Esterification activity and operational stability of Candida rugosa lipase immobilized in polyurethane foams in the production of ethyl butyrate

Ethyl butyrate is a fruity flavor ester widely used in food and pharmaceutical products. The synthesis of ethyl butyrate in n-hexane, catalyzed by Candida rugosa lipase immobilized in two hydrophilic polyurethane foams (“HYPOL FHP 2002” and “HYPOL FHP 5000”) was performed. In this study, the effects of (i) the immobilization supports, (ii) the initial substrate concentrations and (iii) the water content of the system, on the activity and operational stability of C. rugosa lipase in both foams, during the esterification in continuous packed-bed reactor (PBR) and in repeated batches, were investigated. When low substrate concentrations were used, no deactivation was observed for both biocatalysts, along the continuous 30-d PBR operation. Conversely, under high substrate concentrations, a fast deactivation of the biocatalysts was observed. In consecutive batches, the deactivation was faster for the lipase in the less hydrophilic foam (“FHP 5000”) with a half-life of 53 h against 170.3 h for the other counterpart. Water molecules in the microenvironment did not present a deactivation effect on the biocatalysts. The low operational stability can be ascribed to the inhibitory effect of ethanol, which tends to accumulate inside the foams.