**2.3 Extraction and analysis**

*Essential Oils - Bioactive Compounds, New Perspectives and Applications*

necessary the case [7].

a variety of other compounds as well.

Poaceae, Zingiberaceae, etc. [18–21].

**2.2 Distribution, uses, and importance**

**2. Essential oils**

**2.1 Definition**

phenylpropanoids (benzene derivatives) which are responsible for their biological activities [5, 6]. At the first glance, terpenes and EOs can seem alike; both can come from plants and are aromatic; for many they are used for the same purpose. These similarities have led to a wide misconception that they are same, but this is not

A plethora of practical definitions of the term essential or volatile oils exist. Essential oils are concentrated aromatic hydrophobic oily volatile liquids characterized by a strong odor and produced by different plant materials such as flowers, peels, rhizomes, buds, seeds, leaves, twigs, bark, herbs or grass, wood, fruits, roots, and whole plant from one single botanic species [7–9]. However, EOs with a specific characteristic (including chemical properties and biological activities) are generally obtained from a single botanical source when the age of the plant, the climate, and the edaphic and harvest period are relatively identical [10]. They are called "essential oils" because they contain the "essence" of the plant material. A few are produced by animals and microorganisms [11]. Mosses, liverworts, seaweeds, and fungi have also been shown to contain EOs. EOs are limpid, rarely colored, and soluble in nonpolar or weakly polar organic solvents and of lower density (lighter) than water, with very few exceptions [12]. They are usually colorless particularly when fresh, but few may also be pale yellow (yellow mandarin), blue (*Matricaria chamomilla* well known as chamomile), orange (sweet orange, *Citrus sinensis*), and green (bergamot, *Citrus bergamia*) [13]. Nevertheless, they may be readily oxidizable with age by light, heat, or air, which resulting to the dark color [14]. Therefore, they need to be stored in a cool and dry place, preferably in amber glass containers. The primary difference between terpenes and EOs is that they contain terpenes and

The quality and the quantity of EOs in plant material depends on the climate, the soil type, the age and vegetable cycle stage, the preparation method, chemotypes, as well as the plant organ [8]. An estimated 3000 EOs, from about 2000 plants, are of great value and are used in a very large variety of fields [15, 16]. All plants possess principally the ability to produce volatile compounds, quite often, however, only in traces. Those plants that can produce an EO of commercial interest are called essential oils plants [17]. EOs occur specially in higher plants (with about 17,500 known species) but are distributed in good amount in a limited number of families including Myrtaceae, Myristicaceae, Oleaceae, Rosaceae, Acoraceae, Cupressaceae, Lauraceae, Compositae, Rutaceae, Lamiaceae, Asteraceae, Umbelliferae, Apiaceae,

In most cases, the biological function of EOs remains obscure. They are nowadays subject of intensive scientific research and also attract attention of diverse industries due to their potentials as active pharmacological compounds or natural preservatives [22]. Their ecological role is however well studied and described. The most known are plant interactions (allelopathic agents, germination inhibitors) and plant–animal interactions for protection against predators (insects, fungi, herbivores) and attraction of pollinating insect to their host [23]. Industries have always

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