()20 VI. CAROTENOIDS AND RELATED COMPOUNDS 



b. Solubilities of Individual Carotenoids. A consideration of the 

 method of separation of the hydrocarbon carotenoids from the carotenols 

 demonstrates the fundamental differences in the sokibility properties of the 

 two groups. The hydrocarbons dissolve readily in diethyl and petroleum 

 ethers, while they are only sparingly soluble in ethanol, and only slightly 

 so in methanol. The carotenols, on the other hand, are quite soluble in 

 alcohol but are relatively insoluble in petroleum ether. The carotenoid 

 alcohols are, however, quite soluble in diethyl ether. 



The solubilities of carotene (chiefly jS-carotene) , lycopene, xanthophyll, 

 and zeaxanthin in some of the commoner solvents are summarized in Table 

 19. 



Table 19 



RoTJ^BTLTTTRS OF SoATE CaROTENOIDS IN SEVERAL LlPin SOLVENTS IN THE CoLD AND 



When Heated 



" RS, readily soluble. SD, soluble with difficulty. 



*- R. Willstatter and W. Mieg, Ann., 355, 1-28 (1907). 



"= F. M. Schertz, J. Agr. Research, SO, 469-474 (1925). ^ 



<* R. Willstatter and H. H. Escher, Z. physiol. Chem., 64, 47-61 (1910). 



' F. M. Schertz, J. Agr. Research, 30, 575-585 (1925). 



f R. Kuhn, A. Winterstein, and E. Lederer, Z. physiol. Chem., W7, 141-160 (1931). 



Chloroform is an excellent solvent for most carotenoids. Glacial acetic 

 acid will dissolve xanthophyll readily when heated, but only slowly in the 

 cold. Fats are also good solvents, although it must be recalled that, in the 

 case of carotenols, the pigments in natural fats do not usually occur in 

 simple solution but esterified as the so-called colored fats. Glycerol is 

 devoid of any solvent action for the carotenoids in the cold or when heated. 

 Benzene is a good solvent, especially when heated. 



c. Colloidal Suspensions of Carotene. Water is entirely ineffective as 

 a solvent for carotene or for any of the other carotenoids. However, 

 carotene can be prepared in colloidal form by the method of Fodor and 

 Schoenfeld,'**^ as well as by the procedure of Karrer et al.'^^^ Sexton and 

 co-workers*^* have also made fairly permanent aqueous carotene suspen- 

 sions by stabilizing with lecithin or propylene glycol. 



^82 A. Fodor and R. Schoenfeld, Biochem. Z., 233, 243-244 (1931). 

 ^83 P. Karrer, H. v. Euler, H. Hellstrom, and M. Rydbom, Svensk Kem. Tid., 43, 105- 

 109 (1931). 



*84 E. L. Sexton, J. W. Mehl, and H. J. Deuel, Jr., J. Nutritim, 31, 299-319 (1946). 



