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Comparative study of free and immobilized lipase from Bacillus aerius and its application in synthesis of ethyl ferulate.

In the present study, a purified lipase from Bacillus aerius immobilized on celite matrix was used for synthesis of ethyl ferulate. The celite-bound lipase exposed to glutaraldehyde showed 90.02% binding efficiency. It took two hours to bind maximally onto the support. The pH and temperature optima of the immobilized lipase were same as those of free enzyme i.e 9.5 and 55°C. Among different substrates both free and immobilized lipase showed maximum affinity towards p-nitrophenyl palmitate (p-NPP). The lipase activity was found to be stimulated in the presence of Mg(2+) in case of free enzyme while Zn(2+) and Fe(3+) showed stimulatory effect on immobilized lipase whereas salt ions as well as chelating agents inhibited activity of both free and immobilized lipase. Maximum enzyme activity was observed in n-hexane as organic solvent followed by n-heptane for both free and immobilized lipase, however CCl4, acetone and benzene inhibited the enzyme activity. Moreover, all the selected detergents (SDS, Triton X-100, Tween 80 and Tween 20) had an inhibitory effect on both free and immobilized enzyme activity. The celite bound lipase (1.5%) efficiently performed maximum esterification (2.51 moles/l) of ethanol and ferulic acid (100 mM each, at a molar ratio of 1:3) when incubated at 55°C for 48 h resulting in the formation of ester ethyl ferulate.