CHEMICAL PROPERTIES OF FATS AND OILS 



299 



ascorbic acid were both present in autoxidizing fat, the induction period 

 was greatly prolonged over that noted when only tocopherol was present.^*^ 

 On the other hand, animal fats containing no tocopherol became rancid 

 while much of the ascorbic acid still remained. ^^^ In the presence of tocoph- 

 erol, however, the ascorbic acid became oxidized. Thus, while ascorbic 

 acid was found to be an excellent stabilizer for tocopherol, ^'*^ it is of little 

 value alone in preventing rancidity, since it is not oxidized by fat per- 

 oxides and does not pre\'ent their formation. However, because ascorbic 

 acid is able to protect tocopherol, the onset of rancidity is greatly delayed 

 by the so-called synergistic action of this substance. 



Clausen, Lundberg, and Burr^^^ have classified the various synergists, in 

 Table 44, according to the degree of protective action which they exert on 

 fats. In addition to ascorbic acid, various amino acids and protein de- 

 rivatives are included as s>aiergistic compounds. 



In addition to the effects listed in Table 44, the authors report definite 



Table 44 



Comparative Synergism of Some Amino Acids and Other Substances with 



Antioxidant Action of Some Phenolic Antioxidants in Lard" 



Phenolic 



antioxidant 4.0-3.1 



Synergists having protective indices ^ as follows 



3.0-2.1 



2.0-1.6 



Qf-Tofopherol None 



ITydroquinone 



Alethi- 

 onine 



Ascorbi(! acid, Threonine, leucine, milk protein hydrolysate 

 methionine #2, norvaline, ascorbyl palmitate, phenyl- 



alanine, milk protein hydrolysate #1, 

 cysteine 



Ascorbic acid, Leucine, milk protein hydrolysate #2, 

 milk protein ascorbjd palmitate, proline, phenylalanine, 

 hj'droh'sate #1, cysteine, alanine, glutamic acid, valine, pep- 



tryptophane 



Nordihydro- 

 guaiaretic acid 



None Methionine 



tic digest of pancreas protein, asparagin, 

 arginine, barbituric acid, arsphenamine, 

 ninhydrin, propanidine, histidine, norleu- 

 cine, glycerophosph'oric acid, trypsin, HCl 

 hydrolysate of casein 



Phenylalanine, leucine, tryptophane, ala- 

 nine, norleucine, milk protein hydrolysate 

 #2, norvaline, valine, ascorbic acid 



" Adapted from D. F. Clausen, W. O. Lundberg, and G. O. Burr, /. Am. Oil Chemists' 

 Soc, 2/,, 403-404 (1947). 



* Protective index is ratio of keeping time in hours of substrate plus 0.01% of phenolic 

 antio.xidaiit and plus 0.01% of synergist to that of substrate with 0.01% of phenolic 

 antioxidant alone. 



effects (protective index 1.3-1.1) in the case of other amino acids and re- 

 lated products as well. 



f. Prooxidants. Prooxidants may be defined as substances which in- 

 crease the susceptibility to oxidation.^"*^ In this group of substances, the 



»« O. Isler, Helv. Chim. Acta, 21, 1756-1759 (1938). 



»« D. F. Clausen, W. O. Lundberg, and G. O. Burr, J. Am. Oil Chemists' Soc, 24, 

 403^04 (1947). 



»" L. A. Hamilton and PL S. Olcott, Ind. Eng. Chem., 29, 217-223 (1937). 



