Purification and characterization of two non‐starch polysaccharides from bulbils of Dioscorea opposita Thunb. ‘Tiegun’ and their antioxidant and hypoglycemic activity

BACKGROUND: Dioscorea opposita Thunb. cv. 'Tiegun' has substantial agricultural and economic value. Its underground tubers are used widely in food and traditional medicine but the bulbils - small globular structures in the leaf axils - are frequently overlooked and discarded. This wastes biological resources and reduces overall plant productivity. RESULTS: To address this, subcritical water extraction was applied to extract substances from the bulbils, followed by separation and purification. As a result, two non-starch polysaccharide components, DBP1 and DBP2, were obtained, with extraction rates of 2.25% and 0.85% respectively. Subsequent research on their properties and activity showed that DBP1 (21.9 kDa) was a neutral polysaccharide mainly made of Gal and Glc, and DBP2 (109.8 kDa) was an acidic polysaccharide composed of GalA and Gal. Due to the higher yield of DBP1, its structure was studied in greater depth. Methylation experiments indicated that its main chain consisted of 1,4-Galp and 1,4,6-Glcp glycosidic bonds with branch points, consistent with nuclear magnetic resonance (NMR) results. Scanning electron microscopy revealed that DBP1 and DBP2 had distinct filamentous structures yet similar spherical morphologies. Fourier transform infrared spectroscopy and thermal analysis were used to study their functional groups and thermal stability. In activity tests, DBP1 and DBP2 both showed antioxidant activity and could inhibit α-glucosidase and α-amylase, demonstrating hypoglycemic activity. CONCLUSION: In conclusion, DBP1 and DBP2, two non-starch polysaccharides, showed good antioxidant and hypoglycemic effects. They can be used as raw materials for functional foods and drugs and merit further development. Maximizing bulbil utilization promotes green, sustainable agriculture and prevents resource waste. © 2025 Society of Chemical Industry.