Óleos essenciais e extratos vegetais de plantas cultivadas no Brasil: impacto no crescimento de cepas toxígenas de Aspergillus Seção Flavi

Abstract

Fungal and mycotoxin contamination in food is one of the greatest problems around the world. Some natural products, such as essential oils, have been shown to be effective inhibitors of fungal growth and production of their toxins. In this study, a total of 40 vegetal extracts were tested for inhibition on Aspergillus section Flavi growth. These extracts were obtained from ten herbs cultivated in Brazil: basil (Ocimum basilicum), cinnamon (Cinnamomum zeylanicum), clove (Eugenia caryophyllata), cumin (Cuminum cyminum), marjoram (Origanum majorana), nutmeg (Myristica fragrans), oregano (Origanum vulgare), rosemary (Rosmarinus officinalis), spearmint (Mentha piperita) and sweet fennel (Pimpinella anisum). Preliminary in vitro tests using the agar diffusion method showed that essential oils were more effective in inhibiting the fungal growth when compared with ethanol and aqueous extracts. Essential oils obtained from oregano and rosemary, clove and cumin ethanolic extracts and the essential hexanic oil of oregano and cinnamon were selected for advanced tests. Differents concentrations of plant material (0, 50, 100, 150, 300 and 600 μg/g) were added to culture medium. A suspension of 103 conidia per inoculation were used. Plates were incubated for ten days while daily measurements of colony diameters were made to obtain growth rate (mm/day) and lag phase (h) of toxigenic strains. The comparison of selected essential oils effect on A. flavus and A. parasiticus showed better inhibition by incorporating oregano essential oil in the culture medium at 600 μg/g concentration. Nevertheless, the hexanic essential oil of oregano showed no statistical difference with the control group, a change occurred in the plant product due to the extraction method. Among the evaluated ethanol extracts, clove had the best result. Aspergillus flavus showed a slight reduction of growth (4.5 to 3.5 mm/day) when compared to control group, but a large increase in the latency period (37 h at a 600 μg/g concentration). Aspergillus parasiticus showed gradual decreases as increased concentrations were assayed, except for the 150 μg/g concentration, and a significant increase on lag phase at the highest concentrations tested (45 and 48 h, respectively). The data presented here are very important for the continued efforts of microbiological control in food, especially when it comes to control fungi.