Synthesis, characterization and application of lipase-conjugated citric acid-coated magnetic nanoparticles for ester synthesis using waste frying oil.

In the present work, magnetic nanoparticles (MNPs) were prepared by chemical precipitation of trivalent and divalent iron ions which were functionalized using citric acid. The bacterial isolate Staphylococcus epidermidis KX781317 was isolated from oil-contaminated site. The isolate produced lipase, which was purified and immobilized on magnetic nanoparticles (MNPs) for ester synthesis from waste frying oil (WFO). The characterization of MNPs employed conventional TEM, XRD and FTIR techniques. TEM analysis of MNPs showed the particle size in the range of 20-50 nm. FTIR spectra revealed the binding of citric acid to Fe3O4 and lipase on citric acid-coated MNPs. The citric acid-coated MNPs and lipase-conjugated citric acid-coated MNPs had similar XRD patterns which indicate MNPs could preserve their magnetic properties. The maximum immobilization efficiency 98.21% of lipase-containing citric acid-coated MNPs was observed at ratio 10:1 of Cit-MNPs:lipase. The pH and temperature optima for lipase conjugated with Cit-MNPs were 7 and 35 °C, respectively. Isobutanol was found to be an effective solvent for ester synthesis and 1:2 ratio of oil:alcohol observed significant for ester formation. The ester formation was determined using TLC and the % yield of ester conversion was calculated. The rate of ester formation is directly proportional to the enzyme load. Formed esters were identified as isobutyl laurate ester and isobutyl myristate ester through GC-MS analysis.