Kinetic and thermodynamic studies on the thermal inactivation of lipase immobilized on glutaraldehyde-activated rice husk silica

The objective of this study was to obtain sufficient information on the thermal stabilization of a food-grade lipase from Thermomyces lanuginosus (TLL) using the immobilization technique. To do this, a new non-porous support was prepared via the sequential extraction of SiO₂ from rice husks, followed by functionalization with (3-aminopropyl) triethoxysilane – 3-APTES (Amino–SiO₂), and activation with glutaraldehyde – GA (GA-Amino-SiO₂). We evaluated the influence of GA concentration, which varied from 0.25% v v⁻¹ to 4% v v⁻¹, on the immobilization parameters and enzyme thermal stabilization. The thermal inactivation parameters for both biocatalyst forms (soluble or immobilized TLL) were calculated by fitting a non-first-order enzyme inactivation kinetic model to the experimental data. According to the results, TLL was fully immobilized on the external support surface activated with different GA concentrations using an initial protein load of 5 mg g⁻¹. A sharp decrease of hydrolytic activity was observed from 216.6 ± 12.4 U g⁻¹ to 28.6 ± 0.9 U g⁻¹ of after increasing the GA concentration from 0.25% v v⁻¹ to 4.0% v v⁻¹. The support that was prepared using a GA concentration at 0.5% v v⁻¹ provided the highest stabilization of TLL – 31.6-times more stable than its soluble form at 60 °C. The estimations of the thermodynamic parameters, e.g., inactivation energy (E_d), enthalpy (ΔH^#), entropy (ΔS^#), and the Gibbs energy (ΔG^#) values, confirmed the enzyme stabilization on the external support surface at temperatures ranging from 50 to 65 °C. These results show promising applications for this new heterogeneous biocatalyst in industrial processes given the high catalytic activity and thermal stability.