James O. Hearnsberger

Extending shelf life of refrigerated catfish fillets using sodium acetate and monopotassium phosphate

The effects of sodium acetate (SA) and monopotassium phosphate (MKP) on total aerobic plate counts (APC), pH, odor, and appearance of catfish fillets during storage at 4°C were determined. Use of 0.75% and 1.0% SA lowered (P < 0.05) initial APC by 0.6 to 0.7 log units compared to the control. Microbial counts of SA-treated fillets remained lower than the control during storage, resulting in a 6-day shelf-life increase. MKP alone had no effect on APC values, but it did influence the activity of SA. The results indicate that a combination of SA and MKP could prolong the microbiological shelf life of catfish to 12 days at 4°C. Fillets treated with 1% SA alone or SA-MKP combinations had pH values and odor scores that were similar to fresh controls for up to 9 days; however, appearance scores were lower after 3 days, probably due to a brownish and watery appearance. MKP alone is not recommended for shelf-life extension of catfish fillets. Conversely, SA alone or combined with MKP is recommended to extend the microbiological shelf life of refrigerated catfish fillets.

Gram-Negative Bacteria in Refrigerated Catfish Fillets Treated with Lactic Culture and Lactic Acid

Catfish fillets were treated with combinations of lactic culture ( Lactococcus lactis spp. cremoris ATCC 19257) and lactic acid using a meat tumbler. Fillets were placed individually in Ziploc bags and stored at 4 or 10°C. Counts of gram-negative bacteria on crystal violet tetrazolium chloride agar (CVT), the pH, and the sensory quality of fillets were evaluated after 0, 3, 6, and 9 days of storage time. The combination of 2.5% lactic culture and either 2% lactic acid dip (5 min) or 3% lactic acid dip (1 or 5 min) effectively (P < 0.05) inhibited counts for 9 days. The most effective treatment combination was 2.5% lactic culture incubated for 48 h and 3% lactic acid dip. The pH of samples treated with lactic culture and lactic acid ranged from 5.6 to 6.1 for 9 days at 4 or 10°C Lactic culture and lactic acid combinations extended the refrigerated shelf life of catfish for an additional 3 days at 4 and 10°C and reduced CVT counts by two log cycles over untreated fish. The combination of lactic culture and lactic acid were generally preferred for flavor and odor compared to controls after 6 and 9 days of storage, respectively.