Coproduction of xylooligosaccharides and monosaccharides from hardwood by a combination of acetic acid pretreatment, mechanical refining and enzymatic hydrolysis

Sequential biorefinery treatments of acetic acid (HAC) pretreatment, Papir Forsknings Institutet (PFI) milling and enzymatic hydrolysis were demonstrated for coproduction of xylooligosaccharides (XOS) and fermentable monosaccharides. Results indicated that 36.2% XOS (50.8% X2-X3) and 17.0% low DP xylans were achieved using a HAC pretreatment with a combined severity factor of 0.78. The HAC pretreatment resulted in a XOS-rich prehydrolyzate with a low molecular weight of 1.28 kDa. The endo-xylanase hydrolysis was conducted on the pretreatment liquor to elevate XOS yield and the content of higher-value X2-X3. Moreover, fermentable glucose production from the pretreated residue increased by 2.3 folds when introducing an additional step of PFI refining prior to enzymatic digestion. Properties of substrate including cellulose accessibility, crystallite size, crystalline index and water retention value were in close relationships with enzymatic digestibility. The implementation of proposed biorefinery process will give more insights into the efficient construction of a wood-derived sugar platform.