Review paperFermentation of lignocellulosic hydrolysates. I: inhibition and detoxification
Introduction
Lignocellulosic materials such as wood provide abundant and renewable energy sources. Lignocellulosics contain sugars polymerised to cellulose and hemicellulose which can be liberated by hydrolysing the material, and subsequently fermented to ethanol by microorganisms, such as Saccharomyces cerevisiae. Lignocellulose-derived ethanol can be used as an environmentally friendly liquid fuel, the exhaust carbon dioxide being taken up by growing biomass and therefore not making a net contribution to the atmosphere. However, rapid and efficient fermentation of the hydrolysates is limited because in addition to monomeric sugars a range of toxic compounds is generated during steam pretreatment and hydrolysis of lignocellulosics (for a review, see Palmqvist and Hahn-Hägerdal, 1999). The inhibiting compounds are divided in three main groups based on origin: weak acids, furan derivatives, and phenolic compounds. In the present article detoxification methods and strategies to enhance the efficiency of the fermentation process are reviewed.
Except where explicitly stated, S. cerevisiae has been used for fermentation of lignocellulose-derived sugars and in model fermentations in all work reviewed herein. S. cerevisiae has been shown to be the best yeast for the fermentation of hexose sugars present in lignocellulose-derived hydrolysates due to its ethanol-producing capacity and high inhibitor tolerance Hahn-Hägerdal et al., 1991, Olsson and Hahn-Hägerdal, 1993.
Section snippets
Detoxification
Biological, physical, and chemical methods have been employed for detoxification (i.e., the specific removal of inhibitors prior to fermentation) of lignocellulosic hydrolysates (for a recent review, see Olsson and Hahn-Hägerdal, 1996). In the following, detoxification methods reported in the literature and their effects on the composition and fermentability of the hydrolysates used will be discussed in relation to the identity of compounds mainly responsible for inhibition. Different
Acknowledgements
This work was supported by grants from the Swedish National Board for Industrial and Technical Development (NUTEK), Swedish Natural Science Research Council (NFR), the Knut and Alice Wallenberg Foundation, and the Carl Trygger Foundation.
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