Comparison of cellulose digestibility from straw and bagasse sugarcane submitted to two-step pretreatment

Studies of new technologies and parameters of pretreatment to modify the biomass to improve cellulose digestibility are a topic of fundamental importance. Biomass conversion technologies are required to become the cellulose available for enzymatic hydrolysis process and consequently improve the yield of fermentable sugars and ethanol.  A combination of hydrothermal pretreatment and alkaline delignification may be adopted to solubilize hemicellulose and lignin, respectively. Straw and bagasse sugarcane present different morphology which impact on result of biomass modification. This study aims to evaluate different conditions of hydrothermal pretreatment followed by a fixed condition of alkaline delignification on straw and bagasse sugarcane assuming the cellulose digestibility as the main response of performance. Results reveal a different behavior of bagasse and straw from sugarcane at the end of its processing. DRX and SEM results show that there was a greater morphological change of sugarcane bagasse compared to straw, which presented exposure of the fibers, but also aggregated. This fact can be explained by less removal of lignin and hemicellulose of this biomass compared to the same processing conditions of bagasse. The exposure of fibers contributed to increase the cellulose of bagasse digestibility, since there was a greater area of contact of the enzyme with the substrate and a minimization of interference from inhibitors, such as lignin. The conditions of pretreatment most promising for bagasse and straw sugarcane were 180^oC for 20 and 30 min. respectively, showing that the straw requires longer treatments to reach a higher digestibility in the enzymatic hydrolysis process.