Influence of emulsion droplet size on antimicrobial properties

In this study the effect of oil droplet size on antimicrobial activity was investigated. Oil-in-water emulsions were made from oil possessing antimicrobial properties (lemon myrtle oil, LMO), and oil which has no antimicrobial properties (soybean oil). The antimicrobial properties were investigated against 5 bacteria. The emulsions containing millimetre size and micron-size droplets were produced by hand-shaking and blending using a high speed blender and nanoemulsions were produced using a microfluidizer at 60 MPa. It was found that all emulsions made from LMO had the same level of antimicrobial effects against the 5 bacteria whereas all soybean oil emulsions had no antimicrobial effect. From these results, it could be concluded that the antimicrobial property of nanoemulsions result from the active ingredients in the emulsions and not from high surface tensions and cell wall diffusion activity of nano-sized droplets.