As stated in section 3.1, besides water-soluble sugars (sucrose, glucose and fructose), sorghum is composed by structural cell wall carbohydrates primarily cellulose and hemicellulose, which in turn can be hydrolyzed and used as substrate for ethanol production (Sipos et al., 2009).

Sorghum bagasse is the residual fraction obtained after juice extraction from sweet sorghum whereas sorghum straw is the remaining material usually left on the field after threshing. The composition and proportion of fibrous-structural fractions in sorghum is widely reported and varies according to intrinsic and extrinsic factors such as cultivar type, maturity and climatic conditions. An average of 15% of the total weight corresponds to the fibrous portion within a range from 12 to 17% (Woods, 2000).

In sweet sorghum bagasse, average content of cellulose, hemicelluloses and lignin is 34-44%, 27-25%, and 18-20% respectively (Ballesteros et al., 2003; Kim & Day, 2011; Sipos et al., 2009).

Table 1. Fiber composition of different ethanol feedstock 1