Metabolomic profiling of <i>Lactiplantibacillus plantarum</i> L10-11 demonstrates stress tolerance and gamma-aminobutyric acid-producing capacity for fermented fish applications

Abstract Although gamma-aminobutyric acid (GABA)-producing lactic acid bacteria are recognised for salt tolerance and GABA production. The metabolic mechanisms that may coordinate stress adaptation with GABA biosynthesis remain incompletely understood. This study investigated the metabolic responses of Lactiplantibacillus plantarum L10-11 under monosodium glutamate (MSG) and combined MSG-salt conditions using 1H nuclear magnetic resonance (NMR)-based metabolomics. MSG supplementation (0.5% w/v) enhanced bacterial growth and promoted GABA biosynthesis, with GABA first detected at 12 h during the early stationary phase. By contrast, combined MSG-salt stress (3% w/v NaCl) imposed osmotic pressure, delaying the stationary phase onset to 16 h, reducing the maximal cell density, and postponing GABA production to 20 h. At this critical time point, 1H NMR profiling identified 32 metabolites across extracellular and intracellular compartments. Orthogonal partial least squares discriminant analysis (OPLS-DA) and pathway enrichment analysis indicated patterns consistent with alterations in central carbon and amino acid metabolism. These changes had the most impact in alanine, aspartate, and glutamate metabolism, which facilitate osmoprotection and GABA biosynthesis. These findings demonstrate that the metabolic adjustments of L. plantarum L10-11 may contribute to intracellular homeostasis and supporting bacterial survival under fermentation stress conditions. This provides valuable insights for optimising GABA-producing strains in functional fermented food applications.