Ultrasound-fabricated thyme essential oil nanoemulsions stabilized by clean-label emulsifiers: Physicochemical properties, antibacterial activity, and food decontamination applications.

In this study, thyme essential oil nanoemulsions stabilized by clean-label emulsifiers (tea saponin, TS; soy lecithin, SL; soy protein isolate, SPI), with Tween 60 (TW) as a synthetic benchmark, were fabricated via ultrasonic emulsification (573 W/cm2, 5 min). Ultrasonication effectively reduced droplet sizes to 120-220 nm, producing narrow size distributions (PDI < 0.22) and high encapsulation efficiencies, which were associated with cavitation-induced droplet disruption and enhanced emulsifier adsorption at newly generated interfaces. Among the formulations, TS- and SL-stabilized nanoemulsions exhibited improved physicochemical stability under centrifugal, ionic, thermal, pH, and storage stresses, suggesting the formation of more stable interfacial layers. All nanoemulsions showed strong antibacterial activity against Escherichia coli O157:H7 and S. aureus, with NE-TS demonstrating the highest potency (MIC = 156.3 µg/mL; MBC = 156.3-312.5 µg/mL) and achieving > 6 log CFU/mL reductions within 30 min. Mechanistic analyses indicated that NE-TS exerted its effect through severe membrane disruption, membrane depolarization, and intracellular reactive oxygen species accumulation, resulting in extensive cell collapse. In contrast, TW mainly induced membrane permeabilization, SL may promote membrane fusion with bacterial envelopes, and SPI may cause electrostatic aggregation with limited lytic activity. In food applications, TS-stabilized nanoemulsions efficiently decontaminated cherry tomato surfaces and significantly reduced pathogens in milk matrices. These findings demonstrate that emulsifier-mediated interfacial architecture regulates nanoemulsion physicochemical properties and antibacterial performance of ultrasound-fabricated nanoemulsions, providing insights for the development of food-grade essential oil nanoemulsions for potential food preservation applications.