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Improving the fermentability of enzymatic hydrolysates of lignocellulose through chemical in-situ detoxification with reducing agents
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2011 (English)In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 102, no 2, 1254-1263 p.Article in journal (Refereed) Published
Abstract [en]

Inhibitory lignocellulose hydrolysates were treated with the reducing agents dithionite and sulfite to achieve improved fermentability. Addition of these reducing agents (in the concentration range 5.0-17.5mM) to enzymatic hydrolysates of spruce wood or sugarcane bagasse improved processes based on both SHF (simultaneous hydrolysis and fermentation) and SSF (simultaneous saccharification and fermentation). The approach was exemplified in ethanolic fermentations with Saccharomyces cerevisiae and by using hydrolysates with sugar concentrations >100g/L (for SHF) and with 10% dry-matter content (for SSF). In the SHF experiments, treatments with dithionite raised the ethanol productivities of the spruce hydrolysate from 0.2 to 2.5g×L(-1)×h(-1) and of the bagasse hydrolysate from 0.9 to 3.9g×L(-1)×h(-1), values even higher than those of fermentations with reference sugar solutions without inhibitors. Benefits of the approach include that the addition of the reducing agent can be made in-situ directly in the fermentation vessel, that the treatment can be performed at a temperature and pH suitable for fermentation, and that the treatment results in dramatically improved fermentability without degradation of fermentable sugars. The many benefits and the simplicity of the approach offer a new way to achieve more efficient manufacture of fermentation products from lignocellulose hydrolysates.

Place, publisher, year, edition, pages
Elsevier Ltd , 2011. Vol. 102, no 2, 1254-1263 p.
Keyword [en]
Lignocellulose hydrolysates, Cellulosic ethanol, Fermentation inhibitors, In-situ detoxification, Reducing agents
URN: urn:nbn:se:umu:diva-38851DOI: 10.1016/j.biortech.2010.08.037PubMedID: 20822900OAI: diva2:383113
Available from: 2011-01-04 Created: 2011-01-04 Last updated: 2013-11-04Bibliographically approved
In thesis
1. Biorefining of lignocellulose: Detoxification of inhibitory hydrolysates and potential utilization of residual streams for production of enzymes
Open this publication in new window or tab >>Biorefining of lignocellulose: Detoxification of inhibitory hydrolysates and potential utilization of residual streams for production of enzymes
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lignocellulosic biomass is a renewable resource that can be utilized for the production of biofuels, chemicals, and bio-based materials. Biochemical conversion of lignocellulose to advanced biofuels, such as cellulosic ethanol, is generally performed through microbial fermentation of sugars generated by thermochemical pretreatment of the biomass followed by an enzymatic hydrolysis of the cellulose. The aims of the research presented in this thesis were to address problems associated with pretreatment by-products that inhibit microbial and enzymatic biocatalysts, and to investigate the potential of utilizing residual streams from pulp mills and biorefineries to produce hydrolytic enzymes.

A novel method to detoxify lignocellulosic hydrolysates to improve the fermentability was investigated in experiments with the yeast Saccharomyces cerevisiae. The method is based on treatment of lignocellulosic slurries and hydrolysates with reducing agents, such as sodium dithionite and sodium sulfite. The effects of treatment with sodium borohydride were also investigated. Treatment of a hydrolysate of Norway spruce by addition of 10 mM dithionite resulted in an increase of the balanced ethanol yield from 0.03 to 0.35 g/g. Similarly, the balanced ethanol yield of a hydrolysate of sugarcane bagasse increased from 0.06 to 0.28 g/g after treatment with 10 mM dithionite. In another study with a hydrolysate of Norway spruce, addition of 34 mM borohydride increased the balanced ethanol yield from 0.02 to 0.30 g/g, while the ethanol productivity increased from 0.05 to 0.57 g/(L×h). While treatment with sulfur oxyanions had a positive effect on microbial fermentation and enzymatic hydrolysis, treatment with borohydride resulted in an improvement only for the microbial fermentation. The chemical effects of treatments of hydrolysates with sodium dithionite, sodium sulfite, and sodium borohydride were investigated using liquid chromatography-mass spectrometry (LC-MS). Treatments with dithionite and sulfite were found to rapidly sulfonate inhibitors already at room temperature and at a pH that is compatible with enzymatic hydrolysis and microbial fermentation. Treatment with borohydride reduced inhibitory compounds, but the products were less hydrophilic than the products obtained in the reactions with the sulfur oxyanions.

The potential of on-site enzyme production using low-value residual streams, such as stillage, was investigated utilizing recombinant Aspergillus niger producing xylanase and cellulase. A xylanase activity of 8,400 nkat/ml and a cellulase activity of 2,700 nkat/ml were reached using stillages from processes based on waste fiber sludge. The fungus consumed a large part of the xylose, the acetic acid, and the oligosaccharides that were left in the stillages after fermentation with S. cerevisiae. In another study, the capability of two filamentous fungi (A. niger and Trichoderma reesei) and three yeasts (S. cerevisiae, Pichia pastoris, and Yarrowia lipolytica) to grow on inhibitory lignocellulosic media were compared. The results indicate that the two filamentous fungi had the best capability to utilize different nutrients in the media, while the S. cerevisiae strain exhibited the best tolerance against the inhibitors. Utilization of different nutrients would be especially important in enzyme production using residual streams, while tolerance against inhibitors is desirable in a consolidated bio-process in which the fermenting microorganism also contributes by producing enzymes.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2013. 80 p.
National Category
Biocatalysis and Enzyme Technology
urn:nbn:se:umu:diva-82486 (URN)978-91-7459-759-2 (ISBN)
Public defence
2013-11-29, KBC-huset, KB3A9, Umeå universitet, Umeå, 10:15 (English)
Available from: 2013-11-08 Created: 2013-11-03 Last updated: 2013-11-08Bibliographically approved

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