Essential oils and their constituents

Essential oils are aromatic and volatile liquids which are produced from plant parts such as roots, fruits, herbs, wood, seeds, bark, buds, twigs, flowers, and leaves. They are a mixture of fragrant substances or a mixture of aromatic and odorless substances. Under normal conditions, the essential oil compounds are volatile, but due to geographical origin, climate, rainfall, and so on, the constituent of essential oils is different. The compounds of essential oils are mainly highly volatile and lipophilic, and are categorized into two groups: terpenoids (mono-, sesqui-, and di-terpenes) and phenylpropanoids. But other types of compounds such as oxygen-, sulfur-, or nitrogen-containing compounds may also be present. These compounds include fats, alkaloids, anthraquinones, and coumarins. These compounds can be extracted from essential oils by methods other than distillation. The purpose of this chapter is to go over the introduction of essential oils, and their biosynthesis pathways and chemical constituents, as well as their biological activities.