Purpose: This study aimed to demonstrate that supercritical CO2 drying could be used as a drying process to obtain safe dried foods.
Methods: Fresh cilantro and strawberries, inoculated with 3 strains-cocktails of Escherichia coli O157:H7, Salmonella Typhimurium and S. Thompson, or Listeria monocytogenes, were treated with pure supercritical CO2. The following conditions were applied: 1) pressurization to 80 bar at 35°C immediately followed by depressurization, 2) pressurization to 100 bar at 40°C immediately followed by depressurization and 3) pressurization to 80 bar and 35°C followed by depressurization after 150 min. The depressurization rate was kept at 5 bar/min. Enumeration of the different strains was performed by standard plate count method. Experiments were performed in triplicate.
Results: When exposed to pressurization/depressurization only, the products lost less than 10% of their initial weight. After 150 min at 80 bar/35°C, the average mass loss was 88.7%. On strawberry, independent of the type of treatments, E. coli O157:H7 and Salmonella strains were reduced by 2 to 3 log units whereas L. monocytogenes strains were more susceptible with 4 log reduction. For coriander 4 to 6 log inactivation of E. coli O157:H7 and Salmonella strains was noted. L. monocytogenes strains were found to be more resistant showing only 4 log reduction.
Significance: These results indicates that supercritical CO2 can be used for drying and for microorganisms reduction in a single process. However, the effect of the food matrix strongly influenced the behavior of the different microorganisms during the process.