Fed-batch SSCF using steam-exploded wheat straw at high dry matter consistencies and a xylose-fermenting Saccharomyces cerevisiae strain: effect of laccase supplementation

Biotechnology for Biofuels

Antonio D Moreno²  Elia Tomás-Pejó²  David Ibarra³  Mercedes Ballesteros¹  Lisbeth Olsson² 

[1] Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, Biofuels Unit, Madrid 28040, Spain

[2] Department of Chemical and Biological Engineering, Industrial Biotechnology, Chalmers University of Technology, Göteborg SE-41296, Sweden

[3] INIA-CIFOR, Forestry Products Department, Cellulose and Paper Laboratories, Madrid 28040, Spain

关键词: Xylose-fermenting Saccharomyces cerevisiae;    Steam explosion;    In situ laccase detoxification;    Simultaneous saccharification and co-fermentation;    Bioethanol;    Lignocellulose;   

Others  :  794695
DOI  :  10.1186/1754-6834-6-160

 received in 2013-09-03, accepted in 2013-10-29,  发布年份 2013

【 摘 要 】

Background

Lignocellulosic bioethanol is expected to play an important role in fossil fuel replacement in the short term. Process integration, improvements in water economy, and increased ethanol titers are key considerations for cost-effective large-scale production. The use of whole steam-pretreated slurries under high dry matter (DM) conditions and conversion of all fermentable sugars offer promising alternatives to achieve these goals.

Results

Wheat straw slurry obtained from steam explosion showed high concentrations of degradation compounds, hindering the fermentation performance of the evolved xylose-recombinant Saccharomyces cerevisiae KE6-12 strain. Fermentability tests using the liquid fraction showed a higher number of colony-forming units (CFU) and higher xylose consumption rates when treating the medium with laccase. During batch simultaneous saccharification and co-fermentation (SSCF) processes, cell growth was totally inhibited at 12% DM (w/v) in untreated slurries. However, under these conditions laccase treatment prior to addition of yeast reduced the total phenolic content of the slurry and enabled the fermentation. During this process, an ethanol concentration of 19 g/L was obtained, corresponding to an ethanol yield of 39% of the theoretical yield. By changing the operation from batch mode to fed-batch mode, the concentration of inhibitors at the start of the process was reduced and 8 g/L of ethanol were obtained in untreated slurries with a final consistency of 16% DM (w/v). When fed-batch SSCF medium was supplemented with laccase 33 hours after yeast inoculation, no effect on ethanol yield or cell viability was found compared to untreated fermentations. However, if the laccase supplementation (21 hours after yeast inoculation) took place before the first addition of substrate (at 25 hours), improved cell viability and an increased ethanol titer of up to 32 g/L (51% of the theoretical) were found.

Conclusions

Laccase treatment in SSCF processes reduces the inhibitory effect that degradation compounds have on the fermenting microorganism. Furthermore, in combination with fed-batch operational mode, laccase supplementation allows the fermentation of wheat straw slurry at high DM consistencies, improving final ethanol concentrations and yields.

【 授权许可】

   
2013 Moreno et al.; licensee BioMed Central Ltd.

【 图 表 】

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