CHAPTER II 



THE CHEMISTRY OF FATTY ACIDS 

 AND GLYCEROL 



1. Introduction 



In his monumental treatise on the chemical constitution of various fats, 

 Hilditch^ has discussed the properties of some 600 different fats, which he 

 has arranged according to their biological relationship. The fats con- 

 sidered include 420 samples from various plant species, 80 from land ani- 

 mals, and about 100 of aquatic origin. In only a few instances have these 

 included more than one fat from different parts of the same animal or 

 plant. 



However, the number of natural fats which differ sufficiently in proper- 

 ties and composition to be considered as entities must be many times those 

 listed by Hilditch. Each plant and animal has at least one lipid which is 

 characteristic of its particular species; in fact, in the case of the higher 

 animals a considerable variety of fats occur in the different tissues and 

 organs of the same animal. It is a well-known fact that the composition of 

 subcutaneous fat varies considerably from that of mesenteric fat, while 

 perirenal, omental, genital, intermuscular, and liver fat each possesses its 

 own characteristic composition and properties. Moreover, the lipids 

 present in the heart, brain, spinal cord, and in fact in every separate tissue, 

 can also be classified as individual fats. 



The number of individual fats is further augmented by species varia- 

 tions. Samples of cottonseed or soybean oil from diverse varieties of the 

 plants have a somewhat different make-up typical of that species. In the 

 case of animals, it is well known that milk fat differs in each kind of ani- 

 mal, and that it may be identified by its characteristic fatty acid content. 

 Even in two species as closely related as the Holstein and the Guernsey 

 cow, the milk fat may appear to be quite different, since it has a low caro- 

 tene content in the first case and a relatively high one in the second in- 

 stance. Such variations make it advisable to consider that butter fat is 

 not a single fat of uniform composition but rather that a number of dif- 

 ferent butters actually exist which may have wide alterations in composi- 

 tion. 



1 T. P. Hilditch, The Chemical Constitution of Natural Fats, Wilev, New York, 2n(l 

 cd., 1947. 



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