Reductions of Listeria monocytogenes on cold-smoked and raw salmon fillets by UV-C and pulsed UV light

Askild Holck,Mats Carlehög,Kristian Hovde Liland,Even Heir

doi:10.1016/j.ifset.2018.10.007

Abstract

Abstract Salmon is the food most frequently reported in the RASFF (Rapid Alert System for Food and Feed) database in conjunction with Listeria monocytogenes and consumption of cold-smoked salmon have led to severe outbreaks of listeriosis infections. UV-C and pulsed UV light were investigated for their ability to reduce L. monocytogenes on salmon. Cold-smoked and raw salmon were spiked with a mix of ten L. monocytogenes strains (104 CFU/sample) and subsequently exposed to UV-C light (0.0075–0.6 J/cm2) or high intensity pulsed UV light (1.3–10.8 J/cm2). Reductions of L. monocytogenes on smoked salmon were 0.7–1.3 log, depending on the fluence. Corresponding reductions for raw salmon muscle side and skin side were 0.2–0.9 log and 0.4–1.1 log, respectively. Generally, reductions using UV-C and pulsed UV light were within the same range, but with some treatments statistically different. L. monocytogenes surviving UV treatments on smoked and raw salmon grew at the same rate as controls during storage at 4 °C, but reached the levels of the controls 13 and 7 days later, respectively. No sensory changes were detected in UV-C treated (0.05 J/cm2) smoked salmon. Industrial relevance Due to the lack of critical control points in salmon production, it is not possible to ensure products that are consistently free from L. monocytogenes in the absence of mitigation strategies. Taking into account the reported generally low levels of L. monocytogenes on contaminated salmon, UV treatments should be considered important tools for the industry to contribute to lower prevalence and levels of Listeria. The present work on microbial and quality effects of UV-C and pulsed UV light treatments performed under industry relevant conditions on raw and cold-smoked salmon provides important information to the salmon industry for implementation of UV-light as risk reducing mitigation tools. This has key relevance for industry and consumers and will contribute to enhanced food safety, reduction of costly recalls and longer shelf-life.

Highlights

Listeria monocytogenes is a ubiquitous foodborne pathogen and has been found in a range of foods including milk and dairy products, meat and egg products, seafood, vegetables, and other ready-to-eat (RTE) foods (Farber & Peterkin, 1991)
The 10 strains used included six strains isolated from salmon and salmon processing facilities (Moretro, et al, 2017), three strains associated with human listeriosis and one strain was isolated from cattle
The bacterial reductions after continuous UV-C and pulsed UV light of the fillet surface of cold-smoked salmon were between 0.7 log and 1.3 log, depending on the UV dose (Fig. 1 and Supplemental material Table S1)

Summary

Introduction

Listeria monocytogenes is a ubiquitous foodborne pathogen and has been found in a range of foods including milk and dairy products, meat and egg products, seafood, vegetables, and other ready-to-eat (RTE) foods (Farber & Peterkin, 1991). It can multiply at low temperatures and under high salt conditions. In 2016, 2536 confirmed invasive cases of human listeriosis were reported in the European Union (European Food Safety Authority, 2017). The incidence of listeriosis was 0.47 cases annually per. The EU case fatality rate was 16.2% among the 1524 confirmed cases with known outcome

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Discussion

Conclusion