Microwave-assisted extraction of bioactive components from date seeds using deep eutectic solvents: Bioactivity and antibiotic adjuvant potential against multidrug-resistant Salmonella Typhimurium DT104

Adjuvants offer a promising strategy against antimicrobial resistance. Deep eutectic solvents (DESs) and their subsequent DES-based polyphenol-rich bioactive compounds (PBCs) were assessed for antimicrobial and adjuvant activity against multidrug-resistant Salmonella Typhimurium DT104. PBCs were extracted from date seeds using polyol-based DESs with microwave assistance. FTIR spectra of synthesized DESs confirmed new hydrogen bond formation. Phytocompound profiling revealed that 1,4-Butanediol (1,4-But)-extract showed the highest TPC (30.05 ± 1.33 mg GA g⁻¹) and DPPH activity (35.02 ± 0.34 mmol TE g⁻¹). UHPLC-PDA identified 4-hydroxybenzoic acid and rutin hydrate as the predominant phenolic compounds. Despite limited intrinsic antimicrobial activity, DES extracts and their corresponding DES-enhanced the antibiotic effectiveness. Checkerboard assay showed that the 1,4-But-DES extract exhibited significant synergy with ACSSuT antibiotics, reducing their MICs by 32- to >1024-fold, with FICI values ≤0.5. Time-kill assays confirmed enhanced bactericidal activity of chloramphenicol with both extracts at sub-inhibitory concentrations. Conclusively, 1,4-But-based extracts can enhance antibiotic efficacy against resistant foodborne pathogens.