Antimicrobial Blue Light Reduces Listeria Contamination on a Rainbow Trout Processing Line - Case study presented in Nor-Fishing 2026

Nor-Fishing, Trondheim, Norway 18 August 2026
"Case Study: Effect of antimicrobial blue light (aBL) on Listeria monocytogenes in a fish processing line." Presentation by Karin Henricson, Spectral Blue

Video: Spectral Blue antimicrobial blue light disinfecting a trout sorting line during production

Nor-Fishing is one of the world’s most influential arenas for fisheries and seafood processing innovation, bringing together thousands of industry leaders, technology providers, and decision makers from more than 50 countries. This year (2026), the spotlight turns increasingly toward hygiene control, food safety, and new technologies that can strengthen production reliability across the seafood value chain.

We are proud that Spectral Blue was invited to speak at Nor Fishing 2026. The presentation given by Karin Henricson introduced new data from a rainbow trout processing line, demonstrating how continuous blue light disinfection can reduce Listeria directly on equipment during operation. This is a significant step forward for food processors seeking practical, non-chemical and non-thermal hygiene solutions that support safer production and reduce contamination-related waste.

Case study - presented at Nor-Fishing 2026

Spectral Blue MWHI® multi-wavelength antimicrobial blue light (aBL) was deployed at a high-capacity rainbow trout processing facility located in the Nordics. The target was to improve hygiene at a sorting line where Listeria contamination had been a recurring problem during previous production seasons.

Listeria monocytogenes is a well-known challenge in fish processing. It survives in cold and wet environments, can attach to surfaces and form biofilms, and can be difficult to remove completely with normal cleaning and disinfection.

This case study was originally presented on 18 August 2026 at Nor-Fishing 2026 conference in Trondheim, Norway.

Background - historical Listeria spp. findings 

At a rainbow trout processing facility handling approximately 80-85 tons of fish per day, the sorting line had been identified as a problematic area. During the 2024 production season, at weekly level, 50-100% of the production samples taken from the line were positive for Listeria.

Blue light setup at the sorting line

During the 2025 production season, a Spectral Blue MWHI® antimicrobial blue light system was installed at the sorting line shortly after the processing had started.

The sorting line is set up as follows: The trout first enter the line on an inlet belt and move through a grader to a sorting belt, from where they are directed to different chutes according to size. Six Spectral Blue L100 disinfection devices were installed above the grader and sorting belt. The devices were operated continuously, 24 hours a day, also during production.

Listeria was monitored regularly before and during production. Swab samples were taken from the belt and chute surfaces and analyzed with a Listeria spp. and L. monocytogenes detection kit. On average, ten samples were collected each week during a nine-week test period, resulting in a total of 90 samples during production. All samples taken before the start of production were negative in 2025.

Results show strong impact

Figure: Total positive Listeria samples during production 2024 and 2025. Spectral Blue system was installed during 2025 season and the sampling frequency was increased.

The results during production showed a clear improvement compared with the previous season. The total share of Listeria-positive samples during production decreased from 50% in 2024 to 26% in 2025. This reduction was achieved in demanding conditions, as the belt system remains wet and covered with organic material during operation and transports more than 80 tons of trout per day. As an additional observation, fish surface samples taken by the customer also showed reduced Listeria and total viable counts (TVC).

Conclusions and discussion

The results demonstrate that continuous antimicrobial blue light can strengthen hygiene on a fish processing line during active production. By providing ongoing antimicrobial action between routine cleaning cycles, the system adds a consistent layer of protection that supports safer operations without increasing workload for production personnel.

Before production, blue light and conventional cleaning together brought the line to a clean starting point. During production, Listeria was naturally reintroduced from the trout itself, yet continuous blue light still achieved a clear reduction in recontamination while the line was running. This is a strong and encouraging outcome for a real processing environment.

Although biofilms were not measured in this particular study, previous research has shown that antimicrobial blue light can affect microbes within biofilms and help limit biofilm formation. Combined with the reduction in Listeria positive samples observed here, the findings suggest that continuous antimicrobial blue light can serve as a valuable additional hygiene measure in demanding fish processing settings.

Overall, the case study highlights how continuous blue light disinfection can support stronger hygiene control, reduce contamination pressure during production, and complement existing cleaning routines in a practical and efficient way.

 

More information:
Karin Henricson, SVP/Global Sales Director, Spectral Blue
karin.henricson@ledtailor.fi
+358 44 766 9022

Further reading:

• Spectral Blue application: Eliminating Listeria in food processing
• Nofima case study: Traditional cleaning and disinfection struggle to control Listeria monocytogenes (2026)
• Spectral Blue works effectively against biofilms
• Atria Oyj's QA laboratory tested Spectral Blue against Listeria monocytogenes (read test report / webinar presentation recording in Youtube)
• Spectral Blue webinar - tacking Listeria (2025, recording)