890 M. SARI ET AL. Copyright © 2006 John Wiley & Sons, Ltd. Flavour Fragr. J. 2006; 21: 890–898 DOI: 10.1002/ffj FLAVOUR AND FRAGRANCE JOURNAL Flavour Fragr. J. 2006; 21: 890–898 Published online 29 June 2006 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/ffj.1738 Chemical composition, antimicrobial and antioxidant activities of the essential oil of several populations of Algerian Origanum glandulosum Desf. Madani Sari, 1 Daniela M. Biondi, 2 Mohamed Kaâbeche, 3 Giuseppina Mandalari, 4 Manuela D’Arrigo, 4 Giuseppe Bisignano, 4 Antonella Saija, 4 Carmelo Daquino 2 and Giuseppe Ruberto 2 * 1 Département de Biologie, Faculté des Sciences et Sciences de l’Ingénieur, Université Mohamed Boudiaf, 28000 M’Sila, Algérie 2 Istituto del C.N.R. di Chimica Biomolecolare, Via del Santuario, 110 I-95028 Valverde CT, Italy 3 Département de Biologie, Faculté des Sciences, Laboratoire d’Ecologie Végétale, Université Ferhat Abbas, 19000 Setif, Algérie 4 Dipartimento Farmaco-Biologico, Università di Messina, Contrada Annunziata, I-98128 Messina, Italy Received 14 June 2005; Revised 12 November 2005; Accepted 30 January 2006 ABSTRACT: Essential oils extracted by hydrodistillation from the aerial parts of 23 samples of Algerian Origanum glandulosum Desf. were analysed by gas chromatography (GC) and GC–mass spectrometry (MS). Overall, 30 components have been fully characterized. However, all the oils were characterized by the predominance of four components, thymol (18.5–73.1%), carvacrol (7.6–72.6%), p -cymene (1.7–18.5%) and γ γ γ -terpinene (1.1–18.7%). Cluster analysis of the iden- tified components allowed us to establish the presence of three main groups, characterized by carvacrol, thymol and com- parable amounts of both compounds, respectively. The free radical scavenging activity of essential oils was determined by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) model system. The SC 50 (scavenging concentration) values were in the range 16.2–26.7 μg/ml, representing a good antioxidant effectiveness. The roles of thymol and carvacrol, the main components of all oils, were estimated by measuring their stoichiometric factors. The essential oils were also evaluated for their antimicrobial activity by the agar disc diffusion method and the determination of minimum inhibitory concentration (MIC) against six standard strains (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus hirae, Candida albicans, Candida tropicalis). All microbial strains employed (Gram-positive and Gram-negative bacteria and yeasts) showed a fairly similar degree of susceptibility to the essential oils under investigation, although no evident difference was observed in their sensitivity. Furthermore, a similar level of toxicity was observed for all oils examined, with MIC values of 31.25–125.00 μg/ml. Finally, the addition of the emulsifier Tween 80 to the oil or to the agar markedly decreases the antimicrobial activity of the essential oils against all microbial strains employed, thus suggesting that the antimicro- bial activity of the essential oils is dependent on the physicochemical characteristics of their components and also on the microbial strains employed. Copyright © 2006 John Wiley & Sons, Ltd. KEY WORDS: Origanum glandulosum Desf.; Lamiaceae; antimicrobial and antioxidant activities; essential oil; cluster analysis; thymol; carvacrol * Correspondence to: G. Ruberto, Instituto del C.N.R. di Chimica Biomolecolare, Via del Santuario, 110 I-95028 Valverde CT, Italy. E-mail: giuseppe.ruberto@icb.cnr.it Contract/grant sponsor: CNR, Rome, Italy. Introduction The genus Origanum (family Lamiaceae) comprises about 38 species, most of which are indigenous to the Mediterranean, Euro-Siberian and Irano-Siberian regions, although 75% of them are restricted to the eastern Mediterranean area. 1 Due to the variability in chemical and aroma composition, Origanum plants are widely used as a culinary herb, to flavour food products and alcoholic beverages 2 and for their pharmacological properties, including antibacterial, antioxidant, antithrombin and antihyperglycaemic activities. 3–6 Origanum species have continuously been studied for their essential oil composition as potential sources of antimicrobial and antioxidant natural agents. On the basis of these studies, as well as the prevalence of the main compounds, Origanum taxa can be divided in three groups: (a) linalool, terpinen-4-ol and sabinene hydrate group; (b) carvacrol and/or thymol group; (c) sesquiter- penes group. 7 As previously demonstrated, the content of essential oil and extracts of Origanum species, like other medicinal plants with antimicrobial, antioxidant and other biological activities, may change depending on the differ- ences in cultivation, origin, vegetative stage and growing season of the plants. 8,9 Origanum glandulosum Desf. (Lamiaceae) is an endemic herbaceous or sub-ligneous plant in the Algerian and Tunisian areas, 10 being one of the most widespread plants of the Setif region of north-eastern Algeria, 11