Behavior of Salmonella and Listeria monocytogenes in Raw Yellowfin Tuna during Cold Storage

Behavior of Salmonella and Listeria monocytogenes in raw yellowfin tuna during refrigeration and frozen storage were studied. Growth of Salmonella was inhibited in tuna during refrigerated storage, while L. monocytogenes was able to multiply significantly during refrigerated storage. Populations of Salmonella in tuna were reduced by 1 to 2 log after 12 days of storage at 5-7 °C, regardless levels of contamination. However, populations of L. monocytogenes Scott A, M0507, and SFL0404 in inoculated tuna (10⁴-10⁵ CFU/g) increased by 3.31, 3.56, and 3.98 log CFU/g, respectively, after 12 days of storage at 5-7 °C. Similar increases of L. monocytogenes cells were observed in tuna meat with a lower inoculation level (10²-10³ CFU/g). Populations of Salmonella and L. monocytogenes declined gradually in tuna samples over 84 days (12 weeks) of frozen storage at -18 °C with Salmonella Newport 6962 being decreased to undetectable level (<10 CFU/g) from an initial level of 10³ log CFU/g after 42 days of frozen storage. These results demonstrate that tuna meat intended for raw consumption must be handled properly from farm to table to reduce the risks of foodborne illness caused by Salmonella and L. monocytogenes.