Modification and characterization of natural aluminosilicates, expanded perlite, and its application to immobilise α – amylase from A. oryzae

Abstract

The aim of this study was to modify natural silicoaluminates as expanded perlite (EP) through simple and inexpensive treatments in order to get a greater reactivity of surface and immobilise α-amylase from A. oryzae by adsorption and covalent binding. The materials obtained (expanded perlite treated with HCl, rehydroxylated expanded perlite, zeolite, and the incorporation of polystyrene in expanded perlite) were analysed by infrared spectroscopy, thermal analysis, zeta potential, adsorption of N2, and Scanning Electron Microscopy. The analysis allowed us to confirm that the modifications on the materials studied were effective. This is perceived by an increase in bands corresponding to OH groups, which is beneficial when considering functional groups that interact directly with the enzyme. It also allowed us to determine that the materials tested exhibit good thermal stability at the temperature range in which enzymatic studies are conducted. The conditions for immobilisation (pH, concentration of glutaraldehyde, time of contact between the enzyme and the substrate, enzyme concentration) and some properties of the immobilised derivatives (optimum pH, temperature of maximum activity, and reuse) were analysed. The suitable range for the immobilisation of α-amylase from A. oryzae by covalent binding was pH between 5 and 6, and for immobilisation by adsorption the suitable pH range was between 5 and 5.5. These values ​​are consistent with the zeta potential values ​​previously determined for the different media studied. The reuse of the immobilised enzyme by covalent binding resulted in a residual activity of 90% up to the sixth reuse. Immobilisation by covalent binding was more effective than immobilisation by adsorption.