Inactivation of Escherichia coli O157:H7 on Lettuce, Using Low-Energy X-Ray Irradiation

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Low-energy X-ray irradiation was assessed as a means of eliminating Escherichia coli O157:H7 on lettuce. Round-cut iceberg lettuce samples (2.54-cm diameter) were dip or spot inoculated with a three-strain cocktail of E. coli O157:H7, stored for 24 h at 4°C, and then irradiated at four dose levels up to 0.25 kGy using a prototype low-energy (70 kV) X-ray irradiator. E. coli O157:H7 survivors were quantified by plating on sorbitol MacConkey agar containing cefixime and tellurite. Dip inoculation yielded a D 10-value of 0.040 ± 0.001 kGy, which is 3.4 times lower than a previously reported value of 0.136 kGy using gamma radiation. The D 10-value for E. coli O157:H7 on spot-inoculated samples was 0.078 ± 0.008 kGy, which is about twice that of dip-inoculated samples. When 10 stacked leaves were irradiated from both sides, a dose of 0.2 kGy was achieved at the center of the stack with a surface dose of 1 kGy, corresponding to a ∼5-log reduction of E. coli O157:H7 at the center of the stack. Based on these findings, low-energy X-ray irradiation appears to be a promising microbial inactivation strategy for leafy greens and potentially for other types of fresh produce.

Document Type: Research Article

Affiliations: 1: Biosystems and Agricultural Engineering, Michigan State University, East Lansing, Michigan 48824, USA. 2: Biosystems and Agricultural Engineering, Food Science and Human Nutrition, Michigan State University, East Lansing, Michigan 48824, USA 3: Food Science and Human Nutrition, Michigan State University, East Lansing, Michigan 48824, USA

Publication date: March 1, 2010

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