Selection of stabilizing additive for lipase immobilization on controlled pore silica by factorial design

Candida rugosa lipase was covalently immobilized on silanized controlled poresilica (CPS) previously activated with glutaraldehyde in the presence of several additives to improve the performance of the immobilized from in long-term operation. Proteins (albumin and lecithin) and organic molecules (β-cyclodextrin and polyethylene glycol PEG]-1500) were added during the immobilization procedure, and their effects are reported and compared to the behavior of the immobilized biocatalyst in the absence (lacking) of additive. The selection of the most efficient additive at different lipase loadings (150–450 U/g of dry support) was performed by experimental design. Two 2²full factorial designs with two repetitions at the center point were employed to evaluate the immobilization yield. A better, stabilizing effect was found when small amounts of albumin or PEG-1500, were added simul-taneou sly to the lipase on to the support. The catalytic activity had a maximum (193 U/mg) for lipase loading of 150 U/g of dry support using PEG-1500 as the stabilizing additive. This immobilized system was used to perform esterification reactions under repeated batch cycles (for the synthesis of butyl butyrate as a model). The half-life of the lipase immobilized on CPS in the presence of PEG-150 was found to increase fivefold compared with the control (immobilized lipase on CPS without additive).