Fat-soluble pigments

Fat includes triglycerides, sterols, lecithins (phospholipids), essential oils, fat-soluble pigments such as chlorophyll, and similar substances. The AOAC recommends that anhydrous diethyl ether kept over freshly cut sodium pieces is used for the extractant (Padmore, 1990, p. 79), but we prefer to use petroleum spirit, also called light petroleum and petroleum ether, with a boiling range of 40-60°C, as it is a less hazardous solvent. 

Crabs, lobsters, and shrimps are important sources for natural carotenoids, which are a group of fat soluble pigments such as astaxanthin,... 

The colour of dairy products such as butter and cheese is due to fat-soluble pigments, especially carotenoids, which are not synthesized by the animal but are obtained from plant sources in the diet. Therefore, feed has a major effect on the colour of milk-fat. Cows fed on grass produce a more yellow-coloured fat than animals fed on hay or concentrates. The ability of cattle to metabolize carotenes to vitamin A varies between breeds and between individuals (Chapter 6). 

Carotenoids. Carotenoids are fat-soluble pigments comprised of isoprene units and, in plants, are generally associated with membranes (30). Carotenoids are generally classified as either carotenes, which are structurally related to hydrocarbons, or xanthophylls which are hydroxy, epoxy and oxy derivatives and are frequently esterified. The carotenoids most important in Imparting color to fruits and vegetables are derivatives of a- and -carotenes and lycopene. Carotenoids vary in their stability but, due to their unsaturated nature, they are generally susceptible to oxidation. Carotenes are important to... 

Carotenoids Carotenoids are a class of natural fat-soluble pigments found principally in plants, algae, and photosynthetic bacteria. They are responsible for many of the red, orange, and yellow hues of plant leaves, fruits, and flowers, as well as the colors of some birds, insects, fish, and crustaceans. Some familiar examples of carotenoid coloration are the oranges of carrots and citrus fruits, the reds of peppers and tomatoes, and the pinks of flamingoes and salmon." From the... 

Fig. 3. Absorption spectra (in ether) of fat-soluble pigments in Ulva taeniata. The carotenoids were measured at the concentration obtaining in the total pigment extract. The chlorophyll curve was calculated by difference. [From F. T. Haxo and L. R. Blinks 16)].

The chlorophylls, carotenoids, and xanthophylls are the best-known fat-soluble pigments and are often referred to as lipochromes. These pigments are found in... 

Of the fat-soluble pigments, carotenoids have been best characterized. They are unsaturated hydrocarbons with branched chains of carbon atoms containing a cyclic structure at one or both ends. For the chemical structures of carotenoids, see Florey (1966). 

Davies, B. H., and Kost, H-P. (1988). Carotenoids. In CRC Handbook of Chromatography—Plant Pigments—Volume J—Fat Soluble Pigments, H-P. Kost (Ed). CRC Press, Boca Raton, FL, pp. 3-183. 

Carotenoids are red and yellow fat-soluble pigments composed of a class of hydrocarbons (carotenes) and their oxygenated derivatives (oxycarotenoids or xanthophylls). The basic structure consists of eight isoprenoid units. A series of conjugated double bonds provides the characteristic chromophore. The basic structure can be modified by hydroxylation, hydrogenation, dehydrogenation, cyclization, or oxidation (Schwieter and Isler, 1967). Bacteria are capable of adding further isoprenoid units. 

The first intracellular localization of a vitamin was described by Quemer in 1932. He found in tissues that certain isotropic fat droplets gave a fluorescence, which quickly faded, with ultraviolet light. He believed that this fluorescence was due to certain fat-soluble pigments, e.g., carotenoids. Later Quemer found this fluorescence to be present in liver, retina, adrenal cortex, and pituitary gland of animals and said that it was due to vitamin A. 

Chlorophylls and phaeophytins are fat-soluble pigments. Chloro-phyhdes and phaeophorbides are hydrophUic pigments soluble in water due to the absence of phytol. The colours of chlorophylls and derived products are given in Table 9.8. 

Commercially, the seeds and flesh are processed by extraction with vegetable oils at reduced pressure, and at temperatures lower than 130 °C. Under these conditions, 9 -cis-hixin undergoes partial isomerisation to the aW-trans isomer called (E)-bixin (frans-bixin, 9-188). Extracts contain from about 0.2 to 0.5% of a mixture of these two pigments in different proportions according to the conditions of extraction. The resulting trans-hixin is a red, relatively stable and fairly fat-soluble pigment. 

Lipoids as a type are non-saponifiable, although some of the sterols may occur as esters with aliphatic acids. A systematic classification of the lipoids is unsatisfactory, since the only common property of these compounds is the physical one of solubility in certain organic solvents. Examples of biological lipoids occur in the essential or volatile oils of plants and the fat-soluble pigments (lipochromes) of plants and animals. In addition, some of the vitamins and the hormones belong to the lipoid type, in that they are fat-soluble. 

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