What question did this study set out to answer?

The aim was to optimize the extraction of pumpkin polysaccharides using dual-frequency ultrasound while characterizing their structure and antioxidant activity.

March 6, 2026Open Access

Dual-frequency ultrasonic-assisted extraction of pumpkin polysaccharides: Process optimization, structural characterization, and antioxidant activity

Key Points

The aim was to optimize the extraction of pumpkin polysaccharides using dual-frequency ultrasound while characterizing their structure and antioxidant activity.
Applied dual-frequency ultrasound-assisted extraction (DF-UAE) at 20/40 kHz.
Compared extraction efficiency with hot-water extraction (HWE).
Utilized response surface optimization for extraction yield.
Conducted structural analysis through methylation and NMR analyses.
Evaluated antioxidant activity using ABTS•+ and •OH assays.
DF-UAE achieved a 1.78-fold higher extraction yield compared to HWE.
Extraction time reduced by 78% and specific energy consumption decreased by 90%.
DF-UAE-derived polysaccharides showed enhanced uronic acid content and pronounced antioxidant activities.
Identified PPs2 as a branched rhamnogalacturonan-I-type pectic heteropolysaccharide with specific linkages.

Abstract

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.

Dual-frequency ultrasonic-assisted extraction of pumpkin polysaccharides: Process optimization, structural characterization, and antioxidant activity

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