Extraction Process Optimization, Structural Characterization, and Antioxidant Activity Evaluation of Polysaccharides from Opuntia ficus-indica (L.) Mill.

Abstract:

[Objective] This study aims to optimize the extraction process of polysaccharides from Opuntia ficus-indica (L.) Mill., improve the polysaccharide yield while reducing anthraquinone residue, and characterize the structure and evaluate the antioxidant activity of the obtained polysaccharides. [Method] The hot water extraction parameters were optimized by single factor and orthogonal tests. The anthraquinone residue was reduced by repeated washing with ethanol. The polysaccharide structure and composition were characterized by ultraviolet (UV) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and high performance gel permeation chromatography (HPGPC). The DPPH radical scavenging rate and oxygen radical absorbance capacity (ORAC) were measured to evaluate the in vitro antioxidant capacity. A HepaRG cell model of H₂O₂-induced oxidative stress was established, and the cell viability, intracellular reactive oxygen species (ROS) level, and the levels of glutathione peroxidase (GSH-Px), malondialdehyde (MDA), catalase (CAT), and superoxide dismutase (SOD) were determined. [Result] The optimal extraction conditions were extraction with a solid-to-liquid ratio of 1 g∶30 mL at 70 ℃ for 2.5 h. Structural characterization revealed three main weight-average molecular weights: 722.3×10³, 50.6×10³, and 1.6×10³. The polysaccharides consisted of 9 monosaccharides: mannose, glucuronic acid, rhamnose, galacturonic acid, glucose, galactose, xylose, arabinose, and fucose. The polysaccharides exerted the DPPH scavenging rate of 96.27% and the ORAC value of 0.66 mmol/L. The cell experiment showed that the polysaccharides (2.50 mg/mL and 5.00 mg/mL) significantly enhanced the activities of CAT, SOD and GSH-Px, while lowering the levels of MDA and ROS in the model HepaRG cells. [Conclusion]The optimized extraction process significantly improves the polysaccharide yield, and the obtained polysaccharides are high-purity heteropolysaccharides. Both in vitro and cell experiments demonstrate that the polysaccharides exhibit significant antioxidant activity, and its mechanism of action is associated with the regulation of oxidative stress-related biomarkers, highlighting its potential as a natural antioxidant for functional food applications.