Enzymatic production of wax esters by esterification using lipase immobilized via physical adsorption on functionalized rice husk silica as biocatalyst.

The present study consists of developing an enzymatic process for the production of wax esters (lauryl stearate and cetyl stearate) by esterification in a heptane medium. Lipase from Thermomyces lanuginosus (TLL) immobilized via interfacial activation on silica particles from rice husks functionalized with triethoxy(octyl)silane (TLL-Octyl-SiO2 ) was used as biocatalyst. Maximum immobilized protein loading of around 22 mg g-1 (that corresponds to an immobilization yield of ≈55%) of support was observed using an initial protein loading of 40 mg g-1 of Octyl-SiO2 . Its hydrolytic activity (olive oil emulsion hydrolysis) was of 620 U g-1 of biocatalyst. The effect of certain factors on the cetyl estearate production was evaluated using a central composite rotatable design (CCDR). Under optimal conditions (64°C, 21% of mass of biocatalyst per volume of reaction mixture, 170 rpm, and stoichiometric acid:alcohol molar ratio 1 mol L-1 of each reactant), maximum acid conversion percentage of 91% was observed after 60 min of reaction. Lauryl stearate was also produced under such conditions, and an acid conversion of 93% after 60 min of reaction was also achieved. Free lipase exhibited acid conversion of only 15%-20% for both reaction mixtures. After nine successive esterification batches, TLL-Octyl-SiO2 retained 85%-90% of its original activity. These results show the promising use of the prepared biocatalyst in wax esters production due to its high catalytic activity and reusability.