Ultrasonic-assisted ternary deep eutectic solvent extraction of polysaccharides from fermented black beans (Dan-Dou-Chi): structural features, antioxidant, and hypoglycemic activities

Semen Sojae Praeparatum polysaccharides (SSPP-UD) were extracted using an ultrasonic-assisted ternary deep eutectic solvent (UD; choline chloride: tartaric acid:ethylene glycol, 2:1:1) optimised by response surface methodology (79 min, 35% water, 30 mL/g, 65 °C). This yield reached 115.37 ± 1.1 mg/g, 4.8- and 3.0-fold higher than hot-water and ultrasonic-assisted water extraction, respectively. SSPP-UD contained predominantly low-molecular-weight fractions (1.50 × 10 3 Da, 55.73%), alongside high-molecular-weight components, with a broad molecular-weight distribution and enrichment in uronic acids, arabinose, and xylose. FT-IR analysis confirmed abundant hydroxyl and carboxyl groups, indicating acidic polysaccharides. SSPP-UD formed stable, negatively charged aqueous aggregates (Dh ~31.8 μm) and showed antioxidant activity at 3 mg/mL (DPPH, 27.4%; ABTS• + , 20.6%; hydroxyl radical, 33.3%), as well as α -amylase and α -glucosidase inhibition (96.8% and 93.7%; IC 50 , 0.77 and 0.68 mg/mL, respectively). These results demonstrate that ultrasound-assisted ternary DES extraction is an efficient, green strategy for obtaining bioactive polysaccharides from fermented black beans for functional food applications.