The activity of invertase immobilized on cashew nut shell liquid-templated large pore silica hybrids

Abstract

The characterization and activity of invertase enzymes immobilized on large pore micelle templated silica (LP-MTS) hybrid materials is reported. The LP-MTS hybrid materials were prepared by a co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltrimethoxysilane (AMPTS) in a cashew nut shell liquid (CNSL) template. A commercially available dodecylamine template was also used to afford similar materials, hereinafter abbreviated as DDA-MTS, for comparison purposes. The prepared materials were characterized by different techniques to determine their physicochemical properties. The maximum loading for the amine groups in LP-MTS and DDA-MTS were 3.3 and 2.8 mmol g⁻¹, respectively. Modification of the materials for immobilization of the invertase enzyme was done by reacting them with glutaraldehyde resulting in Glu-LP-MTS or Glu-DDA-MTS. The as-prepared hybrid materials have surface areas ranging from 100 to 214 m² g⁻¹ with pore diameters ranging from 3.1 to 25 nm. Scanning electron microscopy (SEM) images show that LP-MTS and DDA-MTS materials comprise of roughly spherical particles whereas enzyme and glutaraldehyde supported micelle templated silicas show a rupture of the spherical particles to a fine powder. The activities of free and immobilized invertases have been determined by measuring the amount of reducing sugar produced upon hydrolysis of sucrose at different temperatures, pH and substrate concentrations. Both free and immobilized invertase enzymes showed a maximum activity at a particular optimum temperature, pH and substrate concentration. The maximum activity for the free invertase was 15 229 U at pH 5.0 and at 40 °C whereas those of the LP-MTS immobilized invertases were 14 833 U and 14 625 U for covalent and cross-linked invertases, respectively, at pH 4.0 and 40 °C. The maximum activity for DDA-MTS covalently immobilized invertase was 4750 U, at pH 4.0 and 40 °C.