Effect of atmospheric pressure cold plasma (APCP) on the inactivation of Escherichia coli in fresh produce

Foodborne outbreaks in the United States are often associated with fresh produce. Emerging pathogens are becoming more resistant to conventional disinfection methods, and thus consumers are looking for food that is free of chemicals. Atmospheric pressure cold plasma (APCP) appears to be an alternative for microbial inactivation without changes in the product. The aim of this work was to study the use of APCP in the inactivation of a surrogate microorganism of the pathogenic strain Escherichia coli inoculated on lettuce, carrots and tomatoes at 105 and 107 cfu/g. Vegetables were exposed to APCP discharges from a needle array from 3.95 kV up to 12.83 kV (60 Hz) in argon, from 30 s to 10 min. After processing, microbiological quality and Hunterʹs color parameters (L*, a*, b*) were assessed. Electron microscopy was also used to study the effect of APCP in the cellular structure. Results showed that the inoculation level had an effect on the degree of inactivation; it was easier to inactivate the bacteria at lower counts. Also, the highest voltage and longest treatment time were more effective in microbial inactivation (1.6 log). Tomatoes, followed by lettuce, were easier to disinfect than carrots, maybe because of the surface structure. Color parameters did not show significant changes after processing. However, cell structure showed a high degree of electroporation, loss and disruption of membrane and deformation after treatment. Although APCP showed limited results for disinfection of produce with the tested conditions, plasma represents a potential technology for disinfection of fruits and vegetables without important changes in physical characteristics, and more research should be done to explore other options such as the use of other gases and more complex produce surfaces.