A comparison between simultaneous saccharification and fermentation (SSF) and separate hydrolysis and fermentation (SHF) of spruce and giant reed using two Saccharomyces cerevisiae strains

For significant fermentative conversion of lignocellulose to ethanol, the yeast Saccharomyces cerevisiae has proved to be a robust organism, albeit inter-strain variations may have a big influence on process performance. In this study, two S. cerevisiae strains were evaluated for their ability to ferment two different lignocellulosic raw materials, giant reed and spruce at 10 % water insoluble solids (WIS). One industrial strain, Ethanol Red, and one laboratory strain carrying the XR/XDH pathway, VTT C-10880, were used. The process concept may also affect the choice of the most suitable strain. Therefore, two principal process concepts, simultaneous saccharification and fermentation (SSF) and separate hydrolysis and fermentation (SHF) were evaluated.The ethanol yield on giant reed based on total soluble sugars in the SHF was higher for VTT C-10880 than for Ethanol Red. On spruce, the yield of ethanol was higher for Ethanol Red. In SSF of giant reed, VTT C-10880 performed better in terms of the ethanol yield based on total sugars in fibres and liquid. However, the ethanol yield on spruce was higher for Ethanol Red than for VTT C-10880, which only produced a minor amount of ethanol. Spruce was more inhibitory than giant reed. Ethanol Red is more robust and converted the inhibitory substances in the pretreated materials faster, and is therefore a suitable industrial strain background for fermentation of both spruce and giant reed. Interestingly, VTT C-10880 performed better in SHF than SSF, primarily due to better xylose conversion in SHF