Antimicrobial multi-component lipid-based nanoemulsion of Eucalyptus globulus and Mentha piperita as natural preservative

Abstract

Natural preservatives were predominantly developed to eliminate the use of synthetic preservatives for food and agriculture industries. Multi-component nanoemulsions (MCN) with significant antibacterial activity should be proper candidates as natural preservatives. This research aimed to formulate a multi-component phospholipid-based nanoemulsion (PNE) with prolonged shelf-life loaded with a mixture of Eucalyptus globulus and Mentha piperita essential oils (EOs). The effects of different chemical and mechanical conditions (ultrasonication) on the stability of MCN were evaluated. The emulsions were monitored from day 1 to 730, and stable formulae were investigated for around two years. The Zeta potential confirmed the anionic surface charge. Dynamic light scattering and transmission light scattering revealed a droplet size ranging between 93.40 and 100.00 nm. A homogeneous formula was stable for more than 730 days. Ultrasonication treatment and 1% v/v of food-grade castor oil as co-emulsifier were critical in fabricating stable formulae. Minimum inhibitory concentration (MIC) values of 31, 8, and 63 µg/ml were observed against Escherichia coli, Staphylococcus aureus and Salmonella enteritidis, respectively. The results showed a significant reduction in MIC values of 32-, 250-, 15-fold against E. coli, S. aureus and S. enteritidis, respectively, compared to an original mixture of essential oils. The mass transfer followed a case-I transfer (Fick law diffusion) evaluated by Koresmeyer-Peppas kinetic model (R 2 = 0.88). In conclusion, MCN could be a promising candidate for natural preservatives to be used in the food, agriculture and cosmetic industries.