Evaluation of Impedance Microbiology for Rapid Assessment of Shelf-Life and Quality of Processed Channel Catfish, Ictalurus punctatus

Abstract

Total bacterial numbers on freshly processed channel catfish, "Ictalurus punctatus," fillets were determined and correlated with shelf-life. In addition, the Bactometer Microbial Monitoring System (bioMérieux-Vitek, Hazelwood, Missouri), an automated instrument using the principles of impedance microbiology, was evaluated as a rapid method to determine microorganism numbers on fillets. Freshly processed channel catfish fillets were collected from two commercial farms from May, 1991 to January, 1992. After using the rinse bag method to isolate bacteria from samples, the microorganisms in the rinsate were enumerated on plates by means of serial dilutions and the spread plate method. The total number of colony-forming units per gram (cfu/g) of channel catfish fillet was then correlated with the capacitence detection time in the bactometer. Fillets collected in May and June typically contained 2.0 to 2.5 x 10⁴ cfu/g, and the bactometer detection time varied from 4.3 to 5.1 hours. The microbial quality of freshly processed fillets decreased in July and August, and 1.3 to 2.4 x 10⁵ cfu/g were isolated with a bactometer detection time that varied from 3.4 to 4.4 hours. Shelf-life was examined in July and August and again for December and January samples and ranged from 6-8 days for the different lots. Fillets that exceeded shelf-life contained over 10⁷ cfu/g. The Bactometer Microbial Monitorial System provided a rapid estimation of microorganism numbers on processed channel catfish fillets. Product with a detect time of 3.8 hours or less (i.e., more than 2.5 x 10⁵ cfu/g) did not have a shelf-life greater than 6 days when maintained at a refrigeration temperature of 1.7°C.