There are several enzymes generally used to convert cellulose and hemicellulose into soluble sugars. They are a mixture of pectinases, cellulases and hemicellulases (Lin et al., 2011; Reddy & Yang, 2005). Cellulose can be hydrolyzed by the synergistic action of endo — acting enzymes knows as endoglucanases, and exo-acting enzymes, known as exoglucanases (Lin et al., 2011). Today it is common to employ enzyme complexes consisting of seven or more degrading enzymes that act synergistically. The enzyme mixture is added before or after chemical or mechanical treatments (Reddy & Yang, 2005). Enzymes appear to be the best prospects for continued improvements because can reduce production costs (Gnansounou et al., 2005).

Sipos et al. (2009) observed that the separation of the solid and the liquid phases after chemical pretreatment is beneficial to the whole process because the xylose-rich liquid fraction can be fermented into ethanol through the pentose pathway or as substrate for microbial cellulase production or transformed into other various valuable products. On the other hand, the solid fraction can be further hydrolyzed and fermented into ethanol. The use of alkali treatment before enzyme hydrolysis generated 540 g glucose/kg raw material, equivalent to a 90% conversion of available cellulose to monomeric sugars. On the other hand, 235 g xylose/kg was released after pretreatment of sorghum straw (McIntosh & Vancov, 2010). These hydrolysates were obtained with an enzyme complex containing endoglucanase, exoglucanase, xylanase, beta-glucosidase and cellulase.