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 degrees C for 4 weeks. Aerobic plate counts (APC) for HC fish at 2 degrees 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 degrees 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 degrees C in the second and third weeks. Salmonella spp. was present in fish stored in all storage atmospheres at 8 degrees C, but only in AIR-packed fish at 2 degrees 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 degrees C.