Isolation and Structural Characterization of an Antioxidant Polysaccharide from Purple Sweet Potato and Metabonomic Evaluation of Its Antioxidant Mechanism

In the present study, a polysaccharide with antioxidant activity, named PSPP03, was obtained from purple sweet potato by purification using high-speed countercurrent chromatography. Its structural, physicochemical and biological properties were evaluated. The results showed that the molecular mass of PSPP03 was estimated to be 29.1 kDa and it was mainly composed of arabinose (Ara), mannose (Man), rhabose (Rha), glucuronic acid (GlcA) and glucose (Glc) with a molar ratio of 16.2:25.3:7.1:8.6:10.8. The glycosidic bond composition of PSPP03 was analyzed after methylation, revealing that it mainly contained →1)-Araf-(→3, →3)-Manp-(1→, →3,4)-Manp-(1→, →3,6)-Manp-(1→, →3)-Glcp-(1→, Glcp-(1→ and →4)-Rhap-(1→. Cyanidin-3-sophoroside-5-glucoside and peonidin-3-sophoroside-5-glucoside were detected in the structure of PSPP03 by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Cellular antioxidant tests showed that PSPP03 at 25 and 100 μg/mL significantly reduced the levels of reactive oxygen species (ROS), malondialdehyde (MDA) and glutathione disulfide (GSSG) (P < 0.01), and increased activities of catalase (CAT), glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) as well as the content of glutathione (GSH) (P < 0.01). Metabolomic analysis suggested that PSPP03 may reduce cellular oxidative damage by promoting the metabolism of related amino acids and the tricarboxylic acid cycle. The results of this study will provide a theoretical basis for the application of purple sweet potato polysaccharides, which is of great significance for the comprehensive development of purple sweet potato.