Antifungal activity of orange (Citrus sinensis var. Valencia) peel essential oil applied by direct addition or vapor contact

Vapor contact is an alternative when essential oils (EO's) and microorganisms are placed separately in some sealed environment. The aim of this study was to compare the antifungal efficacy of orange peel EO at selected concentrations, applied either by vapor exposure or direct addition on the growth of Aspergillus flavus. Orange peel EO was obtained from fresh oranges (Citrus sinensis var. Valencia). EO was obtained by vapor distillation, analyzed by means of GC-MS chromatography, and applied to potato-dextrose agar inoculated with A. flavus, using the techniques of direct addition to the agar or by generating EO vapors in airtight containers. Radial growth rate and lag phase were calculated using the Gompertz equation. Main compounds identified in the orange peel EO were: limonene, β-myrcene, β-pinene, α-pinene, as well as citral Z and E; of which, limonene represented 96.62%. The minimum inhibitory concentration for the growth of A. flavus by direct addition was 16,000 mg l−1, while for the vapor contact was 8000 mg of EO l−1 of air. For both studied methods A. flavus growth decreased when increasing EO concentration. Although the effect of orange peel EO direct addition was faster, orange peel EO vapors were more effective, since lower concentrations were required to achieve the same antifungal effect.