Immobilization on magnetic PVA/SA@Fe₃O₄ hydrogel beads enhances the activity and stability of neutral protease

Enzyme immobilization technology has a key role in improving the stability of enzyme reaction systems and biocatalyst utilization rates. In this study, polyvinyl alcohol/sodium alginate@Fe₃O₄ (PVA/SA@Fe₃O₄) magnetic immobilized-enzyme hydrogel beads were prepared. Their structure and morphology were characterized by scanning electron microscopy, surface area and porosity analyses, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and a vibrating sample magnetometer. The capability of PVA/SA@Fe₃O₄ to adsorb neutral protease was investigated with variations in composition, temperature, pH, stirring speed, enzyme concentration, and crosslinking concentration. The optimal parameters of the immobilization process were determined by response surface methodology (3% neutral protease, 4% crosslinking at 200 rpm, 45 °C and pH 7.2), under which an immobilization rate of 41.98 mg/g was obtained. The thermal stability, acid-base stability, and reusability of the immobilized enzyme were improved significantly. After seven cycles, the immobilized enzyme activity remained at 30.8% that of the initial enzyme activity. The results indicate that the immobilization of NP onto magnetic PVA/SA@Fe₃O₄ hydrogel beads improves enzyme efficiency, giving this process potential industrial applications.