Photochemical preparation of magnetic chitosan beads for immobilization of pullulanase

Abstract

Magnetic chitosan beads were prepared via photochemical polymerization in Fe 3O 4 magnetite aqueous suspension, and characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), photocorrelation spectroscopy (PCS) and vibrating sample magnetometer (VSM). The FT-IR result indicated that the magnetic chitosan beads were synthesized successfully under UV irradiation in aqueous system. The magnetic chitosan beads were of regularly spherical shape, had a mean diameter of 86 nm, exhibited superparamagnetic property and the saturation magnetization was 52.6 emu/g. Pullulanase was covalently immobilized on magnetic chitosan beads by cross-linking with glutaraldehyde. The maximum quantity of pullulanase immobilized onto 1.0 mg magnetic chitosan beads was 180 μg. The optimum temperature of immobilized pullulanase was 50° C, which was identical to that of free enzyme, and the immobilized pullulanase exhibited a higher relative activity than that of free pullulanase over 50° C. The optimal pH for immobilized pullulanase was 5.0, which was lower than that of the free pullulanase (pH 5.5), and the immobilization resulted in stabilization of enzyme over a broader pH range. The kinetic constant value ( Km) of immobilized pullulanase was three times higher than that of free pullulanase. However, the thermal and operational stabilities of immobilized pullulanase were improved greatly.