274 IIT. CHEMISTRY OF NEUTRAL FATS 



that such asjTnmetry without measurable optical activity may well be a 

 characteristic of triglycerides made up of fatty acid residues. When 

 aromatic nuclei such as occur in a:-(29-nitrobenzoyl)-o:',i8-dibenzoglycerol 

 are present, an intense optical rotation is observed. It is further suggested 

 that, although the natural asymmetric triglycerides do not show a rotation, 

 they may not be racemic but might be present in either of the two possible 

 enantiomorphic forms. The optical isomerism observed by Suzuki and 

 Inoue^"*'*"^ in freshly isolated natural fats may possibly be attributed to a- 

 monoglycerides, since these compounds show a gradual decrease in rotation 

 on standing at room temperature. 



7. Chemical Properties of Fats and Oils 



{1) Hydrolysis 



The most vulnerable spots in the triglyceride molecule are the ester link- 

 ages. In the digestion and absorption of fat, the first change which, it is 

 generally agreed, takes place, is the hydrolysis of the ester linkage, with the 

 resultant formation of glycerol and three free fatty acid molecules. Not 

 until this primary rupture has taken place can any profound alteration occur 

 in a saturated fat molecule ; however, it is possible for changes to be brought 

 about on unsaturated triglycerides without the breaking down of the ester 

 linkage, although this does not take place in the alimentary tract. Such 

 reactions as occur at the double bonds may completely change the physical 

 properties of the fat. 



There are a number of ways in which hydrolysis of the triglycerides may 

 be produced. These methods are all ordinarily referred to as saponifica- 

 tion (soap-making), since most frequently employed procedures require 

 alkali, with the formation of soap as one of the end products. Soaps are 

 not produced where saponification results from acid or enzyme hydrolysis. 



Four methods for alkaline hydrolysis are in general use. The common- 

 est procedure involves the heating of the fat with a solution of sodium or 

 potassium hydroxide at a boiling temperature. Aqueous solutions of the 

 alkalies may be employed, but more rapid results obtain with alcoholic 

 solutions (such as alcoholic potash), where the reaction can proceed in a 

 one-phase sj'stem. A slight modification of this procedure involves the 

 use of sodium ethylate. Hydroh^sis is completed when the fat and sodium 

 ethylate are refluxed for at least 30 minutes. Saponification can be readily 

 produced by autoclaving, in which the fats are treated with superheated 

 steam in the presence of small amounts of calcium hydroxide. 



The cold saponification method is the mildfest one which employs alkali. 



«3 B. Suzuki, Proc. Imp. Acad. Tokyo, 7, 230-233 (1931); Chem. Zentr., 1931, II, 2345. 

 «^ B. Suzuki and Y. Inoue, Proc. Imp. Acad. Tokyo, 6, 71-74 (1930); Chem, Abst., 24, 

 4265 (1930). 



