**2. How do essential oils work**

Essential oils include biological compounds like growth factors, hormones, and neurotransmitters that are concentrated from the plant. Several researches have been performed on PEOs in order to confirm their biological efficacy against bacteria and fungi [13]; PEOs have an antibacterial activity where they cause damage to cells via an interface with plasma membrane components which lead to leak the most important compounds and damage the transportation channels, especially of potassium ion [12, 13]. Volatiles from PEOs not only work on single target site in the cell but also they bind to protein structures of the cell. Some of the PEOs and their volatiles are found to be responsible in inhibiting the enzymatic proteins in some bacterial pathogens [14–16].

Essential oils used all over the world for disinfection, as anti-inflammatory, relaxing, and stimulating substances, and with potential and modern exploitation in clinical medicine are most commonly used in the practice of aromatherapy, in which they are inhaled, or be swallowed, or can interact with your body in several ways when applied to your skin, some plant chemicals are absorbed also commonly used in food and cosmetic industries [17] (**Figure 1**).

**31**

*Essential Oils*

liquid [11].

• Hydrodistillation

• Hydrodiffusion

• Effleurage

• Cold pressing

• Steam distillation

• Solvent extraction

**3.1 Hydrodistillation**

extraction procedure.

were found in comparison with HD.

• Microwave Assisted Process (MAP)

• Carbondioxide extraction

*DOI: http://dx.doi.org/10.5772/intechopen.92216*

Essential oils are produce from valuable plant products, generally of complex composition including the volatile principles contained in the plant and the more or less modified during the preparation process. The earliest recorded mention of the techniques and methods used to produce essential oils is believed to be that of Ibnal-Baitar (1188–1248). The oil droplets being stored in the oil glands or sacs can be removed by either accelerate diffusion through the cell wall or crush the cell wall [17–20]. The assumed techniques depend on the part of the plants where the oil is to be extracted, the stability of the oil to heat and susceptibility of the oil constituents to chemical reactions. An extract is derived when the plant material is soaked in a substance such as water, alcohol or other liquid for long periods of time so that its flavor, aroma or medicinal properties, infuses into the

Common techniques used for the extraction of essential oils are:

Hydrodistillation represents one of the most used traditional and a commonly methods of extraction used method of extracting essential oils from plant samples (wood and flower). This method may be further classified into the subcategories of steam distillation, water distillation, or a combination of water and steam distillation. Hydrodistillation include saturation of the powdered wood in the water in the first step, while the next step is to use the steam that result from the heating of the water reservoir then finally gather the oil that result after the reservoir cold. The advantage of this technique is that the required material can be distilled at a temperature below 100°C. There are many studies provided that the different extraction processes on yield and properties of essential oil from rosemary (*Rosmarinus officinalis* L.) by HD and solvent-free microwave extraction (SFME) [21]. While Golmakani and Rezaei (2008) [22] researched the microwave-assisted HD (MAHD), which is an advanced HD technique utilize a microwave oven in the

MAHD was preferable in extraction time (75 min, compared to 4 h in HD). Ohmic-assisted HD (OAHD) is another advanced HD technique [23]. OAHD method had the extraction time of 24.75 min, while HD took 1 h for extraction of essential oil. No changes in the compounds of the essential oils obtained by OAHD

**3. Extraction of essential oils**
