Stabilizing Probiotics by Drying: A Review on Processes, Protective Strategies, and Viability Assessment

Scientific interest in probiotics continues to grow as accumulating evidence links microbiome modulation to improvements in host health. Probiotics are usually described as live microorganisms that, when administered in adequate amounts, confer a health benefit to the host. However, products are exposed to multiple stresses during manufacturing, storage, and gastrointestinal transit. Among these, drying, often employed to stabilize powders and extend shelf life, can impose high viability loss. This review synthesizes recent advances in drying process engineering, formulation design, and viability assessment aimed at improving survival during drying. Freeze drying remains the most widely used technology, while alternative approaches, including conventional spray drying, vacuum drying, spray freeze drying, and electrostatic spray drying, are increasingly evaluated. Protective strategies are discussed, encompassing sublethal conditioning (stress adaptation), optimization of operating parameters, incorporation of excipients, and encapsulation. Lastly, methods for viability assessment are also compared, contrasting culture-dependent assays (e.g., plate enumeration) with culture-independent techniques such as flow cytometry and PCR-based approaches. However, across studies, performance is highly strain-specific, and optimization often entails trade-offs among immediate survival, cycle time, powder stability, and downstream functionality.