Structural characterization of a fructan from Polygonati Rhizoma and its anti-diabetic effects associated with insulin-signalling-related readouts and gut microbiota modulation

Type 2 diabetes mellitus (T2DM) involves insulin resistance, hyperglycaemia, and metabolic stress. Polygonati Rhizoma (Huangjing), a traditional edible and medicinal plant widely used in East Asia, has gained attention as a functional food resource. In this study, a fructan-rich polysaccharide fraction (PRP-W-1) was purified and characterized by HPGPC, FT-IR, GC–MS, and NMR. PRP-W-1 showed a single HPGPC peak with a weight-average molecular weight of approximately 4.8 kDa and consisted mainly of fructose ( > 93%) with minor glucose. Linkage and NMR analyses indicated that PRP-W-1 is a low-molecular-weight fructan mainly composed of a 1,2-linked fructofuranosyl backbone, together with a minor glucosyl component and limited branching. In HFD/STZ-induced T2DM mice, PRP-W-1 mitigated body-weight loss, lowered fasting glucose, improved glucose tolerance, and enhanced insulin sensitivity. It also attenuated dyslipidaemia and liver index elevations. PRP-W-1 was associated with increased hepatic PI3K and p-AKT, reduced p-JNK, and restored adipose GLUT4 abundance. It also improved intestinal barrier-related markers, reshaped the gut microbiota, and increased cecal short-chain fatty acids (SCFAs). Collectively, these results identify PRP-W-1 as a structurally defined, low-molecular-weight fructan from Polygonati Rhizoma with hypoglycaemic and gut-modulatory effects, supporting its potential as a natural dietary ingredient for metabolic health.