E150d (Sulphite ammonia caramel or Caramel Color IV or E150d) is a chemical compound, a type of caramel produced by the controlled heat treatment of carbohydrates, in this case the sugar, in  presence of both sulphites and ammonium compounds, an ingredient included in the list of European food additives as a colouring agent.

The name describes the structure of the molecule:

• "Sulfite" refers to the use of sulfite compounds in the process. Sulfites are a type of sulfur-based compound that is often used as a preservative in foods and beverages.
• "Ammonia" refers to the use of ammonia or ammonium compounds in the process. Ammonia is a compound of nitrogen and hydrogen.
• "Caramel" refers to the product of the process, a brown liquid or powder used primarily as a dye in food and beverages.

The synthesis process takes place in several stages:

• Preparation of carbohydrates. The carbohydrates used in the production of caramel can come from various sources, including corn syrup, sugar beet or cane sugar.
• Heat treatment. Carbohydrates are heated in a pressure vessel to produce caramelization. This process involves the transformation of sugars into a variety of complex compounds that give caramel its characteristic color and flavor.
• Addition of sulfite and ammonium compounds. During heat treatment, sulfite and ammonium compounds are added to the mixture. These compounds act as catalysts, favoring the formation of certain types of compounds that give caramel its specific properties.
• Purification. The reaction mixture is purified to isolate the color of the caramel. This typically involves processes such as filtration and centrifugation to remove any insoluble materials.
• Dilution. The concentrated caramel color is then diluted with water to produce a product with the desired color intensity.
• Quality control test. The final product is tested to ensure it meets the required specifications. This may involve testing for color intensity, clarity, and other physical and chemical properties.

It appears in the form of a light brown powder.

What it is used for and where

Food

A food additive colouring agent included with the number E150 in the list of European food additives. This number includes 4 types of Caramel :

• E150a : Plain caramel
• E150b : Caustic sulphite caramel
• E150c : Ammonia caramel
• E150d : Sulphite ammonia caramel

They are obtained from sugar by an industrial process using high temperatures and burning. The colour is dark and can vary from brown to black.

For E150c and E150d, there is an Acceptable Daily Intake (ADI) of about 200mg/kg body weight, while for E150a and E150b there is no ADI.

In particular, E150d - sulphite-ammoniacal caramel is a rather controversial colouring agent that is used in foodstuffs and is part of the E150 family of additives, all of which are colourants.  

Cosmetics

Dye

The most relevant studies and their abstracts have been selected to explore this topic:

Caramel studies

• Molecular Formula    C₇H₁₀O₂
• Molecular Weight   126.15
• CAS   8028-89-5
• UNII    T9D99G2B1R
• EC Number   232-435-9
• DSSTox ID  DTXSID0047660
• IUPAC  3,5-dimethylcyclopentane-1,2-dione
• InChl=1S/C7H10O2/c1-4-3-5(2)7(9)6(4)8/h4-5H,3H2,1-2H3
• InChl Key      MIDXCONKKJTLDX-UHFFFAOYSA-N
• SMILES  CC1CC(C(=O)C1=O)C
• NCI    C80151
• JECFA   421   
• FEMA   3269      
• UN  

Synonyms:

• ap680
• bc420(color)
• burntsugar
• burntsugarcoloring
• c.i.naturalbrown10
• caramelcolordye
• ds400
• p255
• rt80
• sethness858
• FEMA 2235
• CARAMEL I
• CARAMEL IV

Some studies selected for importance on the physical-chemical characteristics of caramel used as a colorant in food products and its safety.

Dietary intake assessment of caramel colours and their processing by-products 4-methylimidazole and 2-acetyl-4-tetrahydroxy-butylimidazole for the Chinese population.
Liang J, Cao P, Wang X, Gao P, Xu H, Ma N.
Food Addit Contam Part A Chem Anal Control Expo Risk Assess. 2019 May 17:1-11. doi: 10.1080/19440049.2019.1615137.

A U.S. population dietary exposure assessment for 4-methylimidazole (4-MEI) from foods containing caramel colour and from formation of 4-MEI through the thermal treatment of food.
Folmer DE, Doell DL, Lee HS, Noonan GO, Carberry SE.
Food Addit Contam Part A Chem Anal Control Expo Risk Assess. 2018 Oct;35(10):1890-1910. doi: 10.1080/19440049.2018.1508892. Epub 2018 Aug 21.

Dialysed caramel as an effective fluorophore for the simultaneous detection of three nitrophenols.
Ma J, Bian L, Zhao L, Feng X, Zhao L, Wang Z, Pu Q.
Talanta. 2019 May 15;197:159-167. doi: 10.1016/j.talanta.2019.01.006.

Notes from the Field: Outbreak of Listeriosis Likely Associated with Prepackaged Caramel Apples - United States, 2017.
Marus JR, Bidol S, Altman SM, Oni O, Parker-Strobe N, Otto M, Pereira E, Buchholz A, Huffman J, Conrad AR, Wise ME.
MMWR Morb Mortal Wkly Rep. 2019 Jan 25;68(3):76-77. doi: 10.15585/mmwr.mm6803a5.

Control of Listeria monocytogenes in Caramel Apples by Use of Sticks Pretreated with Potassium Sorbate.
Carstens CK, Salazar JK, Bathija VM, Narula SS, Wang P, Tortorello ML.
J Food Prot. 2018 Dec;81(12):1921-1928. doi: 10.4315/0362-028X.JFP-18-175.

Dispersive liquid-liquid microextraction with in situ derivatization coupled with gas chromatography and mass spectrometry for the determination of 4-methylimidazole in red ginseng products containing caramel colors.
Lee J, Lee Y, Nam TG, Jang HW.
J Sep Sci. 2018 Sep;41(17):3415-3423. doi: 10.1002/jssc.201800559. 

Caramel colour and process contaminants in foods and beverages: Part II - Occurrence data and exposure assessment of 2-acetyl-4-(1,2,3,4-tetrahydroxybutyl)imidazole (THI) and 4-methylimidazole (4-MEI) in Belgium.
Fierens T, Van Holderbeke M, Cornelis C, Jacobs G, Sioen I, De Maeyer M, Vinkx C, Vanermen G.
Food Chem. 2018 Jul 30;255:372-379. doi: 10.1016/j.foodchem.2018.02.013.

Safety

Caramel color safety - An update.
Vollmuth TA.
Food Chem Toxicol. 2018 Jan;111:578-596. doi: 10.1016/j.fct.2017.12.004.