832 XIII. ESSENTIAL FATTY ACIDS 



available for these samples. The method of hydrogenation was shown 

 to have an interesting effect not evident from the spectrophotometric 

 assays.''^ Thus, a shortening prepared by selective hydrogenation showed 

 a close agreement between the EFA content determined spectrophoto- 

 metrically and biologically (2.1% vs. 2.74%). On the other hand the 

 corresponding figures for shortening prepared by non-selective hydro- 

 genation were 6.8% and 13.24%. This would indicate that the actual 

 EFA content can be established only by actual bioassay, and cannot 

 always be predicted from analytical results. 



e. Presence in Butters and Milk Fats. The EFA content of butter is 

 the lowest present in any single grou]) of fats (see Table 3). Thus, in a 

 series of forty-one butters analyzed by the thiocyanogen method by 

 Andrews and Richardson,--'' the range of linoleic acid content varied only 

 from 4.8 to 1.4%, with an average of 3.1%. However, this does not take 

 into consideration the arachidonic acid which is also present in butter. 

 In an examination of the EFA content of two butters from the New York 

 market (one with the lowest and the other with the highest iodine number) , 

 values of 2.4% and 3.81% of EFA were reported on bioassay, although the 

 spectrophotometric analysis might lead one to expect somewhat higher 

 values.''^ According to Thomasson,^^ the value as determined by bioassay 

 for three summer butters averaged only 1.1 (0.6, 1.3, 1.3). Human milk 

 fat appears to have a higher content of essential fatty acids than does 

 that of cow's milk fat. Farther experiments are in order to obtain addi- 

 tional data on the EFA content of butters and milks })y bioassay, as influ- 

 enced by various environmental conditions and liy feeding of the animal. 



(^) Distribution in Animal Tissues 



The quantity of the several EFA present in the tissues depends to a con- 

 siderable extent upon the dietary conditions. This is particularly true in 

 the case of the blood. Thus, Wiese et al.^^~ showed that the average EFA 

 contents of the blood of sixty healthy children who had partaken of diets 

 containing approximately 3% of the total calories as linoleate were as 

 follows, in percentages of the total fatty acids: dienoic acids, 30.3%; 

 trienoic acids, 1.5% ; and tetraenoic acids, 10.2%. The value for hexaenoic 

 acid in the serum of healthy children was variable. These workers state 

 that the role of the pentaenoic and hexaenoic acids, if any, is not known. 

 On the other hand, Hansen and Wiese^^^ were unable to find any significant 

 differences in the total fatty acids in the blood of poorly nourished children 



225 A. E. Hansen and H. F. Wiese, J. Nutrition, 52, 367-374 (1954). 



