Safe Seaweed Processing/Handling Infographic

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Below are the main findings from peer reviewed literature in support of the claims made on our infographic. The outline below is not representative of all relevant peer reviewed literature available on seaweed food safety but is a curated selection. Please use these references as a jumping off point for more in-depth exploration.

Harvest

Fresh Kelp

  • Low levels of enterohemorrhagic Escherichia coli O157:H7, Vibrio parahaemolyticus, Vibrio alginolyticus and Salmonella enterica ser. Typhimurium were isolated from the surface of freshly harvested sugar kelp off the coast of southern Maine.
    • Barberi, O. N., Byron, C. J., Burkholder, K. M., St. Gelais, A. T., & Williams, A. K. (2020). Assessment of bacterial pathogens on edible macroalgae in coastal waters. Journal of Applied Phycology, 32(1), 683–696. https://doi.org/10.1007/s10811-019-01993-5
  • In Long Island Sound, NY, no human pathogens were identified on sugar kelp. Some non-pathogenic Vibrio spp. were recovered at the end of the harvest season in May, but only on the old blade tips.
    • Liu, Y., Wikfors, G. H., Clark, P., Pitchford, S., Krisak, M., Dixon, M. S., & Li, Y. (2022). A deep dive into the epibiotic communities on aquacultured sugar kelp Saccharina latissima in Southern New England. Algal Research, 63, 102654. https://doi.org/10.1016/j.algal.2022.102654
  • Raw S. latissima and A. esculenta was found to have microbial loads of 10 – 1000 cells per gram. Food pathogen of concern Bacillus spp. was isolated, however no enterococci, coliforms, pathogenic vibrios or L. monocytogenes were detected.
    • Microbiology under Results and Discussion – Blikra, M. J., Løvdal, T., Vaka, M. R., Roiha, I. S., Lunestad, B. T., Lindseth, C., & Skipnes, D. (2019). Assessment of food quality and microbial safety of brown macroalgae (Alaria esculenta and Saccharina latissima). Journal of the Science of Food and Agriculture, 99(3), 1198–1206.

Processing

Blanching

  • One study found that blanched sugar kelp had lower aerobic microbial load compared to raw kelp. Regarding food pathogens of concern, none were isolated from raw kelp samples, so an inoculation study is necessary to truly validate the effects of blanching on seaweed food safety.
    • Table 4 – Akomea-Frempong, S., Skonberg, D. I., Camire, M. E., & Perry, J. J. (2021). Impact of Blanching, Freezing, and Fermentation on Physicochemical, Microbial, and Sensory Quality of Sugar Kelp (Saccharina latissima). Foods, 10(10), 2258. https://doi.org/10.3390/foods10102258

Drying

  • Air- and freeze-drying seaweed is an effective means to significantly reduce the pathogen load on the surface of S. latissima and A. nodosum
    • Oral presentation – Vorse, J.G., K. Burkholder, C. Byron, C. Moody, L. Massoia. The effect of storage temperature and drying method on the pathogen load of edible seaweed. Northeast Aquaculture Conference and Exposition, April 2022
  • Seaweed’s most prevalent food pathogens of concern can survive at a minimum water activity level of 0.83 – 0.97 so the water activity level of current dried commercial shelf stable products (0.3 – 0.65) should be effective at controlling pathogens of concern.
    • Table 2 – Løvdal, T., Lunestad, B. T., Myrmel, M., Rosnes, J. T., & Skipnes, D. (2021). Microbiological Food Safety of Seaweeds. Foods, 10(11), 2719. https://doi.org/10.3390/foods10112719

Salting

  • After 30 days of preservation, kelp (unspecified brown algae from China) with 10%, 20% and 30% salt concentrations were undamaged when stored at 4˚C (refrigeration). Kelp preserved with a 30% salt concentration was also undamaged after 30 days at 25˚C (room temperature) however, kelp preserved at 10% and 20% salt concentrations showed significant deterioration after 30 days at 25˚C. Before salt preservation kelp was processed under a UV light undergoing a sterile water rinse, blanching, and then draining.
    • Wei, W., Zhang, X., Hou, Z., Hu, X., Wang, Y., Wang, C., Yang, S., Cui, H., & Zhu, L. (2021). Microbial Regulation of Deterioration and Preservation of Salted Kelp under Different Temperature and Salinity Conditions. Foods (Basel, Switzerland), 10(8), 1723. https://doi.org/10.3390/foods10081723

Fermenting

  • A pH of 6.1 – 6.4 was found for both raw and cooked S. latissima and A. esculenta. This natural pH is not low enough to control major pathogens of concern.
    • pH under Results and Discussion – Blikra, M. J., Løvdal, T., Vaka, M. R., Roiha, I. S., Lunestad, B. T., Lindseth, C., & Skipnes, D. (2019). Assessment of food quality and microbial safety of brown macroalgae (Alaria esculenta and Saccharina latissima). Journal of the Science of Food and Agriculture, 99(3), 1198–1206. https://doi.org/10.1002/jsfa.9289
  • In optimal conditions the most prevalent food pathogens of concern for seaweed can survive pH ranges from 3.7- 6 (min) to 7.2 – 11 (max). These ranges are broad which is why further heat processing or temperature control is required for fermented products.
    • Table 2 – Løvdal, T., Lunestad, B. T., Myrmel, M., Rosnes, J. T., & Skipnes, D. (2021). Microbiological Food Safety of Seaweeds. Foods, 10(11), 2719. https://doi.org/10.3390/foods10112719
  • One study found that fermentation did not have a significant effect on aerobic microbial load of sugar kelp, however initial microbial load of raw kelp was noticeably low to begin with. This same study did find one presumptive Vibrio spp. on raw kelp that was then undetectable after fermentation. Due to the naturally low microbial activity and contamination frequency on fresh sugar kelp an inoculation study is needed to further validate the effects of fermentation.
    • Table 4 – Akomea-Frempong, S., Skonberg, D. I., Camire, M. E., & Perry, J. J. (2021). Impact of Blanching, Freezing, and Fermentation on Physicochemical, Microbial, and Sensory Quality of Sugar Kelp (Saccharina latissima). Foods, 10(10), 2258. https://doi.org/10.3390/foods10102258

Storage

Refrigeration

  • Seaweed’s most prevalent food pathogens of concern are known to grow at temperatures that range from -0.4 – 15˚C (min) to 40 -55.7˚C (max) and can survive without replication at even wider ranges. To limit pathogen replication, seaweed products without acceptably low water activity levels should be stored at or below 4˚C.
    • Table 2 – Løvdal, T., Lunestad, B. T., Myrmel, M., Rosnes, J. T., & Skipnes, D. (2021). Microbiological Food Safety of Seaweeds. Foods, 10(11), 2719. https://doi.org/10.3390/foods10112719
  • Refrigeration is an effective means stop pathogen replication on S. latissima and A. nodosum‘s surface
    • Oral presentation – Vorse, J.G., K. Burkholder, C. Byron, C. Moody, L. Massoia. The effect of storage temperature and drying method on the pathogen load of edible seaweed. Northeast Aquaculture Conference and Exposition, April 2022

Freezing

  • Freezing has not been found to influence the aerobic microbial load on sugar kelp
    • Table 4 – Akomea-Frempong, S., Skonberg, D. I., Camire, M. E., & Perry, J. J. (2021). Impact of Blanching, Freezing, and Fermentation on Physicochemical, Microbial, and Sensory Quality of Sugar Kelp (Saccharina latissima). Foods, 10(10), 2258. https://doi.org/10.3390/foods10102258

Shelf-stable

  • Air- or freeze-dried S. latissima and A. nodosum, vacuum sealed and stored at room temperature for 6-weeks, showed reduced pathogen load when compared to S. latissima and A. nodosum immediately post-dry
    • Oral presentation – Vorse, J.G., K. Burkholder, C. Byron, C. Moody. The effect of storage temperature and drying method on the pathogen load of edible seaweed. Northeast Aquaculture Conference and Exposition, April 2022