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. 2023 Feb 10;8(7):6431–6438. doi: 10.1021/acsomega.2c06713

Comparative Study on the Essential Oils Extracted from Tunisian Rosemary and Myrtle: Chemical Profiles, Quality, and Antimicrobial Activities

Ines Dhouibi †, Guido Flamini ‡, Mohamed Bouaziz †,§,*
PMCID: PMC9947950  PMID: 36844591

Abstract

graphic file with name ao2c06713_0004.jpg

Rosemary (Rosmarinus officinalis L.) and myrtle (Myrtus communis L.) are perennial herbs, typical of the Tunisian flora, with an intense aromatic flavor. Their essential oils, obtained by hydro-distillation, were analyzed by gas chromatography coupled to mass spectrometry and by infrared Fourier transform spectrometry. In addition, these oils were assessed for their physicochemical properties as well as their antioxidant and antibacterial activities. The physicochemical characterization proved to be of good quality by analyzing pH, water content (%), density at 15 °C (g/cm3), and iodine values according to standard test methods. The study of the chemical composition allowed for the identification of 1,8-cineole (30%) and α-pinene (40.4%) as the main constituents of myrtle essential oil, while 1,8-cineole (37%), camphor (12.5%), and α-pinene (11.6%) were identified as principal components in rosemary essential oil. The evaluation of their antioxidant activities permitted to obtain the IC50 values, which ranged between 22.3 and 44.7 μg/mL for DPPH and between 15.52 and 28.59 μg/mL for ferrous chelating assay, for rosemary and myrtle essential oils, respectively, thus indicating that rosemary essential oil is the most effective antioxidant. Furthermore, the antibacterial activity of the essential oils was tested in vitro against eight bacterial strains by the disc diffusion method. The essential oils showed antibacterial effects on both Gram-positive and Gram-negative bacteria.

1. Introduction

Aromatic and medicinal plants are known to play a considerable economic role in the industrial, agro-food, perfume, cosmetics, and pharmacy sectors.1 Indeed, plants represent a limitless source of traditional and effective remedies, thanks to their active ingredients, namely, alkaloids, flavonoids, phenols, tannins, vitamins, and essential oils.

Among these plants, rosemary belongs to the Lamiaceae family, and it is native to the Mediterranean region. Although it grows spontaneously, it is widely cultivated throughout the world as an ornamental plant and small evergreen perennial that grows up to 2 m in height.2

The importance of rosemary essential oil (REO) lies in its uses in medicine and its powerful chemopreventive properties.3 Moreover, REO stands out for its biological activities,4 which obviously depend on its chemical composition.5

Myrtle (Myrtaceae family) is a wild aromatic diploid shrub. It is among the high drought tolerant evergreens 0.5–3 m in height and ovate leaves 3–5 cm long. This plant is not only native to North Africa, Southern Europe, and Western Asia but is also typical of the Mediterranean flora.6 In Tunisia, the only species found is Myrtus communis L., which grows wild in the coastal areas, inland hills, and northern forest areas. Two varieties of myrtle have been described by the old local Tunisian flora: M. communis var. italica L. and M. communis var. baetica L.7 Although they possess similar vegetative characters, they have different morphologies.

The myrtle essential oil (MEO) is essentially used for the treatment of bronchitis, tuberculosis, diarrhea, hemorrhoids, and prostatitis.8 Furthermore, its anti-inflammatory, antibacterial, and wound-healing properties make it a potential candidate for reducing pain and ulcer size in cases of minor recurring aphthous stomatitis.9 In addition, this plant has important applications in several fields, namely, culinary, pharmaceutical, therapeutic, and industrial. Indeed, MEO has been used by food industries as a flavoring for meats and sauces and by the cosmetic industry as a hair tonic.10 Its chemical composition may vary according to many factors (organ type, harvesting time, and agricultural practices, among others) that are likely to be responsible for the observed diverse biological responses observed.11

Bearing in mind the properties of rosemary and myrtle, this study aims to explore the yield and quality of Tunisian rosemary and myrtle essential oils. It also aims to determine the physicochemical properties of these oils and to evaluate its antioxidant and antibacterial activities.

2. Materials and Methods

2.1. Plant Material

The essential oils were extracted using the aerial part (leaves and twigs) of plants. Rosemary was collected in October 2020 in the Chebba region, Central-Eastern Tunisia, while myrtle was collected in June of the same year in the Haouaria region, North-East of Tunisia.

2.2. Extraction of the Essential Oils

A Clevenger-type apparatus was used for the extraction of the essential oil of each plant. Indeed, 1 kg of fresh aerial parts of each plant was hydrodistilled for 4 h.12

After extraction, the essential oils were recovered as such without the addition of any solvent and subsequently stored in a refrigerator at 4 °C in hermetically closed opaque-glass flasks.

The dry weight of samples was calculated based on the previously determined moisture content, which was used to calculate the yield of the essential oils as follows:

2.2.

2.3. Analyses of Volatile Compounds

The gas chromatography coupled to mass spectrometry analysis was performed with a Varian CP 3800 gas-chromatograph coupled with a Saturn 2000 mass spectrometer (both Varian, Palo Alto, CA). Analytical conditions: injector and transfer, line temperatures 220 and 240 °C, respectively; oven temperature was programmed from 60 to 240 °C at 3 °C/min; carrier gas was helium at 1 mL/min; injection volume was 0.2 μL (10% hexane solution); the split ratio was 1:30. The identification of the essential oil constituents was performed by comparing their retention time with those of the authentic samples and by means of their LRI relative to the n-hexane.

2.4. Fourier-Transform Infrared Spectroscopy

A Perkin Elmer spectrometer was used to obtain the FT-IR spectra of the samples, each of which was scanned at a wave number range of 4000–400 cm–1 with a resolution of 2 cm–1.13

2.5. Quality Evaluation

Density at 15 °C measurement was performed as recommended by the Brazilian Pharmacopeia V edition.14 The iodine index was measured by simple titration under AOAC (2000).15 In addition, the moisture content determination was carried out following the method of AOAC.16 Furthermore, the determination of the pH was performed following the method recommended by the National Agency for Sanitary Surveillance.17

2.6. Antioxidant Activities

2.6.1. Antiradical Activity against DPPH

The determination of the DPPH free radical-scavenging activity of REO and MEO was conducted following the method of Rekik et al.18 A volume of 500 μL of each sample at different concentrations (1–5 mg/mL) was added to 375 μL of 99% ethanol and 125 μL of DPPH solution (0.02% in ethanol) knowing that DPPH (1,1-diphenyl-2-picryl-hydrazyl; M = 394 g/mol) is a free radical source. The obtained mixtures were shaken and then incubated for 60 min in the dark at room temperature. The measurement of the scavenging capacity was carried out spectrophotometrically by controlling the decrease of absorbance at 517 nm. In its radical form, the DPPH has an absorption band at 517 nm, disappearing with the reduction by an antiradical compound. A low absorbance of the reaction mixture reveals high DPPH-free radical-scavenging activity. A reaction mixture with a low absorbance has a strong capacity to scavenge DPPH free radicals. The measurement of DPPH radical-scavenging activity involved the use of ascorbic acid as a positive control following the steps below:

2.6.1.

with AE denoting the absorbance of the solution when the sample extract is added at a specific level, and ADPPH is the absorbance of the DPPH solution.

2.6.2. Iron (Fe2+) Chelating Activity

The iron chelating activity of the different samples was estimated according to the method of Decker and Welch,19 with slight modifications. Indeed, 50 μL of 2 mM FeCl2, 4H2O was added to 100 μL of each sample diluted in 450 μL of water (since oil does not dissolve in water, we used Tween 80 as a surfactant (5% oil; 2.5% Tween 80)). The obtained mixtures were incubated at room temperature for 5 min. The reactions were started by adding 200 μL of 5 mM of 3-(2-pyridyl)-5,6-bis (4-phenyl-sulfonic acid)-1,2,4-triazine (ferrozine). The mixtures were then strongly shaken and left to stand at room temperature for 10 min. Similarly, the control tube was prepared, replacing the sample with distilled water. Ascorbic acid was used as a positive control. The solutions absorbance was measured at 562 nm, and the inhibition percentage of ferrozine-Fe2+ complex formation was calculated as follows:

2.6.2.

where AC, AB, and AS are the control absorbance, the blank, and the sample reaction tubes, respectively.

2.7. Antibacterial Activity

2.7.1. Microbial Strains

The antibacterial activities of REO and MEO were tested against four Gram-positive bacteria: Staphylococcus aureus (ATCC 25923), Micrococcus luteus (ATCC 4698), Bacillus cereus (ATCC 14579), and Listeria monocytogenes (ATCC 19115) and four Gram-negative bacteria: Escherichia coli (ATCC 25922), Salmonella enterica (ATCC 43972), Pseudomonas aeruginosa (ATCC 27853), and Enterobacter aerogenes (ATCC 13048).

2.7.2. Agar Diffusion Method

For the antibacterial activity assay, the culture suspensions (200 μL) of the microorganisms (106 colony-forming units CFU/mL of bacteria cells anticipated by absorbance at 600 nm) were placed on Luria-Bertani (LB) agar, already casted in Petri dishes. Next, an amount of 60 μL of each extract (at a concentration of 25 and 50 mg/mL) was loaded into the wells (6 mm in diameter) perforated in the agar layer. Hence, the Petri dishes were incubated for 1 h at 4 °C and then for 24 h at 37 °C. Gentamicin was utilized as a positive standard. Antibacterial activity was assessed by the determination of the growth inhibition zone (whose diameter is expressed in millimeters) around the wells.20

2.8. Statistical Analysis

The obtained results were expressed as mean standard deviation (SD) of three measurements. The determination of the significant differences between the values of all parameters was carried out at P < 0.05 in compliance with the one-way ANOVA: Student Newman–Keuls test, using SPSS Statistics 17.0 for Windows (SPSS Inc., 2008).

3. Results and Discussion

3.1. Yield and Chemical Composition of Essential Oils

While the EO yield obtained for rosemary (0.91%) was in good agreement with those reported in the literature by Hcini et al. and Hosni et al. for Tunisian plants,21,22 that of myrtle was lower (0.75%). However, this is not surprising as the yield depends on numerous biotic and abiotic factors, such as the harvest period, the harvested organs type, soil, and rainfall, to cite a few.

The oils compositions summarized in Table 1 were colorless and with a strong fragrant odor. In myrtle essential oil, 28 constituents were characterized, accounting for 99.1% of the whole oil, while in rosemary, 24 volatiles were identified with 91.9% of the oil.

Table 1. Chemical Composition of MEO and REOa.

components molecular formula MW (g/mol) LRI (compound) RT (min) myrtle EO rosemary EO
monoterpene hydrocarbons 49.5 26.9
tricyclene C10H16 136.23 928 4.46   0.2
α-thujene C10H16 136.23 933 4.55 0.4  
α-pinene C10H16 136.23 941 4.72 40.4 11.6
camphene C10H16 136.23 955 5.07 0.2 4.5
β-pinene C10H16 136.23 982 5.77 0.6 3.1
myrcene C10H16 136.23 993 6.14 0.2 1.5
α-phellandrene C10H16 136.23 1006 6.54   0.2
δ-3-carene C10H16 136.23 1013 6.71 0.7 0.5
α-terpinene C10H16 136.23 1019 6.92   0.4
p-cymene C10H14 134.21 1028 7.18 2.0 2.1
limonene C10H16 136.23 1032 7.31 4.3 2.1
γ-terpinene C10H16 136.23 1062 8.30 0.3 0.3
terpinolene C10H16 136.23 1090 9.36 0.4 0.4
oxygenated monoterpenes 44.0 59.5
1,8-cineole C10H18O 154.24 1034 7.40 30.0 37.0
4-terpineol C10H18O 154.25 1179 12.90 0.6 1.1
α-terpineol C10H18O 154.25 1191 13.51 3.5 2.9
bornyl acetate C12H20O2 196.29 1287 17.49   0.3
linalyl acetate C12H20O2 196.29 1259 16.24 1.0  
linalool C10H18O 154.25 1101 9.83 2.0 0.7
endo-fenchol C10H18O 154.25 1112 10.35   0.1
trans-pinocarveol C10H16O 152.23 1141 11.31 0.4  
camphor C10H16O 152.23 1145 11.50 0.4 12.5
exo-2-hydroxy cineol acetate C12H20O3 212.29 1345 19.95 0.2  
α-terpinyl acetate C12H20O2 196.29 1352 20.27 1.7  
geranyl acetate C12H20O2 196.29 1383 21.85 4.2  
sesquiterpene hydrocarbons 1.5 13.0
α-copaene C15H24 204.35 1377 21.35   0.8
β-caryophyllene C15H24 204.36 1419 23.18 1.2 8.0
α-ylangene C15H24 204.36 1373 21.15   0.2
α-humulene C15H24 204.36 1455 24.62 0.2 1.0
germacrene B C15H24 204.36 1557 28.88 0.1  
oxygenated sesquiterpene 0.3 0.4
caryophyllene oxide C15H24O 220.35 1582 29.95 0.3 0.4
nonterpene derivatives 3.8  
2-methylbutyl 2-methylbutyrate C10H20O2 172.26 1103 9.93 1.9  
2-methylbutyl isobutyrate C9H18O2 158.24 1015 6.87 0.3  
isobutyl 2-methylbutyrate C9H18O2 158.24 1002 6.46 0.9  
propyl butyrate C7H14O2 130.18 898 4.24 0.7  
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a

Linear retention index (LRI).

Monoterpenes were the main chemical class of both oils (Figure 1), even if hydrocarbon derivatives prevailed in myrtle (49.5%) and oxygenated ones in rosemary (54.6%).

Figure 1.

Figure 1

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Different classes of compounds in (a) MEO and (b) REO.

In the case of myrtle, α-pinene (40.4%) and 1,8-cineole were the main volatiles, followed by limonene and geranyl acetate (4.3 and 4.2%, respectively). REO was mainly composed of 1,8-cineole (37.0%), camphor (12.5%), and α-pinene (11.6%), together with β-caryophyllene and camphene (8.0 and 4.5%, respectively).

3.2. Infrared Analysis

Figure 2A,B shows the FT-IR spectra (4000–400 cm–1) for MEO and REO and the specific band positions and intensities, respectively. They reveal some key feature bands that are likely to be used for the differentiation between the major volatile substances found in MEO and REO, such as 1,8-cineole, camphor, and α-pinene. The identification of the functional groups was based on the FT-IR peaks ascribed to stretching and bending vibrations.

Figure 2.

Figure 2

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FT-IR spectra (4000–400 cm–1) of (A) MEO and (B) rosemary EO.

The vibrational spectra of MEO presented in Figure 2A were dominated by the bands of its major components, namely α-pinene (at 843 and 787 cm–1) and 1,8-cineole (at 1375; 1234; 1080; 996 and 843 cm–1). These bands corroborated distinctive signals in the FT-IR spectrum due to the wagging vibrations of CH and CH2 groups (996 cm–1 for 1,8-cineole and 843 cm–1 for α-pinene). Thus, less intensive bands of 1,8-cineole located in the FT-IR spectrum were accredited to C–O–C symmetrical (1080 cm–1) and asymmetrical (1234 cm–1) stretching vibrations. An extra band was noticed at 3384 cm–1, which is likely to be ascribed to a stretching vibration of hydroxyl group. The aforementioned characteristic key absorption bands are in good agreement with those previously reported in the literature for essential oils from Myrtaceae species.23 As can be seen in Figure 2B, the REO FT-IR spectrum displays diverse distinctive peaks. All the above-mentioned components contribute to C–H stretching bands not only from 2967 to 2881 cm–1, but also 1447 and 1375 cm–1. The peak observed at 1741 cm–1 is essentially ascribed to the carbonyl group of camphor, while the peaks at 1215 and 992 cm–1 revealed the presence of an ether function, present on 1,8-cineole. Eventually, the peaks at 1080 and 1053 cm–1 are closely related to C–O bond asymmetric stretching. As for the peak at 3472 cm–1, it is linked to the principal IR band, and particularly to the O–H stretching of the O–H group of α-terpineol, 4-terpineol, borneol, linalool, and trans pinocarveol, as reported in a previously published study.24

3.3. Physicochemical Properties

Table 2 shows the physicochemical parameters of REO and MEO. The iodine value of oil is indicative of the oil unsaturation degree. The higher the iodine values are, the higher the degree of unsaturation (carbon to carbon double bonds) of the oil is.25

Table 2. Physical and Chemical Properties of REO and MEOa.

properties units REO MEO
density g/cm3 0.98 ± 0.00a 0.87 ± 0.00b
pH   3.42 ± 0.01a 3.056 ± 0.01b
iodine value mg I2/100g 145 ± 0.30b 155 ± 0.32a
water content % 0.98 ± 0.00b 1.22 ± 0.00a
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a

Values are means ± SD (standard deviation). Values with different superscript letters a,b within each row are significantly different at P < 0.05.

A greater iodine value implies a high susceptibility of the oil to oxidation,26 and the iodine values of the essential oils were found to be 145 mg I2/100g oil for REO and 155 mg I2/100g oil for MEO. In this context, MEO has the highest iodine value.

Both oils had densities lower than water, 0.98 and 0.87 g/cm3 for REO and MEO, respectively. This parameter is associated with each oil chemical composition, which is affected by many factors such as phenotype, harvest time, soil type, storage, process, and extraction conditions.27 The obtained values are in good agreement with those found in a research work from South Africa about essential oils for cosmetic use.28 On the other hand, values comprised between 1.206 and 1.228 g·cm–3 were found for the density of the essential oils from nine medicinal herbs grown in Egypt, which were obtained through hydrodistillation.29

Humidity or moisture is an important factor that influences the extraction and yield of essential oil. Furthermore, volatile problems represent the weight loss undergone by the product after heating to 105 °C in the operating conditions.30 In fact, obtained the results of REO and MEO are 0.98 and 1.22%, respectively. In addition, these essential oils are clear liquids with a pH value of around 3.42 (REO) and 3.05 (MEO).

According to the parameters found in the literature and reported by the official AFNOR (2002) rules,31 both essential oils are fresh and of good quality. The results have proven that the MEO and REO are stable and do not cause worrying oxidation with proof of good storage.

3.4. Antioxidant Activity

Table 3 lists the results of the REO and MEO antioxidant activities. Both essentials were able to decrease the stable, purple-colored radical DPPH into the yellow-colored DPPH–H.

Table 3. Antioxidant Activities of REO and MEO: DPPH Radical Scavenging Activity and Ferrous Chelating Effecta.

  IC50 (μg/mL) for REO IC50 (μg/mL) for MEO bIC50 (μg/mL) for standard
DPPH radical scavenging activity 44.7 ± 0.09c 52.5 ± 0.11b 75 ± 0.15a
ferrous chelating effect 13.52 ± 0.03b 28.59 ± 0.06a 14.26 ± 0.03c
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a

Data are expressed in mm and given as means ± SD; a,b,c Different letters in different samples within the same concentration indicate significant differences (P < 005).

b

IC50 value for standard: ascorbic acid in DPPH scavenging activity and EDTA in ferrous chelating effect.

Indeed, the IC50 values were 22.3 μg/mL for REO and 44.7 μg/mL for MEO (Table 3). The oxygenated monoterpenes and mixtures of mono- and sesquiterpene hydrocarbons have been reported to be the main responsible for the DPPH radical neutralization.32 Camphor, one of the main constituents of REO, is well recognized to have high antioxidant activity levels.33 This can explain the higher antioxidant activity of REO with respect to MEO (IC50 = 22.3 vs IC50 = 44.7 μg/mL). Besides, 1,8-cineole, the main constituent of REO (Table 1), may play an important role.

The results about the antioxidant activity of REO are in very good agreement with those of the literature. Indeed, Jedidi et al.34 have reported that the REO radical scavenging capacity, expressed as IC50 in the DPPH assay, is 100.6 μg/mL. This difference in activity has been related to the different chemical compositions of REOs. In another study, Adel et al.35 found that the antioxidant activity of REO, which was collected from Gafsa (south-west of Tunisia), measured by the DPPH assay is 61% at 300 μg/mg.

Moreover, the findings of the MEO activity in the present study are higher than those previously reported36 for another Tunisian one, although 1,8-cineole and α-pinene were the major components for both oils. The same was also true in the case of another Tunisian essential oil.37

Table 4 also illustrates the ferrous chelating effect of REO and MEO. This test confirmed the higher activity of REO, whose results are even more effective than that reported by Raeisi et al.38 (81.23 mg/mL). On the contrary, its activity result was lower than found in another study (0.4–2 μg/mL),39 even if the major constituent of REO was still 1,8-cineole (49.7%). According to the results reported in Table 3, the IC50 = value (15.52 μg/mL for REO and 28.59 μg/mL for MEO) reveals the capacity of the two oils to interfere with the Fe2+-ferrozine complex formation, suggesting their ability to capture ferrous ions before ferrozine. A similar activity has been reported by Wannes et al.40 for the essential oils of Tunisian myrtle flower (IC50 = 5 mg/mL), having α-pinene, 1,8-cineole, and limonene as major constituents.

Table 4. Antibacterial Activities of REO and MEO against Different Gram+ and Gram– Strainsa.

  gentamicine REO
 MEO
concentration (mg/mL) 30 mg/mL (mm) 25 mg/mL (mm) 50 mg/mL (mm) 25 mg/mL (mm) 50 mg/mL (mm)
Escherichia coli 15.0 ± 0.03b 09.0 ± 0.02e 10.0 ± 0.02d 11.0 ± 0.02c 16.0 ± 0.03a
Salmonelle enteric 15.0 ± 0.03c 11.0 ± 0.02d 20.0 ± 0.04a 15.0 ± 0.03c 17.0 ± 0.03b
Pseudomonasaeruginosa 22.0 ± 0.05a 14.0 ± 0.03d 20.0 ± 0.04b 14.0 ± 0.03d 19.0 ± 0.04c
Enterobacter aerogenes 19.0 ± 0.04c 18.0 ± 0.04d 27.0 ± 0.05a 17.0 ± 0.03e 24.0 ± 0.05b
Listeria monocytogenes 18.0 ± 0.04a 14.0 ± 0.03d 14.0 ± 0.03d 15.0 ± 0.03c 16.0 ± 0.03b
Staphylococcus aureus 36.0 ± 0.07a 12.0 ± 0.02c 14.0 ± 0.03b 12.0 ± 0.02c 14.0 ± 0.03b
Bacillus cereus 22.0 ± 0.05a 12.0 ± 0.02d 14.0 ± 0.03c 12.0 ± 0.02d 21.0 ± 0.04b
Micrococcus luteus 18.0 ± 0.04b 13.0 ± 0.03c 21.0 ± 0.04a 12.0 ± 0.02d 18.0 ± 0.04b
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a

Data are expressed in mm and given as means ± SD; a,b,c,d,e Different letters in different samples within the same concentration indicate significant differences (P < 005).

The DPPH scavenging ability and ferrous chelating effect extent confirmed a positive relationship. However, the assessment of the metal chelating effect revealed that REO and MEO were more active than those were observed in the DPPH free radical scavenging activity.

Both antioxidant tests showed that REO and MEO were less effective as an antioxidant than the reference compound ascorbic acid.

3.5. Antibacterial Activity

The antibacterial activity of rosemary and myrtle essential oils against four strains of Gram-positive and four strains of Gram-negative bacteria is listed in Table 4.

REO and MEO proved a varying degree of antibacterial activity at both 25 and 50 mg/mL. However, MEO exhibited the highest activity as the diameters of inhibition were larger than those observed for REO, which is in agreement with the findings of Fadil et al.41 Furthermore, both responses should be considered as “sensitive” (between 9 and 14 mm) for S. aureus. The comparison of the essential oil activities with the control antibiotic gentamicin demonstrated that both essential oils exhibited an important activity against E. coli (16.0 for MEO), S. enterica (20.0 mm for REO and 17.0 mm for MEO), Enterobacter aerogenes (27.0 and 24.0 mm), and M. luteus (21.0 and 18.0 mm) at 50 mg/mL. Besides, the used solvent (ethanol) did not convey any activity on the strains under investigation, which supports the adequate choice of this solvent.

REO and MEO were found to be rich in monoterpene compounds (86.4 and 93.5%, respectively), which is in good accordance with the results reported in the literature for their antibacterial activities.42 Interestingly, the richness of the oils in monoterpenes such as 1,8-cineole confirms their strong antibacterial activities against several bacteria.43 On the other hand, the antibacterial effects of minor compounds, such as caryophyllene oxide and terpinene-4-ol, were also known.43

4. Conclusions

In the current investigation, the essential oils of rosemary and myrtle were extracted and their biological activity and chemical composition were described. Out of the obtained 32 components, the composition of REO showed that 1,8-cineole (37%), camphor (12.5%), and pinene (11.6%) were the main constituents. Out of the identified 28 components, pinene (40.4%) and 1,8-cineole (30%) were the predominant substances in MEO. The presence of these compounds was totally supported by IR spectroscopy thanks to noticeable bands. The findings of the physicochemical investigation, on the other hand, showed that both essential oils were of high grade.

Chelating power and DPPH tests on the antioxidant activity revealed that REO had the highest level of activity. Finally, the studied pathogenic bacteria were susceptible to the essential oils’ in vitro antibacterial activity at modest doses, between 25 and 50 mg/mL. The bacteria against which an important activity was discovered by REO’s antibacterial test were S. enterica, P. aeruginosa, E. aerogenes, and M. luteus. As for MEO, it exhibited an important activity against E. coli, S. enterica, P. aeruginosa, E. aerogenes, L. monocytogenes, B. cereus, and M. luteus. In view of these results, MEO was proven to be the most effective. Furthermore, REO and MEO can be reliably used in commercial applications as an antioxidant and antibacterial agent alone or in combination with conventional preservatives to prevent harmful microbial deterioration in some food modules or as a treatment for wounds.

This research work has confirmed that these two aromatic and medicinal plants represent a very interesting reservoir, whose essential oils are characterized by specific therapeutic and pharmacological properties that need to be exploited by future research.

Glossary

Abbreviations

REO

rosemary essential oil

MEO

myrtle essential oil

GC–MS

gas chromatography/mass spectrometry

The authors thank the Ministry of Higher Education and Scientific Research (Laboratory LR14ES08), Tunisia, and MedOOmics Project—“Mediterranean Extra Virgin Olive Oil Omics: profiling and fingerprinting”—“Arimnet2/0001/2015”, for its financial support to this research work.

The authors declare no competing financial interest.

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