Storage time influences salmonella sensitivity to irradiation and sodium hypochlorite on leafy greens

Authors: Niemira, Brendan

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 1/29/2011
Publication Date: 6/13/2011
Citation: Niemira, B.A. 2011. Storage time influences salmonella sensitivity to irradiation and sodium hypochlorite on leafy greens [abstract]. Institute of Food Technologists Annual Meeting, June 11-14, 2011, New Orleans, Louisiana. 1:1.

Interpretive Summary:

Technical Abstract: Contamination of leafy green vegetables with human pathogens is a source of ongoing concern for consumers. Bacteria in mature microbial communities such as biofilms are relatively resistant to chemical treatments, but little is known about the response of leaf surface biofilms to irradiation. Leaves of romaine lettuce and baby spinach were dip inoculated in a three strain cocktail of Salmonella and stored at 4 deg C for various times (0, 24, 48, 72h) to allow biofilms to form. After each time, the leaves were treated with either a 3 minute wash with a sodium hypocholorite solution (0,300 or 600ppm) or increasing doses of irradiation (0,0.25, 0.5, 0.75 or 1.0 kGy). Viable bacteria were recovered and enumerated. Chlorine washes were moderately effective, and resulted in maximal reductions of 1.9 log cfu/g for baby spinach and 1.7 log cfu/g for Romaine. For spinach, storage times up to 48h had no effect on chlorine efficacy, while after 72h in storage, 600 ppm was significantly more effective than 0 or 300 ppm. For Romaine, 600 ppm was signficantly more effective at 0 and 28h, but not at 24 or 72h of storage, indicating a more variable response. For both types of leaves, time in storage reduced the efficacy of irradiation. D10 values (the dose required for a 1 log reduction) signficantly increased with increasing storage time. From 0h of storage, D10 increased from 0.28 kGy to a maximum of 0.34 kGy for spinach. For Romaine, D10 increased from 0.30 kGy at 0h to 0.37 kGy at 72h. These results indicate that the biofilm habitat can reduce the efficacy of irradiation in eliminating pathogens from leafy vegetables.