• engineering;
  • food irradiation;
  • food safety;
  • fruits and vegetables

Abstract:  This study evaluated the effect of produce type, resuspension medium, dose uniformity ratio (DUR), and sample preparation conditions (tissue exposure, MAP, anoxia) on the D10-value of an Escherichia coli cocktail (BAA-1427, BAA-1428, and BAA-1430) and Salmonella Typhimurium LT2 inoculated on the surfaces of tomato, cantaloupe, romaine lettuce, and baby spinach. Produce at room temperature were irradiated using a 1.35 MeV Van de Graaf electron beam accelerator at 0.2 to 0.9 kGy. The D10-values for E. coli and Salmonella were 0.20 ± 0.01 kGy and 0.14 ± 0.01 kGy, respectively. Bacterial inactivation was not affected by produce type as long as the samples were irradiated in unsealed bags, the bacteria were suspended in broth, and the sample tissue was exposed. Sample location in front of the e-beam source during exposure is crucial. A 20% increase in DUR yielded a 53% change in the D10-values. Variations in sample preparation, microbiological methods and irradiation set-up, result in variable D10-values for different microorganisms on fresh produce.

Practical Applications:  Most irradiation studies disregard the effect of sample handling and processing parameters on the determination of the D10-value of different microorganisms in fresh and fresh-cut produce. This study shows the importance of exposure of sample, resuspension medium, available oxygen, and dose uniformity ratio. D10-values can differ by 35% to 53% based on these factors, leading to considerable under- or over-estimation of the irradiation treatment. Results from this study will help to lay firm groundwork for future studies on D10-values determination for different pathogens on fruits and vegetables.