A comparative study on the effects of emulsification methods on the antimicrobial activity of essential oil emulsions

A 3 × 3 factorial design was used to systematically evaluate the impact of three widely used emulsification methods (ultrasonication (UT), high shear homogenization (HSH) or vortex mixing (VM)) at three treatment times (30, 60 or 120 sec) on the antimicrobial efficacy of sage (SEO) and garlic (GEO) essential oil emulsions. Independent of essential oil used, antimicrobial activity was significantly (p < 0.05) influenced by both emulsification method and treatment time, with Gram-negative bacteria showing greater resistance. From the tested methods, emulsions prepared by UT or HSH for at least 60 sec exhibited significantly (p < 0.05) higher antimicrobial activity, which might be associated with their significantly (p < 0.05) smaller particle size and polydispersity index. Additionally, UT and HSH produced more stable SEO emulsions, while GEO required ≥ 60 second treatment for stability and VM led to rapid destabilization regardless of oil or time. This study highlights the importance of selecting an appropriate emulsification method for producing essential oil emulsions with enhanced antimicrobial activity, which is important not only for antimicrobial testing but also for the overall functional performance of the emulsion.