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

Abstract

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 4^th cycle of esterification. On scaling-up the reaction volume to 30 ml, 32.5 mM butyl ferulate was synthesized under optimized conditions.