Design of nanoemulsion-based delivery systems of natural antimicrobials: effect of the emulsifier.

This work aims at investigating the effect of the nanoemulsion delivery systems on the antimicrobial activity of different essential oil components. Carvacrol, limonene and cinnamaldehyde were encapsulated in the sunflower oil droplets of nanoemulsions prepared by high pressure homogenization and stabilized by different emulsifiers: (a) lecithin, (b) pea proteins, (c) sugar ester and (d) a combination of Tween 20 and glycerol monooleate. The antimicrobial activity was measured against three different microorganisms, such as Escherichia coli, Lactobacillus delbrueckii and Saccharomyces cerevisiae. The measured antimicrobial activity was significantly affected by the formulation of the nanoemulsion, where the different bioactive compounds were encapsulated. In particular, the effect of the delivery systems on the antimicrobial activity was correlated to the concentration of the essential oil components in the aqueous phase in equilibrium with the nanoemulsion droplets, suggesting that the ability of the active molecules to interact with cell membranes is associated to their dissolution in the aqueous phase. These considerations can lead to a more rational design of the nanoemulsion-based delivery systems for essential oils, based on the opportune choice of the emulsifiers in dependence of the desired function of the antimicrobials within the food system.