Synergistic activity of cinnamaldehyde and citronellal against green mold in citrus fruit

The citrus postharvest pathogen Penicillium digitatum is responsible for the green mold decay in citrus fruit, causing tremendous economic losses. In this study, we observed that the combination of cinnamaldehyde and citronellal (CO, 5: 16, v/v) exhibited synergistic action compared to the individual compounds on the mycelial growth of P. digitatum, with the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) both being 0.40 mL L−1. And this synergistic action also verified by the spores’ germination results of cinnamaldehyde, citronellal and CO against P. digitatum. Significantly, the postharvest wax + CO (WCO, 1 × MFC) treatment on Satsuma mandarin citrus fruit incubated with P. digitatum could effectively reduce the decay of green mold. After 5 d of storage, the rotting rate of WCO treatment was only 38 %, which was clearly lower than the control fruit (100 %). Simultaneously, WCO treatment maintained the quality of citrus fruit. Additionally, the effects of cinnamaldehyde, citronellal and CO on the cell wall and cell membrane integrity of P. digitatum showed that the combined use of citronellal or cinnamaldehyde accelerated the damage of cell wall and cell membrane. Therefore, the combination of cinnamaldehyde and citronellal (5: 16, v/v) is a promising natural preservative in controlling green mold and prolonging the shelf life of citrus fruit.