Preparation of an agavin-type fructan from Polygonatum sibiricum via fermentation-ultrafiltration and its effect on DSS-induced ulcerative colitis.

Polygonatum sibiricum possesses a complex chemical composition and multiple pharmacological activities, among which polysaccharides are recognized as key functional constituents. To obtain high-yield bioactive polysaccharides, this study employed a fermentation-ultrafiltration coupling strategy to extract and separate fermented Polygonatum sibiricum polysaccharides (FPSP). Bacillus licheniformis was used in fermentation and the extraction efficiency in the extract reached 66.5% after optimization of the fermentation conditions. Subsequent ultrafiltration of the extract ultimately yielded a homogeneous fraction named FPSP-2. The yield of FPSP-2 reached as high as 36.30%. Structurally, FPSP-2 consists mainly of β-(2 → 1)-Fru-Fru linkages in the backbone and β-(2 → 6)-Fru-Fru linkages in the side chains, with a small amount of glucose incorporated, forming a typical agavin-type fructan structure with an average molecular weight of 5.4 kDa. Animal experiments demonstrated that FPSP-2 significantly alleviated clinical symptoms of DSS-induced colitis in mice, reduced the levels of pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 in serum and colon tissues, and upregulated the expression of the anti-inflammatory cytokine IL-10. Moreover, gut microbiota analysis revealed that FPSP-2 intervention effectively ameliorated DSS-induced dysbiosis and promoted the growth of beneficial bacteria such as Lactobacillus. This effect may be closely related to the agavin-type fructan structure of FPSP-2.