Storage temperature as a determinant of probiotic long-term stability in commercial dietary supplements.

Background: Fueled by growing consumer demand for health-promoting interventions, probiotics have become widely used dietary supplements. Product quality assessment, however, still relies predominantly on label claims, highlighting the need to verify the presence and viability of declared microorganisms. Furthermore, the lack of harmonized methodologies and defined storage conditions complicates stability assurance and contributes to frequent discrepancies between declared and experimentally determined viable counts at the point of consumption. To address these gaps, we conducted a 12-month longitudinal evaluation of commercial multi-strain probiotic supplements stored under ambient, refrigeration, and freezing conditions, using culture-based enumeration of viable microbial counts. Results: Storage temperature was the primary determinant of viability. Under ambient storage conditions, a trend toward the greatest losses was observed, whereas lower storage temperatures appeared to better preserve bacterial counts over time. Taxon-specific patterns did not allow an unequivocal ranking of refrigeration versus freezing. Survival among bifidobacteria was strongly taxon-dependent, with Conclusion: Overall, our findings show that cold storage conditions, specifically refrigeration and freezing, most effectively preserve probiotic viability over time. These results underscore the importance of aligning formulation strategies, including strain selection, excipient composition, and encapsulation, with intended storage conditions to ensure sustained viability and consistent product quality throughout shelf life.