Vanillin and its derivatives, potential promising antifungal agents, inhibit Aspergillus flavus spores via destroying the integrity of cell membrane rather than cell wall

To study the structure-antifungal activity of vanillin against Aspergillus flavus (A. flavus), the susceptibilities of A. flavus to vanillin and its isomers (o-vanillin, 2-hydroxy-4-methoxybenzaldehyde (HMB), 2-hydroxy-5-methoxybenzaldehyde) and the possible antifungal mechanisms have been investigated. All the four volatile aldehydes could inhibit the germination of spores, and the minimum inhibitory concentrations (MICs) of them were in this order: vanillin (200 μg/mL), o-vanillin (100 μg/mL), 2-hydroxy-5-methoxybenzaldehyde (100 μg/mL), HMB (70 μg/mL). The minimum fungicidal concentrations (MFCs) of them were in this order: vanillin (240 μg/mL), o-vanillin (160 μg/mL), HMB (140 μg/mL), 2-hydroxy-5-methoxybenzaldehyde (140 μg/mL). Spore size was arrested at 0 h with the treatment of the four volatile aldehydes. Effects of the four volatile aldehydes on the cell wall and cell membrane integrity of A. flavus were observed by calcofluor white (CW) staining and propidium iodide (PI) staining. The results showed that HMB exerted the strongest antifungal and fungicidal effects on the growth of A. flavus. The four volatile aldehydes had little influence on cell wall integrity after 3-hour treatment, however, they could strongly damage the cell membrane integrity. All the four volatile aldehydes could effectively prevent the growth of A. flavus on peanut seeds. The antifungal mechanisms of the four volatile aldehydes provide theoretical foundations for their development of new antifungal agents.