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ABSTRACT: Viable cells of Candida guilliermondii were immobilized by inclusion into polyvinyl alcohol (PVA) hydrogel using the freezing-thawing method. Entrapment experiments were planned according to a 2(3) full factorial design, using the PVA concentration (80, 100, and 120 g L(-1)), the freezing temperature (-10, -15, and -20 degrees C), and the number of freezing-thawing cycles (one, three, and five) as the independent variables, integrated with three additional tests to estimate the errors. The effectiveness of the immobilization procedure was checked in Erlenmeyer flasks as the pellet capability to catalyze the xylose-to-xylitol bioconversion of a medium based on sugarcane bagasse hemicellulosic hydrolysate. To this purpose, the yield of xylitol on consumed xylose, xylitol volumetric productivity, and cell retention yield were selected as the response variables. Cell pellets were then used to perform the same bioconversion in a stirred tank reactor operated at 400 rpm, 30 degrees C, and 1.04 vvm air flowrate. At the end of fermentation, a maximum xylitol concentration of 28.7 g L(-1), a xylitol yield on consumed xylose of 0.49 g g(-1) and a xylitol volumetric productivity of 0.24 g L(-1) h(-1) were obtained.
Applied biochemistry and biotechnology 06/2009; 157(3):527-37. · 1.94 Impact Factor
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ABSTRACT: Xylitol was recovered from fermented sugarcane bagasse hemicellulosic hydrolysate by adsorption and crystallization procedures. Silica gel adsorption was employed to purify the broth containing xylitol. In this step, different mixtures of the solvents ethyl acetate, ethanol and acetone were used as eluent, and different proportions of fermented broth volume incorporated per gram of silica gel (Vb/Msg, varying from 1.0 to 2.0 cm3 g−1) were used to pack the column employed as stationary phase bed. The xylitol purification efficiency varied for each mixture of solvent, and for each Vb/Msg ratio used. The purified broth was submitted to different crystallization procedures (cooling, concentration and supplementation with commercial xylitol) aiming to recover xylitol crystals. The best result (60% crystallization yield and 33% total recovery of xylitol from fermented broth) was obtained when the column was packed with a Vb/Msg ratio of 2 cm3 g−1, and the broth was purified with a mixture of ethyl acetate and ethanol, concentrated 6.5-fold, and supplemented with commercial xylitol to force the precipitation. Copyright © 2006 Society of Chemical Industry
Journal of Chemical Technology & Biotechnology 10/2006; 81(11):1840 - 1845. · 2.17 Impact Factor
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ABSTRACT: Xylitol was produced by Candida guilliermondii by fermentation of sugarcane bagasse hemicellulosic hydrolysate. Undesirable impurities were extracted from the broth using either ethyl acetate, chloroform or dichloromethane. The best results on clarification of the broth without xylitol loss were obtained with ethyl acetate. When ethanol, acetone or tetrahydrofuran were used for precipitation of impurities, only tetrahydrofuran clarified the fermented broth, but a high xylitol loss (approximately 30%) was observed.
Biotechnology Letters 09/2005; 27(15):1113-5. · 1.68 Impact Factor
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ABSTRACT: Xylose-to-xylitol bioconversion was performed utilizing Candida guilliermondii immobilized in sugarcane bagasse and cultured in Erlenmeyer flasks using sugarcane bagasse hydrolysate as the source of xylose. Fermentations were carried out according to a factorial design, and the independent variables considered were treatment, average diameter, and amount of bagasse used as support for cell immobilization. By increasing the amount of support, the xylitol yield decreased, whereas the biomass yield increased. The diameter of the support did not influence xylitol production, and treatment of the bagasse with hexamethylene diamine prior to fermentation resulted in the highest amount of immobilized cells.
Applied Biochemistry and Biotechnology 02/2005; 121-124:673-83. · 1.94 Impact Factor
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ABSTRACT: Adsorbing carriers for immobilisation of Candida guilliermondii cells to use for xylitol production from sugarcane bagasse hemicellulose hydrolysate were tested. Biomass was immobilised in situ by natural adsorption, i.e. through direct contact between cells for the inoculum and carrier particles at the beginning of fermentations. The carriers employed were: Syrane porous glass beads with 2.53 mm diameter in average and pore diameter in the range 60–300 μm, supplied by Bioengineering (Wald, Switzerland), and NaX zeolite UOP WE 894 purchased from Plury Química S.A. (Diadema, SP, Brazil). At the end of the run with free cells taken as a reference test, xylitol concentration (Pf) achieved 35.5 g/l, corresponding to a xylose-to-xylitol yield factor (YP/S) of 0.72 g/g and a volumetric productivity (QP) of 0.49 g/l h, while final cell concentration (Xf) and productivity (Qx) were only 5.32 g/l and 0.048 g/l h, respectively. Both systems with immobilised cells exhibited lower xylitol productions (Pf = 28.8–29.5 g/l, YP/S = 0.52–0.53 g/g, QP = 0.32–0.33 g/l h) and higher cell growth, with particular concern to porous glass (Xf = 10.5 g/l, Qx = 0.10 g/l h). Electronic microscopy observations demonstrated that the excellent performance of porous glass as cell support was due to the development of a thick extracellular matrix either within the large pores or on the surface of this material. As a consequence, almost 50% of the cells resulted to be adsorbed to the carrier at the end of the run. This growth was also responsible for a decrease in the fraction of xylose available for xylitol production. Employing zeolite, a material with pore size smaller than cell size, immobilised cells represented only 30% of the final population and immobilisation was just observed on the carrier surface. The low cell attachment on this material can be explained by the stress exerted on the outer immobilised cells by the friction among beads.
Biochemical Engineering Journal. 01/2005;
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ABSTRACT: Biotechnological conversion of xylose into xylitol using hydrolysates obtained from the hemicellulosic fraction of lignocellulosic materials is compromised by the presence of compounds released or formed during the hydrolysis process, some of them being toxic to microorganisms. In order to improve the bioconversion of these hydrolysates it is necessary to find methods to reduce their toxicity. In the present work, rice straw hemicellulosic hydrolysate was treated by six different procedures (all of them involving pH adjustment, with or without activated charcoal adsorption), before being used as a fermentation medium for xylitol production. The most effective method of treatment was to increase the initial pH (0.4) to 2.0 using solid NaOH, followed by the addition of activated charcoal (25 g kg−1) and increase in the pH to 6.5 using solid NaOH. Lignin degradation products were the most inhibitory compounds present in the hydrolysate; their removal was selective and strongly dependent on the pH employed in the treatment. The highest yield of xylitol was 0.72 g g−1 xylose, with a productivity of 0.55 g dm−3 h−1. Copyright © 2004 Society of Chemical Industry
Journal of Chemical Technology & Biotechnology 05/2004; 79(6):590 - 596. · 2.17 Impact Factor
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ABSTRACT: A new approach to the biotechnological production of xylitol from sugarcane bagasse using Candida guilliermondii cells immobilized on porous glass in a fluidized bed reactor (FBR) is presented. The influence of aeration rate (AR) and carrier concentration (Cs) on the production process was evaluated. Seven batch fermentation runs were conducted according to a 22 factorial design. The results obtained showed that Cs had a negative influence on xylitol yield (Yp/s) and volumetric productivity (Qp), whereas AR had a positive influence on Qp and a negative influence on Yp/s. With an AR=0.093 min−1 and Cs=62.5 g/l, the Yp/s value was low (0.25 g/g), but the Qp was highest (0.44 g/l h), probably because cell metabolism was faster when more oxygen was available to the yeast. When the highest levels of the AR and Cs were used, the xylitol yield and concentration were the lowest and the cell concentration was the highest, suggesting that cell metabolism was directed preferentially towards biomass production instead of xylitol accumulation.
Process Biochemistry.
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ABSTRACT: Sugarcane bagasse pretreated by three different procedures (with 2% [v/v] polyethyleneimine (PEI), with 2% [w/v] NaOH, or with a sequence of NaOH and PEI) was used as cell immobilization carrier for xylitol production by Candida guilliermondii yeast. Fermentations using these pretreated carriers were performed in semidefined medium and in a hydrolysate medium produced from sugarcane bagasse hemicellulose. Sugarcane bagasse pretreated with NaOH was the best carrier obtained with respect to immobilization efficiency, because it was able to immobilize a major quantity of cells (0.30 g of cells/g of bagasse). Fermentation in semidefined medium using the NaOH-pretreated carrier attained a high efficiency of xylose-to-xylitol bioconversion (96% of the theoretical value). From hydrolysate medium, the bioconversion efficiency was lower (63%), probably owing to the presence of other substances in the medium that caused an inadequate mass transfer to the cells. In this fermentation medium, better results with relation to xylitol production were obtained by using PEI-pretreated carrier (xylose-to-xylitol bioconversion of 81% of the theoretical and volumetric productivity of 0.43 g/[L.h]). The results showed that sugarcane bagasse is a low-cost material with great potential for use as cell immobilization carrier in the fermentative process for xylitol production.
Applied Biochemistry and Biotechnology 141(2-3):215-27. · 1.94 Impact Factor
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ABSTRACT: The operational conditions for xylitol production by fermentation of sugarcane bagasse hydrolysate in a fluidized bed reactor with cells immobilized on zeolite were evaluated. Fermentations were carried out under different conditions of air flowrate (0.0125-0.0375 vvm), zeolite mass (100-200 g), initial pH (4-6), and xylose concentration (40-60 g/L), according to a 2(4) full factorial design. The air flowrate increase resulted in a metabolic deviation from product to biomass formation. On the other hand, the pH increase favored both the xylitol yield (Y(P/S)) and volumetric productivity (Q(P)), and the xylose concentration increase positively influenced the xylitol concentration. The best operational conditions evaluated were based on the use of an air flowrate of 0.0125 vvm, 100 g of zeolite, pH 6, and xylose concentration of 60 g/L. Under these conditions, 38.5 g/L of xylitol were obtained, with a Y(P/S) of 0.72 g/g, Q(P) of 0.32 g/L.h, and cell retention of 25.9%.
Biotechnology Progress 21(6):1639-43. · 2.34 Impact Factor
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ABSTRACT: This work evaluated the xylitol production from sugarcane bagasse hemicellulosic hydrolysate in a bubble column bioreactor using cells of the yeast Candida guilliermondii immobilized in calcium-alginate. The fermentation runs were performed according to a 22 full factorial design with three replicates at the center point in order to determine the effect of the variables: aeration rate (0.66–1.33 vvm) and immobilized system concentration (20–40% v/v), on the efficiency of xylose-to-xylitol conversion and on the xylitol volumetric productivity. The results indicated a significant influence of both variables on xylitol production. The highest conversion efficiency (41%) was attained using 1.33 vvm aeration rate and 40% immobilized system. Under these conditions, the volumetric productivity was 0.21 g l−1 h−1.
Process Biochemistry.
