Bacteriological and Color Changes in Modified Atmosphere-Packaged Refrigerated Channel Catfish

Channel catfish ( Ictalurus punctatus ) fillet strips were packaged under aerobic (AIR), 25% carbon dioxide (CO₂) (LC) and 80% CO₂ (HC) environments with the remainder being air; and stored at 2 and 8°C for 4 weeks. Aerobic plate counts (APC) for HC fish at 2°C declined from 6 log CFU/g to 1.4 log CFU/g after 2 weeks but increased to 5 log CFU/g by the third week. The HC-stored strips at 8°C had an initial increase in APC followed by a decline to 1.4 log CFU/g on the third week, and a rise to 9 log CFU/g by the fourth week. Aerobic plate counts in AIR- and LC-packed fish at either temperature increased steadily throughout storage. Fish surface pH declined in HC-packed product from 6.2 to 5.6 by the fourth week, but did not change in LC and AIR packs. Hunter L-values increased in CO₂-packed products, while Hunter a-values decreased. Listeria monocytogenes was isolated from fish under LC and AIR at 8°C in the second and third weeks. Salmonella spp. was present in fish stored in all storage atmospheres at 8°C, but only in AIR-packed fish at 2°C. Clostridium botulinum was not found in product at any of the storage atmospheres at either temperature at any time. The best treatment was fish packed in HC and stored at 2°C.