Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

Wanda J. Lyon


Fresh catfish (Ictalurus punctatus) fillets (CF) can serve as vehicles for spoilage and pathogenic bacteria. Concern for the microbiological safety of chilled CF has grown lately because psychrotrophic pathogens can survive and grow at refrigeration temperatures. The Grovac method, a new, patented (U.S. 5,543,163) process is being used in an attempt to reduce the growth of pathogens and spoilage microorganisms in CF. This process involves the using of a process solution of ascorbic acid (AA) and sodium chloride (NaCl), vacuum and tumbling. Specific objectives of this study included the isolation and identification of endogenous microflora associated with fresh whole catfish (WC) and CF; and the evaluation of the Grovac process for reducing microbial populations on CF. A total of fifty-one bacterial isolates were isolated and identified from WC and CF using selective and nonselective media, phenotypic tests, and the Vitek(TM) System (bioMerieux). Psychrotrophic foodborne pathogens included: Aeromonas hydrophila, Escherichia coli, Listeria sp., Plesiomonas shigelloides, Proteus sp., Staphylococcus aureus, and Vibrio parahaemolyticus. High APC (2.6 x 10 7 CFU/g) and E. coli (3.2 x 103 CFU/g) counts for CF indicated that fillets were heavily contaminated during processing of catfish. The Grovac process showed that treatment combinations of AA (0.4, 0.8 and 1.2%) and NaCl (0.2, 0.4 and 0.6%) under the following experimental conditions (400 g of catfish fillets, 2,000 ml process solution, 28 in. Hg vacuum, 8 rpm tumbler rotation, and 8 min tumbling time) resulted in a 1.2 to 2.3 CFU/g log reduction of microbial counts in CF. The effectiveness of the process may be related to the synergistic effect of tumbling, AA, NaCl and vacuum. In addition, A. hydrophila grew in CF treated with the Grovac process and aerobically stored at 4°C for 7 days. The results suggested that the Grovac process could be used as an alternative processing procedure to reduce microbial populations on CF and be useful to improve the shelf-life and food safety of the product. Microbiological data from this study will be used for the development of a hazard analysis for the implementation of the Hazard Analysis Critical Control Point (HACCP) program for processed CF.