Statistical optimization and operational stability of Rhizomucor miehei lipase supported on magnetic chitosan/chitin nanoparticles for synthesis of pentyl valerate.

The chemical-catalyzed transesterification process to produce biofuels i.e. pentyl valerate (PeVa) is environmentally unfriendly, energy-intensive with tedious downstream treatment. The present work reports the use of Rhizomucor miehei lipase (RML) crosslinked onto magnetic chitosan/chitin nanoparticles (RML-CS/CH/MNPs). The approach used to immobilize RML onto the CS/CH/MNPs yielded RML-CS/CH/MNPs with an immobilized protein loading and specific activity of 7.6 mg/g and 5.0 U·g-1, respectively. This was confirmed by assessing data of field emission scanning electron microscopy, X-ray diffraction, thermal gravimetric analysis and Fourier transform infrared spectroscopy. A three-level-four-factor Box-Behnken design (incubation time, temperature, substrate molar ratio, and enzyme loading) was used to optimize the RML-CS/CH/MNP-catalyzed esterification synthesis of PeVa. Under optimum condition, the maximum yield of PeVa (97.8%) can be achieved in 5 h at 50 °C using molar ratio valeric acid:pentanol (1:2) and an enzyme load of 2 mg/mL. Consequently, operational stability experiments showed that the protocol adopted to prepare the CS/CH/MNP nanoparticles had increased the durability of RML. The RML-CS/CH/MNP could catalyze up to eight successive esterification cycles to produce PeVa. The study also demonstrated the functionality of CS/CH/MNP nanoparticles as an eco-friendly support matrix for improving enzymatic activity and operational stability of RML to produce PeVa.