Probe-Ultrasonicated Thyme Essential Oil Nanoemulsions: Physicochemical Characterization and Application in Chicken Burgers

The bioactive compounds in thyme essential oil (TEO) have been investigated as natural preservatives. However, their direct application in foods is limited by their poor water solubility and high volatility. In this context, nanoemulsions represent promising delivery systems for bioactive compounds due to their improved physicochemical stability and functional performance. This study aimed to develop and characterize TEO nanoemulsions prepared by ultrasound-assisted encapsulation using an ultrasonic probe and whey protein concentrate as a surfactant, with potential application in chicken burgers. Different sonication times (1, 3, 5, 7, and 10 min) were evaluated, and ultrasonication time was evaluated as the experimental variable. The formulation processed for 3 min presented the smallest hydrodynamic diameter (289 nm) and a homogeneous spherical morphology. The nanoemulsions showed low cytotoxicity, maintaining cell viability above 90% at all evaluated concentrations. In vitro antibacterial assays demonstrated activity against Staphylococcus aureus and antifungal effects against Aspergillus and Penicillium species. When applied to chicken burgers, the treatment containing 100 ppm of nanoencapsulated TEO contributed to reductions in S. aureus and mesophilic aerobic microorganism counts during 7 days of refrigerated storage. These findings indicate that TEO nanoemulsions present potential as natural antimicrobial systems for food preservation applications.