Reduction in Listeria monocytogenes and spoilage bacteria on smoked catfish using X-ray treatments.

Aims: To determine the efficacy of X-ray processes in inactivating L. monocytogenes levels in smoked catfish during storage at 5°C and to determine the effects of X-ray doses on controlling the growth of spoilage bacteria on smoked catfish during storage at 5°C for up to 5 weeks.

Methods And Results: Smoked catfish fillets inoculated with L. monocytogenes were treated with 0.0-2.0 kGy X-ray and stored at 5°C for 5 weeks. The negative controls (uninoculated/untreated) and uninoculated samples treated with the lowest (0.1 kGy) and highest (2.0 kGy) doses were stored at 5°C and tested for psychrotrophs count during the 5 weeks of storage. The initial L. monocytogenes population on smoked catfish was significantly (P < 0.05) reduced to undetectable level by a treatment of 1.0 kGy or higher. The initial psychrotrophs count on smoked catfish was significantly reduced from 4.7 CFU g(-1) to below the detectable level by a treatment with 2.0 kGy.

Conclusions: Smoked catfish treated with 2.0 kGy X-ray had no detectable L. monocytogenes throughout 35 days of storage at 5°C. A treatment with 2.0 kGy X-ray also kept the levels of psychrotrophs in the smoked catfish within the acceptable level until 35 days.

Significance And Impact Of The Study: The results of this investigation indicate that X-ray at 2.0 kGy can eliminate L. monocytogenes and extend the shelf life of smoked catfish stored at refrigeration temperature.