Sodium tetraborate

Sodium tetraborate, commonly known as borax, is a boron mineral compound used as a preservative in the same highly restricted application as boric acid (E284): the preservation of sturgeon roe (caviar) in the EU. Borax dissolves in food matrices to release borate ions, which exert antimicrobial activity and help maintain the colour and texture of processed caviar. Its use outside this specific caviar context is not authorised in EU food regulations.

JECFA evaluated sodium tetraborate in 1998 alongside boric acid and assigned the same ADI of 0.16 mg/kg body weight per day expressed as boron. The shared ADI reflects the fact that both compounds contribute to total dietary boron, and it is the boron content, not the specific salt form, that drives the toxicological assessment. The concern at high boron intake levels involves potential reproductive toxicity in animal models, though observational human studies at normal dietary boron levels do not show these effects at typical exposures.

Sodium tetraborate is approved in the EU as E285 exclusively for the preservation of caviar, mirroring the restriction on boric acid (E284). In regulatory terms, both E284 and E285 are grouped together as boron-containing preservatives for this specific application. Consumers of caviar — the only food source of these additives — should note that their boron intake from this food is managed within the ADI framework. For the vast majority of consumers who do not eat caviar, these additives are not encountered. The name "borax" is familiar to some consumers from household cleaning products, but food-grade sodium tetraborate meets different purity and specification requirements than industrial borax grades.