Mechanisms of Inactivation of Dry Escherichia coli by High-Pressure Carbon Dioxide.

High-pressure carbon dioxide processing is a promising technology for nonthermal food preservation. However, few studies have determined the lethality of high-pressure CO on dry bacterial cells, and the mechanism of inactivation remains unknown. This study explored the mechanisms of inactivation by using AW1.7 and mutant strains differing in heat and acid resistance, in membrane composition based on disruption of the locus of heat resistance, and in genes coding for glutamate decarboxylases and cyclopropane fatty acid synthase. The levels of lethality of treatments with liquid, gaseous, and supercritical CO were compared. The cell counts of AW1.7 and mutants with a water activity (a) of 1.0 were reduced by more than 3 log (CFU/ml) after supercritical CO treatment at 35°C for 15 min; increasing the pressure generally enhanced inactivation, except for AW1.7 Δ AW1.7 Δ was more susceptible than AW1.7 after treatment at 10 and 40 MPa; other mutations did not affect survival. Dry cells of were resistant to treatments with supercritical and liquid CO at any temperature. Treatments with gaseous CO at 65°C were more bactericidal than those with supercritical CO or treatments at 65°C only. Remarkably, AW1.7 was more susceptible than AW1.7 Δ when subjected to the gaseous CO treatment. This study identified CO-induced membrane fluidization and permeabilization as causes of supercritical mediated microbial inactivation, and diffusivity was a dominant factor for gaseous CO The safety of dry foods is of increasing concern for public health. Desiccated microorganisms, including pathogens, remain viable over long periods of storage and generally tolerate environmental insults that are lethal to the same organisms at high water activity. This study explored the use of high-pressure carbon dioxide to determine its lethality for dried and to provide insight into the mechanisms of inactivation. The lethality of high-pressure CO and the mechanisms of CO-mediated inactivation of dry depended on the physical state of CO Liquid and supercritical CO were ineffective in reducing the cell counts of dry isolates, and the effectiveness of gaseous CO was related to the diffusivity of CO Results provide a novel and alternative method for the food industry to enhance the safety of low a products.