Abstract
Essential oils (EOs) have been described as promising eco-friendly secondary products of aromatic plants with several biological activities. The present study aimed to characterize the chemical composition and explore phytotoxic and antimicrobial activities of Teucrium polium and Thymus decussatus EOs extracted using hydrodistillation (HD) and microwave-assisted extraction (MAE) methods. Twenty-seven and twenty-eight compounds were identified from HD and MAE extracted EOs of T. polium, respectively. The oxygenated sesquiterpenes (57.68%) were characterized as the main components of the hydrodistilled EO with a prominence of 6-epi-shyobunol (33.00%), while sesquiterpene hydrocarbons (54.48%) were the main components of the MAE method, with a prominence of delta-cadinene (25.13%). Eighteen and nineteen compounds, were characterized in T. decussatus EOs extracted using HD and MAE methods, respectively, and oxygenated monoterpenes represented the main components of both EOs with carvacrol (94.40% and 75.91%, respectively) as the main compound. The EOs extracted using the MAE method were slightly more phytotoxic than those extracted using the HD method. The T. decussatus EO extracted using the MAE method showed a higher inhibitory effect than T. polium by 16-, 32-, and 24-fold, regarding seed germination, shoot, and root growth of lettuce, respectively. Moreover, EOs extracted by HD method showed a similar pattern with 16-, 28-, and 14-fold effects. Both T. decussatus EOs exhibited potent inhibitory effect against all tested bacteria with an inhibition zone of 34–39 mm and the lowest minimum inhibitory concentration (MIC) of 0.49, 0.98, and 1.95 μg/mL against Aspergillus niger, Escherichia coli, and Staphylococcus aureus, respectively. However, the EOs of T. polium showed weak antibacterial activity and no antifungal effect. Further studies are needed for the characterization of bioactive major compounds, either singular or synergistic, at field scale and to determine their modes of action and safety.
Highlights
From the first days of ancient civilizations, especially the Egyptian one, medicinal herbs have been used as the main source of medicinal agents
Twenty-seven compounds were identified from the hydro-distilled Essential oils (EOs), representing 100% of the total mass, while 28 compounds were identified from microwave-assisted extraction (MAE) extracted EO
The results showed that sesquiterpene hydrocarbons (54.48%) were found as the main identified compounds of the T. polium EO extracted using the MAE method, followed by monoterpene hydrocarbons (23.52%) and oxygenated sesquiterpenes (22.0%)
Summary
From the first days of ancient civilizations, especially the Egyptian one, medicinal herbs have been used as the main source of medicinal agents. Egypt is one of the countries that is characterized by unique biodiversity. Nile delta, oases, depressions, and mountains [1], Egypt is characterized with verifications of medicinal plants, including 529 medicinal plants, 60 endemic plants, and 13 pharmacopeias [2,3]. The Sinai Peninsula, especially the Saint Katherine protectorate, represents the most promising source of traditional herbs in Egypt. The plant species collected from Sinai are characterized by unique metabolites and potent pharmacological effects [4,5]. Aromatic plants are considered a natural source of essential oils (EOs). EOs are considered as a promising source of complex mixtures of metabolites, especially terpenoids [6,7]. The Lamiaceae (Labiatae) family is considered an important family, having many aromatic plants. The most famous genera of the Lamiaceae family are Salvia, Scutellaria, Stachys, Plectranthus, Hyptis, Teucrium, Vitex, Thymus, and Nepeta [16]
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