Purpose: The effectiveness of orange peel EO to control Aspergillus flavus growth was evaluated, comparing the antimicrobial efficacy of vapor exposure with EO direct addition.
Methods: EO was extracted from fresh orange peel by steam distillation with a yield of 0.5%. This EO had a density of 850 kg/m3, a refractive index of 1.47, and Hunter color coordinates L, a, and b that described a clear liquid with a slight shade of orange. The main compounds identified in the orange peel oil by gas chromatography coupled with mass spectrometry were: limonene, β-myrcene, β-pinene, α-pinene, and citral Z and E; of which, limonene represented a 96.62 %. Orange peel oil was applied to model systems (potato-dextrose agar) inoculated with A. flavus, using the techniques of direct addition to the agar or the generation of EO vapors in airtight containers where inoculated plates were also placed. Inoculated plates were incubated at 25 °C for 30 days. Every day mold colony diameters were measured; with these data and using Gompertz equation, radial growth rate and lag phase were calculated.
Results: In both methods A. flavus growth decreased when increasing EO concentration. Furthermore, although the effect of EO direct addition was faster, orange peel EO vapors were more effective, since lower concentrations were required to achieve the same antifungal effect. The minimum inhibitory concentration for the growth of A. flavus by direct addition was between 8,000 and 16,000 ppm, while for the vapor-exposure was between 4.7 and 9.4 ml of essential oil / l of air.
Significance: Although direct addition of EO has a rapid effect on A. flavus growth, exposure to EO vapors was more effective, requiring lower concentrations to achieve similar effect.