2S8 III. CHEMISTRY OF NEUTRAL FATS 



increase in peroxide occurs. The wide variation in induction period be- 

 tween six different samples of lard is graphically represented in Figure 16. 



Lea^^'' demonstrated that the induction period is markedly shorter when 

 the fat has previously been exposed to light. The various steps employed 

 in the commercial preparation of corn oil were sho\vn to decrease its induc- 

 tion period to a considerable extent.*''^ The purified fatty acids and glyc- 

 erol prepared from olive oil were found by Hilditch and Sleightholme^^* 

 to be much more susceptible to rancidity than was the crude olive oil. 

 These experimental facts all point to the common conclusion that some 

 natural antirancidit^y principles are present in fat which may be lost on 

 purification. 



d. Inhibitols and Antioxidants. Moureu^^"'^^^ first employed the term 

 antioxygens to define those substances which prevent the oxidation of 

 unsaturated triglycerides until they themselves have been destroyed. 

 It has been postulated that the effectiveness of the antioxidants or inhibi- 

 tols, as they are now called, lies in their ability to break the chain reaction 

 involved in oxidative rancidity. Christiansen*^^ originally proposed that a 

 chain mechanism is involved not only in rancidity but in the drying of oils. 

 Mattill, Olcott, and co-workers''^^"'*''* believe that a "moloxide" is first 

 formed. This latter compound rearranges to the more stable peroxide. 

 Either the moloxide or peroxide spontaneously breaks down, or it reacts 

 with water to facilitate the degradation whereby aldehydes are formed. 

 These aldehydes autoxidize to form peracids which are changed into 

 acids. Such a series of reactions, once started, continues to completion un- 

 less it is interrupted at some stage. This chain reaction hypothesis explains 

 why a trace of oxidized fat brings about oxidative rancidity in a large quan- 

 tity of neutral fat. 



Antioxidants presumably act to disrupt this cycle of changes in the 

 following way.*^** The oxidant, A, unites with oxygen to form a peroxide, 

 AO2. The next stage involves the simultaneous oxidation of the anti- 

 oxidant, B, by the peroxide, and the transformation of the oxidized oxidant 

 to a lower oxide, AO, according to the scheme, AO2 + B — ^ AO + BO. It 

 is assumed that these two oxides are mutually antagonistic; hence, they 



«' C. H. Lea, J. Soc. Chem. Ind., 52, 146-149T (1933). 



478 H. A. Mattill and B. Crawford, Ind. Eng. Chem., 22, 341-344 (1930). 



4" T. P. Hilditch and J. J. Sleightholme, J. Soc. Chem. Ind., 51, 39-44T (1932). 



«» C. Moureu and C. Dufraisse, Chem. Revs., 3, 113-162 (1926). 



481 C. Moureu, C. Dufraisse, and P. Lotte, Ind. Eng. Chem., 22, 549-551 (1930). 



482 J. A. Christiansen, Trans. Faraday Soc., 24, 714-715 (1928). 

 «3 H. A. Mattill, /. Biol. Chem., 90, 141-151 (1931). 



484 H. S. Olcott, J. Am. Chem. Soc, 56, 2492-2493 (1934). 



488 R. B. French, H. S. Olcott, and H. A. Mattill, Ind. Eng. Chem.., 27, 724-728 (1935). 



486 H. S. Olcott and H. A. Mattill, Oil & Soap, 13, 98-100 (1936). 



487 L. A. Hamilton and H. S. Olcott, Oil & Soap, 13, 127-129 (1936). 



<88 H. S. Olcott and H. A. Mattill, J. Am. Chem. Soc, 58, 1627-1630 (1936). 



