PEG-based-ultrasound-microwave synergistic extraction of mucilage polysaccharides from chia seed: Structural characterization and bioactivity.

In this study, the effects of microwave, ultrasound, ultrasound-microwave synergy, and polyethylene glycol (PEG)-200 on the chia seed mucilage's (CSM) structural, thermal, and functional properties have been evaluated by modern spectroscopic techniques, crystal diffraction, and thermal analyses. The results showed that CSM, extracted by PEG-200 aqueous solution has the largest particles (1120-1231 μm), and the smallest size (44.06-317.19 μm) has been observed in microwave extraction. Furthermore, microwave exposure seems to impact the primary structure of CSM profoundly, evidenced by shifts and changes in spectroscopy under high-frequency microwave conditions. However, the incorporation of ultrasound significantly mitigates microwave's effect on the particle size, structural characteristics, coloration, and thermal stability of CSM. Interestingly, the exclusive use of PEG-200 in extraction results in a notably decreased absorption at 280 nm in the UV-vis spectrum, suggesting the near-complete exclusion of nucleic acids and proteins. CSM extracted by PEG-200 aqueous solution exhibits the highest enthalpy value (199.960 ± 2.920 J/g), glass transition temperature (200.449 ± 1.118 °C), the most abundant monosaccharide composition, and the highest molecular weight (3,456,558 Da), far exceeding the reported values in literature. In vitro bioactivity demonstrates that CSM extracted through the synergistic use of ultrasound and microwave exhibits the strongest DPPH and ABTS radical scavenging abilities, while CSM extracted with PEG-200 performs exceptionally well in iron ion chelating capacity. This study introduces a novel approach to CSM extraction by innovatively employing the green solvent PEG-200 and broadening the application of ultrasound-microwave synergistic technology in the extraction of plant polysaccharides.