showed that Gklip@ZIF-8 and Gklip@ZIF-8-genipin exhibited 2.74- and 5.86-fold higher stability at 50 °C compared to the free enzyme, respectively. Furthermore, the biodiesel production efficiency of the enzyme samples was evaluated using coconut, cold-pressed sunflower, and flaxseed oils. The free enzyme effectively produced biodiesel from coconut oil, which is rich in short-chain fatty acids, but failed to convert long-chain fatty acid-rich oils like sunflower and flaxseed into biodiesel. In contrast, Gklip@ZIF-8 and Gklip@ZIF-8-genipin efficiently produced biodiesel from all three oil types. The obtained results demonstrate that Gklip@ZIF-8 and Gklip@ZIF-8-genipin can be effectively applied in biodiesel production.