Abstract
Background
Xylo-oligosaccharides (XOS) are promising biomass-derived chemicals that can be widely used in preparing medicines, food additives, and industrial chemicals. The pre-hydrolysis liquor (PHL) produced in the kraft-based dissolving pulp production process is rich in hemicelluloses and especially in XOS/xylan.
Results
In this study, a sustainable sequential process that included calcium hydroxide (CH), simultaneous laccase and xylanase (LX) and activated carbon (AC) treatments was proposed for more efficient recovery of XOS/xylan from PHL. Overall, the concentration of lignin, furfural and xylosugars decreased by 81.7 wt.%, 100 wt.% and 5.1 wt.%, respectively, but XOS concentration was increased by 36.6 wt.%. More importantly, the 2D-HSQC NMR and FT-IR were used in understanding the structure of sugar and lignin components in each step of the process and in the final products. The CH treatment mainly altered the chemical structure of XOS due to the release of acetyl groups, and downstream treatment steps have insignificant effect on XOS structures. Also, lignin carbohydrate complexes (LCC, i.e. PhGlc3) minimally existed in the purified XOS. The GPC and DSC results revealed that the molecular weight of the extracted lignin was 1768 ~ 2532 g/mol and it had a wide glass transition temperature (Tg) range (63 ~ 115 °C).
Conclusions
The results confirmed that a combination of sequentially treating PHL with calcium hydroxide (CH), simultaneous laccase and xylanase (LX) and activated carbon (AC) was effective in removing lignin and concentrating XOS in the PHL.
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