THE DIGESTION OF FATS 141 



acted on a homogeneous solution of tripropionin, 1,2-dipropionin was 

 first formed, followed later by monopropionin, which was proved to be 

 mainly the 2-isomer. Whereas the first hydrolysis, namely tripropionin -*■ 

 1,2-dipropionin, represented a fairly rapid reaction, the next change, viz., 

 1,2-dipropionin -*■ 2-monopropionin, proceeded at an extremely slow rate. 

 The presence of free alcoholic groups, especially of primary groups, was 

 found to greatly decrease the rate of hydrolysis of the in vitro reaction in a 

 manner similar to that of its inhibition of the in vivo hydrolysis. Peers 661 

 reported experiments with tributyrin which would seem to indicate that the 

 action of lipase on tributyrin is only partial. When this triglyceride was 

 treated with a purified cat lipase, only one fatt3>- acid was split off, and the 

 hydrolysis did not proceed further. 



Loncin 662 reported a confirmation of the stepwise degradation of tri- 

 glycerides based upon an entirely different approach. This worker ob- 

 served that palm oil, on storage, undergoes a partial hydrolysis by the 

 process of "spontaneous autocatalytic hydrolysis." The fact that the speed 

 of hydrolysis increases with the elevation of the temperature to fairly high 

 levels precludes an enzymatic or bacterial mechanism. The first phase 

 of the reaction involves the formation of diglycerides and free fatty acids 

 from the palm oil; after the acidity has reached a certain degree, mono- 

 glycerides and free fatty acids tend to be formed from the diglycerides. 

 No free glycerol could be demonstrated until more than 18% of the fatty 

 acids had been liberated. After 115 days of storage at 70 °C, the follow- 

 ing percentage composition was noted: triglycerides, 22.2%; diglycerides, 

 26.4%; monoglycerides, 10.85%; and free fatty acids, 40.6%. 



c. The Bile Requirement. Irrespective of which of the theories best 

 explains the mechanism of the absorption of fats, there is no question that 

 bile plays an essential role in promoting both the digestive and the absorp- 

 tive phases of this physiological phenomenon. We have discussed earlier 

 how the action of bile can be largely attributed to the bile salts present 

 therein. These bile salts help to activate steapsin, and in this manner ac- 

 celerate the digestion of the fat molecule. The bile salts also have a solu- 

 bilizing effect on the neutral fats, di- and monoglycerides, as well as on 

 the fatty acids. In the case of incompletely digested fats, this behavior 

 will allow a more intimate contact between the water-soluble lipases and the 

 fatty substrates. 



There are many explanations for this so-called "solubilizing" effect. 



661 F. G. Peers, Nature, 171, 981-982 (1953). 



662 M. Loncin, L'Hydrolyse spantanSe des huiles glyceridiqy.es el en particulier de I'hvile 

 de palme, Couillet, Brussels. 



