Fermentation Using Yeasts
The most frequently used microorganism for fermenting sugars to ethanol is Saccharomyces cerevisiae, which has proved to be very robust and well suited to the fermentation of lignocellulosic hydro- lyzates [22]. Saccharomyces cerevisiae can easily ferment C-6 mono and disaccharides like glucose, fructose, maltose and sucrose. However, S. cerevisiae is not able to ferment C-5 sugars like xylose obtained during hemicellulose hydrolysis, and this is a huge disadvantage since biomass hydrolyzates are mixtures of C-5 and C-6 sugars. This inability of S. cerevisiae to ferment C-5 sugars is due to a lack of enzymes that convert xylose to xylulose [23].