Dual-frequency ultrasonic-assisted extraction of pumpkin polysaccharides: Process optimization, structural characterization, and antioxidant activity
Yuyuan Duan, Wei Li, Yixiao Zhu, Junkai Chen, Jianfei Xue, Huizhu Wang, Shuai Chen
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.