Ultrasound assisted hot water extraction of polysaccharides from Taraxacum mongolicum: Optimization, purification, structure characterization, and antioxidant activity

Ultrasound assisted hot water extraction (UAHWE) was applied to extraction of polysaccharides from Taraxacum mongolicum with hot water as extract solvent. Experimental factors in UAHWE process were optimized by response surface methodology. The optimal extraction parameters to achieve the highest Taraxacum mongolicum polysaccharides (TMPs) yield (12.08 +/- 0.14)% by UAHWE were obtained under the ultrasound power of 200 W, extraction temperature of 62 degrees C, solid-to-liquid ratio of 1:20 g/mL, and extraction time of 40 min, and then the crude TMPs were further purified by DEAE-52 and Sephadex G-100 chromatography to obtain a homogenous polysaccharide fraction (TMPs-1-SG). Subsequently, the structure of TMPs-1-SG was characterized by UV-vis, Fourier transform infrared spectroscopy (FT-IR), high performance gel permeation chromatography (HPGPC), high performance liquid chromatography (HPLC), scanning electron microscope (SEM), transmission electron microscopy (TEM), and Congo red test. The results display that TMPs-1-SG with an average molecular weight of 5.49 x 10(4) Da was comprised of mannose (Man), galactose (Gal), xylose (Xyl), and arabinose (Ara) with a molar ratio of 39.85:52.61:27.14:6.30. Moreover, TMPs-1-SG did not contain a triple helix structure. Furthermore, TMPs-1-SG and TEM presented a sheet-like, rod-shaped, and irregular structure. Finally, the antioxidant activity of TMPs-1-SG was evaluated by in vitro experiment. The IC50 values of scavenging DPPH and OH radicals for TMPs-1-SG achieved 0.71 mg/mL and 0.75 mg/mL, respectively. The findings can provide an effective method for extracting polysaccharides from natural resources.