Effect of irradiation on kinetic behavior of Salmonella Typhimurium and Staphylococcus aureus in lettuce and damage of bacterial cell envelope

This study evaluated effect of gamma irradiation on survival of Salmonella Typhimurium and Staphylococcus aureus on lettuce and damage of cell envelope. S. Typhimurium and S. aureus were inoculated on red leaf lettuce, and they were irradiated at 0, 0.5, 1, 1.5, 2, 2.5, and 3kGy, and the samples were then stored at 7 and 25°C for 7 days. Survival of S. Typhimurium and S. aureus were enumerated on xylose lysine deoxycholate agar and Baird–Parker agar, respectively. D10 value (dose required to reduce 1log CFU/leaf) was calculated, and kinetic parameters (maximum specific growth rate; μmax and lag phase duration; LPD) were calculated by the modified Gompertz model. In addition, cell envelope damage of the pathogens was observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). D10 values were 0.35 and 0.33kGy for S. Typhimurium and S. aureus, respectively. During storage at 7°C, S. Typhimurium and S. aureus had significant (P