Radiation D10 values for Salmonella Typhimurium LT2 and an Escherichia coli cocktail in pecan nuts (Kanza cultivar) exposed to different atmospheres

- Irradiation set-up affects the uniformity of dose absorbed in raw pecans.
- Pecan shape affects dose uniformity and consequently the D10-values for specific microorganisms.
- This information is critical since most studies do not address the effect of product shape or e-beam set-up.
- MAP and e-beam combinations offer an alternative to decontaminate nuts while maintaining their quality.

Electron beam irradiation can help prevent outbreaks due to consumption of raw nuts. However, their high-fat content makes irradiation difficult and methods to reduce the dose required for decontamination (D10-value) are needed; in addition, accurate D10-values are currently lacking. Our objectives were (1) to determine the effect of irradiation set-up on the D10-values of the populations of an Escherichia coli cocktail (BAA-1427, BAA-1428, BAA-1430) and Salmonella Typhimurium LT2 inoculated in pecans and (2) to assess the effect of Modified Atmosphere Packaging (MAP) conditions on the D10-values.Pecan halves [Carya illinoinensis (Wangenh.) K. Koch cv. Kanza] were inoculated either in the dorsal grooves or on their flat surface and irradiated at room temperature using a 1.35-MeV e-beam accelerator at 0.2, 0.4, 0.6, and 0.8 kGy under vacuum-packaging (VP), air-packaging (AP), 100% nitrogen-packaging (NP), and 100% oxygen-packaging (OP). There were no (P > 0.05) differences in D10-values between the microorganisms under the different atmospheres. The D10-values obtained when pecans were irradiated under vacuum were higher (P < 0.05) for both microorganisms. Irradiation under nitrogen atmosphere seems a promising alternative because it will help delay the onset of rancidity, when compared to irradiation under atmospheric or 100%-oxygen conditions. The D10-values obtained when the microorganisms were inoculated on the pecans' flat surface were 44-13% higher than when inoculated within the dorsal grooves, because the grooves absorbed higher doses. This finding illustrates the importance of proper irradiation set-up when treating raw, unshelled pecans, for accurate calculation of the D10-values of selected microorganisms.