**4. Antioxidant activity**

The antioxidant activity by the ABTS method [2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)] was adapted according to the methodology suggested by [70]. The ABTS˙+ radical was prepared by the reaction of 5.0 mL of a 3840 μg mL<sup>−</sup><sup>1</sup> of ABTS solution with 88 μL of the 37,840 μg mL<sup>−</sup><sup>1</sup> potassium persulfate solution. The mixture was left in the dark for 16 h. After formation of the radical, the mixture was diluted in ethanol (approximately 1:30 v/v) and absorbance was obtained at 734 nm. From the extracts and essential oils concentrations (5–150 μg mL<sup>−</sup><sup>1</sup> ), the reaction mixture was prepared with the ABTS radical cation. In a dark environment, a 30 μL aliquot of each extract and essential oil concentration was transferred into 23 test tubes containing 3.0 mL of the ABTS radical cation and homogenized on a tube shaker. After 6 min, absorbance of the reaction mixture was obtained in a spectrophotometer at 734 nm. The analyzes were performed in triplicate and the capture of the free radical was expressed as percent inhibition (% I) of the ABTS radical cation.

**155**

**Table 6.**

*Comparative Analysis of the Chemical Composition, Antimicrobial and Antioxidant Activity…*

The ABTS method allowed the calculation of the 50% effective concentration of the essential oils, which express the minimum concentration required to reduce the initial concentration of ABTS by 50%, and these are expressed in **Table 6**. The lowest concentration and consequently the best antioxidant activity was observed

The antioxidant effect of *C. zeylanicum* essential oil differs from that observed by [71] using the ABTS technique, where these authors verified a lower EC50. This difference is explained by the authors due to variation in the chemical composition of the essential oils studied, which depends on factors such as the geographic loca-

The result for *R. officinalis* essential oil exhibited by [57] shows a fairly high effective concentration comparing that obtained in this article. Also [72], when evaluating the antioxidant activity of this essential oil from five different crop fields, found a lower EC50 than this study. According to [73], the main responsible for the free radical stabilization capacity of this species is 1,8-cineol. In this way, it is possible to relate the lower antioxidant potential of the rosemary essential oil

On the other hand [72], while evaluating the antioxidant capacity of rosemary essential oil using DPPH, it had a relatively higher concentration than this study *Salmonella thyphimurium*. Also highlighting the difference of methods used, since its concentration, it presented higher concentrations at levels of approximately 700

Regarding the antioxidant potential of oregano essential oil, the author [74] obtained a higher value of efficient concentration than presented in our study, which highlights the data obtained satisfactory in this research. However [75], while still evaluating the antioxidant activity of *O. vulgare* essential oil, using the ABTS radical discoloration technique, a lower EC50 is observed than that observed in this study. According to these authors, the antioxidant potential of this oil is related to the presence of phenolic compounds, but it can also be attributed to a possible

When checking the antioxidant activity of *C. longa* [76], it is found that concentrations are much higher than those quantified for the essential oil using the DPPH assay, whereas, when using the ABTS assay, we exposed satisfactorily lower

When studying the anti-inflammatory and anti-inflammatory activity of ginger

essential oil [77], a much higher EC50 value is obtained which was presented in this study. These results are lower than that obtained in this study, and the authors attribute to this fact that the low concentration of phenolic compounds is mainly

**)**

**EC50 (μg mL<sup>−</sup><sup>1</sup>**

*C. zeylanicum* 215.93 11.11 *O. vulgare* **14.00 90.74** *Z. officinale* 308.16 25.9 *R. officinalis* 153.7 25.7 *C. longa* 173.43 14.8 *C. latifolia* 250 24.89

and consequently also the highest

**% ABTS inhibition (50 μg mL<sup>−</sup><sup>1</sup>**

**)**

*DOI: http://dx.doi.org/10.5772/intechopen.86576*

percentage of ABTS inhibition.

more units.

concentrations.

to oregano, with an EC50 quantified in 14 μg mL<sup>−</sup><sup>1</sup>

tion and the time of collection of the plant.

synergy between the various constituents.

responsible for the antioxidant activity.

*ABTS free radical sequestering activity by essential oils.*

**Essential oil Effective concentration 50%**

obtained in this research with the low content of 1,8-cineol.

#### *Comparative Analysis of the Chemical Composition, Antimicrobial and Antioxidant Activity… DOI: http://dx.doi.org/10.5772/intechopen.86576*

The ABTS method allowed the calculation of the 50% effective concentration of the essential oils, which express the minimum concentration required to reduce the initial concentration of ABTS by 50%, and these are expressed in **Table 6**. The lowest concentration and consequently the best antioxidant activity was observed to oregano, with an EC50 quantified in 14 μg mL<sup>−</sup><sup>1</sup> and consequently also the highest percentage of ABTS inhibition.

The antioxidant effect of *C. zeylanicum* essential oil differs from that observed by [71] using the ABTS technique, where these authors verified a lower EC50. This difference is explained by the authors due to variation in the chemical composition of the essential oils studied, which depends on factors such as the geographic location and the time of collection of the plant.

The result for *R. officinalis* essential oil exhibited by [57] shows a fairly high effective concentration comparing that obtained in this article. Also [72], when evaluating the antioxidant activity of this essential oil from five different crop fields, found a lower EC50 than this study. According to [73], the main responsible for the free radical stabilization capacity of this species is 1,8-cineol. In this way, it is possible to relate the lower antioxidant potential of the rosemary essential oil obtained in this research with the low content of 1,8-cineol.

On the other hand [72], while evaluating the antioxidant capacity of rosemary essential oil using DPPH, it had a relatively higher concentration than this study *Salmonella thyphimurium*. Also highlighting the difference of methods used, since its concentration, it presented higher concentrations at levels of approximately 700 more units.

Regarding the antioxidant potential of oregano essential oil, the author [74] obtained a higher value of efficient concentration than presented in our study, which highlights the data obtained satisfactory in this research. However [75], while still evaluating the antioxidant activity of *O. vulgare* essential oil, using the ABTS radical discoloration technique, a lower EC50 is observed than that observed in this study. According to these authors, the antioxidant potential of this oil is related to the presence of phenolic compounds, but it can also be attributed to a possible synergy between the various constituents.

When checking the antioxidant activity of *C. longa* [76], it is found that concentrations are much higher than those quantified for the essential oil using the DPPH assay, whereas, when using the ABTS assay, we exposed satisfactorily lower concentrations.

When studying the anti-inflammatory and anti-inflammatory activity of ginger essential oil [77], a much higher EC50 value is obtained which was presented in this study. These results are lower than that obtained in this study, and the authors attribute to this fact that the low concentration of phenolic compounds is mainly responsible for the antioxidant activity.


#### **Table 6.**

*ABTS free radical sequestering activity by essential oils.*

*Essential Oils - Oils of Nature*

*O. vulgare* 15.33

*C. longa* 14.33

*Z. officinale* 10.70

*R. officinalis* 9.70

*activity against bacterial strains.*

**IH (mm)**

12.67 (±1.00)

(±0.58)

(±0.58)

(±0.58)

(±0.58)

**MIC (μg mL<sup>−</sup><sup>1</sup> )**

> 216.67 (±14.43)

> **133.33** (±28.87)

> 266.67 (±28.87)

1000.00 9.70

1700.00 10.70

and *Salmonella typhimurium*. Sarikurkcu et al. [38, 63], also performed an assay to determine the MIC against *S. aureus* and *E. coli*, obtaining results similar to those

*Diameters of inhibition halos (IH) and minimum inhibitory concentrations (MIC) for the essential oils* 

bacteria, similar to results found by Gupta et al. [64], Teles et al. [38] and Mishra et al. [65] who reported the formation of halos against the same bacteria in this study submitted to antimicrobial activity assays. Singh et al. [66] also observed satisfactory MIC values for the control of the microorganisms tested in

were similar to those found by Sasidharan and Menon [69].

of ABTS solution with 88 μL of the 37,840 μg mL<sup>−</sup><sup>1</sup>

For *C. longa* essential oil, the largest halos were quantified for Gram-positive

*E. coli* **(ATCC 25922)** *S. aureus* **(ATCC 12600)** *P. aeruginosa* **(ATCC** 

**MIC (μg mL<sup>−</sup><sup>1</sup> )**

> **83.33** (±28.87)

> 216.67 (±28.87)

> 166.67 (±14.43)

200.00 8.67

1500.00 7.67

**IH (mm)**

15.33 (±0.58)

14.67 (±0.58)

**15.66** (±0.58)

(±0.58)

(±0.58)

*C. latifolia* 21 250 10 500 11 1000

**27853)**

**MIC (μg mL<sup>−</sup><sup>1</sup> )**

> 383.33 (±0.01)

550.00 (±28.87)

483.33 (±57.74)

1500.0

1700.0

**IH (mm)**

9.33 (±0.58)

10.33 (±0.58)

12.00 (±0.58)

(±0.58)

(±0.58)

In relation to the bactericidal effect of the *Z. officinale* essential oil, the values obtained in our disc diffusion test are superior to those obtained in the study by Singh et al. [67], where the authors did not obtain inhibition halos for *E. coli* and *S. aureus*, and the same were reported by Grégio et al. [68]. However, MIC values

The antioxidant activity by the ABTS method [2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)] was adapted according to the methodology suggested by [70]. The ABTS˙+ radical was prepared by the reaction of 5.0 mL of a 3840 μg mL<sup>−</sup><sup>1</sup>

The mixture was left in the dark for 16 h. After formation of the radical, the mixture was diluted in ethanol (approximately 1:30 v/v) and absorbance was obtained at 734 nm. From the extracts and essential oils concentrations (5–150 μg mL<sup>−</sup><sup>1</sup>

the reaction mixture was prepared with the ABTS radical cation. In a dark environment, a 30 μL aliquot of each extract and essential oil concentration was transferred into 23 test tubes containing 3.0 mL of the ABTS radical cation and homogenized on a tube shaker. After 6 min, absorbance of the reaction mixture was obtained in a spectrophotometer at 734 nm. The analyzes were performed in triplicate and the capture of the free radical was expressed as percent inhibition (% I) of the ABTS

potassium persulfate solution.

),

**154**

radical cation.

observed.

**Table 5.**

*C zeylanicum*

this study.

**4. Antioxidant activity**

A relatively lower EC50 value was found for *Z. officinale* essential oil by the β-carotene/linoleic acid system [78]. The author attributes the antioxidant activity of the oil to the geranium and neral aldehydes, which were found in their essential oil at concentrations much higher than in this work.
