Co‐Culture of Lactobacillus bulgaricus With Streptococcus thermophilus and Bifidobacterium Impact the Metabolism and Flavor of Fermented Milk

Incorporating Bifidobacterium into fermented milk alters the balance between Lactobacillus bulgaricus and Streptococcus thermophilus . We investigated the bacterial interaction and metabolism post‐fermentation and during 21‐day storage. Utilizing non‐targeted metabolomics and electronic nose technology, we assessed impacts on product quality and flavor. Bifidobacterium significantly increased the viability of the other two species, with AI‐2 levels rising in the mixed culture. Metabonomic analysis revealed distinct metabolic profiles, with Bifidobacterium ‐fermented milk showing enriched key metabolites. Volatile compounds like ketones, aldehydes, esters, alcohols, and acids were identified, with 2‐heptanone and 2‐pentanone as initial discriminators and 2‐pentanone and acetaldehyde as key flavor compounds after storage. This study advances understanding of symbiotic interactions and metabolite profiles in fermented dairy ecosystems. The level of autoinducer‐2 (AI‐2) is maximized in dairy products fermented with Bifidobacterium species. Bifidobacterium significantly promoted the survival rate of Lactobacillus bulgaricus and Streptococcus thermophilus . The contents of caffeic acid and D‐galactose increased significantly after co‐culture. 2‐pentanone is the key flavor substance of three groups of fermented milk in two periods.