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. Km values were 0.839, 1.227, and 1.701 mg/mL, and Vmax 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.