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United States Department of Agriculture

Agricultural Research Service

Research Project: INTERVENTION TECHNOLOGIES FOR MINIMALLY PROCESSED FOODS

Location: Food Safety and Intervention Technologies

Title: Influence of modified atmosphere and varying time in storage on the irradiation sensitivity of Salmonella on sliced roma tomatoes

Authors
item Niemira, Brendan
item Boyd, Glenn

Submitted to: Journal of Radiation Physics and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 22, 2013
Publication Date: April 30, 2013
Citation: Niemira, B.A., Boyd, G. 2013. Influence of modified atmosphere and varying time in storage on the irradiation sensitivity of Salmonella on sliced roma tomatoes. Journal of Radiation Physics and Chemistry. http://dx.doi.org/10.1016/j.radphyschem.2013.04.021.

Interpretive Summary: Salmonella contamination of tomatoes is a recurrent food safety concern. Irradiation inactivates pathogens on fresh and fresh cut produce. However, the interaction of time in refrigerated storage and modified atmosphere packaging may influence the response of pathogens to irradiation. Roma tomatoes were sliced and inoculated with a cocktail of outbreak strains of Salmonella. The inoculated tomatoes were packaged under air and various reduced-oxygen atmospheres. Before irradiation, the packages were kept in refrigerated storage for 24 or 48 hours after inoculation, to simulate the potential time delay between packaging and irradiation treatment. The surviving populations were recovered and enumerated. Irradiation effectively reduced Salmonella at all times. The dose necessary to reduce Salmonella by 90% varied significantly among the combinations of time and atmospheres. Reduced oxygen generally resulted in higher doses being required, with the highest dose required for tomatoes packaged in pure nitrogen. Time in storage pre-irradiation tended to increase the dose needed for air and 5% oxygen, but not for 10% oxygen or pure nitrogen. These results suggest that time required for refrigerated holding of processed Roma tomatoes or shipment to an off-site irradiation service provider may alter the efficacy of irradiation if reduced oxygen MAP is used.

Technical Abstract: Salmonella contamination of tomatoes is a recurrent food safety concern. Irradiation inactivates pathogens on fresh and fresh cut produce. However, the interaction of time in refrigerated storage and modified atmosphere packaging (MAP) may influence the response of pathogens to irradiation. Roma tomatoes were sliced and inoculated with a cocktail of outbreak strains of Salmonella. The inoculated tomatoes were packaged under one of four atmospheres: air, 10/20 O2/N2, 5/95 O2/N2 or 100% N2. The packages were kept in refrigerated storage (10 deg C) for various times after inoculation, to simulate the potential time delay between packaging and irradiation treatment. Tomatoes were irradiated immediately (0 h), or after 24 or 48 h in storage. The surviving populations were recovered and enumerated. Irradiation effectively reduced Salmonella at all times. D-10 value (the dose necessary for 1 log reduction) varied significantly among the combinations of time and MAP, ranging from 0.165 – 0.335 kGy. Tomatoes packaged in air, irradiated at 0 h, had a D-10 of 0.165 kGy; all other combinations showed significantly higher D-10. Reduced oxygen generally resulted in higher D-10 values, with the highest D-10 of 0.335 kGy obtained for 100% N2, 0 h. Time in storage pre-irradiation tended to increase D-10 for air and 5/95 O2/N2, but not for 10/90 O2/N2 or 100% N2. These results suggest that time required for refrigerated holding of processed Roma tomatoes or shipment to an off-site irradiation service provider may alter the efficacy of irradiation if reduced oxygen MAP is used.

Last Modified: 10/22/2014
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