Studies on the essential oil composition and antimicrobial activity of Thymus algeriensis Boiss. et Reut

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Summary

Many species of Thymus have been widely used in Algerian folk medicine as astringent, expectorant and cicatrising agents. This study was designed to investigate for the first time the essential oil of the aerial parts of wild growing Thymus algeriensis endemic in North Africa. The volatile oil obtained by hydrodistillation was characterized by the physico-chemical properties, GC and GC/MS techniques. The yield of the oil was 1.13% (w/w), based on dry weight. Fifty-five components, representing 94.3% of the total oil, were identified. The oil was distinguished by its high content of oxygenated monoterpenes (79.5%) and was found to possess the following major components: linalool (47.3%), thymol (29.2%) and p-cymene (6.8%). Furthermore, the oil was tested for antimicrobial activity against four bacteria, two fungi and two yeasts. This oil exhibited a significant in vitro antimicrobial activity against Bacillus subtilis (MIC = 0.5 μL/mL), as well as against all yeast and all filamentous fungi tested (MIC = 0.5 and 1.0 μL/mL).

Introduction

The Thymus genus belonging to the Lamiaceae family includes approximately 350 species, existing mainly in Europe, Western Asia and the Mediterranean regions (Mabberley, 1997). Many species of Thymus have been widely used in folk medicine in the world for their carminative, antispasmodic, emmenagogic and tonic properties (Bruneton, 1993). In Algeria, they have been used as astringent, expectorant and cicatrising agents (Baba Aïssa, 1991). The species of this genus are rich in essential oils and were characterized by a great variability of both morphology and chemotypes (Stahl-Biskup, 1991). Many studies on the antimicrobial activity (Tzakou et al., 1998, Zambonelli et al., 2004, Dorman and Deans, 2004) and antioxidative activity (Dorman and Deans, 2004, Youdim et al., 2002) of these oils have been reported. On the other hand, several extracts of these plants were tested for their pharmacological activity (Marti et al., 2005) and other activity (Okazaki et al., 2002).

For the Algerian area, Quezel and Santa describe 12 Thymus species of which eight are endemic in Algeria or in North Africa. Between this eight endemic species we find Thymus algeriensis Boiss. et Reut. (syn. Thymus zattarellus Pomel). This herb is an herbaceous annual fragrant plant, known in Algeria by the name of “Djertil” (Quezel and Santa, 1963).

To the best of our knowledge there are not previous reports on the phytochemical research and biological activities of T. algeriensis. Therefore, as a part of our project investigation on aromatic and medicinal plants of Algeria, we report here the chemical composition and the antimicrobial activity of the essential oil of the aerial parts of T. algeriensis, collected from Media region (Algeria).

Section snippets

Plant material

The aerial parts of T. algeriensis during full blooming stage in May were collected from wild-growing plants from the Media region, a city in north-central Algeria; 80 km south of the capital, Algiers. (Coordinates; UTM: DA71; Latitude: 36° 16′ 03″; Longitude: 2° 45′ 00″; Elevation: 920 m). Botanical identification of the plant was made by comparison with an authentic sample at the herbarium of the Agronomic National Institute of Algiers, Algeria; voucher specimens (HINA/FA/No.: P69) have been

Chemical analysis

The air-dried aerial parts of T. algeriensis investigated here gave an average yield of oil of 1.13% (w/w) based on dry weight of sample. The oil isolated by hydrodistillation was described as liquid, pale yellow in colour and the odour was representative of the plant. Some physicochemical characteristics of the oil were also determined: specific gravity [d]20 = 0.898; refractive index [η]D20=1.4979; optical rotation [α]D20=-0.26°; acid value, 5.69; ester value, 4.27.

Qualitative and quantitative

Conclusion

There is obviously a chemical polymorphism of essential oils within the plants belonging to the genus Thymus. In addition, the infraspecific variability of the essential oils in the genus Thymus was also observed (Stahl-Biskup, 1991). These differences observed in the oil composition may be due to the collection time (development stage) and ecological factors. Finally, these results permit us to classify the essential oil of T. algeriensis collected in Media region (Algeria) into the alcoholic

Acknowledgements

The authors thank Pr. M. Koch and Pr. F. Tillequin, Laboratoire de Pharmacognosie, Faculté de Pharmacie de l’Université René Descartes, Paris-France, for their help and cooperation and the authors are very grateful to Dr. P. Roland-Gosselin Thermo-Finnigan, France, for her help and GC/MS technical assistance.

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      The essential oil yield (0.223–1.428%) in the present study was comparable to reports by Labiad et al. (2022), who found the yield of the essential oils from aerial parts of T. algeriensis to be 0.8% (Labiad et al., 2022). While in T. algeriensis from Algeria, the yield of the oil was 1.13% (w/w) (Dob et al., 2006). Zouari et al. (2012), found that the T. algeriensis EO, ranged from 1.03 to 3.66% (v/w)(Zouari et al., 2012).

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