Strain-level contribution of three lactic acid bacteria to consortium stability and milk fermentation assessed by untargeted metabolomics and volatile compound analysis

In this study, a leave-one-out inoculation strategy was employed for the fermentation of milk using the strains Lactococcus lactis LA1, Lactococcus cremoris LA10, and Lactiplantibacillus plantarum LA30. During fermentation, strain dynamics were monitored by culturing and qPCR, and metabolites profiled by targeted and untargeted high-resolution mass-spectrometry. Lc. cremoris LA10 reached the highest cell counts and stimulated the growth of Lc. lactis LA1 in co-culture. During refrigeration storage, Lpb. plantarum LA30 remained stable for 28 days and supported the long-term viability of lactococci. The most complex metabolic profiles were observed in fermentations involving Lc. cremoris LA10, either alone or in combination. Although limited strain-strain metabolic cooperation was observed for the utilization and synthesis of compounds, some key metabolites were co-produced. These metabolites may contribute to the consortium's stability by boosting strain growth and survival during storage. The knowledge gathered might help design more cooperative and resilient dairy starters.