Prior frozen storage enhances the effect of edible coatings against Listeria monocytogenes on cold-smoked salmon during subsequent refrigerated storage

Aims: Listeria monocytogenes is a major safety concern for ready-to-eat foods. The overall objective of this study was to investigate whether prior frozen storage could enhance the efficacy of edible coatings against L. monocytogenes on cold-smoked salmon during subsequent refrigerated storage. Methods and Results: A formulation consisting of sodium lactate (SL, 1.2-2.4%) and sodium diacetate (SD, 0.125-0.25%) or 2.5% Opti.Form (a commercial formulation of SL and SD) was incorporated into each of five edible coatings: alginate, kappa-carrageenan, pectin, gelatin and starch. The coatings were applied onto the surface of cold-smoked salmon slices inoculated with L. monocytogenes at a level of 500 CFU cm(-2). In the first phase, the slices were first frozen at -18 degrees C for 6 days and stored at 22 degrees C for 6 days. Alginate, gelatin and starch appeared to be the most effective carriers. In the second phase, cold-smoked salmon slices were inoculated with L. monocytogenes, coated with alginate, gelatin or starch with or without the antimicrobials and stored frozen at -18 degrees C for 12 months. Every 2 months, samples were removed from the freezer and kept at 4 degrees C for 30 days. Prior frozen storage at -18 degrees C substantially enhanced the antilisterial efficacy of the edible coatings with or without antimicrobials during the subsequent refrigerated storage. Conclusions: Plain coatings with >= 2 months frozen storage and antimicrobial edible coatings represent an effective intervention to inhibit the growth of L. monocytogenes on cold-smoked salmon. Significance and Impact of the Study: This study demonstrates the effectiveness of the conjunct application of frozen storage and edible coatings to control the growth of L. monocytogenes to enhance the microbiological safety of cold-smoked salmon.