The encapsulation of essential oils in nanoemulsions represents an effective approach not only to disperse them in the aqueous systems where microorganisms proliferate but also to enhance their permeability through biological membranes.
In this work, different food-grade emulsifiers, such as whey proteins, lecithin, Tween 80, alginate or zein, were tested in the preparation of carvacrol nanoemulsions in water. In order to prevent the occurrence of instability phenomena associated with Ostwald ripening, carvacrol was mixed at different ratios with peanut oil or medium chain triglycerides. The high-pressure homogenization method (200 MPa, three passes, using an orifice valve) was used to reduce the droplet size in the nanometric range.
The nanoemulsions were tested for their stability over time at varying the main formulation parameters, and then carvacrol permeability across dialysis membranes was investigated, using a Franz cell assembly.
The results showed that, in order to prevent droplet coalescence due to Ostwald ripening, the minimum ripening inhibitor oil-carvacrol ratio in the dispersed oil phase should be 3:1.
In addition, despite comparable droplet sizes (< 150 nm), the nanoemulsions stabilized by lecithin or whey proteins enabled a higher carvacrol diffusion through the cellulose membranes, which was one order of magnitude higher than Tween 80-based systems.