Effect of ultrasonic-assisted H2O2/ascorbic acid modification on Platycodon grandiflorum polysaccharide: structural characterization and in vitro functional activities.

To improve the bioavailability of Platycodon grandiflorum polysaccharides (PGS), an ultrasound-assisted hydrogen peroxide/ascorbic acid (H2O2/Vc) modification method was developed. PGS was first extracted using an ultrasound-assisted deep eutectic solvent (DES) method, followed by synergistic H2O2/Vc treatment under ultrasound for 60, 120, and 180 min to obtain three modified fractions, namely DPGS-60, DPGS-120, and DPGS-180. Structural changes in PGS and its modified fractions were characterized by gel permeation chromatography (GPC), high-performance liquid chromatography (HPLC), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet spectroscopy, Congo red assay, and scanning electron microscopy (SEM), and their in vitro bioactivities were evaluated. The results showed that, compared with native PGS, the molecular weight and particle size of DPGS decreased with increasing ultrasound time, while solubility and galactose content showed an increasing trend. All four fractions exhibited a triple-helix conformation. Partial depolymerization occurred after modification, whereas the monosaccharide composition and major functional groups were not altered. Moreover, the antioxidant, hypoglycemic, and hypolipidemic activities of the modified fractions were positively correlated with ultrasound treatment time. In addition, PGS and all modified fractions significantly promoted the growth of Weissella confusa, Lactobacillus plantarum, Lactobacillus acidophilus, and Leuconostoc mesenteroides, indicating potential prebiotic activity, with DPGS-180 showing the strongest effect. Overall, ultrasound-assisted H2O2/Vc modification is an effective strategy to enhance the bioactivity of PGS, and ultrasound treatment time plays a critical role in this process.