Indigo carmine

Blue dye derived from indigo

Indigo carmine, or 5,5′-indigodisulfonic acid sodium salt, is an organic salt derived from indigo by aromatic sulfonation, which renders the compound soluble in water. Like indigo, it produces a blue color, and is used in food and other consumables, cosmetics, and as a medical contrast agent and staining agent; it also acts as a pH indicator. It is approved for human consumption in the United States and European Union. It has the E number E132, and is named Blue No. 2 by the US Federal Food, Drug, and Cosmetic Act.

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