In 2007, Chinese authorities pulled a batch of imported snack chips from store shelves because they believed the chips contained potassium bromate, a food additive banned in China. The chips' country of origin? The United States.

Potassium bromate is also illegal in the European Union, Canada, Brazil and elsewhere because it causes cancer in rats and mice. In the United States, however, it has remained legal since it was first patented for use in baking bread, in 1914.

Bread dough's beige and shapeless appearance belies the staggering complexity of the molecules that hold it together. Gluten — the wheat protein infamous for its indigestible components that some people have to avoid — is the glue that binds bread dough to itself. (Gluten-free bread relies on other thickening agents such as xanthan gum).

But in order for two gluten molecules to bind to each other, molecular bridges have to form between them.

Such bridges do not form spontaneously. Rather, they're the product of oxidation. Historically, bakers relied on oxygen in the air to form the molecular bridges in dough — they "aged" flour after milling it by exposing it to open air for weeks, and then slowly mixed the flour in dough, all the while allowing ambient oxygen to do the hard work of bridge building.

But potassium bromate is a powerful oxidizing agent that chemically ages flour much faster than open air. Potassium bromate bleaches dough, and enhances its elasticity by strengthening its network of molecular bridges, which makes for the formation of tiny, thin-walled bubbles as the bread rises. The end product is fluffy, soft and unnaturally white.

Ideally, that end product is also entirely devoid of potassium bromate, which changes to potassium bromide, a harmless byproduct, during baking.

In 1982, researchers in Japan published the first of a series of studies showing that potassium bromate causes cancer in the thyroids, kidneys and other body parts of rats and mice.

As a result of these findings, countries around the world banned the additive, but the U.S. Food and Drug Administration held back, in part because the amount of potassium bromate that remains in bread after baking should be negligible: less than 20 parts per billion (ppb).

According to information published by baking industry trade groups, it is "well within the normal production control measures in any modern bakery to ensure that bromate residues are well below 20 ppb."

However, whenever bromated flour isn't baked for long enough or at a high enough temperature, or if too much potassium bromate is added in the first place, this harmful additive can potentially be found in the final product in far greater quantities.

Today, many small and commercial bakeries voluntarily avoid using bromated flour. However, it's still found in many fast food buns and some flours, among other products.

To avoid this additive, check ingredients lists for "potassium bromate" and "bromated flour." Shoppers in California will have an easier time steering clear of potassium bromate: since 1991, California law has required products containing this additive to bear a warning on their labels.

Pass it on: Potassium bromate is an unnecessary and potentially harmful food additive, and should be avoided.

Food Facts explores the weird world of the chemicals and nutrients found in our food, and appears on MyHealthNewsDaily on Fridays. Follow MyHealthNewsDaily on Twitter @MyHealth_MHND.

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