| 1. |
- Björklund, Linda, et al.
(författare)
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Treatment with lignin residue - A novel method for detoxification of lignocellulose hydrolysates
- 2002
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Ingår i: Applied Biochemistry and Biotechnology. - 1559-0291. ; 98, s. 563-575
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Tidskriftsartikel (refereegranskat)abstract
- Acid hydrolysis of lignocellulose to hydrolysates intended for production of fuel ethanol results in the formation of byproducts in addition to fermentable sugars. Some of the byproducts, such as phenolic compounds and furan aldehydes, are inhibitory to the fermenting microorganism. Detoxification of the hydrolysates may be necessary for production of ethanol at a satisfactory rate and yield. The lignin residue obtained after hydrolysis is a material with hydrophobic properties that is produced in large amounts as a byproduct within an ethanol production process based on lignocellulosic raw materials. We have explored the possibility of using this lignin residue for detoxification of spruce dilute-acid hydrolysates prior to fermentation with Saccharomyces cerevisiae. Three dilute-acid hydrolysates of spruce were treated with lignin residue, which in all cases resulted in improved fermentability in terms of productivity and yield of ethanol. The effect was improved by washing the lignin before treatment, by using larger amounts of lignin in the treatment, and by performing the treatment at low temperature. Treatment with the lignin residue removed up to 53% of the phenolic compounds and up to 68% of the furan aldehydes in a spruce dilute-acid hydrolysate. A larger fraction of furfural was removed compared to the less hydrophobic 5-hydroxymethylfurfural.
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| 2. |
- Cassland, Pierre, et al.
(författare)
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Heterologous expression of barley and wheat oxalate oxidase in an E-coli trxB gor double mutant
- 2004
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Ingår i: Journal of Biotechnology. - : Elsevier BV. - 1873-4863 .- 0168-1656. ; 109:1-2, s. 53-62
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Tidskriftsartikel (refereegranskat)abstract
- Oxalate oxidase catalyses the degradation of oxalic acid to carbon dioxide and hydrogen peroxide and is of commercial importance for clinical analyses of oxalate in biological samples. Novel potential applications for oxalate oxidase include the prevention of the formation of calcium oxalate incrusts in pulp and paper manufacture and rapid determination of oxalic acid in process waters. The potential in using oxalate-degrading enzymes in industrial processes increases the interest in finding systems for heterologous expression. Oxalate oxidase from barley is a secreted multimeric glycosylated manganese-containing enzyme with several disulfide bridges, which have been found to be essential for the catalytic activity. Attempts to achieve expression of active heterologous oxalate oxidase in bacteria have up to now met little success. In this study, one oxalate-oxidase-encoding cDNA from barley and two from wheat were cloned and tested with regard to expression in Escherichia coli. The results suggest that the selection of a novel commercially available E. coli host strain, which has the ability to form disulfide bridges in heterologous proteins expressed in its cytoplasm, was important for successful expression. Although a considerable part of the heterologous protein was produced in an insoluble and inactive form, this strain, E. coli Origami B(DE3), in addition yielded soluble and active barley and wheat oxalate oxidase. One of the wheat cDNAs, Ta(M)OXO1, gave three-fold higher activity than the barley cDNA, Hv(H)OXO1, while the other wheat cDNA, Ta(M)OXO2, gave no detectable activity. This indicates that the choice of cDNA was also critical despite the high identity between the cDNAs and the encoded polypeptides (88-89% on the nucleotide level and 88-92% on the amino-acid level). Gel filtration of cell extracts containing heterologous barley and wheat oxalate oxidase resulted in an increase in the activity. This indicates that low molecular weight inhibitory compounds were present in the E. coli lysates but could be removed by the introduction of a purification step.
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| 3. |
- Larsson, S, et al.
(författare)
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The generation of fermentation inhibitors during dilute acid hydrolysis of softwood
- 1999
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Ingår i: Enzyme and Microbial Technology. - 0141-0229. ; 24:3-4, s. 151-159
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the severity of dilute sulfuric acid hydrolysis of spruce (softwood) on sugar yield and on the fermentability of the hydrolysate by Saccharomyces cerevisiae (Baker's yeast) was investigated. Fermentability was assessed as the ethanol yield on fermentable sugars (mannose and glucose) and the mean volumetric productivity (4 h). The hydrolysis conditions, residence time, temperature, and sulfuric acid concentration were treated as a single parameter, combined severity (CS). When the CS of the hydrolysis conditions increased, the yield of fermentable sugars increased to a maximum between CS 2.0-2.7 for mannose, and 3.0-3.4 for glucose above which it decreased. The decrease in the yield of monosaccharides coincided with the maximum concentrations of furfural and 5-hydroxymethylfurfural (5HMF). With the further increase in CS, the concentrations of furfural and 5-HMF decreased while the formation of formic acid and levulinic acid increased The yield of ethanol decreased at approximately CS 3; however, the volumetric productivity decreased at lower CS. The effect of acetic acid, formic acid, levulinic acid furfural, and 5-HMF on fermentability was assayed in model fermentations Ethanol yield and volumetric productivity decreased with increasing concentrations of acetic acid, formic acid, and levulinic acid. Furfural and 5-HMF decreased the volumetric productivity but did not influence the final yield of ethanol. The decrease in volumetric productivity was more pronounced when 5-HMF was added to the fermentation, and this compound was depleted at a lower rate than furfural. The inhibition observed in hydrolysates produced in higher CS could not be fully explained by the effect of the by-products furfural, 5-HMF, acetic acid, formic acid: and levulinic acid. (C) 1998 Elsevier Science Inc.
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| 4. |
- Martin, C, et al.
(författare)
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Comparison of the fermentability of enzymatic hydrolyzates of sugarcane bagasse pretreated by steam explosion using different impregnating agents
- 2002
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Ingår i: Applied Biochemistry and Biotechnology. - 1559-0291. ; 98-100:1-9, s. 699-716
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Tidskriftsartikel (refereegranskat)abstract
- Sugarcane bagasse is a potential lignocellulosic feedstock for ethanol production, since it is cheap, readily available, and has a high carbohydrate content. In this work, bagasse was subjected to steam explosion pretreatment with different impregnation conditions. Three parallel pretreatments were carried out, one without any impregnation, a second with sulfur dioxide, and a third with sulfuric acid as the impregnating agent. The pretreatments were performed at 205 degreesC for 10 min. The pretreated material was then hydrolyzed using cellulolytic enzymes. The chemical composition of the hydrolyzates was analyzed. The highest yields of xylose (16.2 g/100 g dry bagasse), arabinose (1.5 g/100 g), and total sugar (52.9 g/100 g) were obtained in the hydrolysis of the SO2 -impregnated bagasse. The H2SO4-impregnated bagasse gave the highest glucose yield (35.9 g/ 100 g) but the lowest total sugar yield (42.3 g/100 g) among the three methods. The low total sugar yield from the H2SO4 -impregnated bagasse was largely due to by-product formation, as the dehydration of xylose to furfural. Sulfuric acid impregnation led to a threefold increase in the concentration of the fermentation inhibitors furfural and 5-hydroxymethylfurfural (HMF) and a two-fold increase in the concentration of inhibitory aliphatic acids (formic, acetic, and levulinic acids) compared to the other two pretreatment methods. The total content of phenolic compounds was not strongly affected by the different pretreatment methods, but the quantities of separate phenolic compounds were widely different in the hydrolyzate from the H2SO4-impregnated bagasse compared with the other two hydrolyzates. No major differences in the content of inhibitors were observed in the hydrolyzates obtained from SO2-impregnated and non-impregnated bagasse. The fermentability of all three hydrolyzates was tested with a xylose-utilizing Saccharomyces cerevisiae strain with and without nutrient supplementation. The hydrolyzates of SO2-impregnated and nonimpregnated bagasse showed similar fermentability,whereas the hydrolyzate of H2SO4-impregnated bagasse fermented considerably poorer.
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| 5. |
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| 6. |
- Nilvebrant, NO, et al.
(författare)
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Enzymatic degradation of oxalic acid for prevention of scaling
- 2002
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Ingår i: Progress in Biotechnology (Biotechnology in the Pulp and Paper Industry - 8th ICBPPI ). - 0921-0423. ; 21, s. 231-238
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Konferensbidrag (refereegranskat)abstract
- Formation of calcium oxalate incrusts, scaling, may cause severe problems in the pulp and paper industry. Enzymatic degradation of oxalic acid provides a novel approach to eliminate the problems with calcium oxalate precipitation. The performance of two oxalate-degrading enzymes, oxalate oxidase from barley and oxalate decarboxylase from Aspergillus, was tested in model experiments with respect to catalytic efficiency under different conditions, including pH, temperature and enzyme concentration. Oxalate decarboxylase was found to be more sensitive to temperature variations than oxalate oxidase, which was selected for further experiments. Authentic samples from pulp bleach plants were used to test the performance of oxalate oxidase. The results showed that oxalic acid could be degraded enzymatically also in the industrial bleaching filtrates, which were obtained from D-, E-, O-, OP-, PO-, Q-, QP-, and Z-stages. The bleaching filtrates contained compounds that inhibited the action of oxalate oxidase. The degree of inhibition was strongly dependent on the filtrate and could be alleviated by dilution.
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| 7. |
- Persson, Per, et al.
(författare)
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Effect of different forms of alkali treatment on specific fermentation inhibitors and on the fermentability of lignocellulose hydrolysates for production of fuel ethanol
- 2002
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 50:19, s. 5318-5325
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Tidskriftsartikel (refereegranskat)abstract
- Treatment with alkali, particularly overliming, has been widely used as a method for the detoxification of lignocellulose hydrolysates prior to ethanolic fermentation. However, the mechanisms behind the detoxification effect and the influence of the choice of cation have not been well understood. In this study, a dilute acid hydrolysate of spruce and an inhibitor cocktail consisting of six known inhibitors were used to investigate different alkali detoxification methods. The various treatments included the addition of calcium hydroxide, sodium hydroxide, potassium hydroxide, and ammonia to pH 10.0 and subsequent adjustment of the pH to 5.5 with either sulfuric or hydrochloric acid as well as treatment with the corresponding amounts of calcium, sodium, and potassium as sulfate or chloride salts at pH 5.5. An RP-HPLC method was developed for the separation of 18 different inhibitors in the hydrolysate, including furaldehydes and phenolics. Detection and quantification were carded out by means of UV, DAD, and ESI-MS in negative mode. Treatment of the spruce hydrolysate with alkali resulted in up to similar to40% decrease in the concentration of furaldehydes. The effects on the aromatic compounds were complex. Furthermore, SFE was performed on the precipitate formed during alkali treatment to evaluate the inhibitor content of the precipitate, and the following RP-HPLC analysis implied that potential inhibitors were removed mainly through conversion rather than through filtration of precipitate. Parallel experiments in which sulfuric acid or hydrochloric acid was used for acidification to pH 5.5 after alkali treatment indicated that the choice of anion did not affect the removal of inhibitors. Detoxification with calcium hydroxide and ammonia resulted in better fermentability using Saccharomyces cerevisiae than detoxification with sodium hydroxide. The results from the experiments with the inhibitor cocktail indicated that the positive effects of alkali treatment are difficult to explain by removal of the inhibitors only and that possible stimulatory effects on the fermenting organism warrant further attention.
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| 8. |
- Persson, Per, et al.
(författare)
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Supercritical fluid extraction of a lignocellulosic hydrolysate of spruce for detoxification and to facilitate analysis of inhibitors
- 2002
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 1097-0290 .- 0006-3592. ; 79:6, s. 694-700
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Tidskriftsartikel (refereegranskat)abstract
- This work describes a novel approach to detoxify lignocellulosic hydrolysates and facilitate the analysis of inhibitory compounds, namely supercritical fluid extraction (SFE). The efficiency of the fermentation of lignocellulosic dilute-acid hydrolysates depends upon the composition of the hydrolysate and the organism used. Furthermore, it has been shown that inhibitors in the hydrolysate reduce the fermentation yield. This knowledge has given rise to the need to identify and remove the inhibiting compounds. Sample clean-up or work-up steps, to provide a clean and concentrated sample for the analytical system, facilitate the characterization of inhibitors, or indeed any compound in the hydrolysates. Removal of inhibitors was performed with countercurrent flow supercritical fluid extraction of liquid hydrolysates. Three different groups of inhibitors (furan derivatives, phenolic compounds, and aliphatic acids) and sugars were subsequently analyzed in the hydrolysate, extracted hydrolysate, and extract. The effect of the SFE treatment was examined with respect to fermentability with Saccharomyces cerevisiae. Not only did the extraction provide a clean and concentrated sample (extract) for analysis, but also a hydrolysate with increased fermentability as well as lower concentrations of inhibitors such as phenolics and furan derivatives. (C) 2002 Wiley Periodicals, Inc.
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