**5. Conclusions**

This chapter examines the influence of nano-emulsion composition and high pressure homogenization conditions on droplet size and stability. Nano-emulsions with a droplet size smaller than 100 nm (diameter) can be produced by precise conditions of pressure, a specific number of steps in the high pressure homogenizer, and the presence of a combination of surfactants and emulsifiers that is capable to perform ideally under those conditions without degrading. Surfactants and natural gums were used to produce nano-emulsions with small droplets of Persian lemon oil, which has antimicrobial properties, with potential applications in the areas of cosmetics, pharmaceuticals and the food industry. In this particular study mesquite gum was used for the first time to maintain the kinetic stability of the Persian lemon oil droplets.

With the results of the MIC characterization it was confirmed that the nanoemulsions of Persian lemon oil developed under the method described in this research have an antibacterial effect against *Staphylococcus aureus* and *Escherichia*  *coli*. And although there is controversy about which components of the citric essential oils increase the antibacterial activity, our study suggest that aldehydes have an important role for the antibacterial effect of Persian lemon oil nano-emulsions.

Considering the series of experiments described in this research and the study of stability as a function of time it is clear that the Control Delta formulation composed of Span 20 (1.45%), Tween 80 (4.9%) and mesquite gum (4.9%) was the best. It was also shown that mesquite gum is superior to Arabic gum for the kinetic stability as shown by the behavior of the nano-emulsion that replaces mesquite gum with Arabic gum (Control 2). Indeed, when an excess of surfactant (Tween 80 and Span 20) is used, it is possible to obtain a smaller droplet size as observed in other control (Control 3 with excess Tween 80 and Span 20), but mesquite gum provides additional steric stabilization that confers a better stability over time against coalescence. The sample that replaces mesquite gum with water (Control 4) confirms the additional steric stability of mesquite gum.
