Carotenoid natural occurrence

Kaplan, L.A., Lau, J.M., and Stein, E.A., Carotenoid composition, concentrations, and relationship in various human organs, Clin. Physiol. Biochem., 8, 1, 1990. Parker, R.S., Carotenoids in human blood and tissues, J. Nutr, 119, 101, 1989. Clifford, M.N., Anthocyanins nature, occurrence, and dietary burden, J. Sci. Food Agric., 80, 1063, 2000. 

Studies of structure-activity relationships of compounds that affect carotenogenesis led to the discovery of a new class of bioregulators that cause the accumulation of poly-cis-carotenoids (25, 26). The natural occurrence of cis and poly-cis-carotenoids has been observed, but is not very common (27-32). 

The natural occurrence of the 15-cw-isomer of violaxanthin [5,6,5, 6 -diepoxy-5,6,5, 6 -tetrahydro-/3,j8-carotene-3,3 -diol (13)] as a minor (0.6% of total carotenoid) constituent of Viola tricolor has been reported. Isomerization to fra 5-violaxanthin and c.d. correlation established the (35,5i ,6S,3 5,5 / ,6 S)-chirality. Reinvestigation of the carotenoids of Elodea canadensis failed to reveal any eloxanthin . It is proposed that the name be abandoned. A minor carotenoid from Valencia orange peel has been identified as jS-citraurin epoxide [3-hydroxy-5,6-epoxy-5,6-dihydro-8 -apo-j8-caroten-8 -al (14)]. 

Structure of carotenoids means that they range in colour from pale yellow to intense red-orange and are most abundant in green photosynthetic plant tissues where their natural colour is masked by chlorophyll or in fruits, roots, flowers, seeds, leaves, etc where the colour provides visual cues as to ripeness, suitability as food, guidance for pollinating insects, photoprotectants and indicators of senescence. Because of the natural occurrence of carotenoids some are also permitted food colourants and maybe added to foods either as the isolated compound, ester or as stabilized dispersible formulations. The amounts added are usually small because some of the carotenoids are very intensely coloured. 

New Structures.—The Key to Carotenoids lists all carotenoids found in Nature up to the middle of 1975, and gives extensive references to occurrence and physical, chemical, and spectroscopic properties. An outline of work on the eluci-... 

Two fundamental building-blocks of natural product chemicals are isopentyl pyrophosphate and isoprene [31, 32], Isoprene is incorporated in compounds known as isoprenoids. The function and occurrence of isoprenoids cover a very broad range in nature according to Stryer [31], "-isoprenoids can bring delight by their colour as well as their fragrance. Indeed, isoprenoids can be regarded as the sensual molecules The colour of tomatoes and carrots comes from carotenoids, specifically lycopene and beta-carotene, respectively."... 

Researchers interested in the properties and occurrence of natural antioxidants concentrate on vitamins E and C, carotenoids, phenolic acids, flavonoids, sesame lignins, phytosterols, extracts from the leaves of the plants belonging to the Lami-aceae family, oryzanols, tea leaf extracts, phosphatides, olive oil phenols, squalene, and propolis. Barrera-AreUano et al. (1999), Boskou (1999), Blekas and Boskou... 

Occurrence and Function. Structures of over 5,000 naturally occurring T. are known. Hiey occur in all living forms, but biological functions are known for only a few. Carotenoids are important as accessory photosynthetic pigments, and several groups of T. act as hormones in plants, insects and higher animals. Many pheromones are T.Some T. are also important in medicine and as raw materials in the industrial preparation of foods, perfumes, varnishes and rubber. 

Besides the more restricted occurrences of the red carotenoids and the red to purple betalains and anthraquinones, anthocyanins are largely responsible for the scarlet through purple to blue colors of flowers, fruits, roots and leaves of higher plants, fruit juices, red wines, etc. They are accumulating in the vacuoles of epidermal or subepidermal cells, but may also be confined to the leaf mesophyll. Around 300 different naturally occurring anthocyanins have been reported (27). 

---