Microbiological Analysis of Rock Cod ( Sebastes spp.) Stored Under Elevated Carbon Dioxide Atmospheres

Abstract

The numbers and types of microorganisms on fresh rock cod fillets and fillets stored in air or in a modified atmosphere (MA; 80% CO₂, 20% air) at 4°C were compared. Samples were analyzed after 0, 7, 14, and 21 days of storage. The isolation plates were incubated aerobically, anaerobically, or under MA at 4, 20, or 35°C. After 7 days of storage in air, the fillets were obviously spoiled and had a 3- to 4-log cycle increase in microbial counts. Plate counts increased more slowly on MA-stored fillets. After 21 days, the counts on the latter had increased only 2 log cycles, and the fillets did not seem spoiled. The microbial flora changed greatly during MA storage. Only Lactobacillus spp. (70%) and an Aeromonas sp.-like isolate (30%) were found on plates incubated aerobically at 4 and 20°C, and only Lactobacillus spp. was found on plates incubated aerobically and anaerobically at 35 and at 20°C under MA. Isolation plates incubated at 20°C in air gave the highest counts in the shortest incubation time and the greatest diversity of bacterial types recovered. No Vibrio parahaemolyticus, Staphylococcus aureus, or Clostridium botulinum type E were isolated from the fresh or MA-stored fillets.