Chemically modified nanoparticles from oil palm ash silica-coated magnetite as support for Candida rugosa lipase-catalysed hydrolysis: kinetic and thermodynamic studies

Abstract

Herein, silica (SiO2) extracted from treated oil palm leaves ash (TOPLA) was coated over Fe3O4 (SiO2–Fe3O4) before surface modification using 3-aminopropyltriethoxysilane (AP–SiO2–Fe3O4). The AP–SiO2–Fe3O4 was further modified with glutaraldehyde for the chemical immobilisation of Candida rugosa lipase (CRL) on the surface of G–AP–SiO2–Fe3O4 (CRL/G–AP–SiO2–Fe3O4). Surface analytical techniques (FTIR, TGA, and XRD) that monitored the successive processes to prepare the CRL/G–AP–SiO2–Fe3O4 biocatalyst affirmed that CRL (14.7 mg/g, 183 U/g activity) was present on the support. Under an optimized condition, CRL/G–AP–SiO2–Fe3O4 (40 °C, pH 8.0 at 200 rpm) and free CRL (35 °C, pH 7.0, 200 rpm) hydrolysed 98.5% olive oil at fixed 2.5:1 olive oil: water ratio, enzyme load 1.0 mg/mL, signifying retention of lipase activity after immobilisation. Despite the lower Vmax (833.3 μmol/mL min), CRL/G–AP–SiO2–Fe3O4 (Km 0.583 g/mL) showed a 12-fold higher affinity for the substrate over free CRL (Km 6.00 g/mL, Vmax 3330 μmol/mL min). Thermodynamic data also corroborated the increased thermal stability of CRL/G–AP–SiO2–Fe3O4 (t1/2 38.94 min, D value 129.4 min, \( \Delta H_{\text{d}}^{^\circ } \) 110.10–110.27 kJ/mol, \( \Delta S_{\text{d}}^{^\circ } \) 292.3–293.2 kJ/mol) over free CRL (t1/2 23.89 min, D value 79.67, \( \Delta H_{\text{d}}^{^\circ } \) 87.55–87.72 kJ/mol, and \( \Delta S_{\text{d}}^{^\circ } \) 233.5–233.7 kJ/mol).