Structure characterization of an agavin-type fructan isolated from Polygonatum cyrtonema and its effect on the modulation of the gut microbiota in vitro

The herbal medicine Polygonatum cyrtonema is highly regarded in China for its medicinal and dietary properties. However, further research is needed to elucidate the structure of its polysaccharide and understand how it promotes human health by modulating the gut microbiota. This study aims to investigate a homogeneous polysaccharide (PCP95–1-1) from Polygonatum cyrtonema and assess its susceptibility to digestion as well as its utilization by intestinal microbiota. The results confirmed that PCP95–1-1 is an agavin-type fructan, which possesses two fructose chains, namely β-(2 → 6) and β-(2 → 1) fructosyl-fructose, attached to the sucrose core, and has branches of β D-Fruf residues. Moreover, PCP95–1-1 demonstrated resistance to digestion and maintained its reducing sugar content throughout the digestive system, indicating it could reach the gut without being digested. In vitro fermentation of PCP95–1-1 significantly decreased the pH value (p < 0.05) while notably increasing the production of short-chain fatty acids (SCFAs), confirming its utilization by human gut microbiota. Additionally, PCP95–1-1 exhibited a significant ability (p < 0.05) to beneficial bacteria such as Megamonas and Bifidobacterium, while reducing the presence of facultative or conditional pathogens such as Escherichia-Shigella and Klebsiella at the genus level. Consequently, PCP95–1-1 has the potential to positively influence physical well-being by modulating the gut microbiota environment and can be developed as a functional food.