828 XIII. ESSENTIAL FATTY ACIDS 



although, in some cases, such as in linseed oil, appreciable amounts of 

 linolenic acid may occur. Arachidonic acid, on the other hand, is never 

 found in vegetable fats. In contradistinction to the relatively high content 

 of EFA in most vegetable fats, the proportion in' animal fats is much lower, 

 and, in many cases, practically none are present. Although arachidonic 

 acid is frequently present in animal fats, linoleic acid may be present in a 

 much larger proportion in these fats. Moreover, after a high intake of 

 linolenate-containing fats, this trienoic acid may also appear in animal fats. 

 For a more complete treatment of this topic, the reader is referred to two 

 recent reviews of Deuel. ^^'^^^ 



b. Presence in Vegetable Fats. As noted above, the vegetable fats 

 have the highest EFA content of any of the natural or processed fats. 

 Data on the essential fatty acid composition of vegetable fats are summar- 

 ized in Table 1. 



In the case of linseed oil and of several other vegetable fats, a poor agree- 

 ment has been noted between the results recorded spectrophotometrically 

 and by bioassay. Thus, although linoleate values as high as 46.7% and 

 figures for linolenate in some cases as high as 60.9% have been recorded 

 for linseed oil, the bioassay values of two samples reported by Thomasson'^ 

 were only 11.9% and 25.6%. In the case of cocoa butter, the bioassay 

 value is given as 2.2% as compared with a figure of 21.1% determined spec- 

 trophotometrically. Coconut (and especially hydrogenated coconut oil) 

 and castor oils have been reported to contain practically no essential fatty 

 acids, as determined by spectrophotometric and bioassay procedures. 



c. Presence in Animal Fats. The quantity of EFA in animal fats is 

 largely a matter of the species from which the fat was obtained; also, in 

 cases in which the EFA can be stored, the proportion in the fat varies with 

 the previous diet of the animal. The essential fatty acid contents of some 

 common animal fats are given in Table 2. 



Andrews and Richardson--'* made a comprehensive study of the distri- 

 bution of linoleic, oleic, and saturated acids in various samples of lard, 

 butterfat, margarine fat, hydrogenated shortening and mixed animal and 

 vegetable shortening, Avhile Holman and Greenberg-* studied the distribu- 

 tion of tetraenoic, pentaenoic, and hexaenoic acid in the non-adipose tissue 

 of lambs, hogs, and beef cattle. In lambs and cattle the highest content of 

 arachidonic acid was in the testes. Hog ovaries had the highest content 

 for this animal, followed closely by testes and uterus.-^ 



The animal fats which may contain relatively high amounts of EFA in- 

 clude that from the hog, from the fowl, and especially that in the egg. 



22^ J. T. R. Andrews and A. S. Richardson, Oil & Soap, 20, 90-94 (1943). 



