Pumpkin polysaccharides (PP) possess valuable bioactivities, yet conventional extraction suffers from low efficiency and structural degradation. In this study, dual-frequency ultrasound-assisted extraction (DF-UAE, 20/40 kHz) was applied to enhance PP extraction efficiency and to elucidate frequency-dependent extraction mechanisms. Compared with hot-water extraction (HWE), DF-UAE achieved a 1.78-fold higher extraction yield (21.55 vs. 12.11 g·100 g -1 ) and a 1.54-fold greater total sugar content. Response surface optimization yielded 40.51 ± 0.35 g·100 g -1 . DF-UAE reduced specific energy consumption by a factor of 0.9 and CO 2 emissions by 0.9, with an estimated industrial payback period of 8 months. Structural analysis showed DF-UAE preserved higher molecular weight polysaccharides (Mw 219.3 vs. 32.4 Da), enriched high-molecular-weight fractions (25.36% vs. 3.26%), and maintained uronic acid content and narrow polydispersity. The purified fraction PPs2 was identified as a branched rhamnogalacturonan-I-type pectic heteropolysaccharide by methylation and NMR analyses. DF-UAE-derived polysaccharides exhibited stronger antioxidant activity, correlated with molecular weight, uronic acid and protein content. Mechanistic evidence indicated that synergistic cavitation at a 2:1 frequency ratio balanced efficient cell disruption with reduced chain degradation. DF-UAE provides an efficient and sustainable strategy for producing structurally preserved bioactive pumpkin polysaccharides for functional food applications. • Dual-frequency ultrasound-assisted extraction (DF-UAE) achieved a 1.78-fold higher extraction yield vs. hot-water extraction (HWE). • DF-UAE reduced extraction time by 78% and energy consumption by 90%. • DF-UAE enhanced uronic acid content and antioxidant activities (ABTS• + /•OH). • PPs2 exhibited AG-II structure with branched →3)-β-Galp-(1→ and →3,6)-β-D-Galp-(1→ linkages.
Duan et al. (2026) studied this question.