• ultrasonication;
  • Cos lettuce;
  • total count;
  • psychrophilic count;
  • bactericidal effect


Washing Cos lettuce in various sanitizers at different concentrations with and without ultrasonication (40 KHz) reduced the microbiological counts by 1 to 2.5 log colony-forming units (CFU)/g immediately after washing. Ultrasonication of Cos lettuce in water, chlorinated water, peracetic acid, hydrogen peroxide, and their combinations at various temperatures (4 °C, 20 °C, 35 °C, 47 °C, and 50 °C) had no significant effects (P > 0.05) on the total or the psychrophilic counts during storage at 10 °C. The total count in Cos lettuce reached 9.74 ± 0.035 log CFU/g after ultrasonication (2 min at 50 °C) in chlorinated water (100 mg/L) and storage for 6 d at 10 °C. Extending the ultrasonication (40 kHz) of Cos lettuce for up to 20 min did not improve the bactericidal effect of ultrasonication. However, long-time ultrasonication (20 min) caused significant (P < 0.05) damage to the quality of Cos lettuce tissues.