Inactivation of Escherichia coli O157:H7 on lettuce, using low-energy X-ray irradiation.
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 degrees 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 approximately 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.
Jeong
Sanghyup
S
Biosystems and Agricultural Engineering, Michigan State University, East Lansing, Michigan 48824, USA. jeongsa1@msu.edu
Marks
Bradley P
BP
Ryser
Elliot T
ET
Moosekian
Scott R
SR
D015169:Colony Count, Microbial; D004307:Dose-Response Relationship, Radiation; D019453:Escherichia coli O157 / Q000254:growth & development / Q000528:radiation effects*; D005514:Food Irradiation; D005516:Food Microbiology; D006801:Humans; D018545:Lactuca / Q000382:microbiology*; D013696:Temperature; D013997:Time Factors; D014965:X-Rays