Inactivation of Listeria innocua in Nisin-Treated Salmon (Oncorhynchus keta) and Sturgeon (Acipenser transmontanus) Caviar Heated by Radio Frequency
Recent regulatory concerns about the presence of the pathogen Listeria monocytogenes in ready-to-eat aquatic foods such as caviar has prompted the development of postpackaging pasteurization processes. However, caviar is heat labile, and conventional pasteurization processes
affect the texture, color, and flavor of these foods negatively. In this study, chum salmon (Oncorhynchus keta, 2.5% total salt) caviar or ikura and sturgeon (Acipenser transmontanus, 3.5% total salt) caviar were inoculated with three strains of Listeria innocua in stationary
phase at a level of more than 107 CFU/g. L. innocua strains were used because they exhibit an equivalent response to L. monocytogenes for many physicochemical processing treatments, including heat treatment. The products were treated by immersion in 500 IU/ml nisin
solution and heat processed (an 8-D process without nisin or a 4-D process with 500 IU/ml nisin) in a newly developed radio frequency (RF; 27 MHz) heating method at 60, 63, and 65°C. RF heating along with nisin acted synergistically to inactivate L. innocua cells and total mesophilic
microorganisms. In the RF–nisin treatment at 65°C, no surviving L. innocua microbes were recovered in sturgeon caviar or ikura. The come-up times in the RF-heated product were significantly lower compared with the water bath–heated caviar at all treatment temperatures.
The visual quality of the caviar products treated by RF with or without nisin was comparable to the untreated control.
Document Type: Research Article
Department of Clinical Nutrition and Dietetics, Faculty of Allied Health Sciences, Hashemite University, Zarqa-Jordan
Department of Food Science and Human Nutrition, Box 646376, Washington State University, Pullman, Washington 99164-6376, USA
Publication date: September 1, 2004
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