Enzymatic hydrolysis is the best procedure for degrading cellulose into reducing sugars. It depends on the temperature, time, pH, enzyme loading, and concentra­tion of substrate during the hydrolysis. Hydrolysis and fermentation can be done together for reducing time and avoiding end product inhibition. This process is called simultaneous saccharification and fermentation. Three types of cellulolytic enzymes such as endo-p-1,4-glucanases, cellobiohydrolases, and p-glucosidases are required for enzymatic hydrolysis of cellulose. Duff and Murray (1996) reported that various types of enzymes such as xylanase, b-xylosidase, glucuroni­dase, acetylesterase, galactomannanase, and glucomannanase are necessary for breaking down the hemicelluloses. Bacteria and fungi are used for enzymatic hydrolysis, but Aspergillus and Trichoderma genera are widely used for enzymatic hydrolysis for cellulose production. The enzyme source is a major effect for effective hydrolysis.

16.5.1 Detoxification ofHemicellulosic Hydrolysate

There are several methods that can be used to detoxify the hydrolysates during ethanol production. These methods are membrane use, ion exchange resins, evaporation, neutralization, and activated charcoal which have been used for ethanol production. The ion exchange resins process are the most effective detoxification method that can remove lignin-derived inhibitors and acetic acid and significantly improve the yield of fermentation (Chandel et al. 2011). This method can be regenerated and reused without disturbing any treatment. On the other hand, adsorption of activated charcoal is widely used to detoxify for lower cost and efficient inhibitor compound removal. This method can remove only phenolic compounds that cannot change the fermentable sugar levels (Canilha et al. 2008). The success of this method depends on charcoal and hydrolysates ratio, contact time, pH, and temperature (Mussatto and Roberto 2004).