Immobilization of Mucor miehei esterase on core-shell magnetic beads via adsorption and covalent binding: Application in esters synthesis

Abstract

In this work, poly(hydroxyethyl methacrylate/glycidylmethacrylate), p(HPMA-GMA), magnetic beads were prepared via suspension polymerization, and grafted with poly(methacrylic acid), p(MMAc) via redox polymerization. Esterase from M. miehei was immobilized onto core-shell magnetic beads with two different methods (i.e., adsorption and covalent binding). For adsorption, the effects of pH and initial esterase concentration on the immobilization efficiency via adsorption have been studied. The maximum adsorption capacity of the magnetic beads for esterase was found to be 27.6 mg/g magnetic beads at pH 7.0. The covalent immobilization of esterase via carbodiimide coupling on mp(HEMA-GMA)-g-p(MAAc) beads was found to be the more effective than the direct immobilization of the enzyme on the mp(HEMA-GMA) beads. The covalently immobilized esterase on the mp(HEMA-GMA)-g-p(MAAc) beads exhibited higher activity compared to the adsorbed esterase on the same magnetic beads. Tributyrin hydrolysis properties of the free and both immobilized esterase preparations were determined under different experimental conditions. The operational, thermal and storage stabilities of the immobilized esterase preparations were increased compared with the free esterase. Finally, esterification reactions have been performed to produce citronellyl-esters (namely: acetate, butyrate and propionate) in n-hexane medium using covalently immobilized esterase. The immobilized esterase was effectively reused in successive batch runs in n-hexane medium for citronellyl-butyrate synthesis, and only 23 % activity was lost after 6 cycles.