What is Indigotine?

Indigotine is an organic compound commonly used as a reddish blue food dye. It can also be referred to using the names:

  • Indigo Carmine
  • FD&C Blue #2
  • CI Food Blue 1
  • CI (1975) No. 73015


The chemical formula for indigotine is C16H8N2Na2O8S2.

Historically, indigo was produced from natural products. The ancient Phoenicians first began to produce indigo dyes from the excrement of sea snails. As you might expect, each snail would only produce a very small amount of dye. This meant that the dye was very rare, and materials coloured with it were very expensive.

Later discoveries allowed the dyes to be produced from a variety of plants. Most plants used to produce indigo are shrubs of species Indigofera.

Synthetic Production of Indigotine

Indigo (or indigo paste) is synthetically produced by first using aniline (which is produced from benzene) and formaldehyde to create molecules called N -phenylglycine. These molecules are then fused in a molten mixture of sodamide and sodium and potassium hydroxides under ammonia pressure. The indigo is then isolated and purified.
Once the indigo has been produced, it is heated in the presence of sulphuric acid. Indigotine is then isolated and subjected to purification procedures.

Common Uses

Indigotine is currently approved for use in the U.S.1, Canada2 and the E.U.3.
There aren’t that many foods that need to be dyed blue. The common use cases are just what you might expect: confectionaries (candies), cereal, and other “junk” food. Two examples are:

Non-Food Uses

It is used as a pH indicator. It is blue at pH 11.4 and yellow at 13.0.

It is used in obstetrics to help detect amniotic fluid leaks.

It is used during surgery to highlight the urinary tract and help to detect leaks.

Health Issues / Side Effects

Indigotine is actually made from some nasty chemicals. Workers who handle it do need to be cautious. It can be harmful to the respiratory tract if inhaled, and it can irritate skin and eyes.

A lot has been written on the internet describing it’s adverse effects. The list of further reading articles at the end of this post includes some links. However, according to the US National Library of Medicine National Institutes of Health, there is no evidence of any toxicity, including carcinogenicity.

E Number

The E number for indigotine is E132. Other blue dyes include Brilliant Blue (E133) and Spirulina Extract (no E number).


  1. FDA List of Color Additives Approved for Use in Human Food
  2. List of Food Additives Approved in Canada
  3. Current EU approved additives and their E Numbers

Further Reading

What is That Ingredient – Blue #2 

Wikipedia – Indigo Carmine

Wikipedia – Indigotin

Wikipedia – Hexaplex trunculus

Saudi Armaco World – Millennia of Murex

Hawkins – Watts (chemical producer / supplier)

Be Food Smart

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