Essential oils are volatile, aromatic secondary metabolites extracted from plants. They are oily liquids composed of simple, low-molecular-weight compounds. Essential oils are primarily derived from the leaves, branches, roots, peels, and seeds of plants from families such as Lauraceae, Asteraceae, Apiaceae, Lamiaceae, Rutaceae, and Myrtaceae. They are widely used in pharmaceuticals, insecticides, antibacterial agents, food additives, and daily cosmetics. Essential oils are complex, consisting of over a hundred components, though some contain hundreds or even thousands.
The first category is terpenes, the primary component of essential oils. Based on their basic structure, they can be divided into three categories: monoterpenes, such as lavender, myrcene, cyclocitral, camphor, and anisol; sesquiterpenes, such as farnesene, eucalyptol, cadinene, and patchouliol; and diterpenes, such as oleocanthal.
The second category is aromatic compounds, second only to terpenes in essential oils. These include terpene derivatives such as thymol and curcumene; another category is phenylpropanoid derivatives, such as cinnamaldehyde in cinnamon and phenylethyl alcohol in rose oil.
The third category is aliphatic compounds, such as isovaleraldehyde in orange and lemongrass essential oils, and ethyl acetate in sea buckthorn oil.
The fourth category is sulfur- and nitrogen-containing compounds, such as allicin, trisulfides in onions, isothiocyanates in black mustard, and pyrroles in lemon.
Most plant essential oils have strong antibacterial properties. Due to their natural and pollution-free sources, some companies in the pharmaceutical field are currently developing fumigants as alternatives to pasteurized disinfectants in public places.
