CHEMICAL rUOPERTIES OF FATS AND OILS 275 



Concentrated alkali is mixed with the fat and is allowed to stand for several 

 days. This procedure is especially useful where the application of heat 

 would bring about changes in some component in the unsaponifiable residue 

 which is to be purified b}^ removal of the triglyceride. 



There are two saponification procedures in general use which employ 

 acid. One involves the heating of the fat with dilute hydrochloric or sul- 

 furic acid under pressure at a temperature which exceeds 100°C. The 

 other method, discovered by Twitchell,^"^-^"'^ makes use of a 1% solution of 

 sulfobenzenestearic acid (Twichell reagent) which acts catalytically to 

 produce hydrolysis. As the result of each of these reactions, glycerol and 

 the free fatty acids (rather than the soaps) are the end products. 



Another method makes use of the lipases or lipolytic enzymes. Fatty 

 acids and glycerol are the end products of this procedure. It is obvious that 

 a minimum alteration in the fat will occur, since the reaction proceeds best 

 near neutrality at about 37°C. Enzyme preparations are available from 

 animal tissues (pancreas and li\'er), as well as from such sources as the cas- 

 tor bean. Although such enzymes are believed to be on the whole non- 

 specific, in that they act on the various fats equally well, this is not always 

 the case. For example, Longenecker and Halej^^"" have sho\m that 

 markedly different rates of hydrolysis obtain when ricinus lipase of the cas- 

 tor bean acts on different fats. The rate of hydrolysis of the fats, in de- 

 scending order, was as follows: peanut, castor, corn, cottonseed, soybean, 

 rapeseed, olive, linseed, neat's foot, peach kernel, coconut, w^hale, fish, 

 and sperm. After a period of 10 hours, 97.2% of the peanut oil was hy- 

 drolyzed, while the sperm oil was split to the extent of only 19.5%. 



{£) Hydrogenation 



The process of hydrogenation of fats has developed into one of tremen- 

 dous commercial importance. By such a procedure, liquid fats can be 

 partially or completely saturated wdth hydrogen to yield solid fats which 

 have possibilities for wide variations in melting points. Hydrogenation 

 has been especially widely employed in the preparation of vegetable 

 shortenings and margarines, in the hardening of soap stock, and more re- 

 cently in improving lard from the standpoint of its hardness, plasticity, 

 and keeping qualities. The methods emploj'ed in hydrogenation have been 

 discussed in Chapter II. 



(3) Interesterification 



Several types of reaction are included under the category of interesteri- 

 fication. The interchange between an alkoxy group of an ester and the 



«' E. Twitchell, /. Am. Chetn. Soc, 28, 196-200 (1906). 

 «6 E. Twitchcll, ./. Am. Chen. Soc, 2D, 566-571 (1907). 

 *'" 11. E. Longeiiockor aiul 1). ll. Haley, J. Am. Ckem. Soc, 57, 2019-2021 (1935). 



