Browsing by Author "Ferreira Dias, S."
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- Batch operational stability of immobilized heterologous Rhizopus oryzae lipase during acidolysis of virgin olive oil with medium-chain fatty acidsPublication . Nunes, Patrícia A.; Cabral, Paula Pires; Guillen, M.; Valero, F.; Ferreira Dias, S.Structured triacylglycerols containing medium-chain fatty acids (M) at positions sn-1,3 and long-chain fatty acids (L) at the sn-2 position (MLM type), were obtained by acidolysis of virgin olive oil with caprylic or capric acid, in solvent-free media, at 40 degrees C, catalyzed by a heterologous Rhizopus oryzae lipase (r-ROL) immobilized in Eupergir (R) C or in Lewatit VP OC 1600. The biocatalyst immobilized in Eupergit was reused in consecutive 23-h batches with rehydration of the biocatalyst between batches. A first-order deactivation was observed (half-life time, t(1/2) = 39.0 h for caprylic; t(1/2) = 54.3 h for capric acid). During acidolysis with capric acid catalyzed by r-ROL immobilized in Lewatit VP OC 1600, without rehydration, a first-order deactivation was observed (t(1/2) = 49.1 h); with rehydration, a considerable increase in stability was observed (t(1/2) = 234 h; Sadana's series-type inactivation kinetics model). (C) 2012 Elsevier B.V. All rights reserved.
- 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 and optimization of ethyl butyrate production catalysed by Rhizopus oryzae lipasePublication . Grosso, Carla; Ferreira Dias, S.; Cabral, Paula PiresResponse surface methodology was used to model and optimise the production of ethyl butyrate, catalysed by Rhizopus oryzae lipase immobilised in a hydrophilic polyurethane foam. Experiments were carried out following a central composite rotatable design, as a function of reaction temperature (T: 22-38 degrees C) initial butyric acid concentration (A: 0.031-0.619 M) and initial molar ratio ethanol/acid (MR; 0.257-2.443). After 48 h reaction time, the production of ethyl butyrate could be fitted to a surface described by a second-order polynomial model. A maximum ethyl butyrate concentration of 0.106 M, corresponding to 47% conversion into ester and a productivity of 2.21 mu mole/mL h, is expected at initial reaction conditions of T, A and MR of 33 degrees C, 0.225 M and 1.637, respectively. This maximum was experimentally confirmed. (c) 2012 Elsevier Ltd. 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.