A more cost-effective option may therefore be the application of crude enzyme extracts obtained from fungi, in which case an array of enzyme activities is maintained and enzyme concentration costs are minimized. Furthermore, few studies have been performed on recycling

of enzymes [30]; where most focus on separating the Erismodegib enzyme from the solid or liquid phase or recycling of the solid and/or liquid phase directly. However, a more straightforward approach to enzyme recycling is direct recycle of the solid fraction to which most of the enzymes are likely bound. Studies have shown that enzyme productivity (product yield per quantity of enzyme applied) can be significantly increased in this type of recycle process [30]. Hexoses such as glucose, galactose, and mannose are readily fermented to ethanol by

many naturally occurring organisms, but pentoses, including xylose and arabinose, are fermented to ethanol by few native strains, and usually at relatively low yields. Commercial utilization of xylose-fermenting microorganisms is often limited due to slow fermentation rates, carefully regulated oxygen requirements, sensitivity to inhibitors and low ethanol tolerance. However, because xylose and arabinose generally comprises a significant fraction of lignocellulosic biomass, its utilization makes the economics of biomass to ethanol conversion more feasible. The development of recombinant ethanogenic strains has resulted in bacteria and yeasts capable of co-fermenting pentoses and hexoses into ethanol and other PLX4032 price value-added products at high yields [31]. On the other hand, the hemicellulose hydrolysate can be used for xylitol and butanol production by xylose fermentation. Xylitol, which is a sugar substitute, has been widely used in food, medicine

and other fields. Additionally, xylitol is identified as one of added-value chemicals that can be produced from biomass. Several yeasts are suitable for xylose fermentation to xylitol. Because the traditional xylitol production process involves the chemical synthesis of xylose crystal using a toxic catalyst, which imposes a high environmental burden and is unfavorable for large-scale production, bioprocessing could potentially be applied for industrial learn more xylitol production [32]. A butanol production system from xylose fermentation was established using the high-density Clostridium saccharoperbutylacetonicum N1-4 generated by cell recycling [33]. The yeast Saccharomyces cerevisiae is that most studied and is known for its inherent resistance to low pH, high temperature, and various inhibitors [34]. Other wild-type microorganisms used in the fermentation process include Escherichia coli, Zymomonas mobilis, Kluyveromyces marxianus, Pichia stipitis and Candida brassicae, where some are capable of fermenting pentose sugars, but often at rates significantly lower than that of S.