Efficient production of xylooligosaccharides rich in xylobiose and xylotriose from poplar by hydrothermal pretreatment coupled with post-enzymatic hydrolysis

A promising approach for production of value-added xylooligosaccharides (XOS) from poplar was developed by combining hydrothermal pretreatment and endo-xylanase post-hydrolysis. Results showed that the 35.4% XOS (DP 2-6) and 17.6% low DP xylans (DP > 6) were obtained at the identified optimal condition (170 °C, 50 min) for hydrothermal pretreatment. Structural features of low DP xylans generated during the hydrothermal pretreatment were examined, revealing that low DP xylans are mainly comprised of 4-O-methylglucuronic xylan and are involved in lignin carbohydrate complexes. Moreover, higher pretreatment intensity promoted the cleavage of side-chain substituents including arabinose and glucuronic acid groups. The subsequent endo-xylanase hydrolysis of the pretreatment liquor hydrolyzed low DP xylans, contributing to a significant improvement in xylobiose and xylotriose proportions. This combined strategy resulted in a XOS with conversion yield of 44.6% containing 78.7% xylobiose and xylotriose starting from the initial xylan in raw poplar.