Residual Effect of CO₂ on Bacterial Counts and Surface pH of Channel Catfish

Channel catfish fillet strips were packaged under aerobic atmosphere (AIR) and under 90% CO₂, 7.5% N₂, and 2.5% O ₂modified atmosphere packaging (MAP). Half of the samples from the MAP treatment were repacked under aerobic conditions after 6 d storage (COM). Packaged fish were stored at 0 and 10°C for 20 d. Aerobic plate counts reached 8 log CFU/g by the eighth day for AIR packs and by day 20 for COM packs. Fish in MAP or COM held at 0°C did not reach above 8 log CFU/g for 20 d, whereas those at 10°C reached 8 log CFU/g after 4 d. Facultative anaerobic counts were similar in trend to aerobic plate counts but lower in numbers. Fish pH was not affected by temperature but changed slightly over time with treatment. The pH of fish packed in AIR did not change, whereas that of MAP treatment decreased from 6.40 to 6.17 by day 12. Holding channel catfish fillet strips at 0°C under MAP for 6 d and transferring to aerobic conditions for the remainder of storage, will result in 8 d shelf-life extension.