CHAPTER VI 

 CAROTENOIDS AND RELATED COMPOUNDS 



A. GENERAL CONSIDERATIONS ON THE RELATIONSHIP 

 BETWEEN CAROTENES AND THE VITAIVIINS A 



The carotenoids were recognized as chemical entities long before anything 

 was known about the existence of vitamin A. In fact, Wachenroder^ iso- 

 lated carotene (carotin) from carrots as early as 1826, while the first con- 

 centrated preparation of vitamin A was not made until 105 years later by 

 Karrer.-'^ Undoubtedly, the early recognition of the carotenoids is due to 

 the fact that they are so widely distributed as coloring agents in vegetable 

 and animal products. Moreover, they can be readily separated from the 

 protein, carbohydrate, and salts of natural products because of their 

 specific solubility in fat solvents; their preparation is especially simple 

 where such foods have a low fat content. However, even in the presence of 

 considerable amounts of fat, the carotenoids can readily be separated from 

 the triglycerides, since they are components of the non-saponifiable frac- 

 tion. 



The first evidence of the existence of vitamin A was the result of the 

 pioneer work of Hopkins'* in Great Britain in 1912. This worker demon- 

 strated that normal growth did not occur in rats unless certain so-called 

 "accessory food factors" were included in the diet. These supplements 

 were necessaiy when the basal diet consisted of mixtures of purified pro- 

 teins, fats, carbohydrates, and minerals, and was devoid of natural foods. 

 One of the groups of these accessory substances was shown by Osborne and 

 MendeP"' and by McCollum and Davis*"^^ to be a fraction, present in 



1 H. Wacheiiroder, Uber das Oleum radicis Dauci Aetherum, das Carotin, den Carotin- 

 zucker, und den officinellen Suceas Dauci, Dissertation de anthelminticis, Gottingen, 

 Geiger's Mag. Pharm., 33, 144-172 (1831). Cited by L. S. Palmer, Carotinoids and Re- 

 lated Pigments, Chemical Catalog Co., New York, 1922, p. 25. 



2 P. Karrer, R. Morf, and K. Schopp, Heir. Chim. Acta, U, 1036-1040 (1931). 



3 P. Karrer, R. Morf, and K. Schopp, Helv. Chim. Acta, U, 1431-1436 (1931). 

 ^ F. G. Hopkhis, J. Physiol., U, 425-460 (1912). 



s T. B. Osborne and L. B. Mendel, J. Biol. Chem., 15, 311-326 (1913). 

 6 T. B. Osborne and L. B. Mendel, J. Biol. Chem., 16, 423-437 (1913). 

 ' T. B. Osborne and L. B. Mendel, J. Biol. Chem., 17, 401-408 (1914). 

 » E. V. McCollum and M. Davis, ./. Biol. Chem., 15, 167-175 (1913). 

 9 E. V. McCollum and M. Davis, J. Biol. Chem., 19, 245-250 (1914). 

 "> E. V. McCollum and M. Davis, J. Biol. Chem., 20, 641-658 (1915). 

 11 E. V. McCollum and M. Davis, /. Biol. Chem., 23, 231-246 (1915). 



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