Growth, organic acids profile and sugar metabolism of Bifidobacterium lactis in co-culture with Streptococcus thermophilus: The inulin effect

The organic acids profile, sugar metabolism and biomass growth of Streptococcus thermophilus (St) and Bifidobacterium lactis (Bl) have been studied in pure cultures or binary co-culture (St–Bl) in skim milk either containing 40mg/g of inulin or not. With inulin, the time required by St, Bl and St–Bl to complete fermentation (i.e., when the pH reached 4.5) was about 14, 8 and 49% shorter than without inulin, respectively. This prebiotic also enhanced the levels of lactic and acetic acids and volatile compounds, showing a positive synbiotic effect between pre- and probiotics. In particular, the St–Bl co-culture showed final concentrations of both microorganisms about 15 and 38% higher than in their respective pure cultures, thus highlighting a clear synergistic effect between these microorganisms due to mutual interactions. In addition, the well-known bifidogenic effect of inulin was confirmed. ► Pure cultures or binary co-cultures of S. thermophilus and B. lactis were studied. ► A synergistic interaction took place between S. thermophilus and B. lactis. ► Inulin enhanced volatile compounds. ► Inulin stimulated biomass growth and levels of lactic and acetic acids.