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- Abdelaziz, Omar Y., et al.
(författare)
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Biological valorization of low molecular weight lignin
- 2016
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Ingår i: Biotechnology Advances. - : Elsevier BV. - 0734-9750. ; 34:8, s. 1318-1346
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Forskningsöversikt (refereegranskat)abstract
- Lignin is a major component of lignocellulosic biomass and as such, it is processed in enormous amounts in the pulp and paper industry worldwide. In such industry it mainly serves the purpose of a fuel to provide process steam and electricity, and to a minor extent to provide low grade heat for external purposes. Also from other biorefinery concepts, including 2nd generation ethanol, increasing amounts of lignin will be generated. Other uses for lignin – apart from fuel production – are of increasing interest not least in these new biorefinery concepts. These new uses can broadly be divided into application of the polymer as such, native or modified, or the use of lignin as a feedstock for the production of chemicals. The present review focuses on the latter and in particular the advances in the biological routes for chemicals production from lignin. Such a biological route will likely involve an initial depolymerization, which is followed by biological conversion of the obtained smaller lignin fragments. The conversion can be either a short catalytic conversion into desired chemicals, or a longer metabolic conversion. In this review, we give a brief summary of sources of lignin, methods of depolymerization, biological pathways for conversion of the lignin monomers and the analytical tools necessary for characterizing and evaluating key lignin attributes.
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| 2. |
- Abdelaziz, Omar Y., et al.
(författare)
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Oxidative Depolymerization of Kraft Lignin for Microbial Conversion
- 2019
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 7:13, s. 11640-11652
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Tidskriftsartikel (refereegranskat)abstract
- The valorization of lignin is being increasingly recognized as crucial to improve the economic viability of integrated biorefineries. Because of its inherent heterogeneity and recalcitrance, lignin has been treated as a waste product in the pulp and paper industry, but new technologies are now being explored to transform lignin into a sustainable resource and enhance its value chain. In the present study, alkaline oxidative depolymerization was investigated as a potential form of pretreatment to enable further biological conversion of LignoBoost kraft lignin (LB). LB lignin oxidation reactions were studied at various temperatures (120-200 °C) and O2 partial pressures (3-15 bar) to identify the optimal conditions for obtaining a biocompatible, oxidatively depolymerized lignin (ODLB) stream. The low molecular weight compounds resulting from this treatment consisted mainly of aromatic monomers and carboxylic acids. The highest yield of aromatic monomers, 3 wt %, was obtained at 160 °C and 3 bar O2. The yield of carboxylic acids increased with both increasing temperature and O2 pressure, exceeding 13% under the harshest conditions investigated. The growth of four aromatic-catabolizing bacterial strains was examined on reaction product mixtures, all of which showed growth on agar plates utilizing ODLB as the sole source of carbon and energy. Rhodococcus opacus and Sphingobium sp. SYK-6 were found to consume most of the aromatic monomers present in the ODLB (e.g., vanillin, vanillate, acetovanillone, and guaiacol). The findings of this study indicate that pretreatment by oxidative depolymerization has potential in the biological valorization of technical lignin streams, for the production of valuable chemicals and materials.
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| 4. |
- Albers, E, et al.
(författare)
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Continuous estimation of product concentration with calorimetry and gas analysis during anaerobic fermentations of Saccharomyces cerevisiae
- 2002
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Ingår i: Thermochimica Acta. - 0040-6031. ; 394:1-2, s. 185-190
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Tidskriftsartikel (refereegranskat)abstract
- Product concentrations may be estimated from gas analysis or calorimetric measurements. These techniques of analysis are fast, simple, and provide a continuous output. To check the accuracy of these estimations, the anaerobic ethanol formation of an industrial strain of the yeast Saccharomyces cerevisiae was selected as a test system. Cultivations were carried out as batch cultures with different nitrogen sources (ammonium, glutamate and a mixture of amino acids) and 20 g/l of glucose as the carbon and energy source. The results showed that there was a good agreement between measured and calculated ethanol values. However, especially when using heat data the results are very sensitive to small changes in the stoichiometry of the catabolic reaction, i.e. ethanol is not the only product but there are also minor amounts of glycerol and acetate. The problems generated by these products when using heat data to calculate ethanol concentrations are discussed in detail. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 9. |
- Alkasrawi, Malek, et al.
(författare)
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Influence of strain and cultivation procedure on the performance of simultaneous saccharification and fermentation of steam pretreated spruce
- 2006
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Ingår i: Enzyme and Microbial Technology. - : Elsevier BV. - 0141-0229. ; 38:1-2, s. 279-286
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Tidskriftsartikel (refereegranskat)abstract
- Yeast to be used in simultaneous saccharification and fermentation (SSF) of lignocelluloses materials has to be prepared in a separate cultivation step. The effects of the cultivation procedure on the performance of SSF of steam pretreated softwood were studied in the current work. The yeast used in the SSF was either directly commercially available Baker's yeast (as packaged yeast) or the same strain of yeast produced from the hydrolysate obtained in the pretreatment of the softwood material. A second strain of Saccharomyces cerevisiae TMB3000. isolated from spent sulphite liquor, was also compared with the commercial Baker's yeast. The strains were tested in SSF at substrate loads of 3, 5 and 8% dry weight of water insoluble material. Final ethanol yields were above 85% of the theoretical (based on the available hexoses) in all cases, except for the package yeast for the 8% substrate load, in which case the final yield was less than 65%. The cultivation procedure was found to have a significant impact on the performance during SSF, as well as in small-scale fermentations of hydrolysate liquor without solid material. The Baker's yeast cultivated on the hydrolysate from the steam pretreatment had in all cases a higher productivity, in particular at the highest substrate load. Cultivated Baker's yeast had a slightly higher productivity than TMB3000. The results suggest that the adaptation of the yeast to the inhibitors present in the medium is an important factor that must be considered in the design of SSF processes.
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| 10. |
- Almeida, Joao, et al.
(författare)
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Carbon fluxes of xylose-consuming Saccharomyces cerevisiae strains are affected differently by NADH and NADPH usage in HMF reduction.
- 2009
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 84, s. 751-761
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Tidskriftsartikel (refereegranskat)abstract
- Industrial Saccharomyces cerevisiae strains able to utilize xylose have been constructed by overexpression of XYL1 and XYL2 genes encoding the NADPH-preferring xylose reductase (XR) and the NAD(+)-dependent xylitol dehydrogenase (XDH), respectively, from Pichia stipitis. However, the use of different co-factors by XR and XDH leads to NAD(+) deficiency followed by xylitol excretion and reduced product yield. The furaldehydes 5-hydroxymethyl-furfural (HMF) and furfural inhibit yeast metabolism, prolong the lag phase, and reduce the ethanol productivity. Recently, genes encoding furaldehyde reductases were identified and their overexpression was shown to improve S. cerevisiae growth and fermentation rate in HMF containing media and in lignocellulosic hydrolysate. In the current study, we constructed a xylose-consuming S. cerevisiae strain using the XR/XDH pathway from P. stipitis. Then, the genes encoding the NADH- and the NADPH-dependent HMF reductases, ADH1-S110P-Y295C and ADH6, respectively, were individually overexpressed in this background. The performance of these strains, which differed in their co-factor usage for HMF reduction, was evaluated under anaerobic conditions in batch fermentation in absence or in presence of HMF. In anaerobic continuous culture, carbon fluxes were obtained for simultaneous xylose consumption and HMF reduction. Our results show that the co-factor used for HMF reduction primarily influenced formation of products other than ethanol, and that NADH-dependent HMF reduction influenced product formation more than NADPH-dependent HMF reduction. In particular, NADH-dependent HMF reduction contributed to carbon conservation so that biomass was produced at the expense of xylitol and glycerol formation.
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