**5. Distribution of the volatile oils in the plant kingdom**

Although only 100 species are widely known for their volatile oils, there are over 2000 plant species widespread over 60 families such as Lamiaceae, which is also


**Table 1.** *Examples of different chemotypes.*


## *Aromatherapy as Complementary Medicine DOI: http://dx.doi.org/10.5772/intechopen.92021*

#### **Table 2.**

**2. Definition and localization of essential oils**

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

[16, 17].

**Table 1.**

**110**

*Examples of different chemotypes.*

**3. Extraction of volatile oils**

Volatile oils are aromatic compounds which occur only in 10% of the plant kingdom and are stored in plants in specific secretory cells such as glands, hairs, ducts, cavities, or resin ducts [10–13]. Essential oils are hydrophobic in nature; they can be dissolved by polar solvent like alcohols and nonpolar solvents, waxes, and oils. Most of them are pale yellow or with no color with the exception of the blue volatile oil of *Matricaria chamomilla* L., and most are liquid and of low density than water except the essential oil of *Cinnamomum verum* Blume. and *Syzygium aromaticum* L. [14, 15]. Volatile oils are easily oxidizable by light, heat, and air due to the presence of olefenic double bonds and functional groups such as hydroxyl, aldehyde, and ester

The oils contained within the plant cells are liberated through heat and compression from different organs of the plant, for example, the leaves, flowers, fruit, bark, and gums. The extraction of the oils from different plant organs is achieved by different methods, such as hydro-distillation, which is the most common method of extraction [18, 19]. Essential oils are composed of a mixture of volatile components and consist of about 20–60 individual compounds, and some may contain more than 100 components as jasmine, lemon, and cinnamon volatile oils [20–23].

The fragrance and chemical composition of the oils can vary according to different factors as the geo-climatic location and growing conditions (soil type, climate, altitude, and amount of water available), season, and time of day when harvesting is done. Therefore, these factors influence the biochemical synthesis of the oils in a plant, so that the same species of the plant make the same volatile oil but maybe of different chemical compounds, which will affect their therapeutic activities. These different chemical compositions led to different chemotypes. Chemotype is in general a different population of the same species of plant which produces many chemical profiles for a particular class of secondary metabolites.

Although only 100 species are widely known for their volatile oils, there are over 2000 plant species widespread over 60 families such as Lamiaceae, which is also

**Plant name Chemotype 1 Chemotype 2 Chemotype 3** Thyme (*Thymus vulgaris* L.) Thymol Thujanol Linalool Peppermint (*Mentha piperita* L.) Menthol Carvone Limonene Rosemary (*Rosmarinus officinalis* L.) 1,8 Camphor Cineole Verbenone Dill (*Anethum graveolens* L.) Carvone Limonene Phellandrene Lavender (*Lavandula angustifolia* Mill.) Linalool Linalyl acetate β-Caryophyllene

**4. Factors affecting chemical composition of volatile oils**

Examples of some chemotypes are shown in **Table 1** [24–27].

**5. Distribution of the volatile oils in the plant kingdom**

*Different classes of volatile oils and their biological activities.*

called the mint family. It is one of most important plant families in the plant kingdom. This family is rich in essential oils, especially menthol thyme, Rosemary, and Oregano. Apiaceae or Umbelliferae is a family of mostly aromatic flowering pla nts, which contains economically important plants as caraway, coriander, cumin, and fennel [28–31]. Volatile oils contribute in a lot of industries as food products, drinks, perfumes, pharmaceuticals, and cosmetics [32–34]. The production and consumption of essential oils increase rapidly all over the world [35]. Regardless of the high costs because of the large amounts of plant material needed, volatile oil production has been increasing. The expected world production of the oils ranges from 40,000 to 60,000 tons/year and represents a market of approximately 700 million US\$ [36, 37]. Examples of some classes of essential oils their medical uses and structures are illustrated in (**Table 2**), (**Figures 1** and **2**) [26, 38–41].
