Co-immobilized enzymes in magnetic chitosan beads for improved hydrolysis of macromolecular substrates under a time-varying magnetic field

Glucoamylase and alpha-amylase co-immobilized with gamma ferric oxide powders in chitosan beads for consecutive starch liquefaction and saccharification under different magnetic fields was investigated. The chitosan concentration in the beads was found to greatly affect the immobilized enzyme performance. Superior immobilization efficiency and enzyme stability were noted when 2% instead of 4% chitosan was utilized. Using confocal microscopy and scanning electron microscopy, the beads with 2% chitosan were seen to exhibit a more rugged surface topology with more macropores and accommodate more protein near the external surface than with the 4% chitosan beads. An optimum loading ratio between alpha-amylase and glucoamylase exists that gives the highest glucose production, and this ratio varies with the size of the beads. The inclusion of the gamma ferric oxide powders renders the beads magnetically anisotropic and causes them to tumble under a single-phase alternating magnetic field, resulted in increased overall reaction rates. When exposed to a three-phase alternating magnetic field, these beads were stirred vigorously, also leading to enhanced reaction rates. The use of multi-enzyme co-immobilization in magnetic anisotropic chitosan beads may be extended to other practical applications that involve coordinated enzymatic reactions of macromolecular substrates.