Green and Efficient PEG-Based Ultrasonic-Assisted Extraction of Polysaccharides from Tree Peony Pods and the Evaluation of Their Antioxidant Activity In Vitro

We adopted and developed an ultrasonic-assisted extraction method to obtain polysaccharides from tree peony pods using polyethylene glycol (PEG) as the solvent. The technological parameters have been designed as a single factor to enhance the tree peony pod polysaccharide extraction yield. Specific conditions (ultrasound irradiation power, 250 W; ultrasound irradiation time, 30 min; reaction temperature 50°C; liquid-solid ratio, 25 mL/g; and concentration of PEG, 0.2 g/mL) generated an experimental yield of 14.14% ± 0.44%. Subsequently, the monosaccharide composition of the tree peony pod polysaccharides was determined by HPLC using a 1-phenyl-3-methyl-5-pyrazolone precolumn derivatization method. The results indicated that tree peony pod polysaccharides contained mannoses, rhamnose, glucuronic acid, galacturonic acid, glucose, galactose, arabinose, and fucose with a molar ratio of 1.44 : 2.87 : 0.32 : 18.99 : 3.99 : 10.21 : 0.96 : 1.85 : 0.21. The tree peony pod polysaccharides obtained are mainly galacturonic acid and galactose, which are acidic polysaccharides. Finally, the antioxidant activities (DPPH and FRAP) of the tree peony pod polysaccharides were assessed, and the compounds exhibited moderate antioxidant activities.