Resultant ethanol can then be removed via distillation. Another means of purifying XOS is to use yeast to ferment the undesired monosaccharide impurities into ethanol, further elevating XOS purity. It is reported that employing a secondary enzymatic hydrolysis upon a XOS solution using endo-β-1-4-xylanase can degrade high-DP XOS to effectively reach X2 and X3 enrichment. Biological function of XOS is most potent in samples with high purity, which indicates low contents of xylose and glucose alongside particular enrichment in xylobiose (X2) and xylotriose (X3).

Based on this concept, it can be claimed that recovery of XOS from the prehydrolyzate generated during dissolving pulp industry appeals to the principles of “green chemistry”. Among these technologies, prehydrolysis is regarded as the most green process for producing XOS due to no chemical reagent added in the process. At present, XOS are commercially produced from xylan-rich lignocellulosic materials through the enzymatic hydrolysis using xylanase, dilute acid digestion using sulfuric acid or acetic acid, or a hot water pretreatment similar to previously described prehydrolysis. Xylooligosaccharides (XOS) are defined as xylanic oligosaccharides that contain 2–10 xylose units linked together by β-1,4 glycosidic bonds. This current dispose does not account for the value of these biomass-derived products in prehydrolyzate therefore, efficient recovery and utilization of valuable products should be realized. In current practice process, the prehydrolyzate is mixed with black liquor from kraft cooking process and then burned to recover energy.

Prehydrolyzate contains various sugar-derived compounds such as xylooligosaccharides, gluco-oligosaccharides, xylose, and glucose. Constituents from biomass fractions can be dissolved in the prehydrolysis liquor, which is termed as prehydrolyzate. For the latter process, water or steam prehydrolysis at 160–200 ☌ is carried out in a primary stage, resulting in partial hydrolysis of hemicelluloses and lignin degradation. Currently, the process for the dissolving pulp comprises two distinct segments: the sulfite process and the prehydrolysis kraft process. Studies of world markets clearly indicate a trend of increasing demand for dissolving-grade pulps, a producible material from hardwood, softwood, bamboo, and cotton linters. These biomass-derived products in prehydrolyzate can be regarded as value-adding prebiotics and antioxidants. The proposed strategy of sequentially combining hydrophobic resin separation, enzymatic hydrolysis, and fermentation was successfully demonstrated and resulted in simultaneous production of high-quality XOS and solubilized lignin. The biological application results showed that the antioxidant capacity of S-L was stronger than XOS, while XOS was superior in promoting growth of intestinal Bifidobacteria adolescentis and stimulating production of short-chain fatty acids by Lactobacillus acidophilus. 2D-HSQC NMR revealed that lignin carbohydrate complexes existed in both XOS and S-L as covalent linkages between lignin and 4- O-methylglucuronoarabinoxylan.

10.4% amount of inherent xylan was found in the S-L fraction obtained by PS-DVB resin separation. The obtained XOS after being purified by enzymatic hydrolysis and fermentation contained 57.7% of xylobiose and xylotriose. Results showed that PS-DVB resin could simultaneously separate XOS and solubilized lignin with excellent yields of 93.2% and 85.3%, respectively. Furthermore, the biological abilities of antioxidants and prebiotics of these fractions were investigated by scavenging radicals and cultivating intestinally beneficial bacterias, respectively. In addition, 2D-HSQC NMR was used to analyze the structural characteristics of XOS and S-L. stipites were sequentially applied to purify XOS to minimize xylose content as well as amplify contents of xylobiose and xylotriose. Enzymatic hydrolysis with endo-1,4-β-xylanase and fermentation with P. In this work, we proposed a sustainable and green process using polystyrene divinylbenzene (PS-DVB) resin to simultaneously separate and recover XOS and S-L. XOS and S-L in prehydrolyzate are difficult to efficiently fractionate due to their similar molecular weights and water solubility. The XOS has several beneficial effects on human physiology. Prehydrolyzate, which is from the prehydrolysis process in dissolving pulps industry, contains various sugar-derived and lignin compounds such as xylooligosaccharides (XOS), gluco-oligosaccharides, xylose, glucose, and soluble lignin (S-L).

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