**4. Biological activities of EO**

The biological activity of EOs depends on their chemical compositions and structures and on the synergistic effects between their major and minor compounds.

### **4.1 Antioxidant capacity**

The antioxidant activity was evaluated, *in vitro*, by various tests. In this respect, Louail et al. [26] assessed antioxidant activities of *Ammodaucus leucotrichus* EO by measuring by inhibiting the β-carotene bleaching. The value of the essential oils showed a better antioxidant activity when compared to ascorbic acid, used as reference antioxidant molecule. In another experiments, Selmi et al. [13], Aloui et al. [27], and Jedidi et al. [28] assessed the antioxidant activities of essential oils obtained from aerial parts of *Junepeus phoenicea*, *Pinus halepensis*, and *Rosmarinus officinalis*, using 2, 2-diphenyl-1-picrylhydrazyl (DPPH• ) and 2,2′-azino-bis [3-ethylbenzthiazoline-6-sulphonic acid] (ABTS) tests. Essential oils of the four species exhibited strong antioxidant abilities to reduce the studied radicals. It has been demonstared that 1,8-cineole, α-pinene and camphor have the dominant components of the EO of a few commercial species. These identified molecules are powerful scavengers of free radicals and therefore responsible for the strong antioxidant activities observed [29].

#### **4.2 Antimicrobial activity**

The EO of many species were screened for their antimicrobial activities against different microorganisms, including Gram-positive and Gram-negative bacteria. Essentail oils exhibited strong inhibitory action against most tested organisms. Furthermore, the essential oil showed significant antibacterial activity against Gram-negative and Gram-positive bacteria. It has been shown that Gram (+) bacteria are more sensitive to essential oils isolated from the species *Pinus pinea* [27], *Ammodaucus leucotrichus* [30], and *Rosmarinus officinalis* [31]. The authors suggested that this finding can be explained by the fact that Gram (−) bacteria have hydrophobic lipopolysaccharide in the outer part of their membranes, which provides effective protection against different agents.

In addition, listerine, which is a solution consisting of thymol and eucalyptol essential oils, has a high bactericidal activity on microorganisms in saliva and dental plaque [32].

On the other hand, it also demonstrated that the sesquiterpenoids identified in the essential oils of *Cyperus iria* leaves exerted a potential fungicidal action against Fusarium graminearum [33].

#### **4.3 Anticholinesterase activity**

Limonene, a monoterpene isolated from Ammodaucus leucotrichus essential oils, has been shown to induce high acetylcholinesterase inhibitory activity with an IC50 of about 51.6 μg ml−1 [34]. Additionally, Aazza et al. [29] proved that 1,8-cineole, α-pinene, and camphor were the dominant components of sage essential oils and were responsible for strong antiacetylcholinesterase activity.

*Phytochemistry, Medicinal Uses, and Beneficial Nutritional Effects of Essential Oils DOI: http://dx.doi.org/10.5772/intechopen.112696*
