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Formation of microbial inhibitors in steam-explosion pretreatment of softwood impregnated with sulfuric acid and sulfur dioxide
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
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2018 (English)In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 262, p. 242-250Article in journal (Refereed) Published
Abstract [en]

Wood chips of Norway spruce were pretreated by steam explosion at 195–215 °C after impregnation with either sulfuric acid (SA) or sulfur dioxide (SD). The effects of different pretreatment conditions on formation of microbial inhibitors were investigated, and the inhibitory effects on yeast of pretreatment liquids and of specific inhibitors that were found in the pretreatment liquids were elucidated. Whereas the concentrations of most inhibitors increased with increasing pretreatment temperatures, there were exceptions, such as formaldehyde and p-hydroxybenzaldehyde. The highest concentration of each inhibitor was typically found in SD-pretreated material, but formic acid was an exception. The toxic effects on yeast were studied using concentrations corresponding to loadings of 12 and 20% total solids (TS). Among individual inhibitors that were quantitated in pretreatment liquids, the concentrations of formaldehyde were by far most toxic. There was no or minimal yeast growth in the formaldehyde concentration range (5.8–7.7 mM) corresponding to 12% TS.

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 262, p. 242-250
Keywords [en]
Lignocellulose, Pretreatment, Sulfuric acid, Sulfur dioxide, Microbial inhibitors
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:umu:diva-145114DOI: 10.1016/j.biortech.2018.04.074ISI: 000433219500030PubMedID: 29709843OAI: oai:DiVA.org:umu-145114DiVA, id: diva2:1184484
Note

Originally included in thesis in manuscript form.

Available from: 2018-02-21 Created: 2018-02-21 Last updated: 2018-06-25Bibliographically approved
In thesis
1. Recalcitrance of wood to biochemical conversion: feedstock properties, pretreatment, saccharification, and fermentability
Open this publication in new window or tab >>Recalcitrance of wood to biochemical conversion: feedstock properties, pretreatment, saccharification, and fermentability
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lignocellulose is an inexpensive and abundant renewable resource that can be used to produce advanced biofuels, green chemicals, and other bio-based products. Pretreatment and efficient enzymatic saccharification are essential features of bioconversion of lignocellulosic biomass. The aims of the research were to achieve a better understanding of the recalcitrance of woody biomass to bioconversion, to explore different pretreatment techniques that can be used to decrease the recalcitrance of the biomass and improve the digestibility of the cellulose, and to investigate by-products of acid pretreatment that cause enzymes and microorganisms to work less efficiently.

The recalcitrance of wood from aspen, birch, and spruce was investigated before and after acid pretreatment. Before pretreatment, birch exhibited the highest recalcitrance, which was attributed to structural factors. After pretreatment, spruce showed the highest recalcitrance, which was attributed to chemical factors, such as high lignin content. Deacetylation of hybrid aspen in planta by a CE5 acetyl xylan esterase decreased the recalcitrance, and the glucose yield of enzymatic saccharification of non-pretreated wood increased with 27%.

Pretreatment options based on ionic liquids and steam explosion were further explored. The effects of the anionic constituents of a series of imidazolium-based ionic liquids on pretreatment of aspen and spruce were investigated. [HSO4]− was efficient only for aspen, which was attributed to acid degradation of xylan. [MeCO2]− was efficient for both aspen and spruce, which was attributed to its capability to create a disordered cell wall structure rather than to removal of lignin and hemicellulose. A comparison was made between using sulfuric acid and sulfur dioxide for pretreatment of spruce. Although sulfur dioxide resulted in a pretreatment liquid that was more inhibitory to both enzymes and yeast, it was still superior to pretreatment with sulfuric acid, a phenomenon that was attributed to the particle size of the pretreated material.

In a comparison of microbial inhibitors in pretreatment liquids from steam explosion of spruce, formaldehyde was found to be the most important inhibitor of yeast. Enzyme inhibition by catalytically non-productive adsorption to lignins and pseudo-lignin was investigated using quantitative proteomics. The results indicate that protein adsorption to pseudo-lignin can be as extensive as adsorption to real lignin. 

Place, publisher, year, edition, pages
Umeå: Umeå University, 2018. p. 59
Keywords
Recalcitrance, Pretreatment, Enzymatic saccharification, Ionic liquid, Steam explosion, Enzyme inhibition, Non-productive binding, Microbial inhibitors
National Category
Bioprocess Technology Wood Science Biochemicals
Identifiers
urn:nbn:se:umu:diva-145045 (URN)978-91-7601-853-8 (ISBN)
Public defence
2018-03-16, KBC-huset, Lilla Hörsalen, KB.E3.01, Umeå, 10:00 (English)
Opponent
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Available from: 2018-02-23 Created: 2018-02-19 Last updated: 2018-06-09Bibliographically approved

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Martín, CarlosWu, GuochaoWang, ZhaoStagge, StefanJönsson, Leif J

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