In this study, the orange peel of 12 cultivars of Citrus sinensis from central-eastern Sicily was employed to obtain essential oils and extracts. The ones were extracted through steam distillation, the others through extraction in hexane. Chemical constituents were evaluated in terms of qualitative and quantitative analyses by gas chromatography/mass spectrometry. Fifty-four components were identified in the steam essential oils and 44 in the extracts. In all the cultivars, the main component is d-limonene (73.9–97%); discrete percentages of linalool, geraniol and nerol were also found. Cluster analysis based on essential oils composition showed a certain degree of affinity between cultivars of the same type. The antimicrobial activity was investigated against three micro-organisms (Staphylococcus aureus, Listeria monocytogens and Pseudomonas aeruginosa). ‘Sanguinello’ and ‘Solarino Moro’ essential oils are significantly active against L. monocytogenes, while ‘Valencia’ hexanic extract against all the tested micro-organisms.

Aims: To evaluate the anti-biofilm activity of the commercially available essential oils from two Boswellia species. Methods and Results: The susceptibility of staphylococcal and Candida albicans biofilms was determined by methyltiazotetrazolium (MTT) staining. At concentrations ranging from 217·3 μg ml⁻¹ (25% v/v) to 6·8 μg ml⁻¹ (0·75% v/v), the essential oil of Boswellia papyrifera showed considerable activity against both Staphylococcus epidermidis DSM 3269 and Staphylococcus aureus ATCC 29213 biofilms. The anti-microbial efficacy of this oil against S. epidermidis RP62A biofilms was also tested using live/dead staining in combination with fluorescence microscopy, and we observed that the essential oil of B. papyrifera showed an evident anti-biofilm effect and a prevention of adhesion at sub-MIC concentrations. Boswellia rivae essential oil was very active against preformed C. albicans ATCC 10231 biofilms and inhibited the formation of C. albicans biofilms at a sub-MIC concentration. Conclusions: Essential oils of Boswellia spp. could effectively inhibit the growth of biofilms of medical relevance. Significance and Impact of the Study: Boswellia spp. essential oils represent an interesting source of anti-microbial agents in the development of new strategies to prevent and treat biofilms.