Psychrotrophic lactic acid bacteria enhance microbial safety in kimchi: Evidence from untargeted metabolomics

Despite its acidic environment, kimchi has occasionally been linked with foodborne pathogen contamination, emphasizing the need to increase its microbial safety. While kimchi fermentation generally occurs at low temperatures, most previous studies on starter cultures have focused on mesophilic lactic acid bacteria (LAB). The present study investigated the potential of psychrotrophic LAB as starter cultures for kimchi fermentation, with particular focus on their antimicrobial activity and metabolic characteristics. Two psychrotrophic strains, Dellaglioa algida and Leuconostoc gelidum subsp. aenigmaticum, were individually co-inoculated with pathogens including Escherichia coli O157:H7, Staphylococcus aureus, and Listeria monocytogenes in kimchi and fermented at 4 °C for 42 days. Their performance was compared with that of a mesophilic LAB strain, Leu. mesenteroides, through microbial, physicochemical, and metabolomics analyses. The psychrotrophic starters accelerated acidification, maintained high dominance, and effectively suppressed pathogens. Moreover, E. coli O157:H7 counts were 1.8-2.4 log CFU/mL lower, and S. aureus reached the limit of detection (1.0 log CFU/mL) 7 days earlier than the mesophilic starter. Untargeted metabolomics using ultra-performance liquid chromatography-quadrupole-Orbitrap mass spectrometry revealed strain-specific inhibition of metabolic pathways in foodborne pathogens. D. algida primarily suppressed nucleotide metabolism, whereas Leu. gelidum subsp. aenigmaticum strongly inhibited energy-related and stress defense pathways, ultimately impairing pathogen growth. In contrast, Leu. mesenteroides exhibited relatively limited metabolic inhibition. In conclusion, psychrotrophic LAB exhibited broad-spectrum antimicrobial activity and strain-specific inhibition mechanisms, underscoring their potential as functional starters to enhance microbial safety and consistency in low-temperature fermented foods.