Extraction, Characterization and Antioxidant Activity of Polysaccharide from Platycodon grandiflorum Based on Deep Eutectic Solvent

Using Platycodon grandiflorum as the raw material and polysaccharide yield as the evaluation index, this study investigated the effects of deep eutectic solvent types, molar ratio, liquid-to-material ratio, water content, and extraction time on polysaccharide extraction. Single-factor experiments and response surface methodology were employed to optimize the extraction process. The structure of the extracted polysaccharides was characterized using ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The antioxidant activity of Platycodon grandiflorum polysaccharides was evaluated by assessing their scavenging abilities against ·OH, ABTS⁺·, and DPPH·. After optimization, the best extraction process for Platycodon grandiflorum polysaccharide was determined as follows: Extraction temperature 79 ℃, liquid-to-material ratio 20.5:1, molar ratio 2.2:1, extraction time 1.5 h, and water content 30%. Under these conditions, the yield of Platycodon grandiflorum polysaccharides was measured to be 31.17%, which was approximately 3.11 times higher than that obtained using the water extraction method. UV-Vis spectra revealed no characteristic absorption peaks of nucleic acids or proteins near 260 nm and 280 nm. FT-IR spectroscopy identified typical characteristic absorption peaks of polysaccharides at multiple wavenumbers, including 3363, 2931, 1739, 1639, 1422, and 1025 cm⁻¹. SEM showed that the surface of Platycodon grandiflorum polysaccharides exhibited a sheet-like structure with a relatively rough texture, few pores, and distinct wrinkles. The antioxidant activity study demonstrated that the maximum scavenging rates of Platycodon grandiflorum polysaccharides on ·OH, ABTS⁺·, and DPPH· were 95.85%, 66.96%, and 52.45%, respectively. In conclusion, the choline chloride/urea DES system could significantly improve the extraction yield of Platycodon grandiflorum polysaccharides, which showed strong antioxidant activity.