Enzymatic purification and structure characterization of glucuronoxylan from water extract of Cassia obtusifolia seeds

Enzymatic hydrolysis was proposed for the first time to purify the sub-fraction of water-extracted cassia polysaccharide (CP-40), and a homogeneous polysaccharide CP-40-M was obtained with relatively high yield. The structural features of CP-40-M were characterized using size-exclusion chromatography equipped with multiple detectors (SEC-MALLS), high-performance anion-exchange chromatography (HPAEC), methylation and gas chromatography-mass (GC-MS), as well as nuclear magnetic resonance (NMR) spectra. The weight-average molecular weight for CP-40-M was determined to be 0.29 × 105 Da, and the molar ratio of xylose to glucuronic acid was 4.62. The structure of CP-40-M was elucidated to be glucuronoxylan, with glucopyranosyluronic acid group terminally attached to O-2 of the →4)-β-Xylp-(1→ backbone. It was the first time to obtain this type of xylan from the water extract of Cassia obtusifolia seeds. The structure elucidation of CP-40-M was meaningful for better understanding the natural characteristics of cassia polysaccharide and important for their potential use in food industry and folk medicine.