Browsing by Author "da Fonseca, M. M. R."
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- Esterification activity and operational stability of Candida rugosa lipase immobilized in polyurethane foams in the production of ethyl butyratePublication . Cabral, Paula Pires; da Fonseca, M. M. R.; Ferreira Dias, S.Ethyl butyrate is a fruity flavor ester widely used in food and pharmaceutical products. The synthesis of ethyl butyl-ate 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 ill 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. (C) 2009 Elsevier B.V. All rights reserved.
- Modelling the microenvironment of a lipase immobilized in polyurethane foamsPublication . Cabral, Paula Pires; da Fonseca, M. M. R.; Ferreira Dias, S.The effects of partition of substrates and product on the modelling of the micro environment of an immobilized lipase were evaluated using Response Surface Methodology. The esterification of butyric acid with ethanol in n-hexane, catalyzed by Candida rugosa lipase immobilized in two biocompatible and relatively hydrophilic polyurethane foams ("Hypol FHP 2002(TM)" and "Hypol FHP 5000(TM)") was used as the model system. For each set of initial conditions, the final concentration of substrates and ethyl butyrate in the microenvironment, at equilibrium, Cmicro, were estimated by mass balancing bulk and foams. The Cmicro values obtained were used to estimate the corresponding partition coefficients of ethanol (P(EtOH)), butyric acid (P(BA)) and ester (P(EB)), between the foams (microenvironment) and the bulk medium. Foams containing previously inactivated lipase, as well as lipase-free foams were used. For both substrates, Cmicro values were, in the majority of the experiments, higher than their macroenvironmental counterparts. The lowest Cmicro values were observed with the less hydrophilic foam ("FHP 5000"). A decrease Of Cmicro(EtOH) in both foams and Cmicro(BA) in "FHP 5000" foams, was obtained upon lipase immobilization. P(EB) values were, in all cases, close to zero. This is beneficial in terms of the shift in reaction equilibrium, product recovery and alleviation of product inhibition effects.
- Modelling the production of ethyl butyrate catalysed by Candida rugosa lipase immobilised in polyurethane foamsPublication . Cabral, Paula Pires; da Fonseca, M. M. R.; Dias, S. FerreiraResponse surface methodology was used to model and optimise the esterification of ethanol with butyric acid in n-hexane, catalysed by Candida rugosa lipase immobilised in two hydrophilic polyurethane foams ("FHP 2002 (TM)" and "FHP 5000 (TM)"). Experiments were carried out following central composite rotatable designs (CCRD), as a function of the initial water activity of the biocatalyst (a,), initial butyric acid concentration (A) and ethanol:acid molar ratio (MR) in the organic medium. Ester production increased with increasing a, of the biocatalysts, probably due to the hydrophilicity of both substrates in contrast with the hydrophobicity of the product, which is released to the bulk medium. Thus, for each biocatalyst (a(w) = 0.98) another CCRD was performed as a function of A and MR. With both preparations, higher conversions (> 95%) were observed for low A values. For the "FHP 2002 (TM)" system, a maximum ester production of 0.23 M is expected, after 18-h reaction, at initial 0.35 M A and 1.51 MR, corresponding to a(w) of 0.95 and 0.84 M A and 1.65 M ethanol in lipase microenvironment. With "FHP 5000 (TM)" system, predicted initial conditions of 0.54 M A and 0.75 MR (0.32 M A; 0.75 M ethanol in microenvironment; a(w) of 0.95), will lead to the maximum ester production of 0.27 M. These maxima were experimentally confirmed. (c) 2006 Elsevier B.V. All rights reserved.
- Partitioning of water in organic systems with lipase immobilized in polyurethane foamsPublication . Cabral, Paula Pires; Dubreucq, E.; da Fonseca, M. M. R.; Dias, S. FerreiraPolyurethane foams are interesting enzyme supports for reactions in organic media. This study investigated the effects of: (i) support hydrophilicity; (ii) presence of immobilized lipase within the foams; and (iii) hydrophilic substrate concentration on water activity and on the partitioning of reactants between the microenvironment of the biocatalyst and the bulk organic phase. Two foams were used with different hydrophilicities. The organic phase was ethanol and butyric acid in n-hexane. The system contained water remaining from the polymerisation reaction. Experiments were carried out following a central composite rotatable design as a function of butyric acid concentration and ethanol/butyric acid molar ratio. Water activity was estimated from global medium composition by the UNIFAC-LLE group contribution method. UNIFAC calculations were also used to compare experimental bulk medium compositions with the theoretical composition of a monophasic or a biphasic system. For most experimental conditions, the organic phase composition was consistent with the presence of a water phase with no influence of the presence of enzyme in the foams. The influence of foam hydrophilicity was only significant for low water content systems (<0.05%, v/v). The system behaved as a reverse emulsion with hexane as the continuous phase and water droplets trapped within the foam matrix. (c) 2005 Elsevier B.V. All rights reserved.
- Synthesis of ethyl butyrate in organic media catalyzed by Candida rugosa lipase immobilized in polyurethane foams: a kinetic studyPublication . Cabral, Paula Pires; da Fonseca, M. M. R.; Dias, S. FerreiraA kinetic study on 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. With the "FHP5000" foams, esterification rates and conversion were always higher than those obtained with "FHP2002". For both immobilized preparations, BA did not cause any inhibition on the enzymatic activity, in the range of concentration tested (0.078-0.7 M) at an initial ethanol concentration of 0.105 M. Michaelis-Menten kinetics was observed: a plateau being reached at the initial bulk BA concentration of 0.40 M and 0.45 M, corresponding to microenvironmental concentrations of 0.851 M and 0.329 M, respectively with the lipase in "FHP2002" and "FHP5000" foams. Inhibition by EtOH was observed for initial bulk concentrations higher than 0.15 M, corresponding to microenvironmental concentrations of 0.426 M and 0.256 M, for the lipase in "FHP2002" and "FHP5000" foams, respectively. Kinetic data could be well described by the substrate-inhibition model, considering the initial bulk or microenvironmental ethanol concentrations as inhibitory. (C) 2008 Elsevier B.V. All rights reserved.