Valorisation of Maclura pomifera Pruning Leaves by Green Crosscurrent Extraction: Process Optimisation, Chemical Profiling, and Preliminary Cytotoxicity Assessment

Urban tree-pruning residues are an underused bioactive resource. This study evaluated a short three-stage crosscurrent process for valorising Maclura pomifera pruning leaves with water and aqueous ethanol. Each stage contacted the preceding residue with fresh solvent and was optimised independently by response surface methodology for temperature, time and, for hydroethanol, ethanol concentration. Responses were total phenolic content (TPC), total flavonoid content (TFC), ABTS radical scavenging, potassium ferricyanide reducing antioxidant power (PFRAP) and silver nanoparticle antioxidant capacity (SNPAC). Extracts from all three optimised stages were pooled per solvent and assessed by UPLC–ESI–MS/MS and for cytotoxicity in four mammalian cell lines. Cumulative TPC reached 21.49 (aqueous) and 23.39 (hydroethanolic) mg gallic acid equivalents/g dry weight, and ABTS reached 52.59 and 49.58 mg ascorbic acid equivalents/g dry weight. Two aqueous stages recovered over 90% of cumulative TPC and ABTS in 15 min. The ethanol-rich third stage contributed 39.2% of cumulative TFC and 28.8% of SNPAC. Hydroethanol favoured flavonoids, whereas water phenolic acids and simple aromatics. Both pooled extracts gave higher IC50 values than ascorbic acid, with the hydroethanolic extract being more cytotoxic. Crosscurrent extraction with water or hydroethanol recovers phenolics rapidly, and staging the ethanol concentration yields compositionally distinct fractions whose suitability for specific applications requires further toxicological evaluation.