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Ethanol from Lignocellulose - Fermentation Inhibitors, Detoxification and Genetic Engineering of Saccharomyces cerevisiae for Increased Resistance

Larsson, Simona LU (2000)
Abstract
Ethanol can be produced from lignocellulose by first hydrolysing the material to sugars, and then fermenting the hydrolysate with the yeast Saccharomyces cerevisiae. Hydrolysis using dilute sulphuric acid has advantages over other methods, however, compounds which inhibit fermentation are generated during this kind of hydrolysis. The inhibitory effect of aliphatic acids, furans, and phenolic compounds was investigated. The generation of inhibitors during hydrolysis was studied using Norway spruce as raw material. It was concluded that the decrease in the fermentability coincided with increasing harshness of the hydrolysis conditions. The decrease in fermentability was not correlated solely to the content of aliphatic acids or furan... (More)
Ethanol can be produced from lignocellulose by first hydrolysing the material to sugars, and then fermenting the hydrolysate with the yeast Saccharomyces cerevisiae. Hydrolysis using dilute sulphuric acid has advantages over other methods, however, compounds which inhibit fermentation are generated during this kind of hydrolysis. The inhibitory effect of aliphatic acids, furans, and phenolic compounds was investigated. The generation of inhibitors during hydrolysis was studied using Norway spruce as raw material. It was concluded that the decrease in the fermentability coincided with increasing harshness of the hydrolysis conditions. The decrease in fermentability was not correlated solely to the content of aliphatic acids or furan derivatives.



To increase the fermentability, detoxification is often employed. Twelve detoxification methods were compared with respect to the chemical composition of the hydrolysate and the fermentability after treatment. The most efficient detoxification methods were anion-exchange at pH 10.0, overliming and enzymatic detoxification with the phenol-oxidase laccase. Detailed analyses of ion exchange revealed that anion exchange and unspecific hydrophobic interactions greatly contributed to the detoxification effect, while cation exchange did not. The comparison of detoxification methods also showed that phenolic compounds are very important fermentation inhibitors, as their selective removal with laccase had a major positive effect on the fermentability. Selected compounds; aliphatic acids, furans and phenolic compounds, were characterised with respect to their inhibitory effect on ethanolic fermentation by S. cerevisiae. When aliphatic acids or furans were compared, the inhibitory effects were found to be in the same range, but the phenolic compounds displayed widely different inhibitory effects.



The possibility of genetically engineering S. cerevisiae to achieve increased inhibitor resistance was explored by heterologous expression of laccase from Trametes versicolor and by homologous overexpression of phenylacrylic acid decarboxylase. Both procedures resulted in S. cerevisiae transformants displaying increased resistance towards lignocellulose-derived aromatic compounds. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Prof van Zyl, W H, Stellenbosch University, South Africa
organization
publishing date
type
Thesis
publication status
published
subject
keywords
detoxification, S. cerevisiae, lignocellulose, inhibition, phenolic compounds, laccase, Microbiology, bacteriology, virology, mycology, Mikrobiologi, bakteriologi, virologi, mykologi
pages
140 pages
publisher
Applied Microbiology (LTH)
defense location
Lund, Kemicentrum, hörsal B
defense date
2000-11-15 10:15
external identifiers
  • Other:ISRN: LUTKDH/TKMB--00/1033--SE
language
English
LU publication?
yes
id
9f0101c0-c386-4973-8eda-0c87950a4649 (old id 40970)
date added to LUP
2007-08-01 12:44:38
date last changed
2016-09-19 08:45:10
@phdthesis{9f0101c0-c386-4973-8eda-0c87950a4649,
  abstract     = {Ethanol can be produced from lignocellulose by first hydrolysing the material to sugars, and then fermenting the hydrolysate with the yeast Saccharomyces cerevisiae. Hydrolysis using dilute sulphuric acid has advantages over other methods, however, compounds which inhibit fermentation are generated during this kind of hydrolysis. The inhibitory effect of aliphatic acids, furans, and phenolic compounds was investigated. The generation of inhibitors during hydrolysis was studied using Norway spruce as raw material. It was concluded that the decrease in the fermentability coincided with increasing harshness of the hydrolysis conditions. The decrease in fermentability was not correlated solely to the content of aliphatic acids or furan derivatives.<br/><br>
<br/><br>
To increase the fermentability, detoxification is often employed. Twelve detoxification methods were compared with respect to the chemical composition of the hydrolysate and the fermentability after treatment. The most efficient detoxification methods were anion-exchange at pH 10.0, overliming and enzymatic detoxification with the phenol-oxidase laccase. Detailed analyses of ion exchange revealed that anion exchange and unspecific hydrophobic interactions greatly contributed to the detoxification effect, while cation exchange did not. The comparison of detoxification methods also showed that phenolic compounds are very important fermentation inhibitors, as their selective removal with laccase had a major positive effect on the fermentability. Selected compounds; aliphatic acids, furans and phenolic compounds, were characterised with respect to their inhibitory effect on ethanolic fermentation by S. cerevisiae. When aliphatic acids or furans were compared, the inhibitory effects were found to be in the same range, but the phenolic compounds displayed widely different inhibitory effects.<br/><br>
<br/><br>
The possibility of genetically engineering S. cerevisiae to achieve increased inhibitor resistance was explored by heterologous expression of laccase from Trametes versicolor and by homologous overexpression of phenylacrylic acid decarboxylase. Both procedures resulted in S. cerevisiae transformants displaying increased resistance towards lignocellulose-derived aromatic compounds.},
  author       = {Larsson, Simona},
  keyword      = {detoxification,S. cerevisiae,lignocellulose,inhibition,phenolic compounds,laccase,Microbiology,bacteriology,virology,mycology,Mikrobiologi,bakteriologi,virologi,mykologi},
  language     = {eng},
  pages        = {140},
  publisher    = {Applied Microbiology (LTH)},
  school       = {Lund University},
  title        = {Ethanol from Lignocellulose - Fermentation Inhibitors, Detoxification and Genetic Engineering of Saccharomyces cerevisiae for Increased Resistance},
  year         = {2000},
}