**3. Antioxidant activity of EOs**

There are many EOs which have antioxidant activity, and their application as natural antioxidants has been increasingly interested due to harmful effects to human health that some synthetic antioxidants (e.g., BHA and BHT) are faced. The antioxidant activity of EOs is due to their potential ability to cease or suspend the oxidation reaction of organic materials in the presence of oxygen which is a result of some special components including phenols. There are EOs which lack of phenolic compounds also show antioxidant activity. Some constituents including terpenoids and other volatile constituents (such as sulfur-containing components) have special radical chemistry which capable them to express antioxidant activity [25, 26].

As it was discussed earlier (Section 2.2), the major constituents of many EOs can be categorized in two specific structural families: terpenoids (monoterpene, sesquiterpene, and diterpene) and phenylpropanoids, which both comprise phenolic compounds. Some phenolic compounds are demonstrated in **Figure 1**.

**195**

α-pinene (21.3%).

radical quickly (**Figure 2b**).

*Some phenolic compounds present in EOs.*

lipids [27].

**Figure 1.**

**Figure 2.**

*Application of Essential Oils for Shelf-Life Extension of Seafood Products*

Generally, phenolic compounds can potentially react with peroxyl radicals and transfer the H atom (**Figure 2a**). Due to the stability of phenoxyl radical, it will not continue the radical chain reactions. Instead it will quench the second peroxyl

*Mechanism of antioxidant activity of phenolic compounds. The reaction between phenolic compounds and* 

*peroxyl radicals (a), quenching the second peroxyl group by phenoxyl radical (b).*

In contrast with phenolic compounds present in EOs, unsaturated non-phenolic

Many researchers have investigated the antioxidant activity of EOs. A potential antioxidant essential oil was extracted from *Achillea millefolium subsp. millefolium* Afan, which significantly reduced DPPH radical (IC50 = 1.56 μg/ml) and showed lipid peroxidation (IC50 = 13*.*5 g/ml). The authors demonstrated that the polar phase of the extract exhibited antioxidant activity [28]. The essential oil extracted from dried rhizome *Curcuma zedoaria* (Berg.) Rosc. (Zingiberaceae) showed a moderate to good antioxidant activity at 20 mg/ml. This activity was measured by three different methods, reducing power (good activity), DPPH radical scavenging (excellent activity), and ferrous ion chelating (low activity) [29]. In another research, the antioxidant activity of *Rosmarinus officinalis* essential oil were determined against gastric injury caused by ethanol. Results showed that the *R. officinalis* essential oil (50 mg/kg) ingestion can make gastro-protective influences by reducing the ethanol induced ulcers. The resultant data suggested possible antioxidant mechanism induced by *R. officinalis* essential oil. The major components of chemical composition of this essential oil were cineole (28.5%), camphor (27.7%), and

terpenoids such as α-pinene (**Figure 3**) can autoxidize similarly to unsaturated

*DOI: http://dx.doi.org/10.5772/intechopen.86574*

*Application of Essential Oils for Shelf-Life Extension of Seafood Products DOI: http://dx.doi.org/10.5772/intechopen.86574*

#### **Figure 1.**

*Essential Oils - Oils of Nature*

in the old plant EOs [19].

borneol (4.91%) and β-pinene (3.90%) [20].

saturated fatty acids were also detected [21].

**3. Antioxidant activity of EOs**

phenols (carvacrol and thymol) and their related monoterpene hydrocarbon precursors (*p*-cymene and γ-terpinene), that demonstrated integrated effects of the different collection periods and seasons on the chemical composition of EOs. The EOs obtained from old plant included much lower quantities of monoterpene hydrocarbones (mostly γ-terpinene) and the highest quantities of the oxygenated monoterpenes (linalool and borneol), monoterpene phenols (mostly thymol) and their derivatives (mostly carvacrol methyl ether), sesquiterpenes (mostly β-caryophyllene) and their oxygenated derivatives (e.g., caryophyllene oxide). A characteristic presence of camphor and thymodihydroquinone was also discovered

The EOs obtained by hydrodistillation from flowering Thyme (*Thymis vulgaris* L.) was investigated by GC/FID and GC/MS. The yield of extraction in this study was reported as 1%, in which 43 chemical compounds (97.85% of total constituents) were identified. The EOs extracted from flowering Thyme were mainly consisted of camphor (38.54%), camphene (17.19%), α-pinene (9.35%), 1, 8-cineole (5.44%),

In an another research, seven EOs of *N. sativa*, which were all extracted by soxhlet extraction and steam distillation, were analyzed by GC/MS. A total of 32 compounds were identified. The major fraction of every EOs was a mixture of monoterpenes. The major components were thymoquinone (30–48%), *p*-cymene (7–15%), carvacrol (6–12%), 4-terpineol (2–7%), t-anethole (1–4%) and the sesquiterpene longifolene (1–8%). Very small quantities of the esters of special un/

Curcumin, the yellowish pigment of turmeric, is generated from turmeric oleoresin. In a study performed in order to investigate the antibacterial activity of turmeric oil extracted by hexane and fractionated by silica gel column chromatography, GC/MS analysis identified 13 major components in turmeric oil, fraction I, and fraction II. *ar-*turmerone (62.0%), *trans-â*-farnesene (6.6%), turmerone (5.1%), and curlone (3.9%) were found to be the major compounds in turmeric oil whereas fraction II contained *ar-*turmerone (77.9%), curlone (5.3%), and turmerone (5.2%) [22]. Rosemary (*Rosmarinus officinalis* L.), a member of mint family, is an ordinary aromatic shrub grown in various places around the world [23]. Some researchers has assessed the chemical composition of rosemary EOs to understand the reason of biological activities such as antimicrobial activity. In an experimentation 22 components were identified from this plant by GC/MS. The major constituents were 1,8-cineole (26.54%), α-pinene (20.14%), Camphor (12.88%), and camphene (11.38%) [24].

There are many EOs which have antioxidant activity, and their application as natural antioxidants has been increasingly interested due to harmful effects to human health that some synthetic antioxidants (e.g., BHA and BHT) are faced. The antioxidant activity of EOs is due to their potential ability to cease or suspend the oxidation reaction of organic materials in the presence of oxygen which is a result of some special components including phenols. There are EOs which lack of phenolic compounds also show antioxidant activity. Some constituents including terpenoids and other volatile constituents (such as sulfur-containing components) have special radical chemistry which capable them to express antioxidant activity [25, 26]. As it was discussed earlier (Section 2.2), the major constituents of many EOs can be categorized in two specific structural families: terpenoids (monoterpene, sesquiterpene, and diterpene) and phenylpropanoids, which both comprise pheno-

lic compounds. Some phenolic compounds are demonstrated in **Figure 1**.

**194**

*Some phenolic compounds present in EOs.*


#### **Figure 2.**

*Mechanism of antioxidant activity of phenolic compounds. The reaction between phenolic compounds and peroxyl radicals (a), quenching the second peroxyl group by phenoxyl radical (b).*

Generally, phenolic compounds can potentially react with peroxyl radicals and transfer the H atom (**Figure 2a**). Due to the stability of phenoxyl radical, it will not continue the radical chain reactions. Instead it will quench the second peroxyl radical quickly (**Figure 2b**).

In contrast with phenolic compounds present in EOs, unsaturated non-phenolic terpenoids such as α-pinene (**Figure 3**) can autoxidize similarly to unsaturated lipids [27].

Many researchers have investigated the antioxidant activity of EOs. A potential antioxidant essential oil was extracted from *Achillea millefolium subsp. millefolium* Afan, which significantly reduced DPPH radical (IC50 = 1.56 μg/ml) and showed lipid peroxidation (IC50 = 13*.*5 g/ml). The authors demonstrated that the polar phase of the extract exhibited antioxidant activity [28]. The essential oil extracted from dried rhizome *Curcuma zedoaria* (Berg.) Rosc. (Zingiberaceae) showed a moderate to good antioxidant activity at 20 mg/ml. This activity was measured by three different methods, reducing power (good activity), DPPH radical scavenging (excellent activity), and ferrous ion chelating (low activity) [29]. In another research, the antioxidant activity of *Rosmarinus officinalis* essential oil were determined against gastric injury caused by ethanol. Results showed that the *R. officinalis* essential oil (50 mg/kg) ingestion can make gastro-protective influences by reducing the ethanol induced ulcers. The resultant data suggested possible antioxidant mechanism induced by *R. officinalis* essential oil. The major components of chemical composition of this essential oil were cineole (28.5%), camphor (27.7%), and α-pinene (21.3%).

#### **Figure 3.**

*The effect of pectin-CEO coating on the bream fillets at day 1 and day 15 of the storage (adopted from Nisar et al. [42]).*

The lipid oxidation is one of the most important limiting factors for the shelflife seafood products. For this purpose the antioxidant activity of the EOs of five Mediterranean spices (*Origanum vulgare*, *Thymus vulgaris*, *Rosmarinus officinalis*, *Salvia officinalis*, and *Syzygium aromaticum*) was analyzed. The *S. aromaticum* essential oil, which comprised the highest level of total phenols (898.89 mg/l GAE), demonstrated the highest antioxidant activity (98.74% for DPPH radical inhibition and 1.47 TEAC for FRAP value). The EOs extracted from *T. vulgaris* and *R. officinalis* showed the highest TBARS inhibition (89.84%) and iron (II) chelating (76.06%) activities, respectively [30].
