Browsing by Author "Dias, S. Ferreira"
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- 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.
- Optimized production of MLM Triacylglycerols catalyzed by immobilized heterologous rhizopus oryzae lipasePublication . Nunes, Patrícia A.; Cabral, Paula Pires; Guillen, M.; Valero, F.; Dias, S. FerreiraResponse surface methodology was used to model and optimize the acidolysis of virgin olive oil with caprylic (C8:0) or capric (C10:0) acids, aimed at the production of low caloric triacylglycerols (TAG) of MLM type, in solvent free media, catalyzed by the heterologous Rhizopus oryzae lipase (r-ROL) immobilized in Eupergit(A (R)) C. This lipase was produced in the methylotrophic yeast Pichia pastoris Mut(s) phenotype (experiments with C10:0) or a Mut(+) phenotype (experiments with C8:0), under different operational conditions. The r-ROL used in experiments with C10:0 presented a hydrolytic activity about 5 times of that presented by r-ROL used in acidolysis with C8:0. The experiments were carried out following a central composite rotatable design, as a function of the molar ratio (MR) medium chain fatty acid/TAG (1.6-4.4) and temperature (25-55 A degrees C). Convex surfaces described by second order polynomials as a function of MR and temperature were well fitted to fatty acid incorporation values. After 24-h reaction, the predicted maximum incorporation of caprylic (15.5 mol%) or capric (33.3 mol%) acids in olive oil occurs at 37 and 35 A degrees C, respectively, and at C8:0/TAG of 2.8:1 or C10:0/TAG of 3:1. These predicted optima were experimentally validated. Fermentation conditions used in r-ROL production highly affected hydrolytic activity and to a lesser extent interesterification activity.
- 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.
- Production of MLM-Type structured lipids catalyzed by immobilized heterologous rhizopus oryzae lipasePublication . Nunes, Patrícia A.; Cabral, Paula Pires; Guillen, M.; Valero, F.; Luna, D.; Dias, S. FerreiraThis work aims to produce triacylglycerols (TAG) containing a medium-chain fatty acid (M) at positions sn-1,3 and a long-chain fatty acid (L) at sn-2 position, i.e. TAG of MLM type, by acidolysis of virgin olive oil with caprylic (C8:0) or capric (C10:0) acids, catalyzed by 1,3-selective Rhizopus oryzae heterologous lipase (rROL) immobilized in Eupergit (R) C and modified sepiolite. This lipase was produced by the methylotrophic yeast Pichia pastoris. Reactions were performed at 25 and 40 degrees C, for 24 h, either in solvent-free or in n-hexane media, at a molar ratio 1:2 (olive oil:free fatty acid). Higher incorporations of C8:0 (21.6 mol%) and C10:0 (34.8 mol%) into the TAG were attained in solvent-free media, at 40 degrees C, when rROL immobilized in Eupergit (R) C was used. In organic media, at 40 degrees C, only 15.9 and 14.1 mol%, incorporation of C8:0 or C10:0 were, respectively observed. Lower incorporations were attained for both acids (3.4-7.0 mol%) when native ROL (nROL) in both supports and rROL in modified sepiolite were used. rROL in Eupergit (R) C maintained its activity during the first four or three 23-h batches, respectively when C8:0 (half-life time, t(1/2) = 159 h) or C10:0 (t(1/2) = 136 h) were used, decreasing thereafter following a time delay model.
- Production of olive oil enriched with medium chain fatty acids catalysed by commercial immobilised lipasesPublication . Nunes, Patrícia A.; Cabral, Paula Pires; Dias, S. FerreiraStructured triacylglycerols, containing medium chain fatty acids, were produced by acidolysis of virgin olive oil with caprylic or capric acid, at a molar ratio of olive oil:fatty acid of 1:2, at 45 degrees C for 24 h, in solvent-free media or in n-hexane, catalysed by Thermomyces lanuginosa (Lipozyme TL IM), Rhizomucor miehei (Lipozyme RM IM) and Candida antarctica (Novozym 435) immobilised lipases. Incorporations were always greater for capric than for caprylic acid. For both acids, higher incorporations were always attained in solvent-free media: the highest caprylic acid incorporations were obtained with Novozym 435 (25.5 mol%) and Lipozyme RM IM (25.7 mol%), while similar capric acid incorporations were obtained with all biocatalysts (27.1-30.4 mol%). After 10 repeated uses of Lipozyme RM IM, the same incorporation level of capric acid was obtained at the end of each 23 h batch. However, with caprylic acid, a first-order deactivation was observed (half-life time, t(1/2) = 299 h). During acidolysis with both acids, Novozym 435 (t(1/2)= 217 h, for caprylic, t(1/2) = 225 h, for capric acid) and Lipozyme TL IM (t(1/2) = 50.4 h, for caprylic; t(1/2) = 47.2 h, for capric acid) presented first-order deactivation. All biocatalysts presented 1,3-regioselectivity. (C) 2011 Elsevier Ltd. 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.