**10. Role of essential oils as antioxidants**

Form the safety point of view, one of the important sources for the search of essential oils is herbs and spices. Since from prehistoric era, these had been used for flavoring and medicinal properties. However, recent reports showed that the radical scavenging activity of various essential oil is very high. The lag time in conjugated diene formation was dose-dependently prolonged by addition of the essential oils of some aromatic plants such as black cumin, cinnamon bark, ginger [100]. At a level of 200 μg/ml DPPH activity ranged from 39 to 90% in different plants. Phenolic compounds such as thymol, eugenol, linalool etc. are considered to be responsible for scavenging activity of essential oils. Biomolecules such as protein, amino acids, unsaturated lipids are mostly oxidized by free radicals and

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tive diseases as well as to preserve food safely [111].

*Essential Oil as Antimicrobial Agents: Efficacy, Stability, and Safety Issues for Food Application*

reactive oxygen species. The human body is equipped with an inherent defense system which can destroy free radicals present in almost all cells [101]. Oxidative

stress is the cause of imbalance between free radical production and their removal from the body. So to overcome oxidative stress antioxidants should be taken externally. Nowadays, there is more interest on natural antioxidants from plants sources to replace those of synthetic origin. Various studies have shown that essential oils are natural source of antioxidants. Aromatic plants are rich in natural antioxidants. The essential oils of coriander, Eucalyptus, juniper, cumin, basil, cinnamon, clove and thyme have proven radical-scavenging and antioxidant properties in the DPPH radical assay at room temperature [2, 40, 102]. The main constituents of the volatile extract of Egyptian corn silk were *cis*-R-terpineol (24.22%), 6,11-oxidoacor-4-ene (18.06%), citronellol (16.18%), *trans*-pinocamphone (5.86%), eugenol (4.37%), neo-iso-3-thujanol (2.59%), and *cis*-sabinene hydrate (2.28%).The water extract inhibited DPPH activity by 81.00 (6.00% at a level of 200 μg/ml). These results suggest that corn silk is a flavor ingredient source and a natural antioxidant supplement for various food products [41]. The antioxidant activity was attributed to the high content of the phenolics thymol and carvacrol (20.5 and 58.1%, respectively). *Thymus spathulifolius* essential oil also possessed an antioxidant activity due to the high thymol and carvacrol content 36.5 and 29.8%, respectively [103]. The activity is again attributed to the content of thymol and carvacrol (35.0 and 32.0%, respectively). Although dietary supplementation of oregano oil to rabbits delayed lipid oxidation, this effect was less than that of supplementation with the same concentration of tocopheryl acetate [104]. However, when tested on turkeys it showed an equivalent performance to the same concentration of α-tocopheryl acetate in delaying iron-induced, lipid oxidation [105]. The essential oils of *Salvia cryptantha* and *Salvia multicaulis* have the capacity to scavenge free radicals. The activity of these oils was higher than that of curcumin, ascorbic acid or BHT [106]. The essential oil of *Achillea millefolium subsp. millefolium* (Asteraceae) exhibited a hydroxyl radical scavenging effect in the Fe3 α-EDTA-H2O2 deoxyribose system and inhibited the non-enzymatic lipid peroxidation of rat liver homogenate [107]. In addition, *Curcuma zedoaria* essential oil was found to be an excellent scavenger for DPPH radical [108]. The antioxidant activity of essential oils cannot be attributed only to the presence of phenolic constituents; monoterpene alcohols, ketones, aldehydes, hydrocarbons and ethers also contribute to the free radical scavenging activity of some essential oils. For instance, the essential oil of *Thymus caespititius*, *Thymus camphoratus*, and *Thymus mastichina* showed antioxidant activity which in some cases was equal to that of alpha-tocopherol. Surprisingly, the three species are characterized by high contents of linalool and 1,8-cineole, while thymol or carvacrol are almost absent. The essential oil of lemon balm (*Melissa officinalis* L.) shows an antioxidant and free radical scavenging activity [109] with the most powerful scavenging constituents comprising neral/geranial, citronellal, isomenthone and menthone. Tea tree (*Melaleuca alternifolia*) oil has been suggested as a natural antioxidant alternative for BHT with the inherent antioxidant activity attributed mainly to the α-terpinene, β-terpinene and β-terpinolene content. Essential oils isolated from *Mentha aquatica* L., *Mentha longifolia* L. and *Mentha piperita* L., were able to reduce DPPH radicals into the neutral DPPHH form [110]. The most powerful scavenging constituents were found to be 1,8-cineole for the oil of *M. aquatica* while menthone and isomenthone were the active principles of *M. longifolia* and *M. piperita*. From the above studies, we may conclude that essential oils are rich sources of natural antioxidants. So we can use essential oils as natural sources of antioxidants instead of synthetic antioxidants to prevent from various degenera-

*DOI: http://dx.doi.org/10.5772/intechopen.92305*

## *Essential Oil as Antimicrobial Agents: Efficacy, Stability, and Safety Issues for Food Application DOI: http://dx.doi.org/10.5772/intechopen.92305*

reactive oxygen species. The human body is equipped with an inherent defense system which can destroy free radicals present in almost all cells [101]. Oxidative stress is the cause of imbalance between free radical production and their removal from the body. So to overcome oxidative stress antioxidants should be taken externally. Nowadays, there is more interest on natural antioxidants from plants sources to replace those of synthetic origin. Various studies have shown that essential oils are natural source of antioxidants. Aromatic plants are rich in natural antioxidants. The essential oils of coriander, Eucalyptus, juniper, cumin, basil, cinnamon, clove and thyme have proven radical-scavenging and antioxidant properties in the DPPH radical assay at room temperature [2, 40, 102]. The main constituents of the volatile extract of Egyptian corn silk were *cis*-R-terpineol (24.22%), 6,11-oxidoacor-4-ene (18.06%), citronellol (16.18%), *trans*-pinocamphone (5.86%), eugenol (4.37%), neo-iso-3-thujanol (2.59%), and *cis*-sabinene hydrate (2.28%).The water extract inhibited DPPH activity by 81.00 (6.00% at a level of 200 μg/ml). These results suggest that corn silk is a flavor ingredient source and a natural antioxidant supplement for various food products [41]. The antioxidant activity was attributed to the high content of the phenolics thymol and carvacrol (20.5 and 58.1%, respectively). *Thymus spathulifolius* essential oil also possessed an antioxidant activity due to the high thymol and carvacrol content 36.5 and 29.8%, respectively [103]. The activity is again attributed to the content of thymol and carvacrol (35.0 and 32.0%, respectively). Although dietary supplementation of oregano oil to rabbits delayed lipid oxidation, this effect was less than that of supplementation with the same concentration of tocopheryl acetate [104]. However, when tested on turkeys it showed an equivalent performance to the same concentration of α-tocopheryl acetate in delaying iron-induced, lipid oxidation [105]. The essential oils of *Salvia cryptantha* and *Salvia multicaulis* have the capacity to scavenge free radicals. The activity of these oils was higher than that of curcumin, ascorbic acid or BHT [106]. The essential oil of *Achillea millefolium subsp. millefolium* (Asteraceae) exhibited a hydroxyl radical scavenging effect in the Fe3 α-EDTA-H2O2 deoxyribose system and inhibited the non-enzymatic lipid peroxidation of rat liver homogenate [107]. In addition, *Curcuma zedoaria* essential oil was found to be an excellent scavenger for DPPH radical [108]. The antioxidant activity of essential oils cannot be attributed only to the presence of phenolic constituents; monoterpene alcohols, ketones, aldehydes, hydrocarbons and ethers also contribute to the free radical scavenging activity of some essential oils. For instance, the essential oil of *Thymus caespititius*, *Thymus camphoratus*, and *Thymus mastichina* showed antioxidant activity which in some cases was equal to that of alpha-tocopherol. Surprisingly, the three species are characterized by high contents of linalool and 1,8-cineole, while thymol or carvacrol are almost absent. The essential oil of lemon balm (*Melissa officinalis* L.) shows an antioxidant and free radical scavenging activity [109] with the most powerful scavenging constituents comprising neral/geranial, citronellal, isomenthone and menthone. Tea tree (*Melaleuca alternifolia*) oil has been suggested as a natural antioxidant alternative for BHT with the inherent antioxidant activity attributed mainly to the α-terpinene, β-terpinene and β-terpinolene content. Essential oils isolated from *Mentha aquatica* L., *Mentha longifolia* L. and *Mentha piperita* L., were able to reduce DPPH radicals into the neutral DPPHH form [110]. The most powerful scavenging constituents were found to be 1,8-cineole for the oil of *M. aquatica* while menthone and isomenthone were the active principles of *M. longifolia* and *M. piperita*. From the above studies, we may conclude that essential oils are rich sources of natural antioxidants. So we can use essential oils as natural sources of antioxidants instead of synthetic antioxidants to prevent from various degenerative diseases as well as to preserve food safely [111].

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

mitochondria are necessary to induce apoptosis [99].

Form the safety point of view, one of the important sources for the search of essential oils is herbs and spices. Since from prehistoric era, these had been used for flavoring and medicinal properties. However, recent reports showed that the radical scavenging activity of various essential oil is very high. The lag time in conjugated diene formation was dose-dependently prolonged by addition of the essential oils of some aromatic plants such as black cumin, cinnamon bark, ginger [100]. At a level of 200 μg/ml DPPH activity ranged from 39 to 90% in different plants. Phenolic compounds such as thymol, eugenol, linalool etc. are considered to be responsible for scavenging activity of essential oils. Biomolecules such as protein, amino acids, unsaturated lipids are mostly oxidized by free radicals and

**10. Role of essential oils as antioxidants**

survive in spite of mitochondrial damage. It has been recently demonstrated in the yeast *Saccharomyces cerevisiae* that induction of mitochondrial damage transforming Rho+ cells into Rhoo cells and the induction of apoptosis/necrosis by a combined exposure to essential oils and nuclear mutagens caused a striking reduction of the frequency of nuclear genetic events [86]. Typical mutagenic agents were used such as ultraviolet C (UV-C) radiation which forms pyrimidine dimers and 6-4 photoproducts, 8-methoxypsoralen (8-MOP) activated by ultraviolet A (UVA) radiation which forms DNA mono- and biadducts, or methyl methanesulfonate (MMS) which methylates DNA bases. The reduction in mutant frequency in the presence of essential oils was accompanied by a strong synergistic induction of cytoplasmic "petite" mutants. The anti-mutagenic effect was independent of the type of mutations, i.e., reversion, intra- or intergenic recombination. The extent of this anti-mutagenic effect depended on the mutagen and oil concentrations. However, unexpectedly, the mechanism of the decrease of mutagenicity did not depend on the type of essential oil but on the type of mutagen, thus on the type of lesions and consequently on the DNA repair or lesion avoidance system involved. In fact, after combined treatment by UVC or 8-MOP/UVA plus essential oils, the transformation of Rho+ cells into rho0 cells resulted in a decrease of the frequency of mutants accompanied by a slight resistance of the survival [97]. After UVC or 8-MOP/UVA alone, less mutants were also found in a rho0 mutant, i.e., a complete BET-induced rho0 selected by the alcaloid lycorine, than in the wild type Rho+. In that case, the reduction in mutation frequency was the same as that after the combined treatments confirming the importance of mitochondrial dysfunction for these effects [98]. The same decrease of mutant frequencies was also found in a nucleotide excision repair (NER) defective rad3 mutant after UVC/essential oil combined treatment. Thus the error-free NER repair system does not play any role in this decrease and probably not the error-free homologous recombination in the case of 8-MOP/UVA. However, as a function of survival, this additional cytotoxicity caused a notable reduction of the mutant frequencies for a same survival level. The decrease of cell survival was also accompanied by a synergistic increase of cytoplasmic petite mutants. Thus, in this case, the essential oils contributed to the elimination of the cells already affected by MMS, leading potential mutants to death by late apoptosis and necrosis [97]. The reduction by essential oils of the frequency of mutations induced by the mutagens was always accompanied by a synergistic induction of complete petite mutants. Moreover, essential oils alone or in combined treatments mainly induced necrosis rather than apoptosis. This corroborates with the fact that petite mutants were true rho0 mutants unable to perform apoptosis but only able to passively undergo necrosis, since functional

**164**
