Evaluation of low-energy x-rays as an alternative to chlorine washing to control internalized foodborne pathogens in lettuce

Low-energy X-rays can be used to reduce the number of pathogenic microorganisms in fresh produce, but the efficacy of this process against internalized bacteria in leafy greens has not yet been reported. The leaves of iceberg lettuce were cut into pieces and subjected to vacuum perfusion to force the foodborne pathogen cells into the intercellular spaces within the leaves. Sodium hypochlorite (200–400 ppm) washes were not effective in inactivating internalized bacterial cells from lettuce leaves. In contrast, treatment with 1.5 kGy low-energy X-rays reduced Escherichia coli O157: H7, Salmonella enterica Serovar Typhimurium, and Listeria monocytogenes levels by 6.89, 4.48, and 3.22 log CFU/g, respectively. Additionally, the maximum dose of X-rays did not adversely affect the color or texture of lettuce. These results suggest that low-energy X-ray treatment can be used to control internalized and surface-adhering pathogens in leafy vegetables without affecting product quality.