Enhanced removal of Escherichia coli O157:H7 and Listeria innocua from fresh lettuce leaves using surfactants during simulated washing

- Addition of surfactants improved detachment of bacteria from fresh produce.
- Surfactants decreased the contact angle between wash water and leaf surface.
- Removal of viral particles from fresh produce is not effective as compared to bacteria.
- The presence of soil increased resistance to remove bacteria during produce washing.
- Surfactants didn't affect the color and electrolyte leakage rate of lettuce leaves.

Removal of foodborne bacterial pathogens from fresh produce during washing and sanitation process can significantly improve inactivation of the bacteria. Currently, produce wash systems mainly rely on mechanical forces to aid in removal of bacteria attached to the produce surface during washing and sanitation. This study evaluates the potential of surfactants to enhance removal of pathogens from the surface of fresh produce. Influence of three types of commercial food-grade surfactants, including Tween-20, sodium dodecyl sulfate (SDS), and lauric arginate (LAE), on the mechanical removal of pathogenic bacteria and viruses from fresh lettuce leaves in the presence of soil was evaluated. The addition of surfactants did not increase the removal of T7 phages from lettuce leaf surface (P > 0.05). The improvement of bacterial removal by addition of surfactants to wash water is corresponding to the decrease of the contact angle between wash water and leaf surface. The most effective Escherichia coli O157:H7-lux removal was obtained by washing with 0.1% LAE, followed by 0.1% Tween-20, then 0.1% SDS. The most enhanced detachment of Listeria innocua was achieved by 0.1% LAE, followed by 0.1% SDS, then 0.1% Tween-20. The presence of soil resulted in an increased resistance of bacterial cells to the washing process. There was no significant difference in the cell persistence on the lettuce surface within the extended incubation period (P > 0.05). The evaluation of lettuce quality indicated that the introduction of surfactants during the washing procedure may affect the firmness of leaves, but the color and electrolyte leakage rate were not affected by the exposure to wash water with surfactants (P > 0.05). Overall, these results suggest the potential of food grade surfactants to enhance the removal of bacteria particularly foodborne pathogens from the surface of fresh produce.