Community Research and Development Information Service - CORDIS

Novel ethanol fermenting systems using tolerant yeasts

Nedalco has developed methods to adapt and select yeast strains on very toxic hydrolysates. The methods can be applied to any given toxic hydrolysate. The method has been published on two international symposia on fuels and chemicals in the USA together with the Technical University of Budapest and a paper was submitted antitled "Fermentation inhibitors from pretreated lignocellulosic materials: Problems and Solutions". The method can be used for customizing existing strains to new raw materials in combination with severe pretreatment conditions.

Furthermore, hydrolysis techniques have been developed on pretreated Corn Stover preparations as provided by ENEA after steam pretreatment. The whole process of sugar hydrolysis and fermentation was demonstrated of these hydrolysates.

More than 20 yeast strains were tested at VTT and ranked by their ability to produce ethanol in the presence of toxic compounds as well as by their ability to grow on pretreated materials. The best ethanol producers and the most tolerant strains were the industrial strains and genetically modified industrial strains, whereas the strains with laboratory strain background were not as tolerant to the toxic compounds. The xylose utilising strains were able to consume all xylose and convert it further to ethanol in aerobic conditions but the rate was lower than on glucose. All main lignocellulose derived sugars except arabinose in pure form were consumed completely aerobically by the most potential strains. All sugars were consumed more slowly on toxic pretreated materials.

The best VTT strain tested was further mutagenised in order to improve the xylose utilisation rate, to improve the tolerance for inhibitors and to increase the ethanol yield. After several mutagenesis trials mutant strains were isolated which could clearly consume xylose better in aerobic and anaerobic conditions compared to the non-mutagenised strain. The rate of ethanol production of the mutants strains was improved around two-fold compared to the parent strain. Best strains produced up to 50% more ethanol. In fermenter experiments, xylose utilisation rate was around 35 % and ethanol production rate around 25% better compared to the host strain.

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Nedalco Research Laboratory
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