Ultrasound-assisted extraction and antioxidant activity of triterpenoid saponins from Platycodon grandiflorum roots: Optimization, purification, and molecular insights

Abstract

Platycodon grandiflorum roots (PGR) is a medicinal plant rich in triterpenoid saponins, which are known for their antioxidant properties. In this study, ultrasonic-assisted extraction (UAE) was employed to extract total saponins from PGR, with the extraction process optimized through single-factor experiments and response surface methodology (RSM). The optimal extraction conditions were determined to be an extraction time of 51.04 min, ultrasonic power of 153.79 W, and a temperature of 49.59°C, resulting in a saponins yield of 4.83 %. Purified using n-butanol extraction followed by ethanol elution produced four distinct fractions, with the PAE-3 fraction containing the highest saponins concentration, primarily composed of Platycodin G1 and Platycodin E. In vitro antioxidant assays revealed that PAE-3 exhibited the strongest radical scavenging capacity and reducing power. A strong negative correlation between the content of Platycodin G1 and Platycodin E and IC 50 values in antioxidant assays suggests that these compounds are key contributors to the antioxidant activity of PAE-3. In vivo studies using Caenorhabditis elegans further validated the antioxidant potential of PAE-3, showing a significant reduction in reactive oxygen species levels and enhanced activity of superoxide dismutase (SOD) and glutathione (GSH). UPLC-Q-TOF/MS analysis identified the structure of Platycodin G1 and Platycodin E, while molecular docking revealed strong binding affinities of these compounds to SOD and GSH-Px, emphasizing their roles in antioxidant defense. Overall, this study highlights the efficacy of UAE in optimizing the saponins yield and underscores the potent antioxidant properties of enriched saponins fractions, offering promising application potential for the development of natural antioxidants. • Ultrasound-assisted extraction optimized for 4.83 % saponin yield from Platycodon grandiflorum. • Key saponins, Platycodin G1 and Platycodin E, enriched via n-butanol extraction and ethanol elution. • In vitro and in vivo assays confirm strong antioxidant activity of purified saponin fractions. • Molecular docking revealed high binding affinity of Platycodin G1 and E with antioxidant enzymes.