Chemical analyses, antioxidant and antifungal effects of oregano and thyme essential oils alone or in combination against selected Fusarium species

Essential oils (EOs) extracted from aromatic plants are interesting natural products due to their large therapeutic potential and benefits as natural preservatives. In the present work, the chemical composition, antioxidant, and antifungal effects of the essential oils of Origanum vulgare (oregano) and Thymus vulgaris (thyme), alone or in combination, were investigated. The chemical analysis was performed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) techniques. The antioxidant activity was investigated using a DPPH radical scavenging activity assay. The in vitro antifungal activity was evaluated by disc diffusion, agar dilution, and spore germination inhibition methods against Fusarium species isolated from dry rot of potato tubers, whereas the combined effect of the two essential oils was evaluated by the checkerboard technique. GC and GC-MS analyses resulted in the identification of 37 and 41 components in T. vulgaris and O. vulgare EOs, representing 80.17% and 93.00% of the total oils, respectively. The main compound of thyme oil was thymol (46.97%) and that of oregano oil was carvacrol (59.03%). The DPPH scavenging assay showed a high antioxidant capacity for both essential oils, alone or in combination. The antifungal activity revealed that O. vulgare and T. vulgaris oils exhibited a great potential antifungal activity with minimal inhibitory concentration (MIC) values of 0.078 - 0.156 μL/mL and 0.156 - 0.313 μ L/mL, respectively. The fractional inhibitory concentration index (FICI) of combined applications of the tested oils ranged from 0.375 to 0.500, suggesting synergistic interactions. Moreover, the oils were found to be effective against the spore germination of all tested Fusarium species. In vivo experiments against Fusarium oxysporum with wounded potato tubers supported these results. The findings indicated that both essential oils, alone or in combination, possess antioxidant and antifungal properties and can therefore be used as a potential source of bioactive molecules for preventing lipid peroxidation and fungal contamination of food.