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Wyman CE, Balan V, Dale BE, Elander RT, Falls M, Hames B, Holtzapple MT, Ladisch MR, Lee YY, Mosier N, Pallapolu VR, Shi J, Thomas SR, Warner RE. WITHDRAWN: Comparative Data on Effects of Leading Pretreatments and Enzyme Loadings and Formulations on Sugar Yields from Different Switchgrass Sources. BIORESOURCE TECHNOLOGY 2011:S0960-8524(11)00524-4. [PMID: 21664813 DOI: 10.1016/j.biortech.2011.04.030] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Revised: 04/08/2011] [Accepted: 04/09/2011] [Indexed: 05/30/2023]
Abstract
This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.
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Gao D, Chundawat SP, Uppugundla N, Balan V, Dale BE. Binding characteristics of Trichoderma reesei cellulases on untreated, ammonia fiber expansion (AFEX), and dilute-acid pretreated lignocellulosic biomass. Biotechnol Bioeng 2011; 108:1788-800. [DOI: 10.1002/bit.23140] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2010] [Revised: 03/01/2011] [Accepted: 03/07/2011] [Indexed: 11/10/2022]
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Humpula JF, Chundawat SPS, Vismeh R, Jones AD, Balan V, Dale BE. Rapid quantification of major reaction products formed during thermochemical pretreatment of lignocellulosic biomass using GC-MS. J Chromatogr B Analyt Technol Biomed Life Sci 2011; 879:1018-22. [PMID: 21444255 DOI: 10.1016/j.jchromb.2011.02.049] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2010] [Revised: 01/07/2011] [Accepted: 02/28/2011] [Indexed: 11/16/2022]
Abstract
Accurate quantification of reaction products formed during thermochemical pretreatment of lignocellulosic biomass would lead to a better understanding of plant cell wall deconstruction for production of cellulosic biofuels and biochemicals. However, quantification of some process byproducts, most notably acetamide, acetic acid and furfural, present several analytical challenges using conventional liquid chromatography methods. Therefore, we have developed a high-throughput gas chromatography based mass spectrometric (GC-MS) method in order to quantify relevant compounds without requiring time-consuming sample derivatization prior to analysis. Solvent extracts of untreated, ammonia fiber expansion (AFEX) treated and dilute-acid treated corn stover were analyzed by this method. Biomass samples were extracted with acetone using an automated solvent extractor, serially diluted and directly analyzed using the proposed GC-MS method. Acetone was the only solvent amongst water, methanol and acetonitrile that did not contain detectable background levels of the target compounds or facilitate a buildup of plant-derived residues in the GC injector, which decreased analytical reproducibility. Quantitative results were based on the method of standard addition and external standard calibration curves.
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Gao D, Uppugundla N, Chundawat SPS, Yu X, Hermanson S, Gowda K, Brumm P, Mead D, Balan V, Dale BE. Hemicellulases and auxiliary enzymes for improved conversion of lignocellulosic biomass to monosaccharides. BIOTECHNOLOGY FOR BIOFUELS 2011; 4:5. [PMID: 21342516 PMCID: PMC3056733 DOI: 10.1186/1754-6834-4-5] [Citation(s) in RCA: 113] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2010] [Accepted: 02/22/2011] [Indexed: 05/07/2023]
Abstract
BACKGROUND High enzyme loading is a major economic bottleneck for the commercial processing of pretreated lignocellulosic biomass to produce fermentable sugars. Optimizing the enzyme cocktail for specific types of pretreated biomass allows for a significant reduction in enzyme loading without sacrificing hydrolysis yield. This is especially important for alkaline pretreatments such as Ammonia fiber expansion (AFEX) pretreated corn stover. Hence, a diverse set of hemicellulases supplemented along with cellulases is necessary for high recovery of monosaccharides. RESULTS The core fungal cellulases in the optimal cocktail include cellobiohydrolase I [CBH I; glycoside hydrolase (GH) family 7A], cellobiohydrolase II (CBH II; GH family 6A), endoglucanase I (EG I; GH family 7B) and β-glucosidase (βG; GH family 3). Hemicellulases tested along with the core cellulases include xylanases (LX1, GH family 10; LX2, GH family 10; LX3, GH family 10; LX4, GH family 11; LX5, GH family 10; LX6, GH family 10), β-xylosidase (LβX; GH family 52), α-arabinofuranosidase (LArb, GH family 51) and α-glucuronidase (LαGl, GH family 67) that were cloned, expressed and/or purified from different bacterial sources. Different combinations of these enzymes were tested using a high-throughput microplate based 24 h hydrolysis assay. Both family 10 (LX3) and family 11 (LX4) xylanases were found to most efficiently hydrolyze AFEX pretreated corn stover in a synergistic manner. The optimal mass ratio of xylanases (LX3 and LX4) to cellulases (CBH I, CBH II and EG I) is 25:75. LβX (0.6 mg/g glucan) is crucial to obtaining monomeric xylose (54% xylose yield), while LArb (0.6 mg/g glucan) and LαGl (0.8 mg/g glucan) can both further increase xylose yield by an additional 20%. Compared with Accellerase 1000, a purified cocktail of cellulases supplemented with accessory hemicellulases will not only increase both glucose and xylose yields but will also decrease the total enzyme loading needed for equivalent yields. CONCLUSIONS A diverse set of accessory hemicellulases was found necessary to enhance the synergistic action of cellulases hydrolysing AFEX pretreated corn stover. High glucose (around 80%) and xylose (around 70%) yields were achieved with a moderate enzyme loading (~20 mg protein/g glucan) using an in-house developed cocktail compared to commercial enzymes.
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Jin M, Balan V, Gunawan C, Dale BE. Consolidated bioprocessing (CBP) performance of Clostridium phytofermentans on AFEX-treated corn stover for ethanol production. Biotechnol Bioeng 2011; 108:1290-7. [PMID: 21280028 DOI: 10.1002/bit.23059] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2010] [Revised: 12/26/2010] [Accepted: 01/03/2011] [Indexed: 11/12/2022]
Abstract
Consolidated bioprocessing (CBP) is believed to be a potentially cost-efficient and commercially viable way to produce cellulosic biofuels. In this study, we have evaluated the performance of the CBP organism Clostridium phytofermentans (ATCC 700394) on AFEX-treated corn stover (AFEX-CS). Fermentation conditions including temperature, inoculation size, nutrients, and initial pH were investigated. At optimal conditions with 0.5% (w/w) glucan loading of AFEX-CS, C. phytofermentans hydrolyzed 76% of glucan and 88.6% of xylan in 10 days. These values reached 87% and 102% of those obtained by simultaneous saccharification and co-fermentation (SSCF) using commercial enzymes and S. cerevisiae 424A. Ethanol titer for CBP was found to be 2.8 g/L which was 71.8% of that yielded by SSCF (3.9 g/L). Decomposition products from AFEX-CS helped to increase ethanol yield somewhat during CBP. Particle size played a crucial role in the enhancement of sugar conversion by CBP.
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81
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Bals B, Dale BE. Economic comparison of multiple techniques for recovering leaf protein in biomass processing. Biotechnol Bioeng 2010; 108:530-7. [DOI: 10.1002/bit.22973] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2010] [Revised: 09/20/2010] [Accepted: 09/28/2010] [Indexed: 11/12/2022]
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Dale BE, Bals BD, Kim S, Eranki P. Biofuels done right: land efficient animal feeds enable large environmental and energy benefits. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2010; 44:8385-8389. [PMID: 20958023 DOI: 10.1021/es1031618] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
There is an intense ongoing debate regarding the potential scale of biofuel production without creating adverse effects on food supply. We explore the possibility of three land-efficient technologies for producing food (actually animal feed), including leaf protein concentrates, pretreated forages, and double crops to increase the total amount of plant biomass available for biofuels. Using less than 30% of total U.S. cropland, pasture, and range, 400 billion liters of ethanol can be produced annually without decreasing domestic food production or agricultural exports. This approach also reduces U.S. greenhouse gas emissions by 670 Tg CO₂-equivalent per year, or over 10% of total U.S. annual emissions, while increasing soil fertility and promoting biodiversity. Thus we can replace a large fraction of U.S. petroleum consumption without indirect land use change.
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Dale BE, Bals BD, Kim S, Eranki P. Biofuels done right: land efficient animal feeds enable large environmental and energy benefits. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2010; 44:8385-8389. [PMID: 20958023 DOI: 10.1021/es101864b] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
There is an intense ongoing debate regarding the potential scale of biofuel production without creating adverse effects on food supply. We explore the possibility of three land-efficient technologies for producing food (actually animal feed), including leaf protein concentrates, pretreated forages, and double crops to increase the total amount of plant biomass available for biofuels. Using less than 30% of total U.S. cropland, pasture, and range, 400 billion liters of ethanol can be produced annually without decreasing domestic food production or agricultural exports. This approach also reduces U.S. greenhouse gas emissions by 670 Tg CO₂-equivalent per year, or over 10% of total U.S. annual emissions, while increasing soil fertility and promoting biodiversity. Thus we can replace a large fraction of U.S. petroleum consumption without indirect land use change.
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Chundawat SPS, Vismeh R, Sharma LN, Humpula JF, da Costa Sousa L, Chambliss CK, Jones AD, Balan V, Dale BE. Multifaceted characterization of cell wall decomposition products formed during ammonia fiber expansion (AFEX) and dilute acid based pretreatments. BIORESOURCE TECHNOLOGY 2010; 101:8429-38. [PMID: 20598525 DOI: 10.1016/j.biortech.2010.06.027] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2010] [Revised: 05/29/2010] [Accepted: 06/04/2010] [Indexed: 05/18/2023]
Abstract
Decomposition products formed/released during ammonia fiber expansion (AFEX) and dilute acid (DA) pretreatment of corn stover (CS) were quantified using robust mass spectrometry based analytical platforms. Ammonolytic cleavage of cell wall ester linkages during AFEX resulted in the formation of acetamide (25mg/g AFEX CS) and various phenolic amides (15mg/g AFEX CS) that are effective nutrients for downstream fermentation. After ammonolysis, Maillard reactions with carbonyl-containing intermediates represent the second largest sink for ammonia during AFEX. On the other hand, several carboxylic acids were formed (e.g. 35mg acetic acid/g DA CS) during DA pretreatment. Formation of furans was 36-fold lower for AFEX compared to DA treatment; while carboxylic acids (e.g. lactic and succinic acids) yield was 100-1000-fold lower during AFEX compared to previous reports using sodium hydroxide as pretreatment reagent.
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85
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Jin M, Lau MW, Balan V, Dale BE. Two-step SSCF to convert AFEX-treated switchgrass to ethanol using commercial enzymes and Saccharomyces cerevisiae 424A(LNH-ST). BIORESOURCE TECHNOLOGY 2010; 101:8171-8. [PMID: 20580549 DOI: 10.1016/j.biortech.2010.06.026] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2010] [Revised: 05/25/2010] [Accepted: 06/04/2010] [Indexed: 05/05/2023]
Abstract
It is well known that simultaneous saccharification and co-fermentation (SSCF) reduces cellulosic ethanol production cost compared to separate hydrolysis and fermentation (SHF). However, the traditional SSCF process of converting Ammonia Fiber Expansion (AFEX) pretreated switchgrass to ethanol using both commercial enzymes and Saccharomyces cerevisiae 424A(LNH-ST) gave reduced ethanol yield due to lower xylose consumption. To overcome this problem we have developed a two-step SSCF process, in which xylan was hydrolyzed and fermented first followed by the hydrolysis and fermentation of glucan. Important parameters, such as temperature, cellulases loading during xylan hydrolysis and fermentation, initial OD(600) for inoculation of S. cerevisiae 424A(LNH-ST), and pH, were studied for best performance. Compared with traditional SSCF, the two-step SSCF showed higher xylose consumption and higher ethanol yield. The sugar conversion was also enhanced from 70% by enzymatic hydrolysis to 82% by two-step SSCF. One important finding is that the residue from enzymatic hydrolysis plays a significant role in reducing xylose consumption and ethanol metabolic yield during SSCF.
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Lau MW, Dale BE. Effect of primary degradation-reaction products from Ammonia Fiber Expansion (AFEX)-treated corn stover on the growth and fermentation of Escherichia coli KO11. BIORESOURCE TECHNOLOGY 2010; 101:7849-55. [PMID: 20627718 DOI: 10.1016/j.biortech.2010.04.076] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2010] [Revised: 04/09/2010] [Accepted: 04/22/2010] [Indexed: 05/05/2023]
Abstract
The primary degradation-reaction products (DRP) identified in Ammonia Fiber Expansion (AFEX)-pretreated corn stover are acetate, lactate, 4-hydroxybenzaldehyde (4HBD) and acetamide. The effects of these products at a broad concentration range were tested on Escherichia coli KO11, a strain engineered for cellulosic ethanol production. Fermentations using glucose or xylose as the sole carbohydrate source and a sugar mixture of glucose and xylose were conducted to determine how these products and sugar selection affected fermentation performance. Co-fermentation of the sugar mixture exhibited the lowest overall ethanol productivity compared to single-sugar fermentations and was more susceptible to inhibition. Metabolic ethanol yield increased with the increasing initial concentration of acetate. Although these degradation-reaction products (with exception of acetamide) are generally perceived to be inhibitory, organic acids and 4-hydroxybenzaldehyde at low levels stimulated fermentation. Adaptation of cells to these products prior to fermentation increased overall fermentation rate.
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Xia J, Jones AD, Lau MW, Yuan YJ, Dale BE, Balan V. Comparative lipidomic profiling of xylose-metabolizing S. cerevisiae and its parental strain in different media reveals correlations between membrane lipids and fermentation capacity. Biotechnol Bioeng 2010; 108:12-21. [DOI: 10.1002/bit.22910] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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88
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Datta S, Bals BD, Lin YJ, Negri MC, Datta R, Pasieta L, Ahmad SF, Moradia AA, Dale BE, Snyder SW. An attempt towards simultaneous biobased solvent based extraction of proteins and enzymatic saccharification of cellulosic materials from distiller's grains and solubles. BIORESOURCE TECHNOLOGY 2010; 101:5444-5448. [PMID: 20206501 DOI: 10.1016/j.biortech.2010.02.039] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2009] [Revised: 01/22/2010] [Accepted: 02/08/2010] [Indexed: 05/28/2023]
Abstract
Distiller's grains and solubles (DGS) is the major co-product of corn dry mill ethanol production, and is composed of 30% protein and 30-40% polysaccharides. We report a strategy for simultaneous extraction of protein with food-grade biobased solvents (ethyl lactate, d-limonene, and distilled methyl esters) and enzymatic saccharification of glucan in DGS. This approach would produce a high-value animal feed while simultaneously producing additional sugars for ethanol production. Preliminary experiments on protein extraction resulted in recovery of 15-45% of the protein, with hydrophobic biobased solvents obtaining the best results. The integrated hydrolysis and extraction experiments showed that biobased solvent addition did not inhibit hydrolysis of the cellulose. However, only 25-33% of the total protein was extracted from DGS, and the extracted protein largely resided in the aqueous phase, not the solvent phase. We hypothesize that the hydrophobic solvent could not access the proteins surrounded by the aqueous phase inside the fibrous structure of DGS due to poor mass transfer. Further process improvements are needed to overcome this obstacle.
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Kim Y, Hendrickson R, Mosier NS, Ladisch MR, Bals B, Balan V, Dale BE, Dien BS, Cotta MA. Effect of compositional variability of distillers' grains on cellulosic ethanol production. BIORESOURCE TECHNOLOGY 2010; 101:5385-5393. [PMID: 20223655 DOI: 10.1016/j.biortech.2010.02.054] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2009] [Revised: 02/11/2010] [Accepted: 02/11/2010] [Indexed: 05/28/2023]
Abstract
In a dry grind ethanol plant, approximately 0.84kg of dried distillers' grains with solubles (DDGS) is produced per liter of ethanol. The distillers' grains contain the unhydrolyzed and unprocessed cellulosic fraction of corn kernels, which could be further converted to ethanol or other valuable bioproducts by applying cellulose conversion technology. Its compositional variability is one of the factors that could affect the overall process design and economics. In this study, we present compositional variability of distillers' grains collected from four different dry grind ethanol plants and its effect on enzymatic digestibility and fermentability. We then selected two sources of distillers grains based on their distinctive compositional difference. These were pretreated by either controlled pH liquid hot water (LHW) or ammonia fiber expansion (AFEX) and subjected to enzymatic hydrolysis and fermentation. Fermentation of the pretreated distillers' grains using either industrial yeast or genetically engineered glucose and xylose co-fermenting yeast, yielded 70-80% of theoretical maximum ethanol concentration, which varied depending on the batch of distillers' grains used. Results show that cellulose conversion and ethanol fermentation yields are affected by the compositions of distillers' grains. Distillers' grains with a high extractives content exhibit a lower enzymatic digestibility but a higher fermentability.
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Plaehn WA, Zhao X, Dale BE, Voice TC. Impact of Dissolved Organic Matter on the Desorption and Mineralization Rates of Naphthalene. ACTA ACUST UNITED AC 2010. [DOI: 10.1080/10588339991339432] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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91
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Shao Q, Chundawat SPS, Krishnan C, Bals B, Sousa LDC, Thelen KD, Dale BE, Balan V. Enzymatic digestibility and ethanol fermentability of AFEX-treated starch-rich lignocellulosics such as corn silage and whole corn plant. BIOTECHNOLOGY FOR BIOFUELS 2010; 3:12. [PMID: 20534126 PMCID: PMC2898753 DOI: 10.1186/1754-6834-3-12] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2010] [Accepted: 06/09/2010] [Indexed: 05/14/2023]
Abstract
BACKGROUND Corn grain is an important renewable source for bioethanol production in the USA. Corn ethanol is currently produced by steam liquefaction of starch-rich grains followed by enzymatic saccharification and fermentation. Corn stover (the non-grain parts of the plant) is a potential feedstock to produce cellulosic ethanol in second-generation biorefineries. At present, corn grain is harvested by removing the grain from the living plant while leaving the stover behind on the field. Alternatively, whole corn plants can be harvested to cohydrolyze both starch and cellulose after a suitable thermochemical pretreatment to produce fermentable monomeric sugars. In this study, we used physiologically immature corn silage (CS) and matured whole corn plants (WCP) as feedstocks to produce ethanol using ammonia fiber expansion (AFEX) pretreatment followed by enzymatic hydrolysis (at low enzyme loadings) and cofermentation (for both glucose and xylose) using a cellulase-amylase-based cocktail and a recombinant Saccharomyces cerevisiae 424A (LNH-ST) strain, respectively. The effect on hydrolysis yields of AFEX pretreatment conditions and a starch/cellulose-degrading enzyme addition sequence for both substrates was also studied. RESULTS AFEX-pretreated starch-rich substrates (for example, corn grain, soluble starch) had a 1.5-3-fold higher enzymatic hydrolysis yield compared with the untreated substrates. Sequential addition of cellulases after hydrolysis of starch within WCP resulted in 15-20% higher hydrolysis yield compared with simultaneous addition of hydrolytic enzymes. AFEX-pretreated CS gave 70% glucan conversion after 72 h of hydrolysis for 6% glucan loading (at 8 mg total enzyme loading per gram glucan). Microbial inoculation of CS before ensilation yielded a 10-15% lower glucose hydrolysis yield for the pretreated substrate, due to loss in starch content. Ethanol fermentation of AFEX-treated (at 6% w/w glucan loading) CS hydrolyzate (resulting in 28 g/L ethanol at 93% metabolic yield) and WCP (resulting in 30 g/L ethanol at 89% metabolic yield) is reported in this work. CONCLUSIONS The current results indicate the feasibility of co-utilization of whole plants (that is, starchy grains plus cellulosic residues) using an ammonia-based (AFEX) pretreatment to increase bioethanol yield and reduce overall production cost.
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Krishnan C, Sousa LDC, Jin M, Chang L, Dale BE, Balan V. Alkali-based AFEX pretreatment for the conversion of sugarcane bagasse and cane leaf residues to ethanol. Biotechnol Bioeng 2010; 107:441-50. [DOI: 10.1002/bit.22824] [Citation(s) in RCA: 150] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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93
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Lau MW, Gunawan C, Balan V, Dale BE. Comparing the fermentation performance of Escherichia coli KO11, Saccharomyces cerevisiae 424A(LNH-ST) and Zymomonas mobilis AX101 for cellulosic ethanol production. BIOTECHNOLOGY FOR BIOFUELS 2010; 3:11. [PMID: 20507563 PMCID: PMC2898752 DOI: 10.1186/1754-6834-3-11] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2009] [Accepted: 05/27/2010] [Indexed: 05/04/2023]
Abstract
BACKGROUND Fermentations using Escherichia coli KO11, Saccharomyces cerevisiae 424A(LNH-ST), and Zymomonas mobilis AX101 are compared side-by-side on corn steep liquor (CSL) media and the water extract and enzymatic hydrolysate from ammonia fiber expansion (AFEX)-pretreated corn stover. RESULTS The three ethanologens are able produce ethanol from a CSL-supplemented co-fermentation at a metabolic yield, final concentration and rate greater than 0.42 g/g consumed sugars, 40 g/L and 0.7 g/L/h (0-48 h), respectively. Xylose-only fermentation of the tested ethanologenic bacteria are five to eight times faster than 424A(LNH-ST) in the CSL fermentation.All tested strains grow and co-ferment sugars at 15% w/v solids loading equivalent of ammonia fiber explosion (AFEX)-pretreated corn stover water extract. However, both KO11 and 424A(LNH-ST) exhibit higher growth robustness than AX101. In 18% w/w solids loading lignocellulosic hydrolysate from AFEX pretreatment, complete glucose fermentations can be achieved at a rate greater than 0.77 g/L/h. In contrast to results from fermentation in CSL, S. cerevisiae 424A(LNH-ST) consumed xylose at the greatest extent and rate in the hydrolysate compared to the bacteria tested. CONCLUSIONS Our results confirm that glucose fermentations among the tested strains are effective even at high solids loading (18% by weight). However, xylose consumption in the lignocellulosic hydrolysate is the major bottleneck affecting overall yield, titer or rate of the process. In comparison, Saccharomyces cerevisiae 424A(LNH-ST) is the most relevant strains for industrial production for its ability to ferment both glucose and xylose from undetoxified and unsupplemented hydrolysate from AFEX-pretreated corn stover at high yield.
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Gao D, Chundawat SPS, Krishnan C, Balan V, Dale BE. Mixture optimization of six core glycosyl hydrolases for maximizing saccharification of ammonia fiber expansion (AFEX) pretreated corn stover. BIORESOURCE TECHNOLOGY 2010; 101:2770-81. [PMID: 19948399 DOI: 10.1016/j.biortech.2009.10.056] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2009] [Revised: 10/12/2009] [Accepted: 10/19/2009] [Indexed: 05/03/2023]
Abstract
In this work, six core glycosyl hydrolases (GH) were isolated and purified from various sources to help rationally optimize an enzyme cocktail to digest ammonia fiber expansion (AFEX) treated corn stover. The four core cellulases were endoglucanase I (EG I, GH family 7B), cellobiohydrolase I (CBH I, GH family 7A), cellobiohydrolase II (CBH II, GH family 6A) and beta-glucosidase (betaG, GH family 3). The two core hemicellulases were an endo-xylanase (EX, GH family 11) and a beta-xylosidase (betaX, GH family 3). Enzyme family and purity were confirmed by proteomics. Synergistic interactions among the six core enzymes for varying relative and total protein loading (8.25, 16.5 and 33 mg/g glucan) during hydrolysis of AFEX-treated corn stover was studied using a high-throughput microplate based protocol. The optimal composition (based on% protein mass loading) of the cocktail mixture was CBH I (28.4%): CBH II (18.0%): EG I (31.0%): EX (14.1%): betaG (4.7%): betaX (3.8%). These results demonstrate a rational strategy for the development of a minimal, synergistic enzymes cocktail that could reduce enzyme usage and maximize the fermentable sugar yields from pretreated lignocellulosics.
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Li BZ, Balan V, Yuan YJ, Dale BE. Process optimization to convert forage and sweet sorghum bagasse to ethanol based on ammonia fiber expansion (AFEX) pretreatment. BIORESOURCE TECHNOLOGY 2010; 101:1285-92. [PMID: 19811909 DOI: 10.1016/j.biortech.2009.09.044] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2009] [Revised: 09/01/2009] [Accepted: 09/10/2009] [Indexed: 05/09/2023]
Abstract
With growing demand for bio-based fuels and chemicals, there has been much attention given to the performance of different feedstocks. We have optimized the ammonia fiber expansion (AFEX) pretreatment and fermentation process to convert forage and sweet sorghum bagasse to ethanol. AFEX pretreatment was optimized for forage sorghum and sweet sorghum bagasse. Supplementing xylanase with cellulase during enzymatic hydrolysis increased both glucan and xylan conversion to 90% at 1% glucan loading. High solid loading hydrolyzates from the optimized AFEX conditions were fermented using Saccharomyces cerevisiae 424A (LNH-ST) without any external nutrient supplementation or detoxification. The strain was better able to utilize xylose at pH 6.0 than at pH 4.8, but glycerol production was higher for the former pH than the latter. The maximum final ethanol concentration in the fermentation broth was 30.9 g/L (forage sorghum) and 42.3 g/L (sweet sorghum bagasse). A complete mass balance for the process is given.
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Lau MW, Gunawan C, Dale BE. The impacts of pretreatment on the fermentability of pretreated lignocellulosic biomass: a comparative evaluation between ammonia fiber expansion and dilute acid pretreatment. BIOTECHNOLOGY FOR BIOFUELS 2009; 2:30. [PMID: 19961578 PMCID: PMC2799388 DOI: 10.1186/1754-6834-2-30] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2009] [Accepted: 12/04/2009] [Indexed: 05/05/2023]
Abstract
BACKGROUND Pretreatment chemistry is of central importance due to its impacts on cellulosic biomass processing and biofuels conversion. Ammonia fiber expansion (AFEX) and dilute acid are two promising pretreatments using alkaline and acidic pH that have distinctive differences in pretreatment chemistries. RESULTS Comparative evaluation on these two pretreatments reveal that (i) AFEX-pretreated corn stover is significantly more fermentable with respect to cell growth and sugar consumption, (ii) both pretreatments can achieve more than 80% of total sugar yield in the enzymatic hydrolysis of washed pretreated solids, and (iii) while AFEX completely preserves plant carbohydrates, dilute acid pretreatment at 5% solids loading degrades 13% of xylose to byproducts. CONCLUSION The selection of pretreatment will determine the biomass-processing configuration, requirements for hydrolysate conditioning (if any) and fermentation strategy. Through dilute acid pretreatment, the need for hemicellulase in biomass processing is negligible. AFEX-centered cellulosic technology can alleviate fermentation costs through reducing inoculum size and practically eliminating nutrient costs during bioconversion. However, AFEX requires supplemental xylanases as well as cellulase activity. As for long-term sustainability, AFEX has greater potential to diversify products from a cellulosic biorefinery due to lower levels of inhibitor generation and lignin loss.
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Garlock RJ, Chundawat SPS, Balan V, Dale BE. Optimizing harvest of corn stover fractions based on overall sugar yields following ammonia fiber expansion pretreatment and enzymatic hydrolysis. BIOTECHNOLOGY FOR BIOFUELS 2009; 2:29. [PMID: 19930679 PMCID: PMC2786907 DOI: 10.1186/1754-6834-2-29] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2009] [Accepted: 11/24/2009] [Indexed: 05/06/2023]
Abstract
BACKGROUND Corn stover composition changes considerably throughout the growing season and also varies between the various fractions of the plant. These differences can impact optimal pretreatment conditions, enzymatic digestibility and maximum achievable sugar yields in the process of converting lignocellulosics to ethanol. The goal of this project was to determine which combination of corn stover fractions provides the most benefit to the biorefinery in terms of sugar yields and to determine the preferential order in which fractions should be harvested. Ammonia fiber expansion (AFEX) pretreatment, followed by enzymatic hydrolysis, was performed on early and late harvest corn stover fractions (stem, leaf, husk and cob). Sugar yields were used to optimize scenarios for the selective harvest of corn stover assuming 70% or 30% collection of the total available stover. RESULTS The optimal AFEX conditions for all stover fractions, regardless of harvest period, were: 1.5 (g NH3 g-1 biomass); 60% moisture content (dry-weight basis; dwb), 90 degrees C and 5 min residence time. Enzymatic hydrolysis was conducted using cellulase, beta-glucosidase, and xylanase at 31.3, 41.3, and 3.1 mg g-1 glucan, respectively. The optimal harvest order for selectively harvested corn stover (SHCS) was husk > leaf > stem > cob. This harvest scenario, combined with optimal AFEX pretreatment conditions, gave a theoretical ethanol yield of 2051 L ha-1 and 912 L ha-1 for 70% and 30% corn stover collection, respectively. CONCLUSION Changing the proportion of stover fractions collected had a smaller impact on theoretical ethanol yields (29 - 141 L ha-1) compared to the effect of altering pretreatment and enzymatic hydrolysis conditions (150 - 462 L ha-1) or harvesting less stover (852 - 1139 L ha-1). Resources may be more effectively spent on improving sustainable harvesting, thereby increasing potential ethanol yields per hectare harvested, and optimizing biomass processing rather than focusing on the selective harvest of specific corn stover fractions.
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Percival Zhang YH, Berson E, Sarkanen S, Dale BE. Sessions 3 and 8: Pretreatment and Biomass Recalcitrance: Fundamentals and Progress. Appl Biochem Biotechnol 2009; 153:80-3. [DOI: 10.1007/s12010-009-8610-3] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Dale BE. Editorial: Consortium for Applied Fundamentals and Innovation (CAFI). Biotechnol Prog 2009; 25:301. [DOI: 10.1002/btpr.216] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Balan V, Sousa LDC, Chundawat SPS, Marshall D, Sharma LN, Chambliss CK, Dale BE. Enzymatic digestibility and pretreatment degradation products of AFEX-treated hardwoods (Populus nigra). Biotechnol Prog 2009; 25:365-75. [DOI: 10.1002/btpr.160] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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