Carotenoids

Carotenoids are always of plant origin. Chemically, they are tetraterpenes, which are symmetrically composed of 8 isoprene units. Their behaviour is determined by the long hydrocarbon chains with many conjugated double bonds: they are fat-soluble and coloured.

Several hundred different carotenoids can be found in the plant kingdom. However, only about 40 of them have provitamin A activity. Of these, β-carotene is probably the most important for humans in terms of quantity.

Lycopene (unlike β-carotene and most other carotenoids, it does not contain closed rings) is the colouring agent of tomatoes and peppers.

Carotenoids with hydroxyl groups in the rings are called xanthophylls. They are responsible for the yellow colouring of leaves in autumn, for example(lutein, therefore also called leaf xanthophyll).
Zeaxanthin is responsible for the yellow colour of maize. Egg yolk contains a feed-dependent mixture of various xanthophylls and β-carotene.

Isoprene

isoprene

C₅H₈ (MW: 24.31)

Apocarotenic acid ethyl ester

carotenic acid ester

C₃₂H₄₄O₂ (MW: 460.70)
Ethyl 8'-apo-β-carotene 8'-oate
Ethyl-all-trans-2,6,11,15-tetramethyl-17-(2,6,6-trimethyl-1-cyclohexen-1-yl)-2,4,6,8,10,12,14,16-heptadecaoctaenoat

Colour: red-brown
Acute toxicity LD₅₀ > 40 000 mg/kg (oral, mouse)
Sensitive to light, heat, air and moisture

Note

With prolonged exposure, pigment deposits in the liver, fatty tissue and skin
No risk of A-hypervitaminosis even with excessive intake

Astaxanthin

astaxanthin

C₄₀H₅₂O₄ (MW: 596.85)
3',3'-dihydroxy-4,4'-diketo-β-carotene
3,3'-dihydroxy-β,β-carotene-4,4'-dione
3,3'-dihydroxy-[all-trans-1,18-(3,7,12,16-tetramethyl-1,3,5,7,9,11,13,15,17-octadecanonaene-1,18-diyl)-bis-(2,6,6-trimethylcyclohexene)]-4,4'-dione (3 S,3' S:3 R,3' R:3 R,3' S = 1:1:2)

Colour: brown-violet, violet, red-violet
Acute toxicity LD₅₀ > 8 000 mg/kg (oral, different species)
Reproductive toxicity: not teratogenic, not embryotoxic (different species)

Note:

Does not develop vitamin A activity, there is no risk of A hypervitaminosis by ingestion of larger amounts.

Canthaxanthin

canthaxanthin

C₄₀H₅₂O₂ (MW: 564.82)
β-Carotene-4,4'-dione
4,4'-diketo-β-carotene

Acute toxicity LD₅₀ > 40 000 mg/kg (oral, mouse)
Colour: red-violet
Mutagenicity: not mutagenic (various test systems)
Carcinogenicity: not carcinogenic
Reproductive toxicity: not teratogenic, not embryotoxic

Canthaxanthin is a colouring agent widely distributed in nature and produced by various plants and animals; in naturally occurring concentrations and distribution, the substance is known to be readily degradable and well tolerated by the environment.