FACTORS ALTERIXG NUTRITIONAL VALUE 899 



mill A occurs in some animal fats, but it is never present as such in \'ege- 

 table fats. Although the \'itamin A content of butters varies with the 

 season, with the breed and diet of the cows from which the milk has been 

 obtained, the average vitamin A content of butter in the United States 

 has been estimated, on the basis of a cooperative study, as 15,000 Inter- 

 national Units per pound.-'* The most concentrated sources of vitamin 

 A are the fish-liver oils. Cod-li\'er oil (Gadiis morrhua), w^hich has 

 general!}^ been considered to be an excellent source of this vitamin, and 

 which has served as a biologic standard for \'itamin A, has a relatively low- 

 concentration of this ^'itamin, namely, 600 I.U./g., when compared with 

 li\'er oils of the soupfin shark (Galeorhinus zyopterus), which has been re- 

 ported to ha\'e as much as 640,000 I.U./g. of oil,^*'' and even, in one case, 

 as high as 800,000 I.U./g.-*' Moderate amounts of vitamin A are found 

 in animal fats other than the fish-liver oils, in sources such as egg yolk 

 fat and in the body fat of chickens. On the basis of growth experiments, 

 Nieman-*- estimated the amount of ^•itamin A in fresh lard as 0.7 I.U./g. 

 of the lard. 



On the other hand, the plants are the principal sources of vitamin A 

 in the diet. In this case the provitamin A,(S-carotene, and related earot- 

 enoids, serA-e as sources of vitamin A. Under ordinar}^ conditions, these 

 carotenoids may occur with the minimum of fat. This is the case with 

 various green leafy vegetables, such as turnip greens, spinach, kale, and 

 broccoli, as well as with yellow, orange, or red-colored foods such as squash, 

 carrots, apricots, persimmons, and tomatoes. Although /3-carotene is not 

 A\ddely distributed in vegetable oils, red palm oil does contain the carot- 

 enoid in average amounts of 1900 I.U./g. of fresh food,'-*^ and in some 

 cases in quantities as high as 3,000 I.U./g.^^^ In fatty foods such as butter, 

 vitamin A occurs both in the form of the vitamin itself and as the pro- 

 \atamin A, namely /S-carotene. It has been the practice in the United 

 States and in some foreign countries for a number of years to add ^- 

 carotene to margarines. To parallel the average level of total vitamin A 

 in butter, established as 15,000 I. U. /pound, -^* practically all margarine 

 manufactured in the United States contains vitamin A at this same level. 



2^9 Anonymous, U. S. Dept. Agr., Miscell. Puh., No. 571, 1-14 (1945). 



"^^ W. E. Ripley and R. A. Bolomey, Calif. Dept. Nat. Resources, Div, Fish and Game, 

 Bur. Marine Fisheries, Fish. Bull. No. 64, .39-72 (1946). 



-*' L. A. Swain and B. H. McKercher, Fisheries Research Bd. Canada, Progr. Repts. 

 Pacific Coast Sta. No. 6.5, 67-69 (1945); Chem. Ahst., 40, 1681 (1946). 



282 C. Nieman, Voeding, 15, 232-240 (1954); Chem. Ahst., 48, 12263 (1954). 



283 T. A. Buckley, Malayan Agr. J., 24, 485-488 (1936). 

 28< H. P. Kaufmann, Fette u. Seifen, 48, 53-59 (1941). 



