Bioprotection of cold-smoked rainbow trout against Listeria monocytogenes biofilm

Abstract

Listeria monocytogenes is a resilient foodborne pathogen that forms biofilms, allowing it to persist and thrive in food-processing environments. This study examined the structural characteristics of biofilms formed by three L. monocytogenes strains, their transfer to cold-smoked rainbow trout fillets, and the bioprotective effects of two lactic acid bacteria (LAB) cocktails during storage. Confocal microscopy revealed that mixed-strain biofilms exhibited more homogeneous structures than single-strain biofilms, emphasizing their relevance in contamination events. Transfer experiments demonstrated that 87.52 % of L. monocytogenes biofilm cells were transferred from stainless steel to cold-smoked rainbow trout fillets after 90 s of contact, highlighting a significant contamination risk. The commercial LAB cocktail containing Lactococcus lactis subsp. Lactis and Leuconostoc carnosum effectively inhibited L. monocytogenes growth under both static (5 °C) and dynamic (4–20 °C) conditions, reducing bacterial concentrations by > 0.70 and > 1.24 log CFU/g respectively, after 21 days. The inhibitory effect was likely driven by bacteriocin production, particularly leucocin, potentially enhanced by diacetyl production. LAB-based bioprotection effectively controlled L. monocytogenes without producing significant changes in pH or water activity. These findings highlight the need for multi-strain biofilm models to better understand contamination dynamics and support LAB-based bioprotection as a natural, effective strategy for improving food safety in smoked fish products.