Investigating the influence of excipients on the stability of biocosmetic nanoemulsions formulated with surfactin as an emulsifier

Abstract: Nanoemulsions are colloidal systems characterized by tiny droplet sizes with increased kinetic stability. Due to their exceptional properties, nanoemulsions find applications in cosmetics, drug delivery, and food industry. Nanoemulsions can encapsulate bioactive compounds and distribute them efficiently for specific purposes. In the current work, we report the formulation of a highly stable nanoemulsion using surfactin as the green emulsifier, which retained its stability for 750 days and could effectively encapsulate excipients such as vitamin C, vitamin A, and TiO₂. Initial shake-flask studies using cashew apple juice as the carbon source yielded a maximum surfactin concentration of 2.87 g/L after 60 h of incubation. The nanoemulsion exhibited a hydrodynamic droplet diameter of 230 nm and a polydispersity index (PDI) of 0.21. Notably, the resilience of the microbial surfactant-based nanoemulsion was convincingly demonstrated utilizing various oil phases, namely coconut oil, olive oil, and castor oil. The nanoemulsion formulated with coconut and olive oil exhibited oil droplets with a droplet diameter of approximately 200 nm and a maximum PDI of 0.20. Conversely, the castor oil–based nanoemulsion displayed a slightly larger droplet diameter of 250 nm. Moreover, the excipients-loaded nanoemulsions exhibited significant antibacterial activities against E. coli, S. aureus, and B. subtilis. We strongly believe that the findings of this research will serve as a crucial stepping stone for future investigations into the utilization of microbial surfactant-based nanoemulsion. Such research holds tremendous potential for encapsulating and distributing bioactive chemicals, enabling customized actions.