Structural characterization and bioactivity evaluation of polysaccharides from Chrysanthemum indicum, Lycium barbarum, Rosa roxburghii, and Platycodon grandiflorum extracted by ultrasound-assisted deep eutectic solvents.

To address the low yield and structural damage of traditional medicinal plant polysaccharide extraction, this study developed a selective ultrasound-assisted deep eutectic solvent (UAE-DES) strategy. Under optimized conditions, Platycodon grandiflorum (PGP), Chrysanthemum indicum (CIP), Rosa roxburghii (RRP) and Lycium barbarum (LBP) polysaccharides achieved yields of 17.65%, 9.75%, 14.68%, 15.89% and purities of 95.91%, 64.77%, 60.08%, 74.55%, respectively. FTIR, GPC and NMR confirmed intact polysaccharide backbones and reduced impurities in UAE-DES extracts. Likewise, structural profiling revealed distinct species-specific architectures. Bioassays identified a novel structure-function relationship: low-Mw linear CIP achieved ∼100% DPPH scavenging at 2.0 mg/mL via high accessibility; branched RRP/LBP exhibited hypoglycemic activity (IC50 2.55/1.80 mg/mL for α-amylase/α-glucosidase) via steric shielding. High-dose polysaccharides formed a physical barrier against E. coli, with CIP active at 40 mg/mL. This study establishes a robust BBD-optimized green UAE-DES platform for high-purity polysaccharides, clarifies their structure-function correlations, and informs design of bioactive food ingredients.