Immobilization of Thermoalkalophilic Lipase from Bacillus atrophaeus FSHM2 on Amine-Modified Graphene Oxide Nanostructures: Statistical Optimization and Its Application for Pentyl Valerate Synthesis

Synthesis of (3-aminopropyl) triethoxysilane (APTES)-functionalized graphene oxide (GO) nanosheets, statistical optimization of conditions for immobilization of Bacillus atrophaeus lipase ( Ba L) on as-synthesized support, and application of the immobilized Ba L for esterification of valeric acid were carried out in this investigation. The optimum specific activity of the immobilized Ba L (81.60 ± 0.28 U mg −1 ) was achieved at 3 mg mL −1 of GO-NH 2 , 50 mM of phosphate buffer, pH 7.0, 60 min sonication time, 100 mM glutaraldehyde, 25 U mL −1 of enzyme, and 8 h immobilization time at 4 °C. The immobilized Ba L retained about 90% of its initial activity after 10 days of storage. Moreover, about 70% of the initial activity of the immobilized Ba L was retained after 10 cycles of application. The results of esterification studies exhibited that maximum pentyl valerate synthesis using the free Ba L (34.5%) and the immobilized Ba L (92.7%) occurred in the organic solvent medium (xylene) after 48 h of incubation at 60 °C.