Nitrosyl chloride
A toxic industrial gas once used to bleach flour white. Not permitted as a food additive in the UK or EU.
Nitrosyl chloride is not an authorised food additive in the UK or EU. It should not appear in any food sold here. As a reactive nitrogen compound, it can generate nitrosamines, a class of chemicals established as carcinogens.
What is it?
Nitrosyl chloride (NOCl) is a bright yellow gas produced industrially, most commonly as a by-product of dissolving metals in aqua regia (a mixture of nitric and hydrochloric acids). It is a strong oxidising and chlorinating agent.
What does it do?
When applied to milled wheat flour as a gas, it bleaches the yellow carotenoid pigments, producing a whiter flour. It also oxidises flour proteins, which can alter gluten structure and baking performance. The gas reacts rapidly and does not remain in the finished flour as a detectable residue, but the reaction products remain.
Where you will see it
Historically used in flour milling in some countries to produce white flour for bread and pastries. It is not authorised for use in any food in the UK or EU and therefore should not appear on any UK or EU food label. In countries where flour bleaching is still permitted (notably the US), bleaching agents are listed in ingredients as 'bleached flour' rather than by the specific agent used.
What the science says
Nitrosamines: a carcinogen concern linked to reactive nitrogen chemistry
Nitrosyl chloride is a recognised nitrosating agent in organic chemistry. When nitrosating agents react with secondary amines, they can form nitrosamines. This reaction pathway for NOCl is well established in peer-reviewed mechanistic chemistry literature. Nitrosamines as a chemical class are classified by IARC as probable or known human carcinogens depending on the specific compound. No specific published study demonstrating nitrosamine formation from nitrosyl chloride in a flour-treatment context has been located in the published literature, partly because the substance has not been in authorised food use in the EU for decades; the concern arises from the established chemistry of reactive nitrogen species rather than direct food-use exposure data.
Many N-nitroso compounds, including nitrosamines formed from reactive nitrogen species, are classified by IARC as Group 2A (probable human carcinogens) or Group 2B (possible human carcinogens), with some specific compounds classified Group 1.
Nitrosyl chloride is explicitly identified as a nitrosating agent capable of reacting with secondary amines to form N-nitrosamines, alongside nitrous acid and dinitrogen trioxide. Computational and kinetic studies confirm this reaction pathway.
Nitrosyl chloride is classified as an acutely toxic gas (GHS Category 3 inhalation toxicity) and a corrosive substance, with well-established industrial safety hazard data. Its reactivity with amines is the basis for nitrosamine formation concerns.
Flour bleaching agents: broader removal from European food law
The EU and UK progressively removed flour bleaching and treatment agents, including nitrosyl chloride, from the permitted additives list. The rationale included concerns about the formation of reaction by-products in treated flour, loss of naturally occurring nutrients such as vitamin E (tocopherols) during oxidation, and the absence of demonstrated consumer benefit. Unbleached flour naturally whitens over a short maturation period without chemical intervention.
Nitrosyl chloride does not appear in Annex II of EU Regulation 1333/2008 on food additives, meaning it has no authorised use in EU or UK food. The UK FSA approved additives list likewise carries no entry for E919.
Flour bleaching agents oxidise carotenoid pigments and tocopherols in flour. Tocopherols (vitamin E precursors) are destroyed in the process, reducing the nutritional value of the treated flour.
Where it stands with the regulators
Who should be careful
Everyone in the UK and EU: this additive is not lawfully present in any food sold here. If you are buying imported products from countries where flour bleaching agents remain permitted, look for 'bleached flour' in the ingredients. The specific agent will not usually be named, but the flour will have undergone chemical treatment.
The honest read
E919 is not a live concern for UK shoppers because it cannot legally be used in any food sold in the UK or EU. The E919 designation reflects the old system of assigning E numbers to substances considered for food use. This one was not carried forward when EU food additive law was consolidated. The underlying chemistry, reactive nitrogen compounds and their potential to form nitrosamines, is a genuine area of regulatory attention in other food contexts, but the direct exposure route via flour treated with nitrosyl chloride does not apply to UK and EU foods. The science on flour bleaching agents more broadly points to nutrient loss and reaction by-product concerns, which is part of why these agents were excluded from the EU permitted list.
Related additives
Common questions
Is E919 banned in the UK?
E919 is not listed as a permitted food additive in the UK. The UK FSA maintains an exhaustive approved-additives list; any additive not on it cannot lawfully be used. E919 does not appear on that list, so it has no authorised food use in the UK.
Could nitrosyl chloride form carcinogenic compounds in food?
Nitrosyl chloride is a recognised nitrosating agent, and peer-reviewed chemistry literature confirms it can react with secondary amines to form nitrosamines. Nitrosamines as a class include several established and probable carcinogens. No study has directly measured nitrosamine formation in flour treated with nitrosyl chloride, partly because the substance has not been in authorised food use in the EU for decades. Because E919 is not used in UK or EU food, no direct dietary exposure route exists for UK consumers through this additive.
What foods contain E919?
No food lawfully sold in the UK or EU contains E919. Historically it was used to bleach wheat flour in some countries. Imported packaged goods from countries where flour bleaching agents are still permitted may contain bleached flour, but the specific agent will typically not be named on the label.
Is E919 vegan?
Nitrosyl chloride is a synthetic industrial gas with no animal-derived components, so it is vegan in origin. However, it is not permitted in UK or EU food, making dietary exposure from compliant products absent.
Sources
- UK FSA Approved Additives and E Numbers
- EU Regulation 1333/2008 on Food Additives, Annex II
- IARC Monographs on the Evaluation of Carcinogenic Risks to Humans (N-nitroso compounds)
- ECHA Hazard Classification: Nitrosyl chloride
- Flour Bleaching overview, American Society of Baking
- Computational mechanistic study on N-nitrosation reaction of secondary amines (confirms NOCl as nitrosating agent for secondary amines)
- Role of Carbonyl Compounds for N-Nitrosamine Formation during Nitrosation: Kinetics and Mechanisms (PMC10938875)
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