Aluminum sulfate inhibits green mold by inducing chitinase activity of Penicillium digitatum and enzyme activity of citrus fruit

Abstract

Aluminum sulfate (AlS), a common food additive, was evaluated for the inhibitory mechanisms that control citrus green mold. In vitro antifungal activity of AlS against P. digitatum was assayed on potato dextrose agar (PDA) Petri dishes with AlS concentrations of 0.38, 0.75, 1.5, 3, 6 mmol/L (mM) after 2 d and 4 d of incubation at 25 °C. The minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of AlS were 1.5 and 3 mM, respectively. The analysis of calcium fluoride white (CFW) fluorescence staining and chitinase activity showed that AlS could increase the chitinase activity and enhance the damage to the cell wall. In vivo, citrus was dipped in 0.75 mM (1/2 MIC) AlS solution for 60 s and then inoculated in wounds with P. digitatum. After 6 d of storage, AlS significantly reduces the incidence and severity of the disease. In addition, citrus enzyme activity was assayed with an enzyme activity kit, the results showed that AlS treatment increased the activity of defense-related enzymes to protect the wound from infection compared with the control group (water). Our study revealed that AlS might be a potent preservative and antistaling agent against the postharvest green mold of citrus.