Fermentation of xylose and cellobiose byPichia stipitis andBrettanomyces clausenii

Conclusions

This paper draws attention to the fact that successful SSF processing of lignocellulosics with high pentosans can be achieved rapidly and efficiently without β-glucosidase supplementation when pentose fermenting yeast is coupled with a cellobiose fermenter.

B. clausenii was identified as a potent cellobiose fermenter. All the major sugars that would be released on saccharification of biomass were fermented byP. stipitis 5776. Strain improvement ofP. stipitis through recycling represented a useful technique and resulted in rapid fermentation of lignocellulosic hydrolysates. A mixed culture ofP. stipitis R and B.clausenii in a single vessel in a SSF mode converted the SO₂ prehydrolyzed aspen wood to monomeric wood sugars and the resulting wood sugars to ethanol at a rapid and efficient rate, with yields that are higher than any reported to date. This also shows for the first time the application of coupled pentose and cellobiose fermentation in SSF process, eliminating the need for β-glucosidase supplementation. Further investigation aimed at eliminating the use of hemicellulase and reducing the amount of cellulase are in progress.