Immobilization of α‐amylase on eggshell membrane and Ag‐nanoparticle‐decorated eggshell membrane for the biotransformation of starch

Enzyme biocatalysts are very sensitive to environmental conditions. To improve their stability and operational lifetime, free enzymes are usually immobilized on a solid support. In this study, α‐amylase was immobilized on eggshell membrane (ESM) and Ag‐nanoparticle‐decorated eggshell membrane (AgNP/ESM) using glutaraldehyde as a cross‐linking agent. After immobilization, enzyme loading, activity, kinetic parameters, reusability, and storage stability were investigated. The AgNP/ESM possessed a larger enzyme loading than ESM alone. The optimal pH and temperature of immobilized α‐amylases remained at 5.0 and 55°C, but the pH tolerance and thermal stability of AgNP/ESM‐immobilized enzyme were better than those of free enzyme. K m values were 0.839, 1.227, and 1.701 mg/mL, and V max values were 220.3, 48.85, and 37.12 μmol/min/mg for free, ESM‐, and AgNP/ESM‐immobilized α‐amylases, respectively. After ten uses, AgNP/ESM‐immobilized α‐amylase exhibited better operational stability as compared with ESM immobilized enzyme. After 50 days of storage at 4°C, the losses of activity were 46.29, 35.11, and 28.74% for free, ESM‐, and AgNP/ESM‐immobilized α‐amylases, respectively. These results indicate that AgNP/ESM is a more promising support as compared with ESM for the immobilization of α‐amylase.