METABOLISM OF CAROTENOIDS AND VITAMINS A 563 



or occasionally 1:30, according to Goodwin.'^- This is not due to a poor 

 absorption of carotenes but rather to the fact that they are efficiently con- 

 verted to vitamin A,-*^''^^^'^"" presumably in the gut wall.-^^'^'*^ However, 

 orallj^-administered carotene is not utilized by chicks less than twenty-two 

 days of age when low protein diets are employed, and utilization is delayed 

 to thirty-five to forty-two days after hatching when high protein regimens 

 are fed. 9"' 



A number of investigators^"^--^"^ have reported that appreciable quanti- 

 ties of ^-carotene do occur in the hen egg. Although the amount of /3-caro- 

 tene is small, Ganguly and co-workers^^ proved its identity by determining 

 the spectrophotometric pattern m several solvents, and by the use of mixed 

 chromatograms with the pure carotenoids. Nash and Zscheile^^^ reported 

 that, in addition to /3-carotene, f-carotene, which occurs in special strains 

 of tomatoes and in carrots, is also present in eggs. f-Carotene is not be- 

 lie\'ed to be a precursor of vitamin A.^"* 



However, as indicated above, the carotenols are the principal carote- 

 noids occurring in egg yolk. The amount of the carotenols deposited 

 varies with their source, as well as with the amount ingested. Hughes and 

 Payne^^^ reported that the content of carotene and cryptoxanthin in the egg 

 varied in different hens. The percentage of xanthophyll deposited in- 

 creased when the amount of yellow corn in the ration was augmented. 

 Only 2.5% of the carotene in alfalfa was found to be deposited in the yolk. 

 Aloreover, according to the findings of Sjollema and Donath,^"^ as recal- 

 culated bj^ Deuel et al.,~°'^ carotene comprised only 7% of the total j^olk ca- 

 rotenoids when the hens had received a diet of alfalfa, or of yellow corn and 

 alfalfa, while it made up 11% of the total when the pigments in the diet 

 were derived from yellow corn alone. 



Lutein is the principal carotenol in egg yolk. It was first isolated in 

 1912 from egg yolk (from which it derives its name) by Willstatter and 



^ H. J. Almquist, G. MacKinnev, and E. Mecchi, /. Biol. Chem., 150, 99-105 (1943). 

 901 T. B. Mann, /. Agr. Sci., 36, 289-300 (1946). 



9«2 H. V. Euler and E. Klussmann, Z. physiol. Chem., 208, 50-54 (1932). 

 903 S. M. Hauge, F. P. Zscheile, C. W. Carrick, and B. B. Bohren, Ind. Eng. Chem., 36, 

 10G5-1068 (1944). 



90" T. B. IMann, Analyst, 68, 233-238 (1943). 



905 C. R. Thompson, M. A. Ervan, S. M. Hauge, B. B. Bohien, and F. W. Quacken- 

 bush, Ind. Eng. Chem., Anal. Ed., 18, 113-115 (1946). 



906 F. Harms, Chem. Zentr., 1941, II, 3007. 



907 H. A. Nash and F. P. Zscheile, Arch. Biochem., 7, 305-311 (1945). 



908 J. W. Porter, H. A. Nash, F. P. Zscheile, and F. W. Quackenbush, Arch. Biochem., 

 10, 261-265 (1946). 



909 B. Siollema and W. F. Donath, Biochem. J., 34, 736-748 (1940). 



