Chlorine dioxide

Chlorine dioxide is an oxidising gas used as a flour bleaching and improving agent, functioning similarly to chlorine (E925) but producing a different by-product profile. It reacts with the carotenoid pigments in fresh flour to produce a whiter appearance and modifies protein chemistry to improve dough handling and baking performance. Like chlorine treatment, it was developed to compress the natural maturation time of freshly milled flour into a rapid industrial process.

No JECFA numerical ADI is maintained for chlorine dioxide as a food flour treatment agent. Safety concerns have centred on the chlorite and chlorate residues that can form as reaction by-products in treated flour. These residues have raised regulatory concern, and EFSA has set conservative maximum levels for chlorate in food to address residues from multiple sources including flour treatment and drinking water chlorination.

Chlorine dioxide for flour treatment is not permitted in the EU. Its E-number (E926) exists in EU regulation as a recognised additive but it is not included in the list of permitted additives for flour under Regulation 1333/2008. It remains authorised in the United States for flour bleaching under FDA regulations. Consumers buying European flour and bread are not exposed to this treatment. In markets where it is used, chlorine dioxide treatment is typically not disclosed on consumer-facing labels, as it is classified as a processing aid rather than an additive in some regulatory frameworks. This highlights the variable transparency of processing aid declarations across global jurisdictions.