Isolation, purification, identification, and discovery of the antibacterial mechanism of ld-phenyllactic acid produced by Lactiplantibacillus plantarum CXG9 isolated from a traditional Chinese fermented vegetable

Phenyllactic acid (PLA) is an antimicrobial compound and has been rarely reported to naturally occur in food sources with the exception of honey, sourdough, and some pickles. In this study, a traditional Chinese fermented vegetable, Stinky xiancaigeng, was found to contain high concentrations of PLA. A high PLA level-producing Lactiplantibacillus plantarum (L. plantarum) CXG9 was subsequently isolated and subjected to genomic analysis. Six L- and two d-lactate dehydrogenase genes were predicted, indicating that PLA produced by L. plantarum CXG9 contained L- and D-isomers. The ratio of L- and D-isomers was 11:1 by chiral high performance liquid chromatography analysis. LD-PLA from L. plantarum CXG9 cultures were then purified by a three-step procedure and identified by mass spectrometry. LD-PLA exhibited strong anti-Listeria monocytogenes activity, with a minimum inhibitory concentration of 2.4 mg/mL. The results of anti-Listeria monocytogenes mechanism demonstrated that LD-PLA damaged cell membrane integrity, increased membrane permeability, induced pore formation, and triggered intracellular material leakage by interacting with cell membrane proteins. These results presented here contribute to the use of PLA in further development and application as an antibacterial agent in the food industry.