This case study highlights how Spectral Blue MWHI® blue light disinfection was used to eliminate persistent Listeria monocytogenes contamination at a ready-to-eat sushi production facility in Central Europe. The results were presented as a poster at the IAFP European Symposium on Food Safety, held in Madrid on 7 May 2025.
Background
- Listeria monocytogenes is a critical food safety concern in ready-to-eat (RTE) sushi production.
- Standard hygiene protocols and chemical disinfectants could not fully control L. monocytogenes contamination in a Central European sushi production site.
- Persistent L. monocytogenes hotspots were found near a 8-meter long packaging conveyor line where meal ingredients were handled.
- At the problem area, the share of positive L. monocytogenes samples ranged from 10% to 47% in environmental swabs (Jan–Sep 2024).
- Operators’ shoes likely contributed to bacterial spread in the area.
Objective of The Case Study
To evaluate the effectiveness of Spectral Blue MWHI® antimicrobial blue light (aBL) in reducing L. monocytogenes contamination in an operational sushi production environment.
Karin Henricson giving the poster presentation at IAFP Madrid European Symposium 2025
Photo of the production line with Spectral Blue devices installed (at stage 2)
Materials & Methods
Location: Central European sushi production site making RTE meals.
Test area: Conveyor line used for manual packaging of sushi into plastic containers.
Disinfection system:
- Spectral Blue L200 devices (200 W, multi-wavelength 405 nm + 450 nm blue light).
- Daily exposure: ~14 hours during non-production time, ~26 J/cm² per day at floor level.
Sampling protocol:
- 4 sites on the floor near the conveyor line: Initially 2 sites treated with blue light and 2 untreated “dark” controls.
- Swabs collected during production, 2–5 times per week over 32 weeks.
- Analyzed using a rapid Listeria monocytogenes test.
Installation timeline:
- Jul 2024: Stage 1 - Sampling frequency increased, no blue light.
- Oct 2024: Stage 2 - Two blue light devices installed above one end of conveyor line.
- Mid-Jan 2025: Stage 3 - Additional two devices installed above conveyor line.
Illustration of the production line, sampling sites and device placements in stages 2 and 3. Sampling sites are marked with red squares in these pictures.
Results & Conclusions
Graph: Percentage of positive findings before and after installing the Spectral Blue system (n=530 samples)
Stage 1 (no blue light, n = 128):
- 22% of samples were L. monocytogenes-positive.
Stage 2 (two devices, partial coverage, n = 218):
- Significant reduction in L. monocytogenes-positive samples.
- Positive findings still observed at untreated sites (dark).
Stage 3 (four devices, full coverage, n = 184):
- Several L. monocytogenes -free weeks across all sampling sites.
- Monthly positive detection rate dropped to 2–4%.
- Weekly data demonstrated a sustained decrease in positive findings (available below under 'Related downloads').
Conclusions
Spectral Blue MWHI® antimicrobial blue light proved highly effective in reducing the presence of L. monocytogenes in the test area. This case study highlights the innovative technology’s potential as a valuable tool for enhanced hygiene management within the food industry.
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Acknowledgements:
We wish to thank the customer and partner involved in carrying out this exceptional test and for making the data available to help other food manufacturing companies around the world to combat Listeria monocytogenes contamination in their facilities. We also thank the IAFP organization for the opportunity to present the results at their European Symposium in Madrid.
Related downloads:
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Poster (pdf)
Henricson, Autio, Schmidt, Saukkonen. Automatic Disinfection of Listeria monocytogenes on a Sushi Production Line Using Multi-Wavelength High-Intensity (MWHI) Blue Light. IAFP European Symposium on Food Safety. May 7 2025. -
Handout - weekly data (pdf)
More information:
Karin Henricson, SVP & Global Sales Director, LED Tailor
karin.henricson@ledtailor.fi
+358 44 766 9022
Also see Spectral Blue solutions for the food industry.