Sodium alginate
A natural thickener and gelling agent extracted from brown seaweed, used to give foods a smooth, stable texture.
What is it?
Sodium alginate is the sodium salt of alginic acid, a polysaccharide found naturally in the cell walls of brown seaweeds such as Laminaria and Macrocystis. It is extracted by treating dried seaweed with an alkali, then precipitating and drying the result to a white or pale cream powder. As a dietary fibre component, it passes largely undigested through the gut.
What does it do?
When dissolved in water, sodium alginate forms a thick, viscous gel. It stabilises emulsions by preventing oil and water phases from separating, thickens liquids, and, in the presence of calcium ions, can set into a firm gel without heat. This cold-setting property makes it useful in restructured foods and spherification in modernist cooking. It also acts as a film-former when applied to the surface of fruits and vegetables as a protective coating.
Where you will see it
Found in ice creams, dairy desserts, salad dressings, sauces, processed cheese analogues, canned fruit, restructured meat and fish products (such as formed scampi), beer and wine processing, and as a thin edible coating on whole fresh fruits and vegetables. On a label it appears as E401 or sodium alginate.
What the science says
Gut and digestive effects
Sodium alginate is classified as a dietary fibre. It resists digestion in the small intestine and reaches the colon, where gut bacteria can partially ferment it. At the doses consumed in food, this is consistent with other soluble dietary fibres and is not considered a toxicological concern.
EFSA's re-evaluation of alginates (E400-E404) found no toxicological concerns at exposure levels from authorised food uses and concluded that no numerical acceptable daily intake was needed.
Iodine content from seaweed origin
Alginates are extracted from iodine-rich seaweed, but the extraction and purification process removes the vast majority of iodine. EFSA reviewed iodine carry-over and found residual iodine in commercial sodium alginate to be very low and not a significant contributor to dietary iodine intake at typical food-use levels.
EFSA noted that iodine carry-over from seaweed-derived alginates into food is negligible at the levels at which E401 is authorised for use.
UK extension of use on fresh fruit and vegetables (2024)
In 2024 the UK FSA assessed a new proposed use of E401 as an edible surface coating on whole fresh fruit and vegetables. The Committee on Toxicity found no health risk from this use, consistent with the EFSA conclusion that alginates are of low toxicological concern.
The UK Committee on Toxicity reviewed the safety of sodium alginate as a surface treatment on whole fresh fruits and vegetables and found no risk to health at the proposed use levels.
Where it stands with the regulators
Who should be careful
People with known seaweed or algae allergies should check labels for E401 or sodium alginate, though allergic reactions to purified alginate are uncommon. People on iodine-restricted diets can disregard alginate as a meaningful iodine source at food-use levels.
The honest read
Sodium alginate has been used in food production for decades and has been subject to a full EFSA re-evaluation. The panel found no basis for a numerical intake limit, which reflects how thoroughly the substance behaves like dietary fibre rather than an absorbed chemical with dose-dependent toxicity. There are no current signals from regulators or the peer-reviewed literature pointing to harm at the levels found in food. The science on this one is settled and unremarkable.
Related additives
Common questions
Is E401 banned in the UK?
No. Sodium alginate is an approved food additive in the UK under the assimilated EU Regulation 1333/2008 and the UK FSA approved-additives list. Its permitted uses were extended in 2024 to include surface coatings on whole fresh fruits and vegetables.
Is E401 natural or synthetic?
It is derived from brown seaweed through an extraction process. It is not synthesised from petrochemicals. Whether a product can be labelled 'natural' depends on national labelling rules, but the raw material is a naturally occurring seaweed polysaccharide.
What foods contain E401?
Ice creams, dairy desserts, processed cheese alternatives, salad dressings, canned fruit, restructured fish products such as formed scampi, and, increasingly, as a thin edible coating on whole fruits and vegetables sold loose in supermarkets. On the label it appears as E401 or sodium alginate.
Is E401 vegan?
Yes. Sodium alginate is derived from seaweed and contains no animal-derived ingredients.
Sources
- EFSA Panel on Food Additives and Nutrient Sources: Re-evaluation of alginic acid and its sodium, potassium, ammonium and calcium salts (E400-E404) as food additives
- UK FSA / COT Safety Assessment on Product E401 (Sodium Alginate) Used as a Surface Treatment in Entire Fruits and Vegetables (RP290)
- Re-evaluation of alginic acid and its sodium, potassium, ammonium and calcium salts (E400-E404) as food additives - PubMed/PMC
- EU Regulation 1333/2008 on food additives (Annex II and Annex III)
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