E-numbers / Antioxidants / E303
also: Potassium salt of ascorbic acid · Vitamin C (potassium form)
The potassium salt of vitamin C, used as an antioxidant to stop food browning and going rancid. Not permitted as a food additive in the UK or EU.
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E303 is not authorised in UK or EU food.
Why it’s worth knowing. E303 is not authorised in UK or EU food. If you see it listed on a product, that product may not comply with UK food additive law. Related permitted antioxidants to recognise are E300 (ascorbic acid), E301 (sodium ascorbate) and E302 (calcium ascorbate).
Potassium ascorbate is the potassium salt of ascorbic acid (vitamin C). It is a white crystalline powder that dissolves readily in water. Like other ascorbate salts, it delivers the same antioxidant function as vitamin C but with a small amount of potassium rather than sodium or calcium as the accompanying cation.
As an antioxidant, potassium ascorbate donates electrons to free radicals and to oxygen, interrupting the oxidation chain reactions that cause food to brown, go rancid, or lose colour. It also acts as a reducing agent in food systems, regenerating other antioxidants such as tocopherols (vitamin E). In meat products it can accelerate colour development by reducing metmyoglobin back to the red oxymyoglobin form.
In countries where it is permitted (such as Australia and New Zealand), potassium ascorbate is used in beverages, processed meats, fruit products, and packaged fresh produce to preserve colour and extend shelf life. It is not authorised for use in UK or EU food products. It would appear on a label as 'potassium ascorbate' or 'antioxidant (potassium ascorbate)', but E303 is not a valid E number for use on UK labels because the substance is not approved.
E303 does not appear in Annex II of assimilated EU Regulation 1333/2008 on food additives, which is the authorised list carried forward into UK law after Brexit. The UK FSA approved-additives list confirms the gap: E300, E301, E302, and E304 are all listed as permitted antioxidants from the ascorbate family, but E303 is absent. A food product sold in the UK containing E303 as a declared additive would not comply with current UK food additive regulations.
E303 potassium ascorbate is not included in the UK FSA list of approved food additives or in the assimilated EU Regulation 1333/2008 Annex II list of permitted food additives.
Potassium ascorbate shares the same core antioxidant mechanism as its approved relatives, ascorbic acid (E300) and sodium ascorbate (E301). Scientific literature on the safety of ascorbate salts generally treats them together, since the active moiety, the ascorbate anion, is identical regardless of the cation. EFSA and its predecessor the EU Scientific Committee on Food evaluated the ascorbates as a class, and ascorbic acid and its sodium, calcium, and ester forms were all authorised. Potassium ascorbate was not included in that authorisation.
Ascorbic acid and its salts share the same mechanism of action and the ascorbate anion is the active antioxidant species in all cases; the cation (sodium, calcium, potassium) does not alter antioxidant function.
Potassium ascorbate is authorised as a food antioxidant in Australia and New Zealand under their respective food standards codes. This divergence from UK and EU rules means that products imported from those countries may lawfully contain it under their domestic rules, but the same product sold in the UK would need reformulation or an exemption. The substance is not on the US FDA's generally recognised as safe (GRAS) list as a food additive either, though ascorbic acid and sodium ascorbate hold GRAS status.
Potassium ascorbate is permitted as a food antioxidant under Food Standards Australia New Zealand (FSANZ) food standards.
Anyone buying food in the UK should not ordinarily encounter E303, as it is not a permitted additive here. If a UK-sold product does list potassium ascorbate or E303, that may indicate a mislabelled import. People on potassium-restricted diets (for example, those with kidney disease) should note that all potassium-containing food additives add to total dietary potassium intake, though the amounts from additives are generally small relative to potassium from food itself.
The absence of E303 from UK and EU approved lists does not mean the substance is harmful. Its close relatives, including the widely used E300 (ascorbic acid, plain vitamin C) and E301 (sodium ascorbate), are authorised and extensively reviewed. The potassium salt simply was never the subject of a formal EFSA or UK approval application in the food additive context. The practical consequence for UK shoppers is that it should not be present in UK food; if it is, that is a compliance question, not a toxicological one. The science on ascorbates as a class is long-standing and well-characterised.
E303 is not authorised in the UK, meaning it is not on the approved list of food additives permitted for use in UK food products. It was also not authorised under EU Regulation 1333/2008, which UK law carried forward after Brexit. 'Not permitted' and 'banned' have the same practical effect for food manufacturers: it cannot lawfully be used as a food additive in UK or EU products.
The EU and UK approve additives individually following a formal application and safety evaluation. E300 (ascorbic acid), E301 (sodium ascorbate), and E302 (calcium ascorbate) each went through that process and received authorisation. Potassium ascorbate appears never to have been the subject of a formal approval application to EFSA or the earlier EU scientific committees in the food additive context, so it was simply not included on the list. The absence reflects administrative process rather than a specific safety finding.
No UK or EU food products should legally contain E303 as a declared food additive. In countries where it is permitted, such as Australia and New Zealand, it can appear in beverages, processed meats, fruit products, and packaged produce. If you see it on a UK product label, that product may not meet UK food additive requirements.
Yes. Potassium ascorbate is produced synthetically from ascorbic acid and potassium compounds. It contains no animal-derived ingredients and is suitable for vegans and vegetarians.
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