Optimization of solid-phase extraction for recovering phenolic compounds from NADES-based olive pomace extracts: A comparison of different copolymeric sorbents and conditioning/desorption conditions

The growing production and consumption of olive oil, driven by its favorable organoleptic properties and recognized health benefits, has concurrently led to an increase in waste generation, raising significant environmental concerns. The valorization of olive pomace (OP), a major by-product of olive oil production, represents a sustainable strategy for recovering high-value bioactive compounds. This study explored the use of solid-phase extraction (SPE) to purify phenolic compounds from OP extracts obtained using two natural deep eutectic solvents (NADES), compared with conventional hydroethanolic extraction. Five distinct SPE cartridges were tested under different conditioning and desorption protocols, including green solvent strategies. Recovery efficiency was assessed through spectrophotometric assays (TPC, TFC, FRAP, and DPPH ● -SA) and chromatographic profiling. The results showed that solvent polarity and pH significantly influence the recovery of phenolics, with acidified desorption enhancing compound elution. The C18 and HLB cartridges, especially when combined with ethanol or methanol acidified with 2% acetic acid, demonstrated the highest total recovery, exceeding hydroethanolic extracts by more than 50%. Additionally, a selective enrichment of compounds, such as hydroxytyrosol, verbascoside, and demethyloleuropein, was observed using specific sorbent–solvent combinations. These findings support the potential of SPE following NADES extraction as a green and effective method for recovering and concentrating phenolic compounds from natural matrices. • SPE improved phenolic recovery from NaDES extracts by up to 50 %. • C18 and HLB sorbents showed the highest bioactive retention efficiency. • Acidified solvents enhanced antioxidant compound desorption rates. • Hydroxytyrosol and verbascoside were efficiently enriched by SPE. • SPE with NaDES is a effective strategy for phenolic purification.