Improved antifungal activity of Origanum vulgare L. essential oil in phospholipid-based nanoemulsions. Role of co-surfactants and surface charge

This study investigates the antifungal efficacy of Origanum vulgare L. essential oil (OEO) encapsulated in phospholipid-based nanoemulsions (NEs) against Candida albicans. The formulations were developed using different amounts of soy phosphatidylcholine (SoyPC) and co-surfactants and/or charge-inducing agents, with the aim of enhancing the stability and bioactivity of OEO. Our results demonstrate that all nanoemulsion formulations significantly outperformed non-formulated OEO in terms of minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC), regardless of surface charge. The inclusion of co-surfactants and/or charge-inducing agents was critical in maintaining the biological efficacy of the NEs over time, primarily by improving colloidal stability and enabling sustained release of the encapsulated active compounds. While cationic surfactants are typically associated with enhanced bioactivity, our findings suggest that stable, negatively charged formulations can achieve comparable antifungal activity without the potential toxicity of cationic agents. Replacing OEO with pure carvacrol allowed for a more accurate evaluation of formulation performance, highlighting the importance of release kinetics and structural integrity, rather than over surface charge, in determining antifungal efficacy. In addition, the study emphasizes the need for careful characterization of essential oil composition post-formulation and calls for further analytical investigation into the behavior of volatile components during emulsification. These insights are pivotal for the rational design and optimization of nanoemulsion-based antimicrobial systems incorporating essential oils.