Structural characterization of pure xylan from corncob and its effect on xylooligosaccharides yield after enzymatic hydrolysis.

The structure of xylan plays a significant role in the degradation rate by xylanase to product xylooligosaccharides (XOS). In this study, xylan was extracted and purified from corncob, yielding two xylan fractions (WUAX-2, WUAX-3) with purities exceeding 90 %. The structures of WUAX-2 and WUAX-3 were characterized and hydrolysis efficiency was studied in relation to their structures. FT-IR results indicated that although xylan fractions had the same types of functional groups, WUAX-3 exhibited a higher level of -OH, CH, and CO groups compared to WUAX-2. NMR, the vibration signal of WUAX-2 and WUAX-3 was β-(1 → 4) -linked D-lignin unit β-D-xylopyran. X-ray diffraction results confirmed that WUAX-2 was a stable single-crystal structure. Meanwhile, the number of side-chains of WUAX-2 in the liquid was smaller than that of WUAX-3. WUAX-2 and WUAX-3 were hydrolyzed by a high-temperature-resistant xylanase (XynA) and yielded primarily xylohexaose (X), xylotriose (X), and xylobiose (X). The XOS yield of WUAX-2 was 4.25 times higher than that of WUAX-3. These results indicate that the fewer xylan side-chains and substituent groups of xylan, the higher the enzymatic hydrolysis efficiency. The findings provide a deep understanding of the effect of xylan structure on the enzymatic behavior.