Optimization of Ultrasound-Assisted Extraction of Thymbra Spicata L. Using Response Surface Methodology: Polyphenol...

Thymbra spicata L. (Zahter) is a medicinal aromatic plant naturally growing in Türkiye. This study aimed to optimize ultrasound-assisted extraction (UAE) conditions using response surface methodology (RSM) to maximize its total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity (DPPH). The optimal conditions were established as 31.071% methanol, 63.467°C, 48.423 min, and a 36.14 mL/g solvent-to-solid ratio. The optimized extract yielded TPC, TFC, and DPPH values of 145.77±2.26 mg GAE/g, 16.19±0.20 mg QE/g, and 97.794±1.78 mg AAE/g dry plant material, respectively, demonstrating positive correlations among them. Orbitrap-MS profiling identified rosmarinic acid, quinic acid, luteolin-7-O-glucuronide, and naringenin as the predominant polyphenols. Furthermore, antibacterial assays revealed minimum inhibitory (MIC) and bactericidal (MBC) concentrations of 5 and 10 mg/mL, respectively, against Salmonella Typhimurium and Listeria monocytogenes, whereas values for Escherichia coli O157:H7 were >10 mg/mL. Conclusively, RSM optimization successfully yielded a polyphenolic-rich T. spicata extract with high antioxidant capacity and measurable antibacterial activity at higher concentrations.