Modulation of wound-induced hydrogen peroxide and its influence on the fate of Escherichia coli O157:H7 in cut lettuce tissues.

Wounding of lettuce tissue has been examined previously by others in regard to browning reactions, and treatments to modulate wounding responses were evaluated for reduction of browning. However, the wounding process also releases oxygen radicals such as hydrogen peroxide. This study focused on the evaluation of two treatments that reduce hydrogen peroxide at cut surfaces (heat treatment and pyruvate addition) and one treatment that enhances its production (infusion with the fungal elicitor harpin). Hydrogen peroxide changes in response to treatment were also associated with resultant survival of Escherichia coli O157:H7, which was inoculated onto the lettuce before cutting. Heat-treated lettuce produced significantly less hydrogen peroxide, and microbial analysis showed that E. coli O157:H7 survival on packaged, heat-treated lettuce was higher than on non-heat-treated controls. Lettuce was also cut under a solution of sodium pyruvate (a well-known hydrogen peroxide quencher), and E. coli O157:H7 survival was found to be enhanced with that treatment. When lettuce was infused with harpin before cutting, hydrogen peroxide production was enhanced, and this was associated with reduced survival of E. coli O157:H7. These results collectively support the hypothesis that modulation of wound-generated hydrogen peroxide can have an influence on E. coli O157:H7 survival on cut and packaged romaine lettuce.