Structural characterization and bioactivity analysis of a polysaccharide extracted from Rehmannia glutinosa libosch...

Conventional high-temperature extraction methods for bioactive compounds can degrade nutritional components and are often energy-intensive. This study developed a mild extraction strategy employing a complex enzyme cocktail and ultrasound at room temperature to isolate a heterogeneous polysaccharide (RGLP) from fresh Rehmannia glutinosa libosch. Compositional analysis revealed RGLP is comprised of 90.35 ± 1.87 % carbohydrate and 1.04 ± 0.13 % protein. Structural characterization indicated RGLP consists of rhamnose, arabinose, galactose, glucose, and mannose with proportions of 0.2661 μg/mL: 0.5456 μg/mL: 23.5393 μg/mL: 15.3891 μg/mL: 3.5603 μg/mL. It possesses a weight-average molecular weight (Mw) of 53.374 kDa and a polydispersity index of 1.568. In vitro assays demonstrated RGLP exhibited dose-dependent scavenging activities against ABTS, DPPH, superoxide, and hydroxyl radicals. At the cellular level, RGLP demonstrated protective, alleviative, and reparative effects against H₂O₂-induced oxidative stress in RAW 264.7 macrophages by modulating the levels of antioxidant enzymes (SOD, CAT, GSH-Px) and reducing malondialdehyde (MDA) content. Furthermore, RGLP significantly stimulated the production of immune mediators, including TNF-α, IL-1β, IL-6, and nitric oxide (NO), in RAW 264.7 cells. These findings suggest RGLP, extracted via this mild and efficient method, is a promising candidate for development as a natural antioxidant and immunomodulatory agent.