Improved performance of Pseudomonas fluorescens lipase immobilized on a magnetic mesoporous solvothermal hybrid-nanocarrier and its application in ultrasonication assisted estolide synthesis

The exponential growth of the biotechnological market necessitates the exploring novel, economically viable materials for enzyme immobilization to enhance the biocatalyst performance. This study involvespreparing a hybrid carrier with a magnetic mesoporous nature, using milled rice husk (MRH) and multi-walled carbon nanotubes (MWCNTs) via a one-pot solvothermal process at 200 °C for 6 h. The carrier, rich in-NH2 groups, was chemically bonded to Pseudomonas fluorescens lipase (PFL) using EDC/NHS cross-linkers. The synthesized support achieved a maximum PFL loading of 94.92 mg of protein per gram of support. Moreover, the maximum activity recovery was achieved at 1196 %, under the optimal conditions: immobilization temperature 25℃, pH 9.0, immobilization time 2 h and PFL mass concentration 4 mg/mL. Subsequently, the derived enzyme was used to catalyze ricinoleic acid esterification to synthesize estolide under ultrasound-assisted conditions. The optimized principal parameters for reaction temperature, reaction time, and immobilized lipase loading were respectively determined to be 48.99 °C, 1.60 h, and 3.09 % via response surface methodology. Ricinoleic acid conversion reached 65.23 % under the optimal conditions with the assistance of 40 % power and 40 kHz ultrasonic frequency. Furthermore, remarkable operational stability was also observed, with a retention rate of 49.28 %, even after 10 consecutive batches. This study demonstrates promising prospects for industrial-scale application using ultrasound as a fast and ecologically friendly procedure.