564 IX. CAROTENOIDS AND VITAMINS A 



Escher.^^" However, it was later demonstrated by Kiihn et al.,''^ by the 

 application of chromatographic technics, that the lutein in egg yolk could 

 actually be separated into two fractions. "Lutein" has continued to serve 

 as the designation for the first of these, while the second one was shown to 

 be zeaxanthin; the latter was prepared in pure form from eggs by the ap- 

 plication of chromatographic methods, by Strain" and by Euler and Gard.''^ 

 Cryptoxanthin, which is a monohydroxycarotenol and a provitamin A, has 

 also been reported in egg yolk by Gillam and Heilbron.^^ 



Vitamin A is regularly present in egg yolk. The amount in the egg varies 

 with diet. According to Sherman,^^^ vitamin A is present to the extent of 

 2500 to 5000 I.U./IOO g. egg yolk; this amounts to 400 to 800 I.U./16 g., 

 which is the weight of the average yolk. Russell and Taylor^^^ cite values 

 of 500 to 800 I.U. per yolk, while Deuel et al.^'^'^ report figures of 803 to 872 

 I.U. of total vitamin A per 18 g. yolk for all birds receiving supplemental 

 vitamin A up to 15,000 I.U./lb. of food. Vitamin A alcohol has been re- 

 ported to comprise 71 to 93% of the total vitamin A in the egg.^'^ 



Diet influences the carotenoid and vitamin A content of eggs, to about 

 the same extent as it does that of milk. Palmer and Kempster^^^ were the 

 first to recognize the relationship between dietary carotenoids and the color 

 of the egg yolk. On carotenoid-free diets, the carotenoid content in egg 

 yolk slowly decreases.^'^-^^^ 



Ganguly and co-workers*^ reported that the administration of a carote- 

 noid-free diet to hens previously on a "farm" diet resulted in a complete 

 disappearance of (8-carotene and a practically complete absence of lutein; 

 the proportion of vitamin A was also decreased. These data are sum- 

 marized in Table 7. 



When hens are placed on a carotenoid-free diet after having received a 

 carotenoid-rich one, the eggs continue to be pigmented for some time, since 

 the xanthophylls are transferred from the skin and shanks to the eggs.^'^ 

 On the other hand, when hens which have been receiving a carotenoid-free 

 diet are transferred to a high-carotenoid diet, xanthophylls appear in the 

 yolk,*^2 although from two to six eggs are laid before the maximum degree 

 of color is noted in the egg yolk.*^^ 



9i» R. Willstiitter and H. H. Escher, Z. physiol. Chem., 76, 214-225 (1912). 



911 H. C. Sherman, Chemistry of Food and Nutrition, 7th ed., Macmillan, New York, 

 1947, p. 634. 



"2 W. C. Russell and M. W. Taylor, /. Nutrition, 10, 613-623 (1935). 



"3 A. W. Neff, D. B. Parrish, J. S. Hughes, and L. F. Payne, Arch. Biochem., ^/, 315- 

 320 (1949). 



91^ L. S. Palmer and H. L. Kempster, /. Biol. Chem., 39, 331-337 (1919). 



9'5 B. B. Bohren, C. R. Thompson, and C. W. Carrick, Poultry Sci., 34, 356-362 

 (1945). 



"6 F. H. Grimbleby and D. J. G. Black, Brit. J. Nutrition, 4, 323-331 (1950). 



