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‐terpinene (1.1–18.7%). Cluster analysis of the identified components allowed us to establish the presence of three main groups, characterized by carvacrol, thymol and comparable 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 antimicrobial 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.