Studies on the activity and stability of immobilized α-amylase in ordered mesoporous silicas

Specific activity of α-amylase immobilized in ordered mesoporous silicas (26-335 Å pore diameter) for hydrolysis of starch has been studied. In mesoporous silica like MCM-41 and SBA-15, enzyme is immobilized only on the external surface and thus the observed specific activity is low. For meso-cellular foams (MCF), MCF-153 and MCF-335 having higher pore diameter, enzyme seems to be immobilized inside the pores and high specific activity increase was observed. In fact, MCF-335 shows specific activity equal to 80% of the specific activity of free enzyme. It was further observed that, thermal and pH stability of the immobilized enzyme is higher compared to free α-amylase. Immobilization of α-amylase in these silicas was carried out using three-step process through alkylamine and glutaraldehyde. Alkylamine was covalently bonded to silanol groups present on the surface of mesoporous silica followed by reaction of aldehyde with alkylamine. Enzyme molecules were immobilized on thus modified silica through reaction of free -CHO with -NH2 of enzyme.