Seaweed: Do we know enough?

With the passing November being World Vegan Month, it seems fitting to train the spotlight on popular vegan-friendly foodstuffs – such as seaweed.

But are we seeing seaweed’s true colours?

Introduction: Seaweed and potential food safety hazards

Due to an enhanced focus on sustainability, a fast-growing world population, and the current challenges regarding animal protein sources, there is high demand for nutritious plant-based food products. Seaweed could potentially help to meet consumer demand and overcome these challenges.

Seaweed, also known as macroalgae, consists of several species of macroscopic multicellular marine algae. Based on the pigmentation of individual species, seaweed can be classified broadly into three main groups: red algae (Rhodophyta), brown algae (Phaeophyceae) and green algae (Chlorophyta).

Seaweed is versatile, with many applications in several industries, including food and feed. A recently published study that focused on food safety hazards in the European seaweed chain stated that in the Western world, the data available on the safety of seaweed for these purposes are scattered. Profiling is required for chemical, physical, and microbiological hazards in seaweed.

Some of the known hazards include (but are not limited to) heavy metals, Iodine, pesticide residues, pathogens, micro- and nano-plastics, marine biotoxins and allergens.

Seaweed as a food source: nori

Nori (dried seaweed) is made from the red algae genus Pyropia, and is generally available in ready-to-use sheets. It is reported that in Japan, approximately nine billion sheets are produced annually, and are consumed in sushi, soups and salads. Nori is known to be rich in various nutrients,  including minerals (calcium and iron), vitamins (vitamins A and C), and fibre; which contributes to its growing popularity in many countries.

Allergen hazards associated with nori

The allergen risk associated with seaweed may be underestimated. For example, it is unknown whether a significant number of consumers could be directly allergic to seaweed. Additionally, the presence of other allergens – shellfish and fish, for example – has not been studied to any extent.

Allergen contamination may occur at various steps in the food supply chain, including during cultivation. It is known that crustacean species (amphipods) such as shrimp are routinely found around the platforms used to grow red algae. Consequently,  these sea creatures are often mixed in with harvested seaweed, and find their way into nori sheets.

Some studies have shown that high levels – several milligrams per sheet – of amphipods can be present in dried nori products. It has also been suggested that these levels may vary significantly between batches and between different nori products.

Allergenicity of amphipods

Edible shrimp and crab, which fall under the crustacean group, are frequently involved in immunoglobulin E-mediated (IgE) allergies, and are both widely classified as a common food allergen (shellfish). Tropomyosin, a myofibrillar protein, is a well-characterised major crustacean allergen.

The literature suggests that amphipods concomitant with dried nori products have the potential to cause serious allergic reactions, particularly in severely sensitised crustacean-allergic patients. Ingestion, even at very low doses, may cause immediate allergic reaction. The VITAL® reference dose (Allergen Bureau VITAL® Science, allergenbureau.net/vital/vital-science, 05/11/2020) for shrimp is currently set at 25mg protein. It is also suggested that the allergenicity of amphipods is not reduced during nori production, including the drying and heating processes, due to the tropomyosin protein being heat stable.

Amphipods should be considered to have the potential to be ‘hidden’ allergens in nori. There is limited research available on this; not just in the South African context, but globally. Substantial investment is needed to better understand the food safety hazards associated with these products, in order to define, determine and control the risks involved.  

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