Lavandula x intermedia essential oil and hydrolate: Evaluation of chemical composition and antibacterial activity before and after formulation in nanoemulsion

In this work, nanotechnology was applied to the development of nanoformulations of essential oil (EO) and hydrolate from Lavandula x intermedia the formulations were appropriately designed to enhance properties and effectiveness of EO and hydrolate in order to widen their application in pharmaceutical, cosmetics or food fields. In particular, nanoemulsions were investigated to evaluate the impact of the formulation process on the chemical composition and antibacterial activity of the encapsulated EO and hydrolate. The solvent displacement method was used for the fabrication of nanoemulsions. It involves a solvent evaporation step, which may lead to volatilisation and/or degradation of EO or hydrolate components, thus influencing their final composition and functional properties. For this reason, a chemical characterization of Lavandula x intermedia essential oil (LEO) and hydrolate (LHY) before and after nanoencapsulation was carried out by Headspace-Gas Chromatography/Mass Spectrometry (HS-GC/MS) to check for any qualitative and/or quantitative changes in its chemical profile. LEO and LHY chemical composition was substantially preserved when formulated as nanoemulsions. The formulations were then evaluated in terms of physical-chemical properties and antibacterial activity performance against Gram positive (G⁺) and Gram negative (G⁻) bacteria. LEO in nanoemulsion showed activity against E. coli (G⁻) and B. cereus (G⁺) higher than the crude form. MIC values of formulated LEO were 0.37 (v/v%) for E. coli and 0.01 (v/v%) for B. cereus, whereas MIC of pure LEO resulted 1.87 (v/v%) for E. coli and 0.94 (v/v%) for B. cereus. On the other hand, only formulated LHY exhibited activity against the two bacteria strains with MIC values of 0.75 (v/v%) for E. coli and 0.06 (v/v%) for B. cereus, whereas pure LHY was inactive on both bacteria strains. To the best of our knowledge, this is the first report showing potential antibacterial use of the generally discarded hydrolate, due to the formulation as nanoemulsion that could be considered a valid green strategy in recycling.