Abstract: Pseudomonas fluorescens is one of the most common psychrophilic bacteria causing spoilage of refrigerated foods. Inhibiting the growth and reproduction of P. fluorescens is of great significance for extending the shelf life of refrigerated foods and improving food safety. In this study, the antibacterial activity of phenyllactic acid (PLA) against P. fluorescens was evaluated by determining the minimum inhibitory concentration (MIC) and time-inhibition curve. The inhibitory mechanism was explored from different perspectives: membrane potential, membrane permeability and integrity, cell ultrastructure, protein expression and DNA structure. The results showed that the MIC of PLA was 1.25 mg/mL. PLA could depolarize the cell membrane in a dose-dependent manner, and cause significant leakage of intracellular potassium ion (P < 0.05), indicating increased permeability of the cell membrane. After treatment for 0.5 h by PLA at MIC concentration, the propidium iodide staining rate of cells was 57.6% as determined by flow cytometry, and ruptured cells were observed by scanning electron microscopy (SEM), suggesting that PLA could damage the membrane integrity. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that PLA had no significant effect on protein expression. Gel retardation electrophoresis and fluorescence spectroscopy showed that PLA could destroy the structure of DNA. Therefore, PLA can exert a bacteriostatic effect by destroying both the cell membrane and DNA, which will provide theoretical evidence for the control of psychrophilic spoilage bacteria in refrigerated foods and the application of PLA in foods.

Key words: phenyllactic acid; Pseudomonas fluorescens; genomic DNA; bacteriostatic mechanism