Characterization, antimicrobial activity, and antioxidant activity of the nanoemulsions of Lavandula spica essential oil and its main monoterpenes

The present study compares the stability, antioxidant, antimicrobial activity of lavender essential oil (Lavandula spica) and its major constituents camphene and a-terpinyl acetate with their nanoemulsions (NEs). Oil-in-water (O/W) coarse emulsions were firstly formed by adding the product to an aqueous solution containing 10 % Tween 80 under constant stirring. Then a 15-min high-energy ultra-sonication was performed to get the NEs. The thermodynamic stability, viscosity, pH, droplet size, polydispersity index, and zeta potential were examined. The NEs of lavender oil, camphene, and a-terpinyl acetate have 104.55, 117.23, and 105.23 nm droplet diameters, respectively. The products recorded high negative zeta potentials (-22.26, -27.10, and -18.14 mV for lavender oil, camphene, and alpha-terpinyl acetate NEs, respectively). Through gas chromatography/mass spectrometry (GC/MS), the essential oil contains a high content of phenolic and flavonoid compounds. The products indicated high antioxidant activity, and the NE of lavender oil exhibited a significant scavenging capacity (IC50 = 261.66 mg/L). The antimicrobial activity was tested against bacteria of Gram-negative (Salmonella typhimurium) and Grampositive (Staphylococcus aureus), fungi Aspergillus flavus and Aspergillus niger, and yeast Candida albicans. alpha-Terpinyl acetate NE was superior active (MIC = 725 and 550 mg/L against S. typhimurium and S. aureus, respectively). Lavender oil NE exhibited the highest inhibitory action against C. albicans with the lowest EC50 value (107.70 mg/L). The antifungal data revealed that all NEs were superior active against both fungi than pure lavender oil and monoterpenes. This work describes bio-products with potential use against infections caused by bacteria, fungi, and yeast as eco-friendly antimicrobials and antioxidants.