One of the most significant problems in ethanol production from lignocellulose is production cost (Mizuno et al., 2009) because the fiber conversion requires of high energy investments in order to obtain high concentrations of fermentable sugars from the insoluble polymers (Kurian et al., 2010; Mamma et al., 1996). A pre-hydrolysis step releases both the hemicellulosic and cellulosic fractions of the fiber (Herrera et al., 2003). The main processes related to the pretreatment of sorghum biomass for ethanol production are the acid and/or enzyme-catalyzed hydrolyses (Mamma et al., 1996; Sipos et al., 2009). Generally, the acid hydrolysis precedes the enzymatic in order to optimize production of C6 and C5 fermentable sugars (Sipos et al., 2009).

4.3 Pretreatments used for sorghum bagasse

The extraction of structural carbohydrates from bagasse cell walls is highly related to the effectiveness of pretreatments. Nowadays there are many proposed treatments for cellulose and hemicellulose extraction, but only few have been commercially implemented. In the following sections some of the proposed technologies for sorghum biomass are discussed.