Antifungal activity of citral, octanal and α-terpineol against Geotrichum citri-aurantii

- Citral, octanal and α-terpineol showed strong inhibition on Geotrichum citri-aurantii.
- Citral was the most potent antifungal substance in the volatile compounds.
- The membrane permeability of G. citri-aurantii was changed by the volatile compounds.
- The membrane integrity of G. citri-aurantii was destructed by the volatile compounds.

This study investigated the antifungal activity and potential antifungal mechanisms of three volatile compounds (i.e., citral, octanal, and α-terpineol) against Geotrichum citri-aurantii, one of the main postharvest pathogens in citrus. Results showed that the volatile compounds exhibited strong antifungal activity against the targeted pathogens, with minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of 0.50 μL/mL and 1.00 μL/mL for citral, 0.50 μL/mL and 2.00 μL/mL for octanal, and 2.00 μL/mL and 4.00 μL/mL for α-terpineol. The volatile compounds alter the morphology of G. citri-aurantii hyphae by causing loss of cytoplasm content and distortion of the mycelia. The membrane permeability of the G. citri-aurantii increased with increasing concentrations of the three volatile compounds, as evidenced by cell constituent release, extracellular conductivity, and pH. Moreover, the volatile compounds induced a decrease in the total lipid content of G. citri-aurantii cells, indicating the destruction of cell membrane structures. These results suggest that the antifungal activity of citral, octanal, and α-terpineol against G. citri-aurantii could be attributed to the disruption of cell membrane integrity and leakage of cell components.