Free Candida Rugosa Lipase-Catalyzed Synthesis of Citronellyl Butyrate in n-Hexane by Direct Esterification : Effect of Reaction Parameters

Free and immobilized Candida rugosa lipases were investigated for the synthesis of citronellyl butyrate by direct esterification reaction in n–hexane as organic solvent. A set of experiments was carried out to verify the influence of various parameters on the formation of citronellyl butyrate by free Candida rugosa lipase, such as lipase loading, substrate molar ratio, temperature, three kinds of support for immobilization, and ratio of immobilization. The conversion was increased with increasing lipase loading. The behavior of leveling–off in esterification was observed at higher lipase loading which gave the optimal amount of lipase loading at 3.33 g/l with 92% conversion. This might be due to the excess of lipase active sites, which remained inside the bulk of lipase particles, was not contributing significantly to the reaction. Increasing butyric acid and citronellol concentrations (at fixed citronellol and butyric acid concentrations, respectively) inhibited the lipase activity due to competitive nature of alcohol and acid binding. Optimal acid conversion was obtained at 40°C after 24–h incubation time. Above this temperature, however, the activity of lipase–catalyzed esterification begins to decrease due to denaturation of protein. From the three kinds of supports for immobilized lipase, Amberlite MB–1 showed the highest conversion compared to Amberlite XAD–1180 and Celite 545. The optimal acid conversion was obtained at lipase loading of 10 mg lipase/g support. At this loading, lipase attempts to optimize its contact with the surface of the support whereby optimum active conformation was retained