Rosmarinus officinalis L. essential oil encapsulated in new microemulsion formulations for enhanced antimicrobial activity

Abstract In this present study, Rosmarinus officinalis essential oil and its new microemulsions (MEs) were evaluated both for the in vitro antibacterial and antifungal activity. The essential oil composition was verified initially both by GC‐FID and GC/MS, where camphor (19.5%), 1,8‐cineol (12%), and verbenone (11.1%) were characterized as the main constituents. A titration method was used and utilized to formulate the MEs. The preparation was formulated using isopropyl myristate as an oil phase, where sorbitan monolaurate and macrogol‐glycerol ricinoleate were used as surfactants. In the same system, ethanol was utilized as co‐surfactant and distilled water as aqueous phase. A total of 0.1% (w/w) of R. officinalis essential oil was dissolved within the formulation, and evaluated for characteristic parameters such as viscosity, pH, electrical conductivity, refractive index, polydispersity index (PDI), droplet size, and zeta potential, respectively. The pH value was 6.2, where the average microemulsion droplet size was 4.58 ± 0.137 nm; the PDI value was found as 0.219 ± 0.016. The viscosity of the microemulsion was determined as 6.93 ± 0.015 cP. The conductivity of MEs was found as 10 μS/cm; finally, the zeta potential was determined as 0.391 ± 0.012 mV. The antimicrobial potential of the preparations was compared using the in vitro broth microdilution, and poisoned PDA assay. A significant increase in the anti‐Candidal activity of the micro‐emulsified essential oil (15.6 μg/ml) was observed, however, the antibacterial susceptibility was rather low at the tested concentrations. In addition, the novel microemulsion preparation significantly inhibited mycelial growth of the plant pathogens used in the study, suggesting its selective antifungal potential.