Advanced

Fermentation of Lignocellulosic Hydrolysates: Inhibition and Detoxification

Palmqvist, Eva LU (1998)
Abstract
The ethanol yield and productivity obtained during fermentation of lignocellulosic hydrolysates is decreased due to the presence of inhibiting compounds, such as weak acids, furans and phenolic compounds produced during hydrolysis. Evaluation of the effect of various biological, physical and chemical detoxification treatments by fermentation assays using Saccharomyces cerevisiae was used to characterise inhibitors. Inhibition of fermentation was decreased after removal of the non-volatile compounds, pre-fermentation by the filamentous fungus Trichoderma reesei, treatment with the lignolytic enzyme laccase, extraction with ether, and treatment with alkali. Yeast growth in lignocellulosic hydrolysates was inhibited below a certain... (More)
The ethanol yield and productivity obtained during fermentation of lignocellulosic hydrolysates is decreased due to the presence of inhibiting compounds, such as weak acids, furans and phenolic compounds produced during hydrolysis. Evaluation of the effect of various biological, physical and chemical detoxification treatments by fermentation assays using Saccharomyces cerevisiae was used to characterise inhibitors. Inhibition of fermentation was decreased after removal of the non-volatile compounds, pre-fermentation by the filamentous fungus Trichoderma reesei, treatment with the lignolytic enzyme laccase, extraction with ether, and treatment with alkali. Yeast growth in lignocellulosic hydrolysates was inhibited below a certain fermentation pH, most likely due to high concentrations of undissociated weak acids. The effects of individual compounds were studied in model fermentations. Furfural is reduced to furfuryl alcohol by yeast dehydrogenases, thereby affecting the intracellular redox balance. As a result, acetaldehyde accumulated during furfural reduction, which most likely contributed to inhibition of growth. Acetic acid (10 g l-1) and furfural (3 g l-1) interacted antagonistically causing decreased specific growth rate, whereas no significant individual or interaction effects were detected by the lignin-derived compound 4-hydroxybenzoic acid (2 g l-1). By maintaining a high cellmass density in the fermentor, the process was less sensitive to inhibitors affecting growth and to fluctuations in fermentation pH, and in addition the depletion rate of biocenvertible inhibitors was increased. A theoretical ethanol yield and high productivity was obtained in continuous fermentation of spruce hydrolysate when the cellmass concentration was maintained at a high level by applying cell recirculation. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor du Preez, James
organization
publishing date
type
Thesis
publication status
published
subject
keywords
fermentation strategies, mechanisms, identification, inhibition, lignocellulosic hydrolysates, Ethanol, Saccharomyces cerevisiae, virology, virologi, mykologi, mycology, Mikrobiologi, bakteriologi, bacteriology, Microbiology
pages
129 pages
publisher
Department of Applied Microbiology, Lund University
defense location
Kemicentrum, Sölveg. 39, Sal C
defense date
1998-02-13 10:15:00
external identifiers
  • other:ISRN: LUTKDH/TKMB--98/1027--SE
language
English
LU publication?
yes
additional info
Article: This thesis is based on the following papers, referred to by their respective Roman numerals in the text. Article: I. Palmqvist, E., Hahn-Hägerdal, B., Galbe, M. and Zacchi, G. (1996).The effect of water-soluble inhibitors from steam-pretreated willow on enzymatic hydrolysis and ethanol fermentation.Enz. Microb. Technol. 19, 470-476. Article: II. Palmqvist, E., Hahn-Hägerdal, B., Szengyel, Z., Zacchi, G., and Rèczey, K. (1997).Simultaneous detoxification and enzyme production of hemicellulose hydrolysates obtained after steam pretreatment.Enz. Microb. Technol. 20, 286-293. Article: III. Jönsson, L. J., Palmqvist, E., Nilvebrant, N. O. N. and Hahn-Hägerdal, B.Detoxification of wood hydrolysates with laccase and peroxidase from the white-rot fungus Trametes versicolor.Submitted for publication. Article: IV. Palmqvist, E., Grage, H., Meinander, N. and Hahn-Hägerdal, B.Main and interaction effects of acetic acid, furfural, and p-hydroxybenzoic acid on growth and ethanol productivity of yeasts.Submitted for publication. Article: V. Palmqvist, E. Galbe, M. and Hahn-Hägerdal, B.Continuous fermentation with cell recirculation of enzymatic hydrolysates of spruce with Saccharomyces cerevisiae and on-line monitoring of glucose and ethanol.Submitted for publication. Article: VI. Palmqvist, E., Almeida, J. and Hahn-Hägerdal, B.Influence of furfural on anaerobic glucose metabolism of S. cerevisiae.Manuscript. The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Applied Microbiology (LTH) (011001021), Theoretical ecology (Closed 2011) (011006011)
id
670f9265-45da-4456-a996-b53d4428a4be (old id 38385)
date added to LUP
2016-04-04 12:16:26
date last changed
2018-11-21 21:10:01
@phdthesis{670f9265-45da-4456-a996-b53d4428a4be,
  abstract     = {The ethanol yield and productivity obtained during fermentation of lignocellulosic hydrolysates is decreased due to the presence of inhibiting compounds, such as weak acids, furans and phenolic compounds produced during hydrolysis. Evaluation of the effect of various biological, physical and chemical detoxification treatments by fermentation assays using Saccharomyces cerevisiae was used to characterise inhibitors. Inhibition of fermentation was decreased after removal of the non-volatile compounds, pre-fermentation by the filamentous fungus Trichoderma reesei, treatment with the lignolytic enzyme laccase, extraction with ether, and treatment with alkali. Yeast growth in lignocellulosic hydrolysates was inhibited below a certain fermentation pH, most likely due to high concentrations of undissociated weak acids. The effects of individual compounds were studied in model fermentations. Furfural is reduced to furfuryl alcohol by yeast dehydrogenases, thereby affecting the intracellular redox balance. As a result, acetaldehyde accumulated during furfural reduction, which most likely contributed to inhibition of growth. Acetic acid (10 g l-1) and furfural (3 g l-1) interacted antagonistically causing decreased specific growth rate, whereas no significant individual or interaction effects were detected by the lignin-derived compound 4-hydroxybenzoic acid (2 g l-1). By maintaining a high cellmass density in the fermentor, the process was less sensitive to inhibitors affecting growth and to fluctuations in fermentation pH, and in addition the depletion rate of biocenvertible inhibitors was increased. A theoretical ethanol yield and high productivity was obtained in continuous fermentation of spruce hydrolysate when the cellmass concentration was maintained at a high level by applying cell recirculation.},
  author       = {Palmqvist, Eva},
  language     = {eng},
  publisher    = {Department of Applied Microbiology, Lund University},
  school       = {Lund University},
  title        = {Fermentation of Lignocellulosic Hydrolysates: Inhibition and Detoxification},
  year         = {1998},
}