Tetraterpenes

β-Carotene (beta-carotene) is an organic, strongly colored red-orange pigment abundant in fungi, plants, and fruits. It is a member of the carotenes, which are terpenoids (isoprenoids), synthesized biochemically from eight isoprene units and thus having 40 carbons.

Astaxanthin is a keto-carotenoid within a group of chemical compounds known as carotenoids, a subclass of the broad group of phytochemicals known as terpenes. Astaxanthin is a metabolite of zeaxanthin and canthaxanthin, containing both hydroxyl and ketone functional groups.

Zeaxanthin is one of the most common carotenoids in nature, and is used in the xanthophyll cycle. Synthesized in plants and some micro-organisms, it is the pigment that gives paprika (made from red sweet peppers), corn, saffron, goji (wolfberries), and many other plants and microbes their characteristic color.

β-Cryptoxanthin is a natural carotenoid pigment. It has been isolated from a variety of sources including the fruit of plants in the genus Physalis, orange rind, winter squashes such as butternut, papaya, egg yolk, butter, apples, and bovine blood serum.

Canthaxanthin is a keto-carotenoid pigment widely distributed in nature. Carotenoids belong to a larger class of phytochemicals known as terpenoids. The chemical formula of canthaxanthin is C40H52O2. It was first isolated in edible mushrooms. It has also been found in green algae, bacteria, crustaceans, and bioaccumulates in fish such as carp, golden grey mullet, seabream and trush wrasse.

α-Carotene (alpha-carotene) is a form of carotene with a β-ionone ring at one end and an α-ionone ring at the opposite end. It is the second most common form of carotene.

Violaxanthin is a xanthophyll pigment with an orange color found in a variety of plants. Violaxanthin is the product of the epoxidation of zeaxanthin where the oxygen atoms are from reactive oxygen species (ROS). Such ROS's arise when a plant is subject to solar radiation so intense that the light cannot all be absorbed by the chlorophyll.

Rhodoxanthin is a xanthophyll pigment with a purple color that is found in small quantities in a variety of plants including Taxus baccata and Lonicera morrowii. It is also found in the feathers of some birds. As a food additive it is used under the E number E161f as a food coloring. It is not approved for use in the EU or US; however, it is approved in Australia and New Zealand (where it is listed under its INS number 161f).

Flavoxanthin is a natural xanthophyll pigment with a golden-yellow color found in small quantities in a variety of plants. As a food additive it used under the E number E161a as a food coloring although it is not approved for use in the EU or USA. It is listed as food additive 161a in Australia and New Zealand where it is approved for usage as an ingredient in food products.

Phytoene () is a 40-carbon intermediate in the biosynthesis of carotenoids. The synthesis of phytoene is the first committed step in the synthesis of carotenoids in plants. Phytoene is produced from two molecules of geranylgeranyl pyrophosphate (GGPP) by the action of the enzyme phytoene synthase. The two GGPP molecules are condensed together followed by removal of diphosphate and proton shift leading to the formation of phytoene.

Rubixanthin, or natural yellow 27, is a natural xanthophyll pigment with a red-orange color found in rose hips. As a food additive it used under the E number E161d as a food coloring; it is not approved for use in the USA or EU but is approved in Australia and New Zealand where it is listed as 161d.

δ-Carotene (delta-carotene) or ε,ψ-carotene is a form of carotene with an ε-ring at one end, and the other uncyclized, labelled ψ (psi). It is an intermediate synthesis product in some photosynthetic plants between lycopene and α-carotene (β,ε-carotene) or ε-carotene (ε,ε-carotene). δ-Carotene is fat soluble. Delta-carotene contains an alpha-ionone instead of a beta-ionone ring; this conversion is carried out by the gene Del which shifts the position of the double bond in the ring structure. The formation delta-carotene under the presence of the Del gene is sensitive to high temperatures.

thumb|right|400px|The chemical structure of cryptoxanthin, a yellow tetraterpenoid of the [[xanthophyll type.]] Tetraterpenes are terpenes consisting of eight isoprene units and have the molecular formula C40H64. Tetraterpenoids (including many carotenoids) are tetraterpenes that have been chemically modified, as indicated by the presence of oxygen-containing functional groups.