Saponins from Solanum nigrum L. Fruit: Extraction Optimization, Structural Characterization, and Dual-Functional Efficacy

Solanum nigrum L., a widely consumed Asian medicinal edible plant, is a promising source of bioactive saponins for functional food applications. This study optimized the extraction of saponins from S. nigrum fruits (8.59% total saponin yield), followed by isolation via column chromatography and structural elucidation using spectroscopic analyses (IR, NMR, and MS). Concurrently, the antioxidant properties and antibacterial activity of the purified substances were detected and analyzed. The three saponins (SNL1, SNL2, SNL3) were identified as γ2-Solamargine , Diosgenin, and β-Solanine. The n-butanol -purified fraction demonstrated a remarkable capacity to scavenge DPPH, hydroxyl, and ABTS radicals (DPPH IC50 = 0.0096 mg/mL; hydroxyl radical IC50 = 0.8 mg/mL; ABTS IC50 = 0.061 μg/mL), indicating the inhibition of a multi-pathway oxidative chain reaction. Concurrently, the saponins exhibited selective antimicrobial efficacy against key foodborne pathogens, particularly Escherichia coli. To the best of our knowledge, this work provides the first empirical evidence of S. nigrum fruit saponins as dual-functional natural preservatives, synergistically suppressing lipid oxidation and microbial growth. These findings highlight their potential as safer, multi-mechanistic alternatives to synthetic additives, aligning with clean-label food industry demands.