Co-extraction of soluble and insoluble sugars from energy sorghum based on a hydrothermal hydrolysis process

•A co-extraction process of soluble and insoluble sugars from ES was developed.•N series of ES presented a higher recalcitrance to sugar release than T series.•More than 80% pentose and hexose was recovered for T series of ES.•A negative correlation for the lignin content, CrI and G/S ratio to ED was observed.•The heterogenization of chemical composition distribution for HH treated ES was broken.

A process for co-extraction of soluble and insoluble sugars from energy sorghum (ES) was developed based on hydrothermal hydrolysis (HH). Two series of ES were investigated: one (N) with a high biomass yield displayed a higher recalcitrance to sugar release, whereas the second (T) series was characterized by high sugar extraction. The highest total xylose recoveries of 87.2% and 98.7% were obtained for N-11 and T-106 under hydrolysis conditions of 180 °C for 50 min and 180 °C for 30 min, respectively. Moreover, the T series displayed higher enzymatic digestibility (ED) than the N series. The high degree of branching (arabinose/xylose ratio) and acetyl groups in the hemicellulose chains of T-106 would be expected to accelerate sugar release during the HH process. In addition, negative correlations between ED and the lignin content, crystallinity index (CrI) and syringyl/guaiacyl (S/G) lignin ratio were observed. Furthermore, finding ways to overcome the thickness of the cell wall and heterogeneity of its chemical composition distribution would make cellulose more accessible to the enzyme.