Traditional Fermented Dairy Products as Reservoirs of Bifidobacterium With Probiotic Potential: From Microbial Diversity to Functional Characterization.

Traditional fermented dairy products (TFDPs) are complex microbial ecosystems that may serve as reservoirs of many microorganisms, including those with probiotic potential such as Bifidobacterium species and lactobacilli. Although bifidobacteria are widely used as probiotic microorganisms in defined formulations, their occurrence, persistence, and functional relevance within TFDPs remain incompletely understood. This review critically synthesizes current evidence on the diversity, ecological roles, and traits associated with probiotic potential of Bifidobacterium spp. detected in TFDPs, including raw-milk fermentations, artisanal dairy products, and selected controlled dairy systems. Species such as Bifidobacterium animalis, Bifidobacterium longum, Bifidobacterium bifidum, and Bifidobacterium breve have been reported across yogurt, kefir, airag (traditional Mongolian fermented dairy beverage from mare milk), and raw milk cheeses, often at low abundance or as transient microbial community members. Many isolates from fermented dairy products exhibit traits commonly associated with probiotic functionality, including acid/bile tolerance, adhesion capacity, exopolysaccharide production, and antimicrobial activity. However, most reports remain limited to presence/absence or in vitro assays, with limited in vivo or clinical validation. Advances in molecular and omics-based approaches have improved detection, characterization, and safety evaluation; however, translation into validated applications remains constrained by challenges in isolation, viability, and strain-level confirmation. Importantly, detection of bifidobacteria in TFDPs does not confer probiotic status, which requires strain-level identification, demonstrated safety, adequate viable counts at consumption, and clinical evidence of health benefit. Collectively, TFDPs, as culturally embedded microbial reservoirs, may support the discovery of novel bifidobacterial strains for future development of functional foods or probiotic products following rigorous validation.