Nanoemulsion formation and characterization by spontaneous emulsification: Investigation of its antibacterial effects on Listeria monocytogenes

A transparent oil-in-water nanoemulsion system consisting of eucalyptus oil, Tween-20 as organic phase and water as an aqueous phase was developed using a low energy emulsification method. Physicochemical properties such as droplet size, optical transparency, and long-term stability was studied. The stable eucalyptus oil nanoemulsion (1:2) having mean droplet size in the range of 50-100 nm with a polydispersity index <0.2. The optimized nanoemulsion formulation exhibited significantly higher antibacterial activity by the well diffusion method against Listeria monocytogenes. Further, alteration in the membrane integrity was assessed, and it is found higher for nanoemulsion treated cells than control cells. Atomic force microscopic observations showed distorted morphology of treated bacterial cells. These results propose the possible use of eucalyptus oil nanoemulsion in the food industries.