Effects of Irradiation on Survival and Growth of Listeria monocytogenes and Natural Microflora in Vacuum-Packaged Turkey Hams and Breast Rolls

Abstract

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.

Fat Content Influences the Color, Lipid Oxidation, and Volatiles of Irradiated Ground Beef

“…Similar trends were found in ground beef with different aging time (Ismail and others 2008). Zhu and others (2008) showed that irradiating ready‐to‐eat (RTE) turkey hams and breast roll at 2 kGy greatly reduced the number of naturally occurring bacteria during refrigerated storage. The production of aldehydes increased as storage time increased, but the increase was the most significant in irradiated control meats (no additives).…”

Scientific Opinion on the efficacy and microbiological safety of irradiation of food

“…Several studies have shown that if L. monocytogenes were to survive the irradiation treatment, they may be injured initially but can recover and multiply during extended storage (Suvang et al, 2007;Zhu et al, 2008). It tends to be more radiation resistant than other vegetative pathogens, such as Salmonella, and can grow at refrigeration temperatures.…”

“…Some authors noted that if some L. monocytogenes did survive the irradiation treatment (usually as a result of a high initial inoculum), the cells could grow during subsequent chill storage of the cooked meat (Foong et al, 2004;Suvang et al, 2007;Zhu et al, 2008).…”

“…This would be particularly relevant for cooked meats. Several studies have shown that if L. monocytogenes were to survive the irradiation treatment, they may be injured initially but can recover and multiply during extended storage (Suvang et al, 2007;Zhu et al, 2008). As already mentioned, irradiation cannot be seen as a substitute for GMP.…”

Development of simple and rapid procedures for purification of egg yolk immuno-globulin and ovotransferrin from chicken egg and antimicrobial activity of ovo-transferrin against Escherichia coli O157:H7 and Listeria monocytogenes

“…monocytogenes survivors in ovotransferrin plus 0.5% citric acid were low (6.2 log 10 CFU/ml to 6.9 log 10 CFU/ml) in irradiated sample, whereas that of non-irradiated hams was large (6.4 log 10 CFU/ml to 8.2 log 10 CFU/ml) during storage at 4 o C for 4 weeks (Table 4). Zhu et al (2000) reported that during refrigerated storage for 28 days, L. monocytogenes in nonirradiated turkey breast rolls grew, and non-irradiated samples had greater natural microflora population than irradiated samples.…”