Medicinal and aromatic plants’ essential oils: chemical composition and antimicrobial potential

Essential oils (EOs) are complex mixtures of volatile compounds produced by the plant secondary metabolism and consisting in relatively low-boiling point, low-molecular weight and lipophilic molecules. About 3000 higher plants (also known as ‘aromatic plants’) are recognized as sources of EOs, among which 300 are very important on a commercial scale and used by the food, agronomic, pharmaceutic, cosmetic and perfume industries [1,2]. Their main industrial applications are as flavouring of foodstuffs and beverages including liqueurs, as fragrances in perfumes and cosmetics and as antimicrobial agents in pharmaceutics and foodstuffs [3]. Notably, the EO composition is made up of hundreds of chemical constituents and generally a few components (usually 3-5) occur in significant amounts so that they determine the EO quality by influencing the chemico-physical and biological properties of the EO itself. EO composition is generally dominated by terpenoids such as monoterpenes, sesquiterpenes and their oxygenated derivatives. In addition, phenylpropanoids and aliphatic compounds may characterize some EOs as well. EOs’ components are able to address different targets of the microbial cell, like altering the cytoplasmic membrane, increasing permeability, altering the proton motive force, inhibiting cytoplasmic enzymes and impacting the quorum sensing activity. On this basis, they may represent alternative strategies for the treatment of infectious diseases and to prevent food spoilage. In this presentation, after a brief description of the main bioactive classes of EOs’ components, a few case studies highlighting the antimicrobial potential of EOs will be reported.