Chapter VIII 

 Methods of Isolation of Carotinoids 



The isolation of the various carotinoid pigments is attended with 

 certain difficulties, which are chiefly mechanical, even if one desires 

 to secure only a few grams of pure crystals. The pigments are all 

 quite intense * so that one is readily deceived by the color as to the 

 actual amount of pigment which is present. This fact makes it neces- 

 sary to carry out the operations involved on a rather generous scale, 

 in order that the yields may justify the effort. The difficulties from 

 a chemical point of view are due primarily to the great ease of oxida- 

 tion of the pigments and secondarily to the presence of colorless lipoid 

 impurities which unavoidably contaminate the crude products because 

 of the necessity of using the lipoid solvents for the extraction process. 

 The great ease of oxidation of the carotinoids requires the employ- 

 ment of vacuum in carrying out all concentrations and the use of 

 inert gases, if possible, during crystallization processes. The removal 

 of lipoid impurities naturally depends somewhat on the nature of 

 the contaminating substances. Where relatively large amounts of 

 glycerides are involved it is necessary to resort to saponification and 

 subsequent extraction of the unsaponified pigment. As far as carotin 

 is concerned, or its isomer lycopin, this can be done without injury to 

 the pigment. There may be some question whether or not certain of 

 the xanthophylls are altered slightly by this process. For the caro- 

 tinoid fucoxanthin, however, saponification should certainly be avoided 

 as it is known to form a compound with alkalis under certain con- 

 ditions. The sterols are removed by washing the crystals with cold 

 solvents, depending upon the carotinoid involved. For carotin, cold 

 alcohol (absolute or 98 per cent) is best, and for xanthophyll cold 

 petroleum ether (b. p. 40-60 C.). Recrystallization must of neces- 

 sity be resorted to for the final purifications. The details of the 

 operations are mentioned below. 



'According to Arnaud (1887) carotin is still visible in carbon disulfldc in 1 part per 

 million of solvent. 



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