Valorization of Chenopodium quinoa residues through saponin recovery: extraction, purification, and evaluation of antioxidant and cytotoxic activities

• Quinoa scarification residues contain up to 25% saponins. • Hydrodynamic cavitation recovered 66% saponins using 80% ethanol. • MF–UF–NF filtration increased saponin purity from 32% to 42%. • AB-8 resin and liquid–liquid extraction raised purity to 65–75%. • High-purity saponins (≥60%) showed antioxidant and cytotoxic activity. Residues of Chenopodium quinoa , accounting for approximately 8% of the grain weight, represent an underutilized resource. In this study, saponins were extracted using hydrodynamic cavitation (HC), followed by membrane filtration, adsorption on AB-8 resin, and liquid–liquid partitioning. HC achieved an extraction yield of 66.54%, while membrane filtration increased saponin purity from 32% to 42%. Adsorption with AB-8 resin yielded a maximum purity of 65% after desorption with 70% (v/v) ethanol (CMC = 0.33 g/L), and further purification by liquid–liquid partitioning increased purity to 75%. Rutin and quercetin were identified as the predominant phenolic compounds in the purified extracts. Higher saponin purity was associated with enhanced antioxidant capacity. In addition, the extract with 65% exhibited better cytotoxic activity against MDA-MB-231, HCT-15, and A549 cancer cell lines, exhibiting low IC 50 values and significantly reduced colony formation. These results demonstrate that quinoa residues are a valuable source of saponins with relevant biological activities and application potential.