Evaluation Of Antioxidant Activity And Free Radical Scavenging Potential Of Strobilanthes Lurida Stem Extracts

Abstract

The antioxidant potential of stem extracts obtained using four solvents of varying polarity — distilled water (SDW), methanol (SMA), ethyl acetate (SEA), and chloroform (SChl) — was systematically evaluated through a battery of complementary in vitro assays, comprising DPPH radical scavenging, ABTS radical cation scavenging, ferric reducing antioxidant power (FRAP), nitric oxide scavenging, and reducing power assays. Marked and statistically significant variations in antioxidant activity were recorded across the four extracts, underscoring the well-established influence of solvent polarity on the selective recovery of bioactive phytochemicals from plant tissues. Among the extracts, the methanolic fraction (SMA) demonstrated the strongest DPPH radical scavenging activity (61.91%), reflecting its capacity to effectively neutralise free radicals in a hydrogen-transfer-dependent mechanism. The ethyl acetate extract (SEA), however, outperformed all other fractions across the remaining assays, recording the highest ABTS scavenging activity (67.77%), FRAP value (11.15 mg/mL GAE), nitric oxide scavenging activity (75.21%), and reducing power (12.01 mg/mL GAE). The distilled water extract (SDW) consistently registered the lowest antioxidant performance across all five assays, suggesting that the predominant antioxidant constituents of this stem material are not readily recovered by highly polar aqueous extraction. The superior performance of the methanolic and ethyl acetate fractions is attributed to their preferential extraction of phenolic compounds and other redox-active secondary metabolites, which are known to contribute to multiple mechanisms of free-radical neutralisation. Collectively, these findings demonstrate that moderately polar solvents offer a more effective strategy for recovering antioxidant-rich fractions from stem tissues and position these extracts as promising candidates for further characterisation and application in food preservation, nutraceutical formulation, and pharmaceutical development.