Digestion and fermentation characteristics of the polysaccharides from Polygalae Radix processed by Glycyrrhizae Radix et Rhizoma and its effects on gut microbiota and metabolites.

Polygalae Radix Processed by Glycyrrhizae Radix et Rhizoma (GPR) contains polysaccharides (PGPR) as key active ingredients, yet their oral digestive fate and gut microbiota interactions remain elusive. In this study, we employed in vitro digestion and fermentation models to investigate PGPR's structural stability, fermentation properties, and modulatory effects on gut microbial communities and metabolites. Digestion experiments revealed no significant alterations in PGPR's molecular weight, free monosaccharides, reducing sugar (RS) content, or Fourier transform infrared spectral characteristics, indicating the preservation of their core structure in the upper gastrointestinal tract and reached the colon in an intact form. In vitro fermentation experiments showed that the degradation and utilization of PGPR led to a significant decrease in levels of total sugar, RS, and pH. Concurrently, the production of short-chain fatty acids increased significantly, especially the acetic acid and propionic acid. More importantly, PGPR selectively enriched the advantageous gut microbiota (especially the Actinobacteria and Bifidobacterium), and inhibited the proliferation of harmful bacterial colonies such as Bilophila and Klebsiella to maintain the host health. Metabolomics analysis further demonstrated that the utilization of PGPR by the gut microbiota significantly altered the composition of metabolites, affecting 5 major metabolic pathways (Linoleic acid metabolism, Sphingolipid metabolism, and alpha-Linolenic acid metabolism pathways, etc.) to promote host health. Collectively, our findings confirm that PGPR exerted prebiotic bioactivity by modulating gut microbiota and metabolite composition. These results provided a new perspective on the functional basis of GPR and support PGPR as a candidate prebiotic derived from this processed herb.