Yeast adaption on the substrate straw

Bioethanol production of lignocellulosics is technologically analyzed, but requires further investigations concerning yield optimization and economic efficiency. One important aspect is to obtain an ideal yeast strain for the fermentation process, which should possess the ability of a stable conversion of C5- and C6-sugars, resistance/tolerance against inhibitory compounds, temperature, ethanol, sugar and industrial stability. For this purpose, several yeast strains have been adapted to the mentioned characteristics using specific natural adaption and systematic selection. For improved utilization of xylose, several yeast strains have been cultivated on xylose-minimal agar for various generations. Yeast strains have been adapted to grow in ascending concentrations of wheat straw hydrolysate medium. Furthermore, several yeast strains have been bred at increased temperatures, with enhanced ethanol and sugar concentrations. Some xylose- as well as hydrolysate-adapted yeast strains show an increased fermentative competence. A few of the thermally adapted yeast strains represent an enhanced fermentative capacity at higher temperature (42 °C). Various yeast strains are tolerant concerning 8-12 % of ethanol and 400-450 g/l of glucose. Some significant improvements concerning ideal yeast strain could have been reached. These improvements offer new possibilities for further optimization.