Antifungal Activity and Possible Mechanism of Action of Phenyllactic Acid Produced by Lactic Acid Bacteria against Penicillium digitatum

This study was attempted to explore the ability of Lactobacillus plantarum CKXP13 and L. plantarum CWXP24 to produce phenyllactic acid (PLA), and the inhibitory effect and mechanism of action of PLA on citrus green mold. The phenyllactic acid-producing ability of L. plantarum was determined by high performance liquid chromatography (HPLC). The antifungal mechanism of action was explored by studying the spore survival rate, colony diameter, mycelial morphology, and extracellular electrical conductivity of P. digitatum after being treated with PLA. The results showed that both strains could produce PLA at yields of 42.4 and 91.9 mg/L, respectively. As the PLA concentration increased from 2.5 to 5.0 and 10.0 mg/mL, the spore viability and colony diameter of P. digitatum decreased significantly (P < 0.05). Meanwhile, the hyphal surface appeared rough with dents or dendritic bulges on it and the hyphae were entangled. At the same time, PLA enhanced the permeability of the cell membrane of P. digitatum, promoted the leakage of cell contents, and caused the death of P. digitatum. PLA at concentrations of 10 and 20 mg/mL could effectively control citrus green mold. In conclusion, PLA has great potential for development and application as a natural fungicide in controlling postharvest green mold of citrus fruit.