VII. OCCURRENCE IN FOODS 



291 



Thus far no microbiological assay methods have been developed for es- 

 sential fatty acids, although it would seem possible to find an organism 

 which requires essential fatty acids. The demonstration of essential fatty 

 acid deficiency in insects points to their possible use as assay animals." 



VII. Occurrence in Foods 



RALPH T. HOLMAN 



The essential fatty acids are abundant in nature. Most common vegetable 

 oils contain linoleic acid or linolenic acid, and lard and other animal 

 lipids contain linoleic, arachidonic, and more highly unsaturated acids. 

 Although linoleic and linolenic acids occur as major constituents in numer- 

 ous vegetable oils, arachidonate is found only as a minor constituent in 



TABLE III 

 Essential Fatty Acid Contents of Some Common Fats and Oils 



Fat or oil 



Corn oil 

 Cottonseed oil 

 Soybean oil 

 Olive oil 

 Lard 



Butterfat 

 Beef tallow 



common animal fats. Its concentration in certain tissue lipids, however, 

 may be as high as a few per cent.' ■ - The presence of linolenic acid in animal 

 fats is probable, but unequivocal evidence for its presence is not available 

 except in a few cases. Many of the reports of linoleic acid and linolenic acid 

 in animal fats are based upon analyses not specific for linoleic acid, such as 

 iodine plus thiocyanogen values, or upon spectrophotometric analyses in 

 which the higher polyunsaturated acids were overlooked (see p. 287). 

 However, the occasional very high values reported for linoleate and lino- 

 lenate, even when such methods of analysis are used, speak loudly for the 

 occurrence of these acids in animal lipids. 



As an illustration of the amounts of the essential fatty acids available 

 in common fats and oils, a few examples are given in Table III. Similar 



" G. Fraenkel and M. Blewett, J. Expil. Biol. 22, 172 (1946). 

 ' C. Widmer and R. T. Holman, Arch. Biochem. 25, 1 (1950). 

 2R. T. Holman and T. S. Taylor, Arch. Biochem. 29, 295 (1950). 



