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Occurrence of carotenoids
Carotenoids are a class of natural pigments that is very widespread and it was demonstrated that they occur in all the three domains of life, i.e. in the eubacteria, the archea and in the eucarya.
A rich source for carotenoids are the algae and more than 100 carotenoids have been isolated and characterized from these organisms.
For humans the most important source for carotenoids are plants, where often the brilliant colours of the carotenoids are masked by chlorophyll, e.g. in green leaves.
The carotenoids are responsible for the beautiful colors of many fruits (pine-apple, citrus fruits, tomatoes, paprika, rose hips) and flowers (Eschscholtzia, Narcissus), as well as the colours of many birds (flamingo, cock of rock, ibis, canary), insects (lady bird), and marine animals (crustaceans, salmon).
Normally carotenoids occur in low concentrations, but this varies enormously from one source to another.
The total carotenoid production in nature has been estimated at about 100.000.000 tons a year.
Recently it was demonstrated by the analysis of serum and human breast milk that up to 50 dietary carotenoids from fruits and vegetables may be absorbed and metabolised by humans.
Examples of carotenoids in common foods :
In natural products the most common carotenoid is the yellow-orange pigment of the carrot (Daucus carota), the ß,ß-carotene . It was isolated in crystalline form as early as in 1831 by
Wackenroder. Later, it gave the name to the entire class of these compounds.
structure of ß-carotene
Total synthesis of ß,ß-Carotene was performed in 1950 by Karrer, Eugster, Inhoffen and Milas . Just four years later ß,ß-carotene was produced commercially and used as pigment in food and feed. In 1995 capacity for the synthesis of more than 500 tons of ß,ß-Carotene per year was planned.
Because of its pro-vitamin A activity ß,ß-carotene is one of the most important carotenoids. The first step in biosynthesis is the cleavage of the central double bond of ß,ß-carotene which results in two molecules of retinal. Afterwards, retinal is reduced to vitamin A (retinol).
The figure below shows the content of ß,ß-carotene in various fresh fruits and vegetables . The values indicated can only serve as an approximation as the content can vary depending on the variety, the season and the degree of ripening and the bioavailability of carotene from fruits and vegetables depends on the method of preparation before ingestion:
Average ß,ß-carotene content in mg/100 g edible portion of the fruits and vegetables mentioned:
Carotenoids found in yellow maize are located in the cob predominantly. Main carotenoids are Zeaxanthin and Cryptoxanthin.
structure of zeaxanthin
Zeaxanthin has also been found in several species of bacteria.
Capsanthin is the main carotenoid in red pepper (paprika, Capsicum annuum).
structure of Capsanthin
Natural carotenoid extracts of pepper are available as food colours. Oleoresin of paprika is the oil extract of paprika, Capsicum annuum . The colour of a food product containing paprika may range from a deep red to a pale pinkish-yellow, depending on the concentrations used. The material can be used in salad dressings, sauces and particularly in meat products, including sausages, where it is allowed as an additive. It is often used in combination with annatto (another natural carotenoid mixture) to dye processed cheese.
The oily extract contains about 37 to 54 different carotenoid pigments depending on the mode of preparation (extract of unbleached or bleached paprika), of which only few could be completely or even tentatively identified. The main pigments are in general esters of capsanthin and capsorubin . Most assay methods are therefore based on the determination of these two carotenoids.
According to a tradition, a lot of research is done in Hungary, where pepper is cultivated extensively.
The main carotenoids in tomato fruit (Lycopersicon esculentum) are:
Phytoene, phytofluene, z-carotene, neurosporene, lycopene, ß-zeacarotene, ß,y-carotene and ß,ß –carotene. The carotenoid content and composition are highly dependent on the tomato variety and on the ripeness of the fruit.
structure of lycopene
Tomato paste, tomato sauce, and tomato-based soups are rich in carotenoid compounds and are frequently consumed. As expected, lycopene was the most abundant carotenoid, ranging in concentration from 0.3 mg/100 g in vegetable beef soup to 55 mg/100 g in tomato paste. The concentration of beta-carotene ranged from 0.23 mg/100 g in tomato soup to 1.51 mg/100 g in vegetable beef soup.
Click here for more information on lycopene.
Salmon and shrimp
The main carotenoids in salmonids is astaxanthin, with some other carotenoids present, such as canthaxanthin and astacene.
Salmonids get their colour from the carotenoids obtained from their food; crustaceans such as shrimps. These, in turn, get the pigments from the algae they ingest.
structure of astaxanthin
Farmed salmon get their colour from synthetic astaxanthin, synthesised from ß,ß-carotene, in their food. The natural colour of salmon is white.
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