Valorization of Paeonia ostii fruit pod polysaccharides by ultrasound-assisted aqueous two-phase extraction and antioxidant activity

We established an ultrasound-assisted aqueous two-phase extraction (UAE-ATPS) for polysaccharides from Paeonia ostii fruit pods. Under optimized conditions [ethanol 28% (w/w), K₂HPO₄ 22% (w/w), 51 °C, 52 min], the extraction yield reached 6.21%, significantly higher than hot-water extraction (2.28%). Control experiments showed that UAE-ATPS outperformed either UAE without ATPS (2.96%) or ATPS without ultrasound (2.49%), indicating a synergistic enhancement rather than mere additive effects. The purified fractions were acidic heteropolysaccharides by preliminary characterization. In vitro assays showed that the IC 50 values for DPPH•, ABTS•⁺, and •OH ranged from 0.116 to 5.681 mg/mL, 0.159–0.271 mg/mL, and 4.083 to > 20 mg/mL, respectively, across PFPP-0, PFPP-2 and PFPP-5 (vitamin C as positive control).The crude polysaccharide (PFPP-0) showed higher apparent activity than purified fractions, which was partly attributable to co-extracted non-polysaccharide components (total phenolics 0.26% (w/w), residual protein < 10 μg/mL). In C. elegans assays, PFPP-0 improved lifespan and stress tolerance; transcriptional changes in skn-1 and downstream genes are consistent with a possible role of endogenous antioxidant responses, though direct evidence of pathway activation remains to be established.