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Effects of extrusion pretreatment parameters on sweet sorghum bagasse enzymatic hydrolysis and its subsequent conversion into bioethanol.

Heredia-Olea E, Pérez-Carrillo E, Montoya-Chiw M, Serna-Saldívar SO - Biomed Res Int (2015)

Bottom Line: This nonchemical and continuous pretreatment did not generate inhibitory compounds.The best conditions were 20% solids loading and 72 h of enzymatic treatment.These particular conditions converted 70% of the total fibrous carbohydrates into total fermentable C5 and C6 sugars.

View Article: PubMed Central - PubMed

Affiliation: Centro de Biotecnología FEMSA, Escuela de Ingeniería y Ciencias, Tecnológico de Monterrey, Avenida Eugenio Garza Sada 2501 Sur, 64849 Monterrey, NL, Mexico.

ABSTRACT
Second-generation bioethanol production from sweet sorghum bagasse first extruded at different conditions and then treated with cell wall degrading enzymes and fermented with I. orientalis was determined. The twin extruder parameters tested were barrel temperature, screws speed, and feedstock moisture content using surface response methodology. The best extrusion conditions were 100°C, 200 rpm, and 30% conditioning moisture content. This nonchemical and continuous pretreatment did not generate inhibitory compounds. The extruded feedstocks were saccharified varying the biocatalysis time and solids loading. The best conditions were 20% solids loading and 72 h of enzymatic treatment. These particular conditions converted 70% of the total fibrous carbohydrates into total fermentable C5 and C6 sugars. The extruded enzymatically hydrolyzed sweet sorghum bagasse was fermented with the strain I. orientalis at 12% solids obtaining a yield of 198.1 mL of ethanol per kilogram of bagasse (dw).

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Related in: MedlinePlus

Response surfaces for total sugars ((a1), (a2), and (a3)), C6 ((b1), (b2), and (b3)), and C5 ((c1), (c2), and (c3)) generated from sweet sorghum bagasse extruded at different temperatures (50, 75, or 100°C), screws speeds (100, 150, or 200 rpm), and moistures inside the barrel (30, 40, or 50%) hydrolyzed with fiber degrading enzymes expressed in sugars milligrams per gram of bagasse (dw).
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Related In: Results  -  Collection


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fig1: Response surfaces for total sugars ((a1), (a2), and (a3)), C6 ((b1), (b2), and (b3)), and C5 ((c1), (c2), and (c3)) generated from sweet sorghum bagasse extruded at different temperatures (50, 75, or 100°C), screws speeds (100, 150, or 200 rpm), and moistures inside the barrel (30, 40, or 50%) hydrolyzed with fiber degrading enzymes expressed in sugars milligrams per gram of bagasse (dw).

Mentions: A high linear correlation coefficient of 93.1 was obtained for the total sugars with respect to temperature, screws speed, and moisture (Figures 1(a1), 1(a2), and 1(a3)). The moisture content and the interaction between temperature and moisture were the most significant extrusion parameters with a P value = 0.000 followed by the screws speed with a P value = 0.013. As expected, the amounts of total free sugars as well as the C5 and C6 sugars concentrations were strongly affected by the extrusion parameters. Higher sugar yields were obtained at low tempering moisture, high screws speeds, and high temperature (Figure 1(a1)). The crystalline cellulose structure represents a strong barrier for the active sites of enzymes [5]. In this nonchemical pretreatment, the extruder shear stress was the mean way of action to enhance the decrystallization of cellulose and its porosity and susceptibility to fibrous degrading enzymes. The tempering moisture of the feedstock was the main factor affecting disruption of fiber components because it directly affected the shear stress rate [3]. When the tempering moisture was increased, the SSB ran more easily through the extruder. Thus, with higher moistures the shear stress was reduced decreasing the susceptibility of the extruded feedstock for the subsequent enzymatic hydrolysis step. The extruder temperature and the screws speeds also affected the yield of individual sugars specially those belonging to the C5 group (Sections 3.2.2 and 3.2.3). It was observed that at high extruder temperatures a lower feedstock viscosity inside the barrel was obtained [3], and this effect improved when the speed of the screws was increased. Karunanithy et al. [18] extruded different varieties of switchgrass, big bluestem, and prairie corn finding a better glucose recovery after enzyme treatment when extruding the feedstocks at 200 rpm in a single screw extruder. In this research, the optimum extruding conditions were 30°C, 200 rpm screws speed, and 30% feedstock moisture content. With these conditions it was possible to release the maximum amounts of sugar after the subsequent enzyme treatment. Approximately 70.4% of the sugars were released from the fiber matrix. Thus, the extruded feedstock processed under the conditions mentioned above was further converted into fermentable sugars and ethanol. The utilization of higher screws speeds (400 or 500 rpm) decreased sugar recovery to only 52.2 and 58.6%, respectively. According to Karunanithy and Muthukumarappan [6], the heat produced from the higher screws speeds affected negatively the viscosity of the feedstock inside the barrel and in some instances caused the blocking of the extruder. The same author [3] obtained an overall yield of 44.5% sugars associated to cell walls of switchgrass without the generation of inhibitory compounds when operating a single screw extruder at 50 rpm, 150°C, and 15% moisture content. Karunanithy et al. [18] employed 4 heaters to maintain the barrel temperature and increase the efficiency of transformation of lignocellulose materials. In this investigation, only one heat exchanger was used to maintain the barrel at high temperature. Only the last section of the extruder was heated because the screw configuration was designed to cause friction and intrinsic heat to properly treat the SSB. Regarding the extruder specific mechanical energy (SME) Lamsal et al. [5] obtained good sugar recoveries in a range of 222 up to 639 Wh·kg−1. The SME at 100, 150, and 200 rpm were 266.8, 276.0, and 314.8 Wh·kg−1 when extruding 30% tempered SSB, respectively. The results indicated that the thermoplastic extrusion was an adequate continuous pretreatment for second-generation bioethanol production without the generation of hazardous compounds that decrease the efficiency of fermentation of hydrolyzed lignocellulosic feedstocks.


Effects of extrusion pretreatment parameters on sweet sorghum bagasse enzymatic hydrolysis and its subsequent conversion into bioethanol.

Heredia-Olea E, Pérez-Carrillo E, Montoya-Chiw M, Serna-Saldívar SO - Biomed Res Int (2015)

Response surfaces for total sugars ((a1), (a2), and (a3)), C6 ((b1), (b2), and (b3)), and C5 ((c1), (c2), and (c3)) generated from sweet sorghum bagasse extruded at different temperatures (50, 75, or 100°C), screws speeds (100, 150, or 200 rpm), and moistures inside the barrel (30, 40, or 50%) hydrolyzed with fiber degrading enzymes expressed in sugars milligrams per gram of bagasse (dw).
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4383157&req=5

fig1: Response surfaces for total sugars ((a1), (a2), and (a3)), C6 ((b1), (b2), and (b3)), and C5 ((c1), (c2), and (c3)) generated from sweet sorghum bagasse extruded at different temperatures (50, 75, or 100°C), screws speeds (100, 150, or 200 rpm), and moistures inside the barrel (30, 40, or 50%) hydrolyzed with fiber degrading enzymes expressed in sugars milligrams per gram of bagasse (dw).
Mentions: A high linear correlation coefficient of 93.1 was obtained for the total sugars with respect to temperature, screws speed, and moisture (Figures 1(a1), 1(a2), and 1(a3)). The moisture content and the interaction between temperature and moisture were the most significant extrusion parameters with a P value = 0.000 followed by the screws speed with a P value = 0.013. As expected, the amounts of total free sugars as well as the C5 and C6 sugars concentrations were strongly affected by the extrusion parameters. Higher sugar yields were obtained at low tempering moisture, high screws speeds, and high temperature (Figure 1(a1)). The crystalline cellulose structure represents a strong barrier for the active sites of enzymes [5]. In this nonchemical pretreatment, the extruder shear stress was the mean way of action to enhance the decrystallization of cellulose and its porosity and susceptibility to fibrous degrading enzymes. The tempering moisture of the feedstock was the main factor affecting disruption of fiber components because it directly affected the shear stress rate [3]. When the tempering moisture was increased, the SSB ran more easily through the extruder. Thus, with higher moistures the shear stress was reduced decreasing the susceptibility of the extruded feedstock for the subsequent enzymatic hydrolysis step. The extruder temperature and the screws speeds also affected the yield of individual sugars specially those belonging to the C5 group (Sections 3.2.2 and 3.2.3). It was observed that at high extruder temperatures a lower feedstock viscosity inside the barrel was obtained [3], and this effect improved when the speed of the screws was increased. Karunanithy et al. [18] extruded different varieties of switchgrass, big bluestem, and prairie corn finding a better glucose recovery after enzyme treatment when extruding the feedstocks at 200 rpm in a single screw extruder. In this research, the optimum extruding conditions were 30°C, 200 rpm screws speed, and 30% feedstock moisture content. With these conditions it was possible to release the maximum amounts of sugar after the subsequent enzyme treatment. Approximately 70.4% of the sugars were released from the fiber matrix. Thus, the extruded feedstock processed under the conditions mentioned above was further converted into fermentable sugars and ethanol. The utilization of higher screws speeds (400 or 500 rpm) decreased sugar recovery to only 52.2 and 58.6%, respectively. According to Karunanithy and Muthukumarappan [6], the heat produced from the higher screws speeds affected negatively the viscosity of the feedstock inside the barrel and in some instances caused the blocking of the extruder. The same author [3] obtained an overall yield of 44.5% sugars associated to cell walls of switchgrass without the generation of inhibitory compounds when operating a single screw extruder at 50 rpm, 150°C, and 15% moisture content. Karunanithy et al. [18] employed 4 heaters to maintain the barrel temperature and increase the efficiency of transformation of lignocellulose materials. In this investigation, only one heat exchanger was used to maintain the barrel at high temperature. Only the last section of the extruder was heated because the screw configuration was designed to cause friction and intrinsic heat to properly treat the SSB. Regarding the extruder specific mechanical energy (SME) Lamsal et al. [5] obtained good sugar recoveries in a range of 222 up to 639 Wh·kg−1. The SME at 100, 150, and 200 rpm were 266.8, 276.0, and 314.8 Wh·kg−1 when extruding 30% tempered SSB, respectively. The results indicated that the thermoplastic extrusion was an adequate continuous pretreatment for second-generation bioethanol production without the generation of hazardous compounds that decrease the efficiency of fermentation of hydrolyzed lignocellulosic feedstocks.

Bottom Line: This nonchemical and continuous pretreatment did not generate inhibitory compounds.The best conditions were 20% solids loading and 72 h of enzymatic treatment.These particular conditions converted 70% of the total fibrous carbohydrates into total fermentable C5 and C6 sugars.

View Article: PubMed Central - PubMed

Affiliation: Centro de Biotecnología FEMSA, Escuela de Ingeniería y Ciencias, Tecnológico de Monterrey, Avenida Eugenio Garza Sada 2501 Sur, 64849 Monterrey, NL, Mexico.

ABSTRACT
Second-generation bioethanol production from sweet sorghum bagasse first extruded at different conditions and then treated with cell wall degrading enzymes and fermented with I. orientalis was determined. The twin extruder parameters tested were barrel temperature, screws speed, and feedstock moisture content using surface response methodology. The best extrusion conditions were 100°C, 200 rpm, and 30% conditioning moisture content. This nonchemical and continuous pretreatment did not generate inhibitory compounds. The extruded feedstocks were saccharified varying the biocatalysis time and solids loading. The best conditions were 20% solids loading and 72 h of enzymatic treatment. These particular conditions converted 70% of the total fibrous carbohydrates into total fermentable C5 and C6 sugars. The extruded enzymatically hydrolyzed sweet sorghum bagasse was fermented with the strain I. orientalis at 12% solids obtaining a yield of 198.1 mL of ethanol per kilogram of bagasse (dw).

Show MeSH
Related in: MedlinePlus