Abstract: Epsilon-polylysine (ε-PL) is a safe and biodegradable natural food preservative without any adverse effects on the environment or human health. The antifungal activity and mechanism of ε-PL on Geotrichum citri-aurantii were investigated in this study. The mycelium growth inhibition rate, spore germination inhibition rate, extracellular relative electric conductivity and absorbance at 260 nm (A260 nm) value of Geotrichum citri-aurantii were determined after being treated with ε-PL. Additionally, laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM) were used to study the effects of ε-PL treatment on the cell membrane integrity and mycelium morphology of Geotrichum citri-aurantii, respectively. The results showed that the minimum inhibitory concentration (MIC) was 400 mg/L, and the half maximal effective concentration (EC50) for inhibiting mycelium growth and spore germination were 128.79 and 214.77 mg/L, respectively. When used at concentrations of 1 600, 3 200 and 6 400 mg/L, ε-PL significantly lowered the incidence of sour rot and lesion diameter in citrus fruit with stab inoculation compared to the control fruit (P < 0.05). After being treated with ε-PL at 1 × MIC and 2 × MIC, extracellular relative electric conductivity, A260 nm and fluorescence intensity were significantly increased relative to the control group (P < 0.05), which indicated increased cell membrane permeability, thereby leading to the leakage of intracellular components such as nucleic acids and causing damage to the integrity of the membrane. Furthermore, ε-PL treatment induced severe distortion and disruption of the mycelia of Geotrichum citri-aurantii. Therefore, ε-PL can destroy the structure of the cell membrane, causing the leaking of intracellular contents and distortion of the mycelia, retarding spore germination, and thus inhibiting the growth and development of Geotrichum citri-aurantii.

Key words: Geotrichum citri-aurantii; ε-polylysine; antifungal activity; cell membrane; antifungal mechanism