Purpose: This study aimed to evaluate and understand the impact of drying conditions on survival, physiology, and invasion capacity of Salmonella Typhimurium and C. sakazakii.
Methods: Salmonella Typhimurium and C. sakazakii were mixed into whole milk powder and dried at different water activity (aw) levels (0.25, 0.58 and 0.80). For each strain, the impact of each drying condition was evaluated by estimating the loss of cultivability, membrane permeabilization, and the loss of a respiratory enzymatic activity by flow cytometry. The invasion capacity in Caco-2 cells was, also, evaluated after drying for each bacterium by the gentamicin test.
Results: Our results showed that intermediary initial drying kinetics increased bacterial inactivation. No significant differences were observed between bacterial cultivability at aw 0.25 and 0.58. Nevertheless, the bacterial cultivability was significantly higher (p <0.05) at aw 0.80 than at 0.25 or 0.58. An increase in percentages of uncultivable cells correlated with percentages of permeabilized cells. Furthermore, our results showed that drying (at 0.80, 0.58, and 0.25) significantly increased (p <0.05) the invasion capacity of S. Typhimurium and C. sakazakii.
Significance: These results indicate that drying parameters have a high impact on S. enterica and C. sakazakii and could be managed to promote foodborne pathogen inactivation. Drying could, also, be improved to avoid virulence pathway activation and ensure the safety of dried food products.