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

Abstract

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.