Ethanol production hemicellulosic materials fermentation

Xylose is the major sugar present in the hemicellulose fraction of agricultural residues, such as wheat straw. Because the raw material cost is greater than one-third of the overall ethanol production cost [5], fermentation of xylose together with glucose is needed to improve the economics of any lignocellulosic-based bioethanol process. 

In direct microbial conversion of lignocellulosic biomass into ethanol that could simplify the ethanol production process from these materials and reduce ethanol production costs, Clostridium thermocellum, a thermoanaerobe was used for enzyme production, hydrolysis and glucose fermentation (755). Cofermentation with C thermosaccharolyticum simultaneously converted the hemicellulosic sugars to ethanol. However, the formations of by-products such as acetic acid and low ethanol tolerance are some drawbacks of the process. Neurospora crassa produces extracellular cellulase and xylanase and has the ability to ferment cellulose to ethanol 139). 

Fermentation of the lignoceliulosic hydrolyzates is more difficult than the well-established processes of ethanol production from e.g. molasses and starch. Hydrolyzates contain a broader range of inhibitory compounds, where the composition and the concentration of these compounds depend on the type of lignoceliulosic materials and the chemistry and nature of foe pretreatment and hydrolysis processes. Secondly, foe hydrolyzates of hemicelluloses contain not only hexoses but also pentoses, where xylose is foe dominant sugar in foe hydrolyzates from hardwood hemicelluloses. Therefore, foe fermenting microorganism should be able to produce efoanol from foe hydrolyzates with a... 

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