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Enzymatic Synthesis of Butyl Ferulate by Silica-Immobilized Lipase in a Non-Aqueous Medium

Butyl ferulate was synthesized using a silica-immobilized commercial lipase (Steapsin) in dimethylsulfoxide (DMSO). Lipase-immobilized by surface adsorption onto silica pretreated with 1% glutaraldehyde showed 89% binding of protein. The esterification of butanol (100 mM) and ferulic acid (50 mM) by silica-bound biocatalyst was carried out at 45℃ for 6 h under shaking (120 rpm). The optimization of various reaction conditions like molar concentration of reactants, biocatalyst concentration, reaction time, temperature, addition of molecular sieves, salt ions, and repetitive bio-catalysis in DMSO were studied, consecutively. The bound lipase (15 mg/ml) catalyzed the esterification of ferulic acid and butanol with a yield of 64 mM under optimized reaction conditions. Among the salt ions Cu2+, Zn2+ and Al3+ ions moderately promoted the ester yield (66 mM) while Mg2+, NH4+, Fe2+ and Ca2+ were found to decrease the ester yield. The by-product (H2O) produced in the reaction was scavenged by the molecular sieves (10 mg/ml) added to the reaction mixture, which enhanced the formation of ester up to 74 mM. During the repetitive reactions, the bound lipase produced 32 mM ester after 4th cycle of esterification. On scaling-up the reaction volume to 30 ml, 32.5 mM butyl ferulate was synthesized under optimized conditions.