Sunday, May 3, 2009
2-53
Effect of lignocellulosic inhibitory compounds on the fermentative capacity of different yeast strains
Sonia Ghatora, Michael Liu, Linoj Kumar, Pablo Chung, Richard Chandra, Alexandra A. Roos, and Jack Saddler. Wood Science, University of British Columbia, 2424 Main Mall, Vancouver, BC V6T 1Z4, Canada
It would be very desirable if yeasts were able to directly ferment the hemicellulose derived sugars obtained after the steam pretreatment of biomass without the need to detoxify the resulting sugar stream. Several Saccharomyces cerevisae strains, such as spent sulfite liquor (SSL) adapted Tembec strains (T1 and T2), an ethanologenic strain Y1528 and a wild strain (BY4742) were selected to assess their ability to ferment the liquor derived from steam pretreated Douglas-fir. These strains were selected on the basis of their unique characteristics: the Tembec strains are very robust and are able to survive in and ferment the SSL containing different inhibitory compounds, whereas, the strain Y1528 exhibits an interesting trait of preferably utilizing galactose over glucose and mannose. Initially, none of the strains was able to ferment the liquor which was likely due to the presence of fermentation inhibitors such as furans and lignin degradation products. However, after the addition of glucose to the liquors, the yeast strains produced comparable amounts of ethanol. High ethanol yields were observed with the Tembec strains as compared to Y1528 and BY4742. The higher sugar concentration possibly supported the growth of the Tembec strains even in the presence of inhibitors. We next studied the effect of different fermentation inhibitors (HMF, Furfural, coniferyl aldehyde, cinnamic acid, 4-hydroxybenzoic acid and vanillic acid) on the fermentative capability of the yeast strains. These experiments showed that the degree of tolerance and fermentative capability of yeast strains towards the inhibitory compounds was confined to the specific inhibitor used.