Headspace/GC–MS Analysis and Investigation of Antibacterial, Antioxidant and Cytotoxic Activity of Essential Oils and Hydrolates from Rosmarinus officinalis L. and Lavandula angustifolia Miller

Abstract

In this work, essential oils (EOs) and hydrolates (Hys) of <i>Rosmarinus officinalis</i> L. and <i>Lavandula angustifolia</i> Mill., grown in Tuscany (Italy), were studied to describe their chemical composition and biological activities. The aromatic profile of the EOs liquid phase was carried out by gas chromatography-mass spectrometry (GC-MS), while the volatile composition of vapor phase EOs and Hys was performed by headspace (HS)/GC-MS. The obtained results show that monoterpene hydrocarbons (71.5% and 89.5%) were the main compounds, followed by oxygenated monoterpenes (26.0% and 10.5%) in the liquid and vapor phase of <i>R. officinalis</i> EO, respectively. The oxygenated monoterpenes were the main components of <i>L. angustifolia</i> EO, reaching 86.9% in the liquid phase and 53.7% in the vapor phase. Regarding Hys, they consisted only of oxygenated monoterpenes, and 1,8-cineole (56.2%) and linalool (42.9%), were the main components of <i>R. officinalis</i> and <i>L. officinalis</i> Hys, respectively. Their cytotoxicity was investigated on an SHSY5Y neuroblastoma cell line by thiazolyl blue tetrazolium bromide (MTT) test, showing a notable effect of the EOs with a time-independent manner of activity and half maximal effective concentration (EC₅₀) values quite similar for the two plant species (from 0.05% to 0.06% <i>v</i>/<i>v</i> for the three time points evaluated). A measurable activity of Hys was also obtained although with higher EC₅₀ values. The antibacterial activity against <i>Escherichia coli</i> ATCC^® 25922, <i>Pseudomonas fluorescens</i> ATCC^® 13525, <i>Acinetobacter bohemicus</i> DSM 102855 as Gram-negative bacteria and <i>Kocuria marina</i> DSM 16420, <i>Bacillus cereus</i> ATCC^® 10876 as Gram-positive bacteria, was evaluated by the agar disk-diffusion method and the VPT (vapor phase test) to determinate the MIC (minimal inhibitory concentration) and the MBC (minimal bactericidal concentration) values. Both EOs possessed a high activity against all the bacterial strains with MIC values ranging from 0.19% to 3.13% <i>v</i>/<i>v</i>. Unlike EOs, Hys did not show an inhibition of the bacterial growth at the tested concentrations. Furthermore, antioxidant power was measured by 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt-based (ABTS•+) and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays, showing a remarkable ability to reduce radicals by both EOs; Hys were slightly less active. The findings highlighted that <i>R. officinalis</i> and <i>L. angustifolia</i> EOs and Hys have a chemical composition rich in bioactive molecules, which can exert different biological activities.