Enhancement of lipase transesterification activity by immobilization on β–cyclodextrin-based polymer

Silica–β-cyclodextrin matrices were prepared by the sol–gel technique using tetraethoxysilane as precursor and different concentrations (0.5–4.0%) of the organic component, β-cyclodextrin (β-CD). Hybrid matrices were activated with glutaraldehyde to introduce functional groups for the attachment of Burkholderia cepacia lipase, used here as a model enzyme. The goal was to produce biocatalysts with high activity and satisfactory properties for transesterification reactions. The biocatalysts exhibited similar hydrolytic activities, coupling yields, and kinetic parameters (K_m and V_max), but differed in terms of thermal stability and transesterification activity. The best biocatalyst, prepared using 2.0% β-CD, was used to study the influence of oil/alcohol molar ratio on ester yield, viscosity, and residual monoacylglycerol (MG) and diacylglycerol (DG) contents. The molar ratio of palm kernel oil to ethanol had a considerable effect on the formation of ethyl esters and the best performance was achieved with an oil/alcohol molar ratio of 1:6. Under this condition, a high ethyl ester yield, a low residual MG content (<0.5%), and undetectable DG levels were obtained. Kinematic viscosity measurements (40 °C) confirmed the high transesterification yield, as the viscosity of palm kernel oil decreased from 30.13 mm²s⁻¹ to <4 mm²s⁻¹.