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

Candida rugosa lipase was covalently immobilized on silanized controlled po re silica (CPS) previously activated with glutaraldehyde in the presence of several additives to improve the performance of the immobilized form in lo ng-term operation. Proteins (albumin and lecithin) and organic molecules (b eta -cyclodextrin and polyethylene glycol [PEG]-1500) were added during the immobilization procedure, and their effects are reported and compared to t he behavior of the immobilized biocatalyst in the absence (lacking) of addi tive. The selection of the most efficient additive at different lipase load ings (150-450 U/g of dry support) was performed by experimental design. Two 2(2) full 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 simultaneous ly to the lipase onto the support. The catalytic activity had a maximum (19 3 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 esterific ation reactions under repeated batch cycles (for the synthesis of butyl but yrate as a model). The half-life of the lipase immobilized on CPS in the pr esence of PEG-1500 was found to increase fivefold compared with the control (immobilized lipase on CPS without additive).