Microbial safety and quality of refrigerated trout using modified atmosphere packaging

Fresh rainbow trout (Oncorhynchus mykiss) fillets were evaluated for microbial safety and an overall quality during storage at 3°C and 10°C. Trout fillets were packaged in a high barrier film in the following atmospheres: air, vacuum, 100% carbon dioxide, 60/40 carbon dioxide/nitrogen, and 10/85/5 carbon dioxide/nitrogen/oxygen. Trout packaged in a modified atmosphere that did not contain oxygen had lower microbial numbers at 3°C and lO'C. Fillets were considered spoiled when the aerobic plate count reached log 8 CFU/g (spoilage reference point). At 10°C, the quality of the rainbow trout began to deteriorate and show signs of spoilage (off odors) after 2 days for fillets packaged in air, vacuum, and 10/85/5 (carbon dioxide/nitrogen/oxygen). At 3°C, the packaged fillets showed signs of spoilage after 7 days for trout packaged in air and 10/85/5 (carbon dioxide/nitrogen/oxygen) and after 10 days for vacuum packaged trout. Fillets packaged in 60/40 (carbon dioxide/nitrogen) and 100% CO₂ showed signs of spoilage after day 14 of storage at 3°C. No evidence of Salmonella spp. or Listeria spp. was detected during storage of trout at 3°C or at 10°C on the fillets in the different atmospheres. The results obtained in this study demonstrated that a high concentration of CO₂ can extend the shelf life of rainbow trout for at least one week at 3°C by inhibiting the growth of spoilage microorganisms.