Structural Characterization and Protective Effects of CPAP-1, an Arabinogalactan from Curcuma phaeocaulis Val., Against H2O2-Induced Oxidative Damage in HUVECs

<i>Curcuma phaeocaulis</i>, a perennial herb of the ginger family, has been used to treat many diseases in traditional medicine systems. This study aimed to extract, isolate, and purify a homogeneous polysaccharide from <i>C. phaeocaulis</i>, conduct preliminary structural characterization, and evaluate its antioxidant activity at the cellular level. The structure of the purified polysaccharide (CPAP-1) was characterized using size exclusion chromatography (SEC), chemical derivatization analysis (CDA), GC-MS, FT-IR, and NMR. The results showed that CPAP-1 has an apparent molecular weight of 118.122 kDa and is hypothesized to be an arabinogalactan with a backbone composed of →3,6)-<i>β</i>-d-Gal<i>p</i>-(1→ and →3)-<i>β</i>-d-Gal<i>p</i>-(1→ residues, a structure that is relatively novel in <i>Curcuma longa</i>. In vitro antioxidant assays demonstrated that CPAP-1 possesses potent antioxidative stress activity, effectively scavenging both DPPH and hydroxyl radicals. Furthermore, cellular experiments revealed that at concentrations of 500 and 750 mg/L, CPAP-1 significantly protected human umbilical vein endothelial cells (HUVECs) against H₂O₂-induced oxidative damage. In conclusion, these findings suggest that CPAP-1 could be developed as a natural antioxidant, functional food, or therapeutic agent for preventing and mitigating oxidative stress-related vascular injury, providing a theoretical basis for further development and application.