Accelerated Solvent Extraction for Effective Isolation of Sea Fennel Phenolic Antioxidants and Antimicrobials

Sea fennel is a halophyte plant recognised as a valuable source of phenolics with good antioxidant and antimicrobial potential. In this study, accelerated solvent extraction (ASE) was optimised to improve the recovery of phenolic compounds from sea fennel, particularly hydroxycinnamic acids, which are known to be dominant. The effect of the applied extraction temperature (20–120 °C) and used solvent (20–80% hydroethanolic mixtures) on total phenolic content (TPC) was systematically evaluated. Individual phenolic composition, antioxidant activity, and antimicrobial properties were measured in the top four samples. TPC was determined spectrophotometrically, while individual compounds were analysed by chromatography. Antioxidant (reducing and free-radical scavenging) activity was assessed using three assays, while the minimum inhibitory concentrations and minimum bactericidal concentrations were determined using the microdilution method against five bacterial strains. Both temperature and solvent composition significantly influenced phenolic extraction efficiency. The highest TPC and concentrations of chlorogenic acid and its derivatives were obtained at 60 °C using 60–80% ethanol (664 and 673 mg of gallic acid equivalents/g of dry extract), while higher temperatures generally resulted in reduced phenolic yield. Extracts obtained under optimal ASE conditions exhibited enhanced antioxidant activity and moderate antimicrobial effects, particularly against Gram-positive bacteria, which demonstrates that accelerated solvent extraction represents an efficient approach for obtaining sea fennel extracts rich in valuable bioactives with potential use in different industries.