» II. CHEMISTRY OF FATTY ACIDS AND GLYCEROL 



The composition of fat from a single tissue in the same species of animal 

 may again show wide variations. One may go so far as to say that in the 

 same animal the fat may change with alterations in diet. One need only 

 be reminded of the variation of fat laid down by hogs on a normal diet as 

 contrasted with "soft pork" produced when the food contains large amounts 

 of soybean oil.- Similar variations in the composition of egg-yolk fat have 

 been produced by changes in the dietary fat.^ 



From these considerations, it should be self-evident that the fats are too 

 numerous and subject to too great variations in composition to allow for a 

 strict classification. Identification by the terminology currently em- 

 ployed will, of course, continue to be of value for many commercial appli- 

 cations. It can hardly be expected to serve for the characterization of 

 fats for research stud}^ or even for critical industrial uses. Here, the 

 composition of any product must be identified by the proportion of the 

 various triglycerides, the quantity and type of unsaturated linkages, the 

 amount of mono- or diglycerides, and by the specific composition of the 

 non-saponifiable fraction. The present chapter will include a discussion 

 of the structure and properties of the fatty acids and glycerol which make 

 up the triglycerides. A similar treatment of the components of the non- 

 saponifiable residue will follow in the later chapters. 



The subject of fatty acids has been exhaustively reviewed in the two ex- 

 cellent recent monographs of Markley^ and of Ralston.* The most com- 

 plete treatment of glycerol is given by Lawrie® in a monograph of the 

 American Chemical Society. 



2. Classification and Structure of Fatty Acids 



The most important conditions which regulate the nature of fat are the 

 kind and proportion of the various fatty acids present in the triglyceride 

 molecule. Since fats and oils consist almost entirely of triglycerides, i.e., 

 fatty acid esters of the trihydrie alcohol, glycerol, the fatty acid component 

 accounts for 90% of the molecule of most natural fats. Although small 

 amounts of di- or monoglycerides may exist in some fats, these constituents 

 are present in too small an amount to alter the 90% proportion of the fatty 

 acids. 



The fatty acids present in animal and vegetable fats are limited to a 

 comparatively small number of representatives. One important generaliza- 



2 N. R. Ellis and H. S. Isbell, J. Biol. Chem., 69, 239-248 (1926). 



3 R. W. Riemenschneider, N. R. Ellis, and H. W. Titus, /. Biol. Chem., 126, 255-263 

 (1938). 



■* K. S. Markley, Fatty Acids, Interscience, New York, 1947. This contains an excel- 

 lent discussion on nomenclature and a complete listing and discussion of the intiividual 

 fatty acids. 



* A. W. Ralston, Fattij Acids and Their Dcrirutivcs, Wiley, New Yoik, 1948. 



* J. W. Lawrie, Glycerol and the Glycols, Rcinhuld, New York, 1928, pi). 1 447. 



