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Poster Presentation 1-21
Effect of Lignocellulosic Degradation Compounds Produced in the Steam Explosion Pretreatment on Ethanol Fermentation by Thermotolerant Yeasts Kluyveromyces marxianus
J.M. Oliva, F. Sáez, I. Ballesteros, A. González, M.J. Negro, P. Manzanares, and M.Ballesteros
DER-CIEMATAvda. Complutense, 22 28040-Madrid, Spain
Telephone: 34 (1) 346 62 61; Fax: 34 (1) 346 60 37; E-mail: m.ballesteros@ciemat.es
Prior to enzymatic hydrolysis of cellulosic materials, some form of pretreatment is necessary to make the fiber structure more accessible. Autohydrolysis steam explosion pretreatment has been recognized as a cost-effective method for pretreating lignocellulosic biomass. During the steam explosion pretreatment of lignocellulosic substrates, which is often performed at temperatures around 210ºC, various toxic compounds are formed that could inhibit microbial fermentation. Although the nature and concentrations of the final inhibiting compounds vary greatly with pretreatment conditions and the raw material used, the compounds produced or released during steam pretreatment of lignocellulose belong to three major groups: weak acids from deacetylation of hemicellulose and breakdown of lignin, furans from sugar degradation, and phenolic compounds from lignin degradation.
Kluyveromyces marxianus CECT 10875, a novel thermotolerant yeast strain obtained at CIEMAT`s laboratory, was used in this study. This strain is capable of ethanol fermentation of glucose from cellulose hydrolysis at 42ºC with a relatively good ethanol production rate.
In this study, the filtrate from steam-preteated poplar was analyzed to identify degradation compounds. The effect of selected compounds that have been previously identified in prehydrolyzates on the growth and ethanolic fermentation of Kluyveromyces marxianus was tested. Several fermentations on glucose media containing individual inhibitory compounds found in the hydrolyzate were carried out. The level of inhibition on yeast strain growth and ethanolic fermentation was determined.
At concentrations found in the prehydrolyzate none of the individual compounds significantly affect the fermentation. For all tested compounds, growth was inhibited to a lesser extent than ethanol production. Lower concentrations of catechol (1 g/L) and p-hydroxy-benzaldehyde (0.5 g/L) were required to produce the 50% reduction in the cell mass in comparison to other tested compounds.
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