Diego Santos - Profile on Academia.edu (original) (raw)

Papers by Diego Santos

Cell immobilization and xylitol production using sugarcane bagasse as raw material

Applied Biochemistry and Biotechnology, 2007

Sugarcane bagasse pretreated by three different procedures (with 2% [v/v] polyethyleneimine (PEI)... more 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 byCandida 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.

Journal of Food Engineering, 2008

This study provides a preliminary contribution to the development of a bioprocess for 2 the conti... more This study provides a preliminary contribution to the development of a bioprocess for 2 the continuous production of xylitol from hemicellulosic hydrolyzate utilizing Candida 3 guilliermondii cells immobilized onto natural sugarcane bagasse fibers. To this purpose, cells 4 of this yeast were submitted to batch tests of "in situ" adsorption onto crushed and powdered 5 sugarcane bagasse after treatment with 0.5 M NaOH. The results obtained on a xylose-based 6 semi-synthetic medium were evaluated in terms of immobilization efficiency, cell retention 7 and specific growth rates of suspended, immobilized and total cells. The first two parameters 8 were shown to increase along the immobilization process, reached maximum values of 50.5% 9 and 0.31 g immobilized cells/g bagasse after 21 h and then sharply decreased. The specific 10 growth rate of suspended cells continuously increased during the immobilization tests, while 11 that of the immobilized ones, after an initial growth, exhibited decreasing values. Under the 12 conditions selected for cell immobilization, fermentation also took place with promising 13 results. The yields of xylitol and biomass on consumed xylose were 0.65 and 0.18 g/g, 14 respectively, xylitol and biomass productivities 0.66 and 0.13 g L -1 h -1 , and the efficiency of 15 xylose-to-xylitol bioconversion was 70.8 %. 16 17

Biotechnology Journal, 2007

Cells of Candida guilliermondii entrapped in Ca-alginate beads were used for xylitol production, ... more Cells of Candida guilliermondii entrapped in Ca-alginate beads were used for xylitol production, from concentrated hemicellulose hydrolyzate of sugarcane bagasse, in a fluidized bed bioreactor (FBR). The maximum xylitol concentration 28.9 g xylitol/L was obtained at a high aeration rate of 600 mL/min after 70 h of fermentation, indicating that the use of high aeration rate in this system is favored for better oxygen transfer into the immobilized cells. The specific xylitol productivity and the xylitol yield were of 0.4 g xylitol/L.h and 0.58 g xylitol/g xylose respectively. The immobilization efficiency at the end of the fermentation was of 65 %. After 90 h of fermentation xylitol productivity and yield decreased to 0.25 g xylitol/L.h and 0.47 g xylitol/g xylose respectively, indicating the beginning of xylitol consumption by the yeast. The use of FBR system with immobilized cells presented high xylitol yield and productivity.

Cell immobilization and xylitol production using sugarcane bagasse as raw material

Applied Biochemistry and Biotechnology, 2007

Sugarcane bagasse pretreated by three different procedures (with 2% [v/v] polyethyleneimine (PEI)... more 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 byCandida 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.

Journal of Food Engineering, 2008

This study provides a preliminary contribution to the development of a bioprocess for 2 the conti... more This study provides a preliminary contribution to the development of a bioprocess for 2 the continuous production of xylitol from hemicellulosic hydrolyzate utilizing Candida 3 guilliermondii cells immobilized onto natural sugarcane bagasse fibers. To this purpose, cells 4 of this yeast were submitted to batch tests of "in situ" adsorption onto crushed and powdered 5 sugarcane bagasse after treatment with 0.5 M NaOH. The results obtained on a xylose-based 6 semi-synthetic medium were evaluated in terms of immobilization efficiency, cell retention 7 and specific growth rates of suspended, immobilized and total cells. The first two parameters 8 were shown to increase along the immobilization process, reached maximum values of 50.5% 9 and 0.31 g immobilized cells/g bagasse after 21 h and then sharply decreased. The specific 10 growth rate of suspended cells continuously increased during the immobilization tests, while 11 that of the immobilized ones, after an initial growth, exhibited decreasing values. Under the 12 conditions selected for cell immobilization, fermentation also took place with promising 13 results. The yields of xylitol and biomass on consumed xylose were 0.65 and 0.18 g/g, 14 respectively, xylitol and biomass productivities 0.66 and 0.13 g L -1 h -1 , and the efficiency of 15 xylose-to-xylitol bioconversion was 70.8 %. 16 17

Biotechnology Journal, 2007

Cells of Candida guilliermondii entrapped in Ca-alginate beads were used for xylitol production, ... more Cells of Candida guilliermondii entrapped in Ca-alginate beads were used for xylitol production, from concentrated hemicellulose hydrolyzate of sugarcane bagasse, in a fluidized bed bioreactor (FBR). The maximum xylitol concentration 28.9 g xylitol/L was obtained at a high aeration rate of 600 mL/min after 70 h of fermentation, indicating that the use of high aeration rate in this system is favored for better oxygen transfer into the immobilized cells. The specific xylitol productivity and the xylitol yield were of 0.4 g xylitol/L.h and 0.58 g xylitol/g xylose respectively. The immobilization efficiency at the end of the fermentation was of 65 %. After 90 h of fermentation xylitol productivity and yield decreased to 0.25 g xylitol/L.h and 0.47 g xylitol/g xylose respectively, indicating the beginning of xylitol consumption by the yeast. The use of FBR system with immobilized cells presented high xylitol yield and productivity.

Journal of Chemical Technology and Biotechnology, 2009

BACKGROUND: Green chemistry, also known as sustainable chemistry, refers to environmentally frien... more BACKGROUND: Green chemistry, also known as sustainable chemistry, refers to environmentally friendly chemicals and processes that result in reduced waste, elimination of costly end-of-the-pipe treatments; safer products, and reduced use of energy and resources. In this context this study aims to evaluate a novel green sensitizer support for photochemistry use. For this propose, Rose Bengal (RB) and juglone production were chosen as a model sensitizer and a model photoreaction, respectively.RESULTS: The results showed that the RB-alginate beads prepared using a solution of 20% CaCl2 had better stability in the solvent t-amyl alcohol. Comparing all the immobilized systems a larger reaction yield (57.5%) was obtained when the proportion of the beads in the photoreactor flask was 5% (v/v). Although when using suspended RB the reaction yield was better (62%) the environmental friendly attributes and economical advantages of immobilized systems overcome it.CONCLUSIONS: The potentiality of this new kind of sensitizer immobilization was demonstrated and a mechanism based on immobilization of cells was proposed. Furthermore the use of this novel green support presents a greater efficiency and potentially lower costs than the commercial supported RB Sensitox. Copyright © 2009 Society of Chemical Industry

Water Science and Technology, 2009

This study provides a preliminary contribution to the development of an industrial process for 2 ... more This study provides a preliminary contribution to the development of an industrial process for 2 the UV/TiO2 water treatment by introducing a novel support for TiO2 immobilization. For the 3 following study, Methylene Blue (MB) was chosen as the model dye to evaluate this novel 4 immobilization system. The results showed that TiO2 immobilized in a Ca-alginate bead 5 retained its photoactivity during all of the experiments and the TiO2-gel beads presented good 6 stability in water for maintaining its shape after several uses. When a proportion of 10% (v/v) 7 of these beads was used, the configuration system demonstrated an improved mass transfer 8 and consequently enhanced degradation efficiency. Experiments were also performed using 9 'recycled' beads., The results showed an increase in the degradation efficiency when the 10 beads were reused, with an eventual 'self-destructive' effect. These studies showed great 11 promise regarding the recyclable reagents with a reduction in waste at no greater cost or 12 reduction in efficiency. Therefore, the potential of TiO2-gel beads as a simple and 13 environmentally friendly catalyst for continuous use was developed. 14

Cell immobilization and xylitol production using sugarcane bagasse as raw material

Applied Biochemistry and Biotechnology, 2007

Sugarcane bagasse pretreated by three different procedures (with 2% [v/v] polyethyleneimine (PEI)... more 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 byCandida 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.

Journal of Food Engineering, 2008

This study provides a preliminary contribution to the development of a bioprocess for 2 the conti... more This study provides a preliminary contribution to the development of a bioprocess for 2 the continuous production of xylitol from hemicellulosic hydrolyzate utilizing Candida 3 guilliermondii cells immobilized onto natural sugarcane bagasse fibers. To this purpose, cells 4 of this yeast were submitted to batch tests of "in situ" adsorption onto crushed and powdered 5 sugarcane bagasse after treatment with 0.5 M NaOH. The results obtained on a xylose-based 6 semi-synthetic medium were evaluated in terms of immobilization efficiency, cell retention 7 and specific growth rates of suspended, immobilized and total cells. The first two parameters 8 were shown to increase along the immobilization process, reached maximum values of 50.5% 9 and 0.31 g immobilized cells/g bagasse after 21 h and then sharply decreased. The specific 10 growth rate of suspended cells continuously increased during the immobilization tests, while 11 that of the immobilized ones, after an initial growth, exhibited decreasing values. Under the 12 conditions selected for cell immobilization, fermentation also took place with promising 13 results. The yields of xylitol and biomass on consumed xylose were 0.65 and 0.18 g/g, 14 respectively, xylitol and biomass productivities 0.66 and 0.13 g L -1 h -1 , and the efficiency of 15 xylose-to-xylitol bioconversion was 70.8 %. 16 17

Biotechnology Journal, 2007

Cells of Candida guilliermondii entrapped in Ca-alginate beads were used for xylitol production, ... more Cells of Candida guilliermondii entrapped in Ca-alginate beads were used for xylitol production, from concentrated hemicellulose hydrolyzate of sugarcane bagasse, in a fluidized bed bioreactor (FBR). The maximum xylitol concentration 28.9 g xylitol/L was obtained at a high aeration rate of 600 mL/min after 70 h of fermentation, indicating that the use of high aeration rate in this system is favored for better oxygen transfer into the immobilized cells. The specific xylitol productivity and the xylitol yield were of 0.4 g xylitol/L.h and 0.58 g xylitol/g xylose respectively. The immobilization efficiency at the end of the fermentation was of 65 %. After 90 h of fermentation xylitol productivity and yield decreased to 0.25 g xylitol/L.h and 0.47 g xylitol/g xylose respectively, indicating the beginning of xylitol consumption by the yeast. The use of FBR system with immobilized cells presented high xylitol yield and productivity.

Cell immobilization and xylitol production using sugarcane bagasse as raw material

Applied Biochemistry and Biotechnology, 2007

Sugarcane bagasse pretreated by three different procedures (with 2% [v/v] polyethyleneimine (PEI)... more 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 byCandida 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.

Journal of Food Engineering, 2008

This study provides a preliminary contribution to the development of a bioprocess for 2 the conti... more This study provides a preliminary contribution to the development of a bioprocess for 2 the continuous production of xylitol from hemicellulosic hydrolyzate utilizing Candida 3 guilliermondii cells immobilized onto natural sugarcane bagasse fibers. To this purpose, cells 4 of this yeast were submitted to batch tests of "in situ" adsorption onto crushed and powdered 5 sugarcane bagasse after treatment with 0.5 M NaOH. The results obtained on a xylose-based 6 semi-synthetic medium were evaluated in terms of immobilization efficiency, cell retention 7 and specific growth rates of suspended, immobilized and total cells. The first two parameters 8 were shown to increase along the immobilization process, reached maximum values of 50.5% 9 and 0.31 g immobilized cells/g bagasse after 21 h and then sharply decreased. The specific 10 growth rate of suspended cells continuously increased during the immobilization tests, while 11 that of the immobilized ones, after an initial growth, exhibited decreasing values. Under the 12 conditions selected for cell immobilization, fermentation also took place with promising 13 results. The yields of xylitol and biomass on consumed xylose were 0.65 and 0.18 g/g, 14 respectively, xylitol and biomass productivities 0.66 and 0.13 g L -1 h -1 , and the efficiency of 15 xylose-to-xylitol bioconversion was 70.8 %. 16 17

Biotechnology Journal, 2007

Cells of Candida guilliermondii entrapped in Ca-alginate beads were used for xylitol production, ... more Cells of Candida guilliermondii entrapped in Ca-alginate beads were used for xylitol production, from concentrated hemicellulose hydrolyzate of sugarcane bagasse, in a fluidized bed bioreactor (FBR). The maximum xylitol concentration 28.9 g xylitol/L was obtained at a high aeration rate of 600 mL/min after 70 h of fermentation, indicating that the use of high aeration rate in this system is favored for better oxygen transfer into the immobilized cells. The specific xylitol productivity and the xylitol yield were of 0.4 g xylitol/L.h and 0.58 g xylitol/g xylose respectively. The immobilization efficiency at the end of the fermentation was of 65 %. After 90 h of fermentation xylitol productivity and yield decreased to 0.25 g xylitol/L.h and 0.47 g xylitol/g xylose respectively, indicating the beginning of xylitol consumption by the yeast. The use of FBR system with immobilized cells presented high xylitol yield and productivity.

Journal of Chemical Technology and Biotechnology, 2009

BACKGROUND: Green chemistry, also known as sustainable chemistry, refers to environmentally frien... more BACKGROUND: Green chemistry, also known as sustainable chemistry, refers to environmentally friendly chemicals and processes that result in reduced waste, elimination of costly end-of-the-pipe treatments; safer products, and reduced use of energy and resources. In this context this study aims to evaluate a novel green sensitizer support for photochemistry use. For this propose, Rose Bengal (RB) and juglone production were chosen as a model sensitizer and a model photoreaction, respectively.RESULTS: The results showed that the RB-alginate beads prepared using a solution of 20% CaCl2 had better stability in the solvent t-amyl alcohol. Comparing all the immobilized systems a larger reaction yield (57.5%) was obtained when the proportion of the beads in the photoreactor flask was 5% (v/v). Although when using suspended RB the reaction yield was better (62%) the environmental friendly attributes and economical advantages of immobilized systems overcome it.CONCLUSIONS: The potentiality of this new kind of sensitizer immobilization was demonstrated and a mechanism based on immobilization of cells was proposed. Furthermore the use of this novel green support presents a greater efficiency and potentially lower costs than the commercial supported RB Sensitox. Copyright © 2009 Society of Chemical Industry

Water Science and Technology, 2009

This study provides a preliminary contribution to the development of an industrial process for 2 ... more This study provides a preliminary contribution to the development of an industrial process for 2 the UV/TiO2 water treatment by introducing a novel support for TiO2 immobilization. For the 3 following study, Methylene Blue (MB) was chosen as the model dye to evaluate this novel 4 immobilization system. The results showed that TiO2 immobilized in a Ca-alginate bead 5 retained its photoactivity during all of the experiments and the TiO2-gel beads presented good 6 stability in water for maintaining its shape after several uses. When a proportion of 10% (v/v) 7 of these beads was used, the configuration system demonstrated an improved mass transfer 8 and consequently enhanced degradation efficiency. Experiments were also performed using 9 'recycled' beads., The results showed an increase in the degradation efficiency when the 10 beads were reused, with an eventual 'self-destructive' effect. These studies showed great 11 promise regarding the recyclable reagents with a reduction in waste at no greater cost or 12 reduction in efficiency. Therefore, the potential of TiO2-gel beads as a simple and 13 environmentally friendly catalyst for continuous use was developed. 14