Precise structural characterization and therapeutic potential of a glucomannan polysaccharide from dried rhizome of plant Bletilla striata against ulcerative colitis.

Bletillae Rhizoma (Baiji), the dried tuber of Bletilla striata (Thunb.) Reichb.f. (BS), a traditional medicinal plant widely used in Chinese medicine. While polysaccharides from BS tuber (BSP) have attracted attention for their broad industrial applications, their detailed structural features and biological functions remain limited. In this study, a neutral polysaccharide (BSPN, 178 kDa), constituting about 80% of BSP, was extracted and purified. Structural analysis elucidated BSPN as a glucomannan (mannose: glucose = 4: 1), featuring a backbone of →4)-β-D-Manp-(1 → and →4)-β-D-Glcp-(1 → linkages with branching at →4, 6)-β-D-Manp-(1 → positions. Targeted enzymatic hydrolysis, with specific endoglycosidases to cleave characteristic glycosidic bonds, not only verified the purity of BSPN, but also generated diagnostic oligosaccharide fragments that revealed the native glycosidic linkage patterns as well as the precise position of acetyl substitution. Furthermore, BSPN significantly alleviated ulcerative colitis in mice in a dose-dependent manner, improving colon histology, enriching beneficial gut microbiota (Faecalibaculum spp., Bacteroides spp., and Bifidobacterium spp.), restoration of short-chain fatty acids levels (including a 69% increase in valeric acid), and upregulating glycoside hydrolase genes (GH1/GH2). Together, our findings provide the first comprehensive structural characterization and anti-colitis evaluation of BSPN, highlighting its potential as a therapeutic agent for ulcerative colitis.