Xylan recovery from alkaline-sulfite pretreated sugarcane bagasse and enzymatic hydrolysis of residual cellulose

Efficient sugar production from lignocellulosics could be anticipated through a combination of thermochemical removal of lignin by pretreatment and removal of xylan prior or concomitant with cellulase digestion. The objective of this study was to extract high molar mass xylan from pretreated sugarcane bagasse prior enzymatic cellulose hydrolysis. Extraction procedures were performed with alkaline solution, assisted or not by xylanases. Structural features of the extracted xylan were also assessed samples. Sugarcane bagasse was chemithermomechanically pretreated with an alkaline/sulfite solution and washed (WB). A similar pretreatment procedure was performed without bagasse washing after pretreatment (UWB). The alkaline/sulfite treatment resulted in a considerable delignification (53% in WB and 43% in UWB) and left most of hemicellulose (76% in WB and 78% UWB) in pretreated solids. Two methods, based on xylan solubilization with alkali were carried out. Also, an enzymatic method of extraction was tested using xylanases. Recovery yields of the extracted xylan ranged from 22-71% and the lower yields were obtained with the enzymatic extraction method (22% in WB and 31% of the UWB). The obtained hemicellulosic subfractions were comprehensively investigated by both destructive methods such as acid hydrolysis and nondestructive techniques such as gel permeation chromatography and Fourier-transform infrared. The type of xylan extraction procedure reflected in xylan-extraction yields and in the chemical composition of prepared xylan. Furthermore, the hydrolysis of the cellulose had a slight increase compared to the pretreated bagasse without extraction of xylan, suggesting that process may be employed in a biorefinery process.