Stability and antimicrobial activity of eucalyptus essential oil emulsions.

We evaluated various formulations of oil-in-water emulsions prepared from eucalyptus essential oil, for their stability and antimicrobial activity against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. These formulations were developed using a response surface experimental design and analyzed with Design-Expert® 10 software. The emulsions were prepared in a colloid mill, and emulsion characterization was performed using the zeta ( ζ)-potential, droplet size distribution, and phase separation. The antimicrobial effects were assessed by death kinetics. The droplet size and ζ-potential of the 16 emulsions ranged from 1.071 to 1.865 µm (based on Feret's diameter) and -34.8 to -24 mV, respectively. Three formulations (14, 15, and 16) demonstrated the highest stability parameters (no phase separation) during the 28 days of evaluation. Eucalyptus essential oil emulsions exhibited antimicrobial activity against E. coli, S. aureus, and P. aeruginosa in less than 1 min.