Both Coca-Cola and PepsiCo have asked their suppliers of the caramel colouring to alter their manufacturing process to meet the requirements of the law

Both Coca-Cola and PepsiCo have asked their suppliers of the caramel colouring to alter their manufacturing process to meet the requirements of the law

The Coca-Cola Co and PepsiCo have insisted that a change in the way their caramel colour additive is made will not impact the formula or taste of its soft drinks.

California's Office of Environmental Health Hazard Assessment implemented changes to the California Safe Drinking Water and Toxic Enforcement Act of 1986 on Friday (9 March), adding the colouring 4-MEI to the list of potentially harmful chemicals. The chemical is used in the caramel colouring used by both Coca-Cola and PepsiCo.

A study by the US government's National Toxicology Programme found an increased incidence of lung cancer in mice exposed to high doses of the carcinogen.

As a result, both Coca-Cola and PepsiCo have asked their suppliers of the caramel colouring to alter the manufacturing process to meet the requirements of the amended law. It also means the firms can avoid having to place cancer-warning labels on their cans.

Coca-Cola, however, has insisted that the caramel colour in all of its products "has been, is and always will be safe".

The soft drinks firm said it is not changing the formula for its beverages. "Over the years, we have updated our manufacturing processes from time to time, but never altered our secret formula," the company said in a statement.

"We have asked our caramel manufacturers to modify their production process to reduce the amount of 4-MEI in the caramel, but that will have no effect on the formula or on the ... products that consumers expect from us. These modifications will not affect the colour or taste of Coca-Cola."

PepsiCo also insisted that it is not altering its formula.

"The safety of our products is a primary concern at PepsiCo," the company said. "When California chose to add 4-MEI to its Prop 65 list, we asked our caramel suppliers to modify their manufacturing processes, which they have done. Over time, they will expand this process for the rest of the country.

"Consumers will notice no difference in our products and have no reason at all for any health concerns," PepsiCo added.