In-vitro Anti-fungal Activity of Aloysia polystachya Essential Oil in High Dilution on Aspergillus flavus Isolated from the Brazil Nut (Bertholletia excelsa)

Background: Bertholletia excelsa, Brazil nut, has significant participation in the food and cosmetic industry. However, contamination by Aspergillus flavus, an aflatoxin-producing fungus that causes post-harvest rot, is a serious impediment to its commercialization. Substances of plant origin are an important therapeutic resource and the dynamization of essential oils is a safe and efficient pharmaco-technical technique. Aloysia polystachya is a plant native to South America whose essential oil has a considerable biocidal effect.

Aim: To determine the ability of the original and dynamized essential oil of A. polystachya to inhibit the in-vitro multiplication of the fungus A. flavus isolated from Brazil nuts.

Methods: The essential oil of A. polystachya, obtained by hydro-distillation, was diluted with Tween 80 (1%) and then dynamized. The activity of the original and dynamized essential oils of A. polystachya was evaluated by the Minimum Inhibitory Concentration (MIC) and Minimum Fungicidal Concentration (MFC) methods. The vehicle control was performed and resazurin was used for the reading. The analyses were performed in triplicate and the results were submitted to ANOVA, the means of the treatments being compared by the Scott-Knott test (p < 0.05).

Results: The original essential oil of A. polystachya presented an MIC of 1.56 μg.mL⁻¹, differing statistically from the MIC of the dynamized form, which was 0.01 μg.mL⁻¹. In the MFC evaluation, both treatments presented fungistatic activity against A. flavus.

Conclusions: The highly diluted essential oil of A. polystachya presented significant fungistatic activity against A. flavus and, therefore, may be a promising resource in the control of post-harvest contamination in Brazil nuts.

Keywords: Aloysia polystachya, Aspergillus flavus, Bertholletia excelsa, dynamization, anti-fungal activity