Preparação e caracterização de partículas de sílica da casca de arroz funcionalizada na imobilização de lipase e aplicação na síntese de ésteres

Abstract

Rice husk silica (RHS) has been extracted by a hydrothermal process and functionali-zed with triethoxy(octyl)silane (OCTES) to produce a hydrophobic support (Octyl–SiO2) to be used in the immobilization of lipase from Thermomyces lanuginosus (TLL) via interfacial activation. The support was characterized by particle size, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electronic microscopy (SEM), atomic force microscopy (AFM), elemental analysis (CHN), N2 physisorption analysis and Rose Bengal dye adsorption, thus confirming their functionalization. Effect of pH, temperature, initial protein loading and contact time on the adsorption process has been systematically evaluated. According to results, RHS functionalization improved the TLL adsorption capacity. Under optimal conditions (5 mM buffer sodium acetate pH 5.0, 25 °C and 150 min of incubation), maximum immobilized protein loading of 21.9 ± 0.1 mg/g of support was observed. Maximum catalytic activity in olive oil emul-sion hydrolysis was 630.3 ± 5.8 IU/g. TLL adsorption was a spontaneous and phy-sisorption process (–20.4 kJ/mol ≤ ΔG ≤ –7.6 kJ/mol). Experimental data on Octyl–SiO2 adsorption were well-fitted to Langmuir isotherm model (R2 = 0.9952). It was also examined whether these biocatalysts could synthesize cetyl esters (cetyl octanoate, cetyl estearate and cetyl oleate) via esterification reaction. It was found that cetyl stea-rate synthesis required a reaction time of 100-110 min to attain maximum conversion percentage. Cetyl estearate synthesis was optimized using a central composite rota-table design (CCDR). Under optimal experimetal conditions (64 °C, biocatalyst concentration of 21% m/v, 170 rpm and acid:alcohol equimolar ratio – 1:1), maximum ester conversion percentage of around 90% after 60 min of reaction was observed. After nine successive cycles of reaction in a batch system, the biocatalyst retained 90% of its original activity. These results show the potential application of the support obtained in lipase immobilization and its use as biocatalyst in hydrolysis and esterification reac-tions.