E127 is a chemical compound containing iodine, an ingredient included in the list of European food additives as a colouring agent. Its chemical name is Erythrosine.

The name describes the structure of the molecule:

• 'Erythro-' comes from the Greek word 'erythros', meaning red, and refers to the colour of the dye.
• "-sine" is a suffix commonly used in chemical names.

The raw materials for the production of Erythrosine are:

• Fluorescein - This is a bright yellow-green organic compound known for its fluorescence properties. It is a xanthene dye that is often used in biochemistry and medicine, for example, to stain cells under a microscope or to trace blood flow in the eyes.
• Iodine - Iodine is a chemical element with the symbol I and atomic number 53. It is a member of the halogen family and appears as a lustrous purple-black solid at room temperature. Iodine has many applications, including use as a disinfectant, as a contrast component in radiography, and as an essential nutrient for the thyroid.

The synthesis process takes place in different steps:

• Preparation of reagents - Fluorescein and iodine are prepared for the reaction. This may include cleaning and accurately weighing the reagents.
• Iodination - Fluorescein is reacted with iodine in a suitable solvent. This process is known as iodination and leads to the formation of erythrosine. The reaction is exothermic, which means it releases heat.
• Product isolation - After the reaction is complete, the erythrosine is isolated from the reaction mixture. This can be done through a series of techniques such as filtration or centrifugation.
• Purification - The isolated erythrosine is then purified to remove any impurities. This may include techniques such as crystallization, distillation, or chromatography.
• Drying and packaging - Finally, the purified erythrosine is dried and packaged for distribution.

It appears in the form of a red powder. 

Food

E127 in the European Food Additives List and CI 45430 in the Colour Index International.

Cosmetics

It is a restricted ingredient as a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009 IV/80 (CI 45430) and II/1337 (Acid Red 51; CI 45430) and its aluminium salt (Pigment Red 172 Aluminium lake) when used as a substance in hair dye products  

Used in toothpastes, it is considered safe for health if the maximum concentration does not exceed 0.0025% (25 ppm).

Colourant. This ingredient has the primary function of colouring the solution in which it is placed in a temporary, semi-permanent or permanent manner, either alone or in the presence of complementary components added for colouring.

Safety

Used in toothpastes and in food, it is considered safe for health if the maximum concentration does not exceed 0.0025% (25 ppm), however, different studies have found that this dye can create problems for human health (1).

It has an effect on the thyroid gland and is considered by the scientific literature to be a secondary tumorigenic agent (2). Further studies are underway.

• Molecular Formula:   C₂₀H₆I₄Na₂O₅   C₂₀H₆I₄Na₂O₅H₂O
• Molecular Weight:  879.86 g/mol
• CAS:   16423-68-0
• UNII    8TL7LH93FM
• EC number:   240-474-8

Synonyms:

• FD & C Red No. 3
• Erythrosin B
• 2-(2,4,5,7-Tetraiodo-6-hydroxy-3-oxo-3H-xanthene-9-yl)benzoic acid
• Sodium 2',4',5',7'-tetraiodo-3-oxo-3H-spiro[isobenzofuran-1,9'-xanthene]-3',6'-bis(olate)
• 2',4',5',7'-Tetraiodofluorescein, disodium salt
• Disodium 2-(2,4,5,7-tetraiodo-6-oxido-3-oxoxanthen-9-yl)benzoate
• 9-(o-Carboxyphenyl)-6-hydroxy-2,4,5,7-tetraiodo-3H-xanthene-3-one disodium salt monohydrate
• Disodium 9-(O-carboxyphenyl)-6-hydroxy-2,4,5,7-tetraiodo-3H-xanthen-3-one monohydrate
• Disodium 3',6'-dihydroxy-2',4',5',7'-tetraiodospiro(isobenzofuran-1(3H),9'-(9H)xanthen)-3-one
• C.I.Solvent Red 140
• Erythrosinic acid

References_____________________________________________________________________

(1) Chequer FM, Venancio VP, Almeida MR, Aissa AF, Bianchi MLP, Antunes LM. Erythrosine B and quinoline yellow dyes regulate DNA repair gene expression in human HepG2 cells. Toxicol Ind Health. 2017 Oct;33(10):765-774. doi: 10.1177/0748233717715186.

Abstract. Erythrosine B (ErB) is a cherry pink food colorant and is widely used in foods, drugs, and cosmetics. Quinoline yellow (QY) is a chinophthalon derivative used in cosmetic compositions for application to the skin, lips, and/or body surface. Previously, ErB and QY synthetic dyes were found to induce DNA damage in HepG2 cells. The aim of this study was to investigate the molecular basis underlying the genotoxicity attributed to ErB and QY using the RT2 Profiler polymerase chain reaction array and by analyzing the expression profile of 84 genes involved in cell cycle arrest, apoptosis, and DNA repair in HepG2 cells. ErB (70 mg/L) significantly decreased the expression of two genes ( FEN1 and REV1) related to DNA base repair. One gene ( LIG1) was downregulated and 20 genes related to ATR/ATM signaling ( ATR, RBBP8, RAD1, CHEK1, CHEK2, TOPB1), nucleotide excision repair ( ERCC1, XPA), base excision repair ( FEN1, MBD4), mismatch repair ( MLH1, MSH3, TP73), double strand break repair ( BLM), other DNA repair genes ( BRIP1, FANCA, GADD45A, REV1), and apoptosis ( BAX, PPP1R15A) were significantly increased after treatment with QY (20 mg/L). In conclusion, our data suggest that the genotoxic mechanism of ErB and QY dyes involves the modulation of genes related to the DNA repair system and cell cycle.

(2) Poulsen E. Case study: erythrosine. Food Addit Contam. 1993 May-Jun;10(3):315-23. doi: 10.1080/02652039309374154.  

Abstract. Erythrosine (FD & C Red No. 3) is an iodine-containing food colour which was used as an example in the application of the proposed approach of data-derived safety factors. The effect of erythrosine on the thyroid and the mechanism by which the effect is induced has been central to the discussion of the establishment of an Acceptable Daily Intake (ADI), or not, and a short account is given of the effect of erythrosine on the thyroid. The evaluation of erythrosine as a secondary tumorigenic agent was based on the evaluations of the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and the Scientific Committee for Food of the Commission of the European Communities (SCF). In the proposed decision tree scheme, three different possibilities were examined. One was based on the long-term data and the second on the hormone data in the rat; the third was based on the NOEL for hormonal changes in humans. The three approaches with different NOEL and default values resulted in the following ADIs: 0.25, 0.3 and 0.1 mg/kg bw. The cases are discussed and it is concluded that the ADI based on the NOEL in human studies seems most appropriate. As there is most uncertainty about the default value for human pharmacokinetic variability, it is suggested that further human studies might elucidate this point.