COMPOSITION OF NATURAL FATS AND OILS 179 



4. Composition of Natural Fats and Oils 



There are an almost infinite number of different fats and oils, each of 

 which possesses a specific composition. One of the conditions which render 

 this phenomenon possible is the wide variation found in the total number 

 of varieties of fatty acids represented in any one fat. Another contribut- 

 ing factor is that the proportions between any given groups of fatty acids 

 may show an almost limitless number of variations. But even with two 

 fats containing the same series of fatty acids in exactly the same propor- 

 tions, noticeable alterations in the physical properties and the chemical 

 characteristics of such fats may still be predicted. This may be at- 

 tributed to the wide variety of mixed triglycerides which are possible; since 

 these components make up a large proportion of the natural fat, variations 

 in them would necessarily change the character of the component fat. 



Hilditch has determined the composition of some 600 different kinds of 

 fats. The results of these investigations are included in his comprehen- 

 sive monograph.''^ Included in his study are 100 fats of aquatic origin, 80 

 fats from land animals, and 420 fats from various plant species. Some of 

 the important conclusions have been summarized in the recent review of 

 Longenecker.^'^ 



The results of Hilditch have demonstrated the close connection in the 

 tjTDe and the proportion of the fatty acids in plants and animals having a 

 close taxonomic relationship. The most intricate structures and the most 

 complex forms of fatty acids have invariably been shown to occur in the 

 simplest forms of plant and animal life. In fact, Hilditch and Lovern*" 

 have called attention to the fact that a simplification in structure and 

 number of the component fatty acids seems to be associated with an ascend- 

 ing evolutionary scale. 



(1) Component Fatty Acids in Natural Fats and Oils 



a. Analysis of Fats. The estimation of the proportion of the several 

 fatty acids composing a fat is a relatively simple procedure as compared 

 with the determination of the arrangement of the fatty acids in the triglyc- 

 eride molecules. A number of different procedures are now available for 

 the quantitative analysis of the fatty acids. 



(a) Fractionation into Saturated and Unsaturated Acids. A preliminary 

 separation of the fatty acids into two portions, depending upon the solubility 

 of their lead soaps in alcohol,*^"^^ is usually the first step. After saponifica- 



" T. P. Hilditch, The Chemical Constitution of the Natural Fats, 2nd ed., Wiley, New 

 York, 1947. 



^ T. P. Hilditch and J. A. Lovern, Nature, 137, 478-481 (1936). 



81 T. P. Hilditch, Chem. Products, 3, 78-81 (1940); Chem. AbsL, So, 1653 (1941). 



" T. P. Hilditch and J. Priestman, Analyst, 66, 354-367 (1931). 



" E. Twitchell, Ind. Eng. Chem., 13, 806-807 (1921). 



