COMPOSITION OF NATURAL FATS AND OILS 215 



disaturated-monounsiituratcd trigl3^cerides (GS2U), if present in small 

 amounts, will become totally saturated before any of the monosaturated- 

 diunsaturated (GSU2) or triunsaturated triglycerides (GU3) are completely 

 hydrogenated. Hydrogenation follows the above pattern, especially if the 

 so-called agitation process is employed. ^^^-^^^'^^^ On the other hand, 

 when the "drip" method is used (in which case the catalyst remains un- 

 disturbed instead of being constantly churned), the addition of hydrogen 

 does not occur in a stepwise fashion but in a haphazard manner. 



In his more recent work, Hilditch'^ has employed the procedure of 

 Brown^^^ for the fractional crystallization of the whole fat from acetone at 

 very low temperatures. Each fraction is analyzed for trisaturated glyc- 

 erides, for the quantitative distribution of the fatty acids by fractional 

 distillation of their esters, and for the unsaturated C18 glycerides after com- 

 plete hydrogenation. From such information, when the solubility of 

 specific triglycerides is kno\\Ti, the approximate glyceride structure can be 

 deduced. The combination of these methods has proved much more 

 satisfactory than the application of any single one.^^^~^^^ 



(c) Estimation of Triglyceride Structure hy Low-Temperature Crystalliza- 

 tion (Brown). The separation of triglyceride fractions by crystallization 

 from acetone at various low temperatures from 0° to — 60°C. as first worked 

 out by Brown"^ has become more and more widely used. The proportion 

 of GS2U and GSU2 can be determined by this procedure. If the fractiona- 

 tions are properly carried out, they may contain: (1) a mixture of GS3, 

 GS2U, and GSU2, (2) GS2U and GSU2, or (3) GSU2 and GU3. If the total 

 fatty acid composition has been determined and the composition of (1) 

 or {£) is kno\m, the amount of GU3 can be calculated. Not only can the 

 value of GSU2 and GU3 be deduced from the total fatty acid content and 

 an analysis of (3), but also that of GS2U. A comparison of the fractiona- 



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