Effects of irradiation on survival and growth of Listeria monocytogenes and natural microflora in vacuum-packaged turkey hams and breast rolls.

The effect of electron beam irradiation on the survival and growth of Listeria monocytogenes and natural microflora in oven-roasted turkey breast rolls and turkey hams was evaluated. Slices of turkey breast rolls and hams were inoculated with a 5-strain mixture of L. monocytogenes to achieve 10(6) to 10(7) cfu/cm2; vacuum-packaged; irradiated at 0 (control), 1.0, 1.5, 2.0, or 2.5 kGy; and stored at 4 degrees C for up to 28 d. Numbers of naturally occurring bacteria on sliced turkey hams and breast rolls were 2.72 and 6.22 log10 cfu/cm2, respectively. The values of the radiation dose that results in 90% reduction of viable L. monocytogenes in breast rolls and hams were 0.52 and 0.47 kGy, respectively. For breast rolls, the log10 reductions of L. monocytogenes after irradiation at 1.0 and 2.5 kGy were 1.5 and 4.7, respectively, whereas they were 2.0 and 5.5 for hams. The log10 reductions of aerobic plate count (APC) in breast rolls after 1.0 and 2.0 kGy of irradiation were 2.9 and 5.2, whereas that of hams was < 10 cfu/cm2 after 1.0 and 2.0 kGy of irradiation. In 2.0-kGy irradiated hams, L. monocytogenes grew to 4.82 log10 cfu/cm2 after 28 d of storage at 4 degrees C, whereas APC increased to 2.98 log10 cfu/cm2, respectively. In breast rolls after 14 d of storage, APC in 1.0-kGy irradiated samples increased to 7.53 log10 cfu/cm2, and APC increased to 2.63 and 4.68 log10 cfu/cm2 for 2.0-kGy irradiated breast rolls after 14 and 28 d of storage. However, during the storage of breast rolls, L. monocytogenes grew slowly or even stopped to grow in both nonirradiated and irradiated breast rolls due to the competitive inhibition of natural flora in breast rolls. This study showed that irradiation (1.0 to 2.5 kGy) effectively reduced the number of L. monocytogenes and natural flora. However, L. monocytogenes and natural flora that survived irradiation could multiply during the 28-d storage period at 4 degrees C. Thus, additional hurdles are needed to ensure the microbial safety after low-dose irradiation.