Nisin treatment to enhance the efficacy of gamma radiation against Listeria monocytogenes on meat.

Treatment of meat with gamma radiation for inactivation of foodborne pathogens might cause undesirable quality changes in the product. The objective of the present study was to use nisin for enhancing the lethality of gamma radiation against Listeria monocytogenes, so that moderate doses of radiation can effectively eliminate the pathogen on meat. Cubes of raw meat (10 g each) were inoculated with L. monocytogenes (10(7)CFU/g) and treated with nisin (10(3) IU/g), gamma radiation (0.25 to 1.5 kGy), or combinations of these treatments. Meat was analyzed for L. monocytogenes survivors immediately after treatment and during storage at 4 °C for up to 72 h. Nisin treatment alone inactivated L. monocytogenes by 1.2 log CFU/g. Gamma radiation caused dose-dependent inactivation of the pathogen. Treatment with combinations of nisin and gamma radiation resulted in an additive antimicrobial effect when inoculated meat was tested during the first 24 h and in a synergistic effect when tested after 72 h of storage at 4 °C. When L. monocytogenes was inoculated onto meat at low levels (4×10(3) CFU/g), treated with nisin (10(3) IU/g), and then irradiated (1.5 kGy) and stored at 4 °C for 72 h, the pathogen's most probable number was <0.03/g, indicating that such a combination is potentially effective in eliminating L. monocytogenes in meat.