Photo by Laufier-Fils,Grassc
Antioxidants for Fats and Oils GEORGER. GREENBANK AND GEORGEE. HOLM Bureau of D a i r y Industry, D e p a r t m e n t of Agriculture, Washington, D. C.
I
NTENSIVE work on antioxidants began with the study by Moureu and Dufraisse (6) of the inhibiting effect of hydroquinone upon the oxidation of acrolein and of benealdehyde. Their initial studies showed that substances having a phenolic group protected a number of autoxidizable compounds against the action of oxygen. Later work showed that various compounds, not necessarily phenolic in character, which under suitable conditions are easily oxidizable, act as antioxidants (6). To explain the mechanism of antioxidants, these authors employ the theory of antagonistic peroxides. The principal steps therein may be illustrated as follows: A 0 2 +A [ 0 2 ] ; A [ 0 * ] B +A 0 BO A 0 +BO + A B 0 2 or A +02+A[021; B+Oz+B[021 A[021 B[Ozl+ A B 202 where A = an activated molecule B = the antioxidant
+
+
+ + + + +
+
The antioxidative effect of phenol, alcohols, and other compounds upon fats and oils has been noted in a former publication from these laboratories ( 3 ) . The present investigations deal with a further attempt to determine what other types of compounds may be effective as antioxidants for fats and oils.
EXPERIMENTAL METHOD During the oxidation of fats and oils, peroxides are formed, their rate of formation being a measure of the ease with which an oil will oxidize. The amount of peroxide formed in a definite period of time under specified conditions serves, therefore, as an index of oxidation. Untreated samples and samples to which 0.01 per cent of the antioxidant had been added were stored at a temperature of 42' C. for 10 days, and the peroxide content was then determined as follows: 50 cc. of a solution consisting of two parts of acetic acid and one part of trichloromethane by volume was added to a weighed sample of fat. To this mixture was added one cc. of a saturated aqueous solution of potassium iodide. The mixture was kept in the dark for 3 minutes, and 50 cc. of distilled water were then added. The liberated iodine was titrated with 0.002 N sodium thiosulfate. The number of cubic centimeters of 0.002 N sodium thiosulfate used per gram of fat is equivalent t o the number of millimoles of peroxide per kg. of fat. The weight of the sample of fat used must be governed by the peroxide content. In no case should the iodine liberated be equivalent to more than 15 cc. of 0.002 N sodium thiosulfate. From 0.25 to 0.75 gram is usually a convenient and satisfactory quantity to use.
The results obtained have been expressed in terms of the relative amounts of peroxide formed in a sample of fat and in another sample of the same fat to which an antioxidant had been added. This has been designated as the protective factor (P. F.) and is obtained as follows: P.F.
=
millimoles of peroxide per kilogram of untreated fat millimoles of peroxide per kilogram of treated f a t
A protective factor of 1.0 indicates, therefore, no protective action.
NATURAL PIGMENTS Certain oils, especially those of plant origin, contain carotinoid pigments. These pigments are also constituents of some animal fats and oils, especially butter fat. That these pigments influence the rate of fat oxidation has been shown by Olcovich and Mattill (8) who maintain that carotene is a procatalyst. Monahan and Schmitt (4), as well as Newton and Richardson (i'), class this compound as an antioxidant. The results of Franke (1) agree in general with those of Olcovich and Mattill. F'ranke found that carotene and lycopene were antioxidants for acids but not for their glycerides. To ascertain the extent to which natural coloring matter might be a factor in determining the rate of peroxide formation, the effect of the lipochromes carotene and lycopene, and a flavone, quercetin, when added to a fat has been determined. The results are given in Table I. TABLEI. NATURAL PIGMENTS AS ANTIOXIDANTS IN COTTONSEED OIL PEROXIDE8
Untreated sample Carotene Lycopene Quercetin
IN:
Treated sample
P. F.
Millimoles per kilooram 25.0 27.1 25.0 24.9 25.0 13.2
1.0 1.9
...
The results with carotene agree with those of Franke, which showed that lipochromes accelerate oxidation of glycerides. Quercetin, on the other hand, seems to possess antioxidative properties.
PHENOLS Hydroquinone has been used extensively in the study of antioxidative action, but no systematic study of the action of its related compounds on fats and oils has been made, although Moureu and Dufraisse (6) found in their initial 243
INDUSTRIAL AND ENGINEERING CHEMISTRY
244
studies that hydroquinone, pyrocatechol, and pyrogallol possessed far greater antioxidative properties than did phenol and resorcinol. The relative values of hydroquinone, catechol, and resorcinol as antioxidants were first determined:
Vol. 26, No. 3
The similarity between the structure of maleic acid, which proved to be a good antioxidant, and that of hydroquinone is indicated in the following formulas: OH
OH
HC-CEO 1
H-C-LC-H
I1 HC-CEO
I/
H-C-C=CH OH
OH
Hydroquinone P. E'. = 3.7
Catechol P. F. = 2.0
Resorcinol P.F. = 1.1
These results are, in general, analogous to those obtained by Moureu and Dufraisse in that 1.2- and 1.4-dihydric phenols give protection against oxidation of oils but 1.&dihydric phenol offers little protection. It seems probable that the explanation may lie in the fact that the 1.2- and 1.4- compounds form quinones and are, therefore, capable of forming oxidation-reduction systems. The trihydric phenols-hydroxyhydroquinone, pyrogallol, and phloroglucinol-were also tried as antioxidants with the following results :
I
I
I
Former work with ricinoleic acid ( 3 ) had indicated that a hydroxy group on carbon atoms farther removed from the double bond is also effective in preventing autoxidation. This grouping in ricinoleic acid is considered to be as follows: H H
i
-c=
-&CI
1
H H Maleic, fumaric, aconitic, and other acids were therefore studied with respect t o their properties as antioxidants. The results obtained are given in Table 111. TABLE111. ACIDS
AS
ANTIOXIDANTSIN COTTONSEED OIL PEROXIDER IN:
AcIn
Hyeoxyhydroquinone
P. F. = 3.6
Pyrogallol P. F. = 3.6
Phloro.g1ucin o1 P.F. = 1.0
I n this experiment phloroglucinol, analogous in structure to resorcinol, failed t o show antioxidative properties.
Maleic Malic Citraconic Itaconic Aconitic Succinic Tartaric Citric Crotonic Fumaric
Untreated Treated sample sample Millimoles ner kilooram 25.6 18.0 25.6 25.6 25.6 28.6 25.2 25.6 25.1 20.0
P. F.
OTHERAROMATIC COMPOUNDS Table I1 shows the protective action of hydroquinone and closely related compounds. The protective action of the acids, especially that of phthalic acid, is of unusual interest, as will be shown later.
As indicated, maleic acid was the most potent antioxidant of those tried. It is a surprising, as well as an important, fact from the standpoint of an explanation of the mechanism of action of antioxidants, that fumaric acid, the isomer of maleic acid, does not act as an antioxidant. The efficiency of maleic acid as an antioxidant when added to various fats TABLE11. AROMATIC COMPOUNDS AS ANTIOXIDAXTF IN COTTOSthat differ in their constituency of unsaturated fatty acids was SEED OIL determined in a manner similar to that already described. PEROXIDES IX: Untreated Treated In each case the concentration of maleic acid in the treated sample sample P. F sample was approximately 0.01 per cent, and the treated and iMillimoles per kilogram untreated samples were stored a t 42" C. for 10 days. The Hydroquinone 25.6 6.9 3.7 Phenol 29.4 29.6 1.0 results are shown in Table I T T . Benzaldehyde 29.4 38.4 ... Phthalic acid 25.6 8.1 3.0 1.2 Cinnamic acid 31.7 25.7 TABLEIV. MALEICACID AS AN ANTIOXIDANT IN DIFFEREW 1.4 Anthranilic acid 20.0 14.1 OILS ALIPHATICACIDS The excellent keeping quality of raw vegetable oils is thought to be due to the natural antioxidants that are present in the ram oil but are destroyed or removed in the refining processes. An unsuccessful attempt was made to isolate an antioxidant from cottonseed. Of the various extracts prepared, only the water-soluble less the heat-coagulable protein fraction showed protective qualities. This extract was slightly acidic, and results with it in addition to the results already obtained with acids formed the basis for a further study of the antioxidative action of various organic acids. I n the choice of acids to study in this connection, the authors were guided somewhat by the assumption that protective action is in some way related t o the structures: H H -C=CC=O or -C=C-C(0H)H H H AH
P m o x r n m IN: Untreated Treated sample" sample", b Mzllomoles per kg. 1.2 3.2 8.2 25.6 11 5 60.9 27.; 8.2 25.t 8.1 8.2 26.7
OIL Butter Cottonseed Corn Sunflower Peanut Cod liver 5.0 15.1 Lard 13.3 40.0 Linseed 20.0 6,5 Oleic acid Stored 10 days a t 4 2 O C. b Contained 0.01 per cent of maleic acid
P F 3.5
3. 1 5.3
3.3 3.1 3.2 3.0 3.0 3.0
RANCIDITY APPEARED Untreated Treated samplea sample b Daus Days 47 15 28 10 15 65 12 38 37 13
..
13 ..
36
For every fat except corn oil the protective factor with maleic acid was approximately 3.0. For corn oil a P. F. of 5.3 was obtained, probably because of the fact that this oil does pot normally oxidize as readily as do the other oils tried. With each fat the fact was noted that greater pjotective action was always obtained with an antioxidant when fresh samples of good keeping quality are used. I n other words, the protective factor increases with improved keeping quality of the oils.
March, 1934
I N D U S T R I A L A N D E N G 1N E E R I N G C H E JI I S T R Y
Throughout the experinients it was also noted that in the presence of traces of water the acids are not so effective as antioxidants as they are in dry oils. It was thought that compounds of maleic acid that are more soluble in fats, such as the salt, anhydride, or ester, would lend themselves better to a quantitative study of the antioxidant than did maleic acid. However, when these were tried, none of the compounds showed antioxidant properties except the anhydride, which may owe this action to a reversion of a small amount to the acid form. SUMMARY Of the phenols, only the ortho and para types are active as antioxidants for fats and oils. Some unsaturated polybasic
245
aliphatic acids ( d ) , notably maleic, are also antioxidants for fats and oils. LITERATURE CITED (1) Franke, IT., Z.physiol. Chem., 212, 234 (1932). (2) Greenbank. G. R.. U. S. Patent 1.898.363 (Feb. 21. 1933) (3) Holm, G. E., Greenbank, G. R., and Deysher, E. F., Ii&. E s o . CHEM.,19, 156 (1927). (4) Monahan, B. R., and Schmitt, F. 0 , J. BioZ. Chem., 96, 387 (1932).
(5) (6) (7) (8)
Moureu, C., and Dufraisse, C., Chem. Ren., 3 ( 2 ) , 113 (1926). Moureu, C., and Dufraisse, C., Compt. rend., 174, 258 (1922). Xewton, R. C., Oil &- Soap, p. 247 (Xov., 1932). Olcovich, H. S., and Mattill, H. A , , J . Bid. Chem., 91, 105 (1931).
RECEIVED September 27, 1933.
Photochemical Studies of Rancidity Peroxide Values of’ Oils as Affected by Selective Light MAYNER. COE AND J. A. LECLERC,Bureau of Chemistry and Soils, Washington, D. C. HE decomposition products of oils have heretofore
T
been used as indices of the degree of rancidity. The presence of these split products has been indicated by the well-known Kreis test (8), the modified Schiff’s test, sometimes called the von Fellenberg test (S), and certain other color tests. The peroxide value of oils likewise has been used as a measure of the degree of rancidity. Heffter ( 5 ) , Taffel and Revis ( l a ) , Lea (9), and more recently Wheeler ( I S ) , Royce (11), Kilgore ( 6 ) , and Xing, Roschen, and Irwin (7) have studied the oil from this viewpoint. Certain investigators have shown that occasionally an oil, known to be freshly made, will give a positive reaction for rancidity with these various color tests. For instance, Powick (IO) concludes: “A positive reaction in the Kreis test when the test is performed in the usual manner, is not always a reliable indication of rancidity in fats. A large number of compounds react with phloroglucinol-hydrochloric acid to give a red color that, to the unaided eye, is indistinguishable from the color obtained with rancid fats.” Recently Greenbank and Holm (4) studied with the use of the Mazda lamp the photochemical oxidaticin of cotton5eed oil as measured by the reduction of methylene blue and arrived a t the conclusion that blue light was the least effective in accelerating oxidation as compared i o green, red, or amber of the same light energy. Davidsohn ( d ) , in a discussion on the rancidity of fats and oils, gives the conclusion of the German Fat Analysis Commission, which declares that taste and odor are so far the only reliable tests for rancidity. It is generally admitted, however, that, when an oil is found to be rancid by these ,organoleptic tests, i t rrill also give a positive Kreis or von Fellenberg reaction. Wheeler, in a modification of Lea’s method, bubbled moist air through corn oil or cottonseed oil maintained a t 100” C. in an enclosed compartment which happened to be lightproof, and found that peroxide values of the oil mounted to a certain point a t which the oil became rancid. The peroxide value, however, continued to increase for a time but finally decreased. A curve was plotted showing the point at which, under the conditions of the experiment, an oil would become rancid. The entire curve u p to that point could be considered as the measure of the induction period,
or the period during which the oil remained free from rancidity. The present investigation is primarily concerned with the photochemical effect of light on the development of peroxides as a measure of rancidity in oils, the purpose being to determine the trend of peroxide formation in oils kept a t room temperature and protected from all light, and also in oils protected by green light delimited by 4900 to 5800 8. RANCIDITY TESTSON OILS CORNOIL. This oil, which in previous experiments (I) had been used for frying potato chips, was divided into two portions. One was protected from light by wrapping with opaque black paper and the other was mapped with unglazed white manifold paper. Both portions were placed in a south window for exposure to direct sunlight. The same was also done with a portion of the original unused oil. The peroxide values were determined a t the beginning and approximately a t each week throughout the experiment. Table I gives the results. TABLEI. PEROXIDE VALUESOF CORNOIL DATE
O R I G I N 4 L OIL EEFORE USE
Black Clear 4/15/32 8.4 8.4 4/22/32 17.7 49,5 5/3/32 28.8 7 3 . 9 Ra 5/9/32 31.5 111.5 R 5/17/32 36.3 2 0 7 . 6 VR 5/26/32 44.2 205.6 VR 6/3/32 49.6 240 3 V R 6/10/32 54.4 2 6 9 , 5 VR 6/17/32 65.1 3 4 0 . 0 YR 7/11/32 99.1 4 8 9 . 2 VR 7/25/32 117.2 6 1 6 . 0 VR a R = rancid: VR = very rancid.
USEDOIL Black Clear 8.8 8.8 15.2 30.7 44.2 R 20.5 61.2 R 28.0 81.2 R 32.1 1 0 5 . 5 VR 40.1 137.5 VR 44.1 1 9 8 . 9 VR 50.3 62.0 2 0 6 . 9 VR 79.1 3 0 6 . 6 VR 100.0 5 0 8 . 5 VR
Peroxide values increased rapidly in the sample unprotected from light, and the oil wrapped with black paper remained free from organoleptic rancidity to the end of the experiment, even though i t had a t that time developed a peroxide value much above that of the unprotected oil at the time rancidity was first recorded (Figure 1). During the time of the experiment there was no decrease in the peroxide value such as was noted by Wheeler (IS) in his experiments carried on a t 100” C. CORNOILBWBLED WITH AIR. I n another experiment, air was bubbled through bottled samples of corn oil at the rate of 6 liters per hour, with the samples protected from light
