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E285 Sodium Tetraborate (Borax) – Food Additive

E285 (sodium tetraborate, borax) is a food additive with preservative properties that is only approved in the EU under very strict restrictions due to toxicological concerns.

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Things worth knowing about "E285"

E285 (sodium tetraborate, borax) is a food additive with preservative properties that is only approved in the EU under very strict restrictions due to toxicological concerns.

What is E285 (Sodium Tetraborate)?

E285 refers to sodium tetraborate, commonly known as borax or disodium tetraborate. It is a naturally occurring boron mineral used as a food additive with preservative properties. The substance appears as a white crystalline powder and belongs to the group of borates.

Use as a Food Additive

Within the European Union, E285 is approved only to a very limited extent. The sole permitted application is the preservation of traditional caviar (sturgeon roe), where borax is used as a preservative to inhibit microbial growth and extend the shelf life of this delicate product. In many other countries and for other food categories, the use of borax in food is not permitted.

Chemical Properties and Mechanism of Action

Sodium tetraborate (chemical formula: Na₂B₄O₇ · 10H₂O) exerts its preservative effect through its antimicrobial activity. It inhibits the growth of yeasts, moulds, and certain bacteria by interfering with microbial metabolism and disrupting enzymatic processes. In aqueous solution, borax dissociates into boric acid and sodium hydroxide, creating an alkaline environment that further inhibits microbial proliferation.

Toxicology and Health Concerns

Borax and boric acid are considered toxicologically concerning, which is why permitted levels are strictly regulated. The main health risks include:

Reproductive toxicity: Boron compounds have been classified as reproductive toxicants. Animal studies indicate adverse effects on fertility and foetal development.
Kidney toxicity: At higher intake levels, boron can impair kidney function.
Accumulation: Boron can accumulate in the body, particularly with prolonged exposure.
Acute toxicity: High doses may cause nausea, vomiting, diarrhoea, skin irritation, and in extreme cases, kidney failure.

The European Food Safety Authority (EFSA) has established a Tolerable Daily Intake (TDI) for boron of 0.16 mg boron per kg body weight per day.

Approval and Legal Framework in the EU

Under EU Regulation No. 1333/2008 on food additives, E285 is exclusively approved for the preservation of caviar, with a maximum permitted level of 4 g/kg (expressed as boric acid). Its use in all other foods is prohibited. In some non-EU countries, particularly in Asia, borax is traditionally used in certain foods such as rice products and noodles, which would be illegal under EU law.

Labelling

Foods containing E285 must declare this additive in the ingredient list either by its E-number E285 or by its name sodium tetraborate. Since its use is restricted to caviar, E285 is rarely encountered in everyday food products.

References

European Food Safety Authority (EFSA): Scientific Opinion on the re-evaluation of boric acid (E 284) and sodium tetraborate (borax) (E 285) as food additives. EFSA Journal, 2013;11(10):3407.
European Parliament and Council of the European Union: Regulation (EC) No 1333/2008 on food additives. Official Journal of the European Union, 2008.
World Health Organization (WHO): Boron in Drinking-water. Background document for preparation of WHO Guidelines for Drinking-water Quality. WHO/SDE/WSH/03.04/54, Geneva, 2003.

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