Purpose: The objective of this study was to determine the efficacy of Neutral Electrolyzed Water (NEW) in reducing Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 on romaine lettuce and tomatoes washed in an automated salad spinner. The effects of different washing-speeds (40 and 65 rpm) and treatment times (1 to 30 min) were tested.
Methods: Whole lettuce leaves and tomatoes were spot-inoculated with 100 μl of a mixture of 5 strains of either E. coli O157:H7 or S. Typhimurium DT 104 and stored for 24h at 4°C to simulate food service operations. Washing produce in a modified salad spinner apparatus was preceded by rinsing under running NEW (155 mg/l free chlorine) whereas for lettuce an additional rinsing with NEW in spinner for 30 sec was included. Treatment with deionized water served as a control and six samples of each treatment were analyzed.
Results: Time and washing-speed had significant effects (P < 0.05) on the efficacy of NEW with reductions between 1.22 to 4.16 log CFU/g and 2 to 5.85 log CFU/g observed for E. coli O157:H7 and S. Typhimurium DT 104, respectively, on lettuce. Washing tomatoes with NEW also led to reductions greater than 5 log CFU/fruit for both pathogens and up to 8 log CFU/fruit for S. Typhimurium DT 104. Treatments with NEW completely inactivated pathogens in wash solutions (detection limit, 0.3 log CFU/ml).
Significance: Results suggest that NEW is effective in reducing Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 on romaine lettuce and tomatoes and can therefore be used in food service kitchens to ensure produce safety.