Parameters Affecting the Improvement of Properties and Stabilities of Immobilized α-amylase on Chitosan-metal Oxide Composites

Abstract

Chitosan-metal oxide composites, chitosan- Fe3O4 (CSM) and chitosan-ZnO (CSZ) were synthesized and intended as suitable supports for immobilization of starch hydrolyzing enzyme, α-amylase. Here α-amylase was chosen as the enzyme to immobilize on these supports due to its wide implementation in industrial applications. The immobilized enzyme, CSZE showed better immobilization yield of 76%, whereas CSME provides high speed and easy separation from the reaction system due to its magnetic property. The quality of the immobilized α-amylases was demonstrated and assessed based on its activity and stability. The immobilized enzymes with higher Ed values provide them more stability towards denaturation compared to free enzyme. At 50℃ the thermodynamic parameters such as ∆Ho, ∆Go and ∆So for thermal deactivation of free enzyme were evaluated as 104.29, 12.83 and -0.28 KJ mol-1 respectively and are found to be higher in case of both immobilized enzymes. The Km values for CSME and CSZE are 0.65 and 0.5mg/mL respectively, which are higher than that of free enzyme (0.45mg/mL). The Vmax of free enzyme is decreased from 34.48μmol mg-1 min-1 to 16.39(CSME) and 23.81 (CSZE) μmol mg-1 min-1 as a result of immobilization. The immobilized enzymes have exhibited better storage stability over 6 months and retained more than 50% of their initial activities after 10 cycles of reuses.