Potential antimicrobials to control Listeria monocytogenes in vacuum-packaged cold-smoked salmon pâté and fillets

Abstract

In the wake of recent outbreaks associated with Listeria monocytogenes in ready-to-eat foods and an increasing desire for minimally processed foods, there has been a burgeoning interest in the use of natural antimicrobials by the food industry to control this pathogen. The minimum inhibitory concentrations (MICs) of nisin and salts of organic acids (sodium lactate (SL), sodium diacetate (SD), sodium benzoate (SB), and potassium sorbate (PS)) against twelve strains of L. monocytogenes in a TSBYE broth medium at 35 degrees C were determined. The MICs were strain-dependent and fell in the range of 0.00048-0.00190% for nisin, 4.60-5.60% for SL, 0.11-0.22% for SD, 0.25-0.50% for SB and 0.38-0.75% for PS, respectively. The two most antimicrobial-resistant strains were used as a cocktail in the following experiments to represent a worst case scenario. The five antimicrobials alone and in binary combinations were screened for their efficacy against the two-strain cocktail in TSBYE at sub-MIC and sub-legal levels at 35 degrees C. Seven effective antimicrobial treatments were then selected and evaluated for their long-term antilisterial effectiveness in cold-smoked salmon pâté and fillets during refrigerated storage (4 degrees C) of 3 and 6 weeks, respectively. The two most effective antimicrobial formulations for smoked salmon pâté, 0.25% SD and 2.4% SL/0.125% SD, were able to inhibit the growth of L. monocytogenes during the 3 weeks of storage. Surface application of 2.4% SL/0.125% SD was the most effective treatment for smoked salmon fillets which inhibited the growth of L. monocytogenes for 4 weeks. These antimicrobial treatments could be used by the smoked salmon industry in the U.S. and Europe in their efforts to control L. monocytogenes as they are effective against even the most antimicrobial-resistant strains tested in this study.