Low energy nanoemulsions as carriers of thyme and lemon balm essential oils
Cátia I. Sampaio, Ana I. Bourbon, Catarina Gonçalves, Lorenzo Pastrana, Alice Dias, Miguel A. Cerqueira
Abstract
The aim of this work was to produce monomodal and stable thyme and lemon balm-loaded nanoemulsions (NE), through a low energy approach. NEs were prepared by the emulsion phase inversion method using sunflower oil as carrier and Tween 80 as surfactant. Different surfactant-to-oil ratios (SOR) and essential oil (EO) loadings were evaluated. Nanoemulsions presented a monomodal diameter distribution below 200 nm and high negative zeta potential (>−40 mV). Nanoemulsions loaded with EOs were physically stable for 3 months at 4 °C and 20 °C. Nanoemulsions with thyme EO presented the highest radical scavenging activity by DPPH and ABTS tests. Loaded nanoemulsions were not effective against Escherichia coli but could inhibit Staphylococcus aureus. Cytotoxicity studies using cell counting kit-8 and resazurin assays revealed a dose-responsive effect of nanoemulsions on Caco-2 cells after incubation for 24 h. A concentration of 100 μg oil/mL of NE for unloaded and thyme loaded and 50 μg oil/mL of NE for lemon balm loaded showed to be safe to use.