Efficient Synthesis of Isoamyl Acetate Using a Thermostable Geobacillus kaustophilus Lipase Immobilized in TPP-Crosslinked ZIF-8

Isoamyl acetate is a widely used aroma ester with growing demand for sustainable and environmentally benign production routes. In this study, a thermostable lipase from Geobacillus kaustophilus ( Gk L) was immobilized within a zeolitic imidazolate framework (ZIF-8) and further stabilized via sodium tripolyphosphate (TPP) crosslinking to enhance its catalytic performance and operational stability. The resulting biocatalysts, Gk L@ZIF-8 and Gk L-TPP@ZIF-8, were comprehensively characterized using SEM, SEM–EDS, XRD, and FTIR analyses, confirming successful enzyme encapsulation and preservation of the ZIF-8 crystalline structure. The immobilized lipases were evaluated for the enzymatic synthesis of isoamyl acetate in hexane medium, and the effects of temperature, substrate molar ratio, enzyme loading, and reaction time were systematically investigated. Compared to Gk L@ZIF-8, Gk L-TPP@ZIF-8 exhibited significantly improved thermal stability, achieving a 2.8-fold increase in half-life at 50°C, as well as enhanced catalytic efficiency, reaching up to 95% ester yield under optimized conditions. Furthermore, Gk L-TPP@ZIF-8 retained 85% of its initial activity after five consecutive reuse cycles, demonstrating superior operational stability. These results highlight the synergistic effect of ZIF-8 encapsulation and TPP crosslinking, offering a robust and reusable biocatalyst platform for the green synthesis of aroma esters.