Reduction of normal flora by irradiation and its effect on the ability of Listeria monocytogenes to multiply on ground turkey stored at PC when packaged under a modified atmosphere

Listeria monocytogenes did not multiply faster during storage at 7 degreesC on irradiated than on nonirradiated raw ground turkey, and there was a con centration-dependent inhibition of its multiplication by CO2. Ground turkey was gamma irradiated at 5 degreesC to 0, 1.5, and 2.5 kGy and inoculated ( similar to 100 CFU/g) after irradiation with a cocktail of L. monocytogenes ATCC 7644, 15313, 49594, and 43256. The meat was then packaged in air-perm eable pouches or under atmospheres containing 30 or 53% CO2, 19% O-2, and 5 1 or 24% N-2 and stored at 7 degreesC for up to 28 days. A dose of 2.5 kGy extended the time for the total plate count (TPC) to reach 10(7) CFU/g from 4 to 19 days compared to that for nonirradiated turkey in air-permeable po uches. Following a dose of 2.5 kGy at the end of the 28-day study, the TPCs were 10(6.42) and 10(4.98) under 25% and 50% CO2 atmospheres, respectively . Under air, 30% CO2, and 53% CO2 atmospheres, the populations of L. monocy togenes after 19 days incubation were 10(4.89), 10(3.60), and 10(2.67) CFU/ g. The populations of lactic acid bacteria and anaerobic or facultative bac teria were also reduced by irradiation. Irradiating ground turkey did not d ecrease its safety when it was contaminated following processing with L. mo nocytogenes.