Elimination of Listeria monocytogenes and changes in physical and sensory qualities of a prepared meal following gamma irradiation Original Research Article

The increase in demand for ready-to-eat foods and recent events involving Listeria contamination in such foods have indicated that processes which can enhance product safety are needed. This study was designed to investigate the effects of irradiation on a prepared meal contaminated with a known foodborne pathogen, Listeria monocytogenes. The product consisting of Salisbury steak, gravy and mashed potatoes was contaminated with L. monocytogenes, irradiated at doses of 0·8, 2·9 and 5·7 kGy, and stored at 4°C for 3 weeks.Listeria was not recovered from any sample at any time point, even after selective enrichment, for product treated at 5·7 kGy which represented a greater than a six-log cycle reduction. Treatment with 2·9 kGy reduced the pathogen by over five logs but treatment with 0·8 kGy was not very effective, only reducing counts by approximately one log. In samples where Listeria survived, counts increased during refrigerated storage. Irradiation with 5·7 kGy also effectively eliminated the background aerobic and yeast and mold populations for the duration of the study. Lower doses have less of an effect on these populations. Instrumental measurements of texture and color revealed no effect of irradiation dose. Furthermore, sensory tests revealed that the irradiated meals were no less acceptable than non-irradiated meals. It appears that irradiation at 5·7 kGy is an effective means of improving safety and extending shelf-life without causing adverse effects on quality.