Chemical composition, antimicrobial and antioxidant activities of the essential oils of nepeta cataria and salvia officinalis from uzbek flora

Summary

The chemical composition of the essential oil from the aerial parts of two Lamiaceae species from Uzbekistan was investigated by GC-MS analysis. The essential oil of Salvia officinalis was dominated by cis-thujone (19.7%), camphor (12.9%), 1,8-cineole (9.2%) and a-humulene (6.4%), while 4a- a,7a,7a-e-nepetalactone (31.1%), 1,8-cineole (12.3%), 4a-a,7-e,7a-a-nepetalactone (8.9%) and thymol (8.4%) resulted as the major oil components in Nepeta cataria. The essential oils had considerable antimicrobial activity against different bacterial strains and fungi. Among the tested samples of essential oils, N. cataria essential oil has the higher antioxidant activity with IC50 value of 66.43 ± 4.67 gl/ml.

Keywords: Salvia officinalis, Nepeta cataria, GC-MS, antimicrobial, antioxidant

Introduction. The 18 members of Nepeta L. genus have been found in Uzbekistan [1]. In traditional medicine, Nepeta cataria L. (local name Mushuk zufo) was used as a sedative, spasmolytic and tonic remedy. Iridoids, essential oils, phenolic compounds and flavonoids, triterpenes, micro and macro elements were detected in N. cataria [2].

In Uzbekistan flora there are 16 species of Salvia L. [1] and Salvia officinalis L. (local name Dorivor marvak, marmarak) is widely cultivated in Uzbekistan. The leaves of S. officinalis are used in folk medicine for the treatment of different kinds of disorders including ulcers, rheumatism, inflammation, gastrointestinal disorders, diarrhea, and hyperglycemia and also as a flavouring agent. The major phytochemicals include alkaloids, carbohydrate, fatty acids, flavonoids, saponins, phenolic compounds, polyacetylenes, steroids, terpenoids [3].

Research aims. Since there has been no study on the essential oil composition of N. cataria and S. officinalis growing in Uzbekistan. We investigated the chemical composition and we tested antimicrobial and antioxidant activities of essential oils obtained from the aerial parts of these species.

Material and methods.

Plant material. The aerial parts of Nepeta cataria was collected in the Tashkent region and Salvia officinalis from the Botanical garden of the Institute of the Chemistry of Plant Substances (Uzbekistan) in the summer 2016. The taxonomic authentication was accomplished by the Dr. Alim Nigmatullaev at the Department of Herbal Plants (Institute of the Chemistry of Plant Substances, Uzbekistan). The voucher specimens of N. cataria and S. officinalis were deposited in the departmental herbarium under the code 2016/1635 and 2016/1690, respectively.

Essential oil isolation. The aerial parts (flowers, leaves and stems) of selected plant species were airdried in-door for 3 days at room temperature. Then air-dried (moisture content was 10-12% w.b.) plant materials of N. cataria and S. officinalis (200 g each) were hydrodistilled for 2 h, using a Clevenger- type apparatus (yields being 0.7 and 1.8% based on the dry weight of the plant material, respectively). As only small amounts of essential oil were present, the oils were trapped in dichloromethane, which was dried over anhydrous sodium sulfate and stored at -4°C until use.

GC-MS. The GC-MS analyses were carried out by a Shimadzu QP-2010 plus gas chromatograph (Shimadzu Corporation, Kyoto, Japan) coupled to a quadrupole mass spectrometer. The chromatograph was coupled with a DB-5 fused bonded cap column (30 m x 0.25 mm, film thickness 0.25 pm, Agilent Technologies, Netherlands). The oven temperature was programmed as isothermal at 50 °C for 2 min, then rising from 50 to 300 °C at 7 °C /min, and finally held isothermal at 300 °C for 10 min; injector temp., 250 °C; detector temp., 300 °C; carrier gas helium (1.5 mL/min); with split mode (split ratio, 1:20). The mass spectra were recorded under the following conditions: filament-emission current, 100 mA; ionization voltage, 70 eV; ion source temp., 175 °C. The sample (0.5 pL) was injected automatically to the chromatograph using a GC auto sampler. GC solution® software ver. 2.4 (Shimadzu Corporation, Kyoto, Japan) was used for recording and integrating the chromatograms. The compounds were identified by comparison of their mass-spectral data and retention indices (RIs) with those of the Wiley Registry of Mass Spectral Data (9th Ed.), NIST Mass Spectral Library (2011), and references [4].

Antimicrobial activity. The antimicrobial activity was evaluated using standard microbial strains: Gram-positive bacteria Staphylococcus aureus (ATCC 25923) and Bacillus subtilis (RKMUz 5); Gramnegative bacteria Pseudomonas aeruginosa (ATCC 27879) and Escherichia coli (RKMUz 221); and the fungus Candida albicans (RKMUz 247). The RKMUz microorganism cultures were obtained from the strain collection of the Institute of Microbiology, Academy of Sciences Uzbekistan. The antibacterial activity of the essential oils was determined by using the modified agar-disc diffusion and broth microdilution methods (MIC and MMC) previously described by us [5].

Antioxidant activity. The antioxidant activity of the essential oils was evaluated by DPPH (2,2- diphenyl-1-picrylhydrazyl) assay was performed as described earlier by us [6, 7].

Results and discussion. The chemical composition of the essential oil from N. cataria and S. officinalis were investigated for the first time by GC-MS analysis. S. officinalis is considered to have the highest essential oil yield among Salvia species. The essential oil of S. officinalis mainly comprises the monoterpenes a- and в—thujone, camphor, 1,8-cineole and borneol and sometimes in larger amounts sesquiterpenes a-humulene and в-caryophyllene [8]. As shown in the present study, in the oil of Uzbek S. officinalis 35 constituents were identified which is representing 85.0% of the material. cis-Thujone (19.7%), camphor (12.9%), 1,8-cineole (9.2%), a-humulene (6.4%), manool (5.9%), viridiflorol (4.6%) were the major oil components. The essential oil composition of N. cataria have earlier been reported by Adiguzel et al. [9]. They characterized 22 compounds, 4aa,7a,7ae—nepetalactone (70.4%), 4aa,7a,7aa-nepetalactone (6.0%), 4aa,7e,7aa-nepetalactone (2.5%) and thymol (2.5%) being the major components. Our results indicated a much more complex composition in the oil from the Uzbek N. cataria specimen: 35 compounds constituting 97.2% of the bulk, and 4a-a,7a,7a-e-nepetalactone (31.1%), 1,8-cineole (12.3%), 4a-a,7-e,7a-a-nepetalactone (8.9%), thymol (8.4%), camphor (4.6%) as the main components.

The antimicrobial activity of the oily compounds extracted from N. cataria and S. officinalis against selected bacteria and fungus [Staphylococcus aureus (ATCC 25923), Bacillus subtilis (RKMUz 5), Pseudomonas aeruginosa (ATCC 27879), Escherichia coli (RKMUz 221) and Candida albicans (RKMUz 247)] was assessed using disc diffusion and micro-dilution methods (Table 1 and 2). According to these tables, some of the samples have considerable antimicrobial activity (zone of inhibition in the range of 4-14 mm with MIC values between 125-500 pl/ml) against a wide range of gram-positive and gram-negative bacterial strains and fungi.

Table 1 - Antibacterial effect evaluated by the diameter of inhibition zone (mm) for N. cataria and S. officinalis essential oil using the agar disk diffusion assay

nd: not determined; nt: not tested; Data were presented as the mean ± standard deviation (SD)

Table 2. Antibacterial effect evaluated by minimum inhibitory concentration (MIC) and minimum microbicidal concentration (MMC) (gl/ml) for N. cataria and S. officinalis essential oil (62.5-500 gl/ml)

Concentration of the essential oil scavenging 50% of DPPH radical is shown in Table 3. Results indicated that the tested samples of essential oils were found to have a weak antioxidant activity. Greater IC50 value (66.43 ± 4.67 gl/ml) was observed with essential oil of N. cataria.

Table 3. Antioxidant activity of the essential oils from Lamiaceae species using the DPPH^* radical scavenging assay. The data are represented as IC50 values (mean ± SD)

Conclusions. In this research, for the first time, we evaluated the chemical profiles of the essential oils obtained from N. cataria and 5. officinalis. The oil of these species growing in Uzbekistan had similar profile than those of the same species growing in other locations. Additionally the antimicrobial and antioxidant activities were primarily to be investigated.

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