Conference Dates

March 8-13, 2009

Abstract

There are various kinds of stresses during the process of ethanol fermentation and more inhibitory factors are produced when lignocelluloses hydrolysate is used as the substrate. The pretreatment of lignocelluloses biomass before fermentation causes the increase in the amount of acids and thus the decrease in pH. Low-molecular weight aliphatic acids, furaldehydes and a broad range of aromatic compounds are produced during the pretreatment process. They are the inhibitors for the ethanol producers, such as Saccharomyces cerevisiae. Furthermore, besides glucose, lignocellulose hydrolysate contains other sugars, such as xylose, arabinose, galactose and mannose etc., among which xylose is taking the major proportion. Stress tolerance and xylose utilization are therefore essential for Saccharomyces cerevisiae strains to get high-efficiency fermentation and high-yield ethanol production.

In this study, a few laboratory and industrial Saccharomyces cerevisiae strains were selected for the evaluation of their potentials in pH tolerance, inhibitor resistance and xylose utilization. Industrial strains such as TJU (an industrial strain used in some of the bioethanol plants in China), ATCC 4126, and ATCC 96581, an isolate from spent sulfite liquor were compared with some laboratory strains such as ATCC 44771, ATCC 24860 and CBS 8066. The difference of these strains in their pH tolerance was insignificant despite the fact that almost all the strains had less growth when pH was below 4. Among all the yeast strains tested, the haploid laboratory strain ATCC 44771 showed the lowest tolerance to the decrease of pH. As to the inhibitor resistance studies almost all the industrial strains tested had higher inhibitor resistance than the laboratory strains, with ATCC 44771 being the least resistant to the increase in the inhibitor concentrations. The laboratory strain ATCC 24860 showed almost equivalent inhibitor resistance compared with these industrial strains. Further analysis of these strains on their xylose utilization was carried out. Random mutagenesis followed by xylose adaptation was applied. Almost all the laboratory strains died after mutation and all the industrial strains survived with their xylose unitization capabilities increased. In addition, the presence of inhibitors such as 5-hydroxymethylfurfural (HMF) and furfural had enhanced their xylsoe assimilation. The above analysis indicated that industrial Saccharomyces cerevisiae strains could be trained for biomass hydrolysate fermentation as they have high pH tolerance, high inhibitor resistance and potentials in xylose utilization. As such, the potential xylose-utilizing mutants are being evaluated for their potentials in biomass hydrolysate fermentation.

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