Thermal stability enhancement of Candida rugosa lipase using ionic liquids

The thermal stability of Candida rugosa (C. rugosa) lipase was investigated and compared in n-hexane, benzene, dibutyl-ether as well as bmim]PF₆ and omim]PF₆ ionic liquids and the effect of solvent polarity and water activity were evaluated. Deactivation of the enzyme followed a series-type kinetic model. First order deactivation rate constants and the ratios of specific activities were determined and the kinetics of deactivation were studied. Among the organic solvents, the best stability was observed in n-hexane with a half-life of 6.5 h at water activity of 0.51. In ionic liquids, however, even longer half lives were obtained, and the enzyme was stable in these solvents at 50°C. The highest half-life times were obtained in bmim]PF₆ (12.3 h) and omim]PF₆ (10.6 h). A direct correlation was found between solvent polarity and thermal stability since the higher the polarity of the solvent, the lower was the stability decrease at 50°C comparing to that at 30°C.