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The yield of hydrodistillation of a botanically certified Oleogum Resin of Boswellia sacra essential oil (5.5%); and its chemical constituents were determined. The GC/MS technique was used for the analysis of the oil. Several oil components were identified based upon comparison of their mass spectral data with those of reference compounds published in literature or stored in a computer library. The oil was characterized by the high content of the monoterpenes (34) which constituted 97.3% in which E-β-ocimene and limonene were the major constituents. The remaining 2.7% was accounted for the sesquiterpenes (16) in which the E-caryophyllene was the major constituent. The analysis proved the complete absence of the diterpenes.

The essential oil compositions of four botanically certified and commercially available samples of Omani lubans (oleo‐gum resins of Boswellia sacra Flueck.), locally known as Hoojri, Najdi, Shathari, and Shaabi in Jibali Arabic, obtained from plants growing in four different geographic locations of the Dhofar region of Oman, were analyzed by GC‐FID, GC/MS, and 13C‐NMR spectroscopy. The market price of these four grades of lubans differed considerably, according to their color, clump size, and texture. However, this study revealed that Hoojri, the first grade luban, and Shaabi, the fourth grade luban, which greatly differed in their price, closely resembled each other in their essential oil composition, yield, and physicochemical characteristics, except the color and texture. The composition, yield, and specific rotation of the oils of Najdi and Shathari, the second and the third grade lubans, respectively, were different from those of Hoojri and Shaabi, but they both had high limonene contents. Najdi oil was different from the other three oils in terms of its high myrcene content. α‐Pinene was the principal component in all the oils and can be considered as a chemotaxonomical marker that confirms the botanical and geographical source of the resins. All the oils showed pronounced activity against a panel of bacteria, and the trend in their bioactivity and their mode of action are discussed.

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Aims:  The traditional uses of the aerial parts of fresh Plectranthus cylindraceus by the Dhofaris in Oman were investigated on the basis of antimicrobial properties and composition of its herb oil. Methods and Results:  The minimal inhibitory concentration (MIC) values of the herb oil of P. cylindraceus against human pathogenic bacteria and yeast were assessed using the broth microdilution method, and the percentage growth inhibition of fungi was determined according to the poisoned food technique. The oil exhibited good activity against Klebsiella pneumoniae, Staphylococcus aureus, Bacillus subtilis and Candida albicans with MIC values in the range of 7·8–62·5 μg ml−1 and also inhibited the growth of Microsporum canis, Microsporum gypseum, Trichophyton rubrum, Alternaria alternata, Bipolaris sp., Curvularia lunata, Fusarium oxysporum and Stemphylium solani for about a week at 250 μg ml−1. The two most abundant components of the oil were identified as carvacrol (46·8%) and α‐terpinolene (18·2%) based on gas chromatography‐mass spectra (GC‐MS) and 13C nuclear magnetic resonance (NMR) analyses. Conclusions:  The oil has a pleasant odour and showed broad spectrum antimicrobial activity. Such bioactivity could be attributed in part to carvacrol. Significance and Impact of the Study:  This study has demonstrated the broad spectrum antimicrobial activity of the herb oil of P. cylindraceus as well as the organic composition of this plant extract. This study provides scientific insight into the ancient practice of utilizing P. cylindraceus as a fragrant disinfectant.