Evaluation of Lentilactobacillus kefiri NM119-2 as a novel probiotic in fermented milk: functional properties and metabolic impact.

The rapid growth of the probiotic industry highlights the need to identify high-quality probiotics. This study evaluated the in vitro probiotic potential of ten Lentilactobacillus kefiri isolated from traditional fermented dairy products. Among them, NM119-2 exhibited strong tolerance to simulated gastrointestinal conditions, favorable antibiotic susceptibility, and desirable properties, including high cell surface hydrophobicity, self-aggregation ability, antioxidant activity, and moderate cholesterol-lowering capacity. Genomic analysis revealed 89 probiotic trait-associated genes, including those involved in stress resistance (cysE, tuf, dps), carbohydrate metabolism (galE, pgi), and protein secretion (lspA, ffh), providing a genetic basis for its robust survival and functional performance. The isolate was further assessed for its impact on fermented milk production and quality. Co-fermenting NM119-2 with a commercial starter culture maintained the fermentation time while enhancing pH stability, physical properties (viscoelasticity, texture, and water-holding capacity), and microbial viability during cold storage compared to the control. Moreover, flavor profiles analyzed by an electronic tongue showed progressive improvement over the storage period. Using untargeted metabolomics, significant metabolic shifts were observed in NM119-2-supplemented fermented milk at the end of fermentation. Differential metabolite analysis identified 165 altered metabolites, primarily enriched in pathways related to amino acid, nucleotide, and lipid metabolism. These included increased levels of amino acids, small peptides, aromatic compounds, flavonoids, organic acids, and fatty acids. Notably, bioactive compounds such as nucleotides, dipeptides, and antioxidants were elevated, suggesting that NM119-2 enhances both the nutritional and sensory qualities of fermented milk. These findings support Lentilactobacillus kefiri NM119-2 as a promising probiotic candidate for functional dairy applications.