In Australia, organic β-carotene is produced by Aquacarotene Limited from dried marine algae Dunaliella salina grown in harvesting ponds situated in Karratha, Western Australia. BASF Australia is also producing β-carotene from microalgae grown in two sites in Australia that are the worlds largest algae farms. In Portugal, the industrial biotechnology company Biotrend is producing natural all-trans-β-carotene from a non-genetically-modified bacteria of the genus Sphingomonas isolated from soil. Carotenes are also found in palm oil, corn, and in the milk of dairy cows, causing cows milk to be light yellow, depending on the feed of the cattle, and the amount of fat in the milk (high-fat milks, such as those produced by Guernsey cows, tend to be yellower because their fat content causes them to contain more carotene). Carotenes are also found in some species of termites, where they apparently have been picked up from the diet of the insects. Synthesis
There are currently two commonly used methods of total synthesis of β-carotene. The first was developed by BASF and is based on the Wittig reaction with Wittig himself as patent holder:
The second is a Grignard reaction, elaborated by Hoffman-La Roche from the original synthesis of Inhoffen et al. They are both symmetrical; the BASF synthesis is C20 + C20, and the Hoffman-La Roche synthesis is C19 + C2 + C19. Nomenclature
Carotenes are carotenoids containing no oxygen. Carotenoids containing some oxygen are known as xanthophylls. The two ends of the β-carotene molecule are structurally identical, and are called β-rings.
β-Carotene is composed of two retinyl groups, and is broken down in the mucosa of the human small intestine by β-carotene 15,15-monooxygenase to retinal, a form of vitamin A. β-Carotene can be stored in the liver and body fat and converted to retinal as needed, thus making it a form of vitamin A for humans and some other mammals. The carotenes α-carotene and γ-carotene, due to their single retinyl group (β-ionone ring), also have some vitamin A activity (though less than β-carotene), as does the xanthophyll carotenoid β-cryptoxanthin. All other carotenoids, including lycopene, have no beta-ring and thus no vitamin A activity (although they may have antioxidant activity and thus biological activity in other ways). Animal species differ greatly in their ability to convert retinyl (beta-ionone) containing carotenoids to retinals. Carnivores in general are poor converters of dietary ionone-containing carotenoids. Pure carnivores such as ferrets lack β-carotene 15,15-monooxygenase and cannot convert any carotenoids to retinals at all (resulting in carotenes not being a form of vitamin A for this species); while cats can convert a trace of β-carotene to retinol, although the amount is totally insufficient for meeting their daily retinol needs. Molecular structure
Carotenes are polyunsaturated hydrocarbons containing 40 carbon atoms per molecule, variable numbers of hydrogen atoms, and no other elements. Some carotenes are terminated by rings, on one or both ends of the molecule. All are coloured, due to the presence of conjugated double bonds. Carotenes are tetraterpenes, meaning that they are derived from eight 5-carbon isoprene units (or four 10-carbon terpene units).