Ultrasonication and fresh produce (Cos lettuce) preservation

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 degrees C, 20 degrees C, 35 degrees C, 47 degrees C, and 50 degrees C) had no significant effects (P > 0.05) on the total or the psychrophilic counts during storage at 10 degrees C. The total count in Cos lettuce reached 9.74 > 0.035 log CFU/g after ultrasonication (2 min at 50 degrees C) in chlorinated water (100 mg/L) and storage for 6 d at 10 degrees 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.