E132 or Indigotine is a disodium salt, synthetic blue dye also called Acid Blue 74, CI 73000, Indigo carmine and others. It is produced by the condensation of 2-formylbenzenesulphonic acid and aniline with a subsequent oxidation process. Mixed with tartrazine (E102) it can produce various shades of green.

It appears as a blue powder

A cosa serve e dove si usa

Food

The  EFSA Panel  on  Food  Additives  and  Nutrient  Sources  added  to  Food concluded that Indigo Carmine is poorly absorbed by the human body and does not raise genotoxicity concerns. No adverse effects were identified in subacute, chronic, reproductive and developmental toxicity studies, and no changes in haematological and biological parameters were identified in chronic toxicity studies at doses less than or equal to 500 mg/kg body weight/day (1).

The  Panel  confirmed  the  ADI  of  5  mg/kg  bw/day  for  Indigo  Carmine  of  at  least  93%  purity manufactured  using  the  same  or  equivalent  manufacturing  process  resulting  in  material  tested in Borzelleca  et  al.  studies.  Given  the  uncertainties  in  the  database,  the  Panel  was not  able  to conclude whether  this  ADI  should  apply  to  Indigo  Carmine  with  lower  purity  manufactured  using these  same processes or material manufactured using a different but not equivalent process. Furthermore, the Panel concluded that the current specifications should be revised in order to restrict the Indigo Carmine (E 132) permitted as food additive to that for which the ADI is applicable.  The  Panel  concluded  that  at  the  maximum  permitted  level  of  use,  exposure  estimates  of  Indigo Carmine (E 132) would exceed the ADI for toddlers and children at the high level. Exposure estimates using  the  available  usage  and  analytical data  did  not  show  an  exceedance  of the  ADI  for  any population groups.The Panel noted that the three main contributing food categories for age-groups where MPL scenario estimates exceeded the ADI showed high number of analytical data far below MPL or had no use level reported combined with no detection in limited analytical data. The Panel therefore considered that it is not likely that the ADI will be exceeded (1).

Medical

It is used in medicine in intravenous administration to examine sections of the human body to be explored with endoscopic probes, is usually biologically safe and inert and can rarely cause adverse reactions, except in rare exceptions (2).

The most relevant studies on this chemical compound have been selected with a summary of their contents:

   Indigotine studies

Appearance	Blu powder
Melting Point	>300°C
Density	1.01 g/mL at 20°C
PSA	189.36000
LogP	3.06060
Refraction Index	n20/D 1.335
Water Solubility	1 g/100 mL (25 ºC)
Safety

• Molecular Formula  C₁₆H₈N₂Na₂O₈S₂
• Molecular Weight    466,346
• Exact Mass   465.951752
• CAS   860-22-0
• UNII    D3741U8K7L
• EC Number   212-728-8
• DSSTox Substance ID  DTXSID1020190    DTXSID0044288    DTXSID6044224
• IUPAC  disodium;2-(3-hydroxy-5-sulfonato-1H-indol-2-yl)-3-oxoindole-5-sulfonate
• InChI=1S/C16H10N2O8S2.2Na/c19-15-9-5-7(27(21,22)23)1-3-11(9)17-13(15)14-16(20)10-6-8(28(24,25)26)2-4-12(10)18-14;;/h1-6,17,19H,(H,21,22,23)(H,24,25,26);;/q;2*+1/p-2  
• InChl Key      JFVXEJADITYJHK-UHFFFAOYSA-L
• SMILES   C1=CC2=C(C=C1S(=O)(=O)[O-])C(=C(N2)C3=NC4=C(C3=O)C=C(C=C4)S(=O)(=O)[O-])O.[Na+].[Na+]
• MDL number  MFCD00005723
• PubChem Substance ID    24847997
• ChEBI  31695
• Colour Index Number   73015    
• Beilstein      4103904
• RTECS   DU3000000
• NACRES   NA.47   
• NCI   C83799

Synonyms :

• Sodium indigotindisulfonate
• disodium;2-(3-hydroxy-5-sulfonato-1H-indol-2-yl)-3-oxoindole-5-sulfonate
• (delta(sup 2,2')-Biindoline)-5,5'-disulfonic acid, 3,3'-dioxo-, disodium salt
• FD C Blue 2
• Sachsischblau
• Murabba
• Indigotine Lake
• Indigo Extract
• Indigo carmine
• Acid Blue 74
• Indigo carmine
• Indigocarmin
• Indigotine
• C.I. ACID BLUE 74
• Indigotindisulfonate sodium
• FD&C Blue No. 2
• Food Blue No. 2
• C.I. Food Blue 1
• C.I. Natural Blue 2
• Amacid Brilliant Blue

References_____________________________________________________________________

(1) EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS), 2014. Scientific Opinion on the re‐evaluation of Indigo Carmine (E 132) as a food additive. EFSA Journal, 12(7), p.3768.

(2) Nandate K, Voelzke BB. Severe Hypotension, Hypoxia, and Subcutaneous Erythema Induced by Indigo Carmine Administration during Open Prostatectomy. Case Rep Urol. 2016;2016:5237387. doi: 10.1155/2016/5237387.