Both hydrolytic and transesterification activities of Penicillium expansum lipase are significantly enhanced in ionic liquid [BMIm][PF 6

Abstract

Both hydrolytic and transesterification activities of Penicillium expansum lipase (PEL) were investigated in the ionic liquid [BMIm][PF 6] as well as in organic solvents such as hexane. The initial rate of PEL-catalyzed hydrolysis of p-nitrophenyl palmitate (pNPP) was 12-fold enhanced in the ionic liquid. The optimal water content required by PEL in [BMIm][PF 6] was 10 times higher relative to that in hexane due to the greater polarity of the ionic liquid. Direct addition of salt hydrates into the two nonaqueous reaction media showed different impacts on the enzyme activity, which could be related to the dual functions of the salt hydrates, i.e., the water buffering effect, and the specific ion effect (Hofmeister effect). The transesterification activity of PEL was reflected by the yield of producing fatty acid methyl esters (FAMEs) in the methanolysis of corn oil for 25 h, which was 69.7% in [BMIm][PF 6], as compared to 19.4%, 14.0%, and 1.0% obtained in tert-butanol, solvent-free system, and hexane, respectively. The high production yield of FAMEs obtained in [BMIm][PF 6] demonstrates the potential use of ionic liquids as the reaction media for PEL-catalyzed biodiesel production.