Effect of Carbon Treatment on Fish Liver Oils VITAMIN A DESTRUCTION AND PEROXIDE FORMATION L. 0. BUXTON hTopcoVitamin Laboratories, National Oil Products Company, Harrison, N. J
Studies on the stability of vitamin A in fish liver oils treated with activated carbon have demonstrated that, irrespective of the rate of oxidation, the percentage destruction of vitamin A is proportionally related to the peroxide content. In all instances the carbon treatment shortened the induction period and increased the ultimate rate of peroxide formation. The percentage vitamin A oxidized in the fish liver oils exhibiting no induction period is directly proportional to the peroxide content and to the time of exposure a t 34.5' C. until at least 60 per cent of the vitamin A is destroyed. OST refined oils, particularly those of marine origin, are more prone to atmospheric oxidation than the respective crude oils. This undesirable feature is largely caused by the removal or destruction of a substantial portion of the naturally occurring antioxidants during the purification process. Marine oils utilized for their vitamin content often require a thorough refining treatment. As the stability of vitamin A in the oil is intimately related to the stability of the oil itself, it is important, when purifying vitamin A oils, to understand the influence of the refining process upon the keeping qualities and the vitamin A potency of the purified oil. During the processing of an oil, especially a vitamincontaining fish liver oil, the latter often becomes increasingly susceptible to atmospheric oxidation, depending on the degree of purification. Mattill and Crawford (6) concluded that the susceptibility of corn oil to oxidation increases steadily throughout the manufacturing and purification process. Hilditch ( 5 ) mentioned that highly refined fats or ,distilled fatty acids and esters absorb atmospheric oxygen almost immediately on exposure to it, whereas natural fats usually exhibit an induction period. Hassler and Hagberg (4) reported that rancidity in cottonseed oil resulting from the effect of various bleaching adsorbents can be controlled t o a large extent by the selection of the proper adsorbent. Any instability induced by the adsorbent was believed to be due to the depletion of stabilizing bodies rather than to the creation of positive catalytic bodies. Brocklesby (1) stated that acid treatment of an oil appears t o be more detrimental than alkali treatment, as far as oxidation of vitamin A is concerned. Denstedt and Brocklesby ( 3 ) showed that pil-
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Furthermore, the increase in peroxide content of such oils is directly proportional to the time. The fact that the carbon-treated fish liver oils had essentially the same vitamin A value and a slightly lower peroxide content than the respective crude oils suggests that the instability is due primarily to a loss in antioxidant content. The quantity of antioxidants removed is related to the percentage carbon used. Upon oxidation, the oils treated with 20 per cent carbon gave evidence of the complete absence of antioxidants. chard oil treated with decolorizing carbon and bleaching earth exhibits a much shortened induction period. Ciusa ( 2 ) found that the antioxidants naturally occurring in olive oil and cod liver oil are adsorbed by carbon and activated earth. Although it is known that vitamin A is readily oxidized in oils exhibiting short induction periods upon exposure to air, the literature nevertheless gives little information on the quantitative relation between the destruction of vitamin A and the accumulation of peroxides in such oils. A previous study (7) indicated that the destruction of vitamin A in several crude fish liver oils is proportional t o the peroxide number. Brocklesby ( 1 ) showed that treatment of an oil with dilute alkali or dilute acid increases the rate of peroxide formation, although the destruction of vitamin A still remains proportional to the peroxide content. The present investigation is restricted t o a study of the destruction of vitamin A as affected by the increase in rate and degree of peroxidation of fish liver oils treated with activated carbon.
Materials and Technique OILS. The fish liver oils were representative of the species generally used in practice and were of the highest quality. They were selected for their vitamin A potency, freshness, and freedom from foreign matter. The free fatty acid content never exceeded one per cent. CARBON.The activated carbon was a well-known commercial product from vegetable source and was not subjected to further activation. Many other commercial carbons and activated earths were examined in the course of this investigation; most of them behaved in a similar fashion, the varia1486
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tions being a matter of degree rather than a demonstration of some other effect. SOLVENTS.The heptane used was the commercial product known as Skellysolve C. While many different solvents were also examined, the differences were again a matter of degree more than anything else. Generally speaking, activated carbons are more effective for the removal of color, taste, and odor-possessing substances from fish liver oils when these are dissolved in nonpolar solvents. The chief reason is probably that the undesirable components are of a polar nature and thus less soluble in the nonpolar vehicle. The conventional method of treating oils with activated adsorbents was not used, which consists in stirring a t an elevated temperature in the presence of a relatively small percentage of the adsorbent. Extensive experience has demonstrated this process to be of limited value for the purification of vitamin A fish liver oils, mainly because a considerable amount of vitamin A is destroyed during the treatment. To obviate this limitation, the process which follows was developed and used throughout the investigation. Several modifications of this process are possible but will not be described here. Five grams of activated carbon were weighed into an 800-ml. beaker equipped with a mechanical stirrer and a nitrogen gas inlet tube, 400 ml. of Skellysolve C were added, and stirring was begun. Nitrogen gas was gently bubbled through the carbon-solvent mixture for 5 minutes, which was ample to deaerate the carbon; 95 grams of the crude fish liver oil to be treated were added, and stirring was continued for another 30 minutes a t room temperature with nitrogen bubbling. The stirring was then stopped and the mass immediately filtered through a Buchner funnel equipped with a No. 7 Ertel filter pad. The carbon on the filter was not washed with additional solvent since that might lead to the introduction of unnecessary variables. The carbon-free filtrate was distilled under reduced pressure in a hot water bath (maximum temperature about 70" C.) in the presence of nitrogen gas to remove all traces of the solvent. The solvent-free carbon-treated oil was then stored in a completely filled closed vial a t -18" C. until the tests were conducted. Two samples of shark (soup-fin) liver oil and one sample each of halibut and tuna (Skipjack) liver oil were treated in this way with various percentages of activated carbon, the only difference being in the amount of carbon used. The effects of the treatment on the vitamin A potency and on the color of the various oils, as compared t o percentage carbon used, are summarized in Table I.
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FIQURE 1. RELATION OF VITAMIN A DESTRUCTION AND PEROXIDATION IN FISHLIVEROILS A , soup-fin shark (A) ; B , soup-fin shark (B); D , blue-fin tuna
(7,
halibut:
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TABLE I. VITAXINA POTENCY, PEROXIDE NUMBER, AND COLQR OF CARBON-TREATED FISHLIVEROILS % Carbon (Based on 011Wt.)
Oil Shark (A)
Vitamin A Units/Gram
10.9 3.9 2.7 2.5
105,000 102,500 101,000 103,000
36.0 22.0 17.0 12.0
4.0
5 10 20
0
2.4 2.3 1.9 1.6
77,800 72,600 74,800 72,400
35.0 25.0 20.0 16.0
12.0 1.8 0.9 0.9
0 5 10 20
3.2 3.4 3.5 3.0
78 000
35.0 35.0 21.0 13.0
2.1 1.2 0.6
0 5
10 20
Tuna
Halibut
Color (Lovibond) Yellow Red
Peroxide Number
78:600 75,600 73,000
1.5
0.7 0.5
6.9
Two milliliter samples of the original crude fish liver oils and of the same oils after treatment with various amounts of activated carbon were accurately measured into thoroughly cleaned open vials, in accordance with a method previously described ( 7 ) . The vials were then stored in a constanttemperature oven a t 34.5" * 0.5' C. Individual peroxide number and spectrophotometric vitamin A determinations were made on three vials of the same oil after definite time intervals, a new set of vials being used for all such intervals. The average value of the three individual measurements was used in plotting the curves. The details for making the vitamin A and peroxide determinations have already been reported ( 7 ) . The color values given in Table I mere determined by the official A. 0. A. C. method. The results outlined in Table I show that the carbon treatment had a marked decolorizing effect on all the oils, the amount of color removed being proportional to the percentage of carbon used. Furthermore, quantities of activated carbon as high as 20 per cent based on the weight of the oil had little or no effect on the vitamin A content of the various oils. The carbon-treated oils usually possessed slightly lower peroxide values than the crude oils. They were also much improved in regard to taste and odor. Samples of the crude and treated oils exposed in open vials a t 34.5" C. gave peroxide and vitamin A values which are graphically presented in Figures 1,2, and 3.
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Relation of Vitamin A Destruction to Peroxidation The curves of Figure 1 bring out the detrimental effect of the carbon treatment upon the stability of vitamin A in the different oils. The higher the peroxide number, the larger becomes the percentage of vitamin A oxidized. In each oil, regardless of its relative rate of oxidation, the percentage vitamin A decrease is proportionally related to the peroxide content. I n the treated oils exhibiting no induction period, the vitamin A destruction is directly proportional to the peroxide value, and this was the case in all oils treated with 10 per cent carbon or more. In Figure 1A the curve for the oil treated with 5 per cent carbon indicates that the adsorbent apparently removed some pro-oxidants as well as antioxidants from the oil. It is probably true that all unrefined fish liver oils, especially those stored over a period of time, contain pro-oxidants as well as antioxidants, although the effect of the latter still predominates. The removal of antioxidants from fish liver oils by carbon treatment is not necessarily objectionable, particularly since some probably contribute to taste and odor. They can be
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HOURS A T 34.5"C. FIGURE 2. VITAMINA DESTRUCTION IN FISHLIVER OILS A , soup-fin shark (A); B , soua-fin shark (B); C, halibut; D,blue-fin tuna
replaced in the refined oils by other and more desirable or more effective antioxidants.
Effect of Time on Vitamin A Destruction Figure 2 summarizes the data on percentage vitamin A destruction plotted against hours of storage a t 34.5" C. Here again the results illustrate clearly the striking effect of the various amounts of carbon on the rate of vitamin A oxidation. I n the oils exhibiting the least resistance to
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FIGURE 3. PEROXIDATION OF FISHLXVER OILS
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A , soup-fin shark (A); B , soup-fin shark (B); C. halibut; D , blue-fin tuna 420
peroxide formation, the rate of vitamin A destruction i s greatest. The percentage of vitamin A destroyed in t h e fish liver oils possessing no induction period on exposure to air a t 34.5” C. is directly proportional to the time; however, this relation holds true only when less than about 60 to 70 per cent of the vitamin A is oxidized. The curves in Figure 2, A and D,for the samples of tuna and shark liver oils treated with 5 per cent or less carbon show that, in the early stages of oxidation, the rate of vitamin A destruction is slower for a time than in the respective crude oils. This behavior can be explained by graphs A , B, and D of Figure 3, which show that the rate of peroxide formation in the initial stages of oxidation of the oils treated with 5 per cent or less of carbon is also slightly slower than for the crude oils. This again is probably due to the removal of pro-oxidants from the oils, although sufficient antioxidants remain to play a definite role.
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Rate of Peroxide Formation
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The oils treated with carbon in all instances (Figure 3) showed a shortened induction period and an ultimately faster rate of oxidation. The increase in peroxide content of the oils exhibiting no induction period is directly proportional to the time of exposure. The absence of an induction period in certain of the treated oils indicates that carbon has depleted the antioxidant content. From the above results it is evident that the antioxidant content of fish liver oils plays a major role in the resistance of these oils to atmospheric oxidation, apart from other effects due to the nature of the fatty acids present and the degree of unsaturation of the glycerides. Lowered resistance to oxidation, as measured by increased susceptibility to peroxidation, in turn governs to a major degree the rate of vitamin A destruction in fish liver oils.
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Literature Cited
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(1) Brookleaby, H.N.,Progress Repts. Pacific Biol. Sta., No. 44,4 (1940). (2) Ciusa, W.,Ann. chim. applicata, 30,141-6 (1940). (3) Denstedt, 0. F., and Brocklesby, H. N., J. Biol. Board Can., I ( 6 ) ,487-96 (1936). (4) Hassler, J. W., and Hagberg, R. A., Oil & Soap, 15, 115-20 (1938). ( 5 ) Hilditoh, T. P., “Chemical Constitution of Natural Fats”, p. 301 (1940). (6) Mattill, H.A,, and Crawford, B., IND. ENO.CHEY., 22, 341-4 (1930). (7) Simona, E.J., Buxton, L. 0..and Colman, H. B., Ibkd., 52, 706-8 (1940). PRESENTED before a joint session of the Divisions of Biologiml Chemistry and of Agrioultural and Food Chemistry at the 104th Meeting 08 the AMERICAN CHEMICAL SOCIETY, Buffalo, N. Y.
Nitroparaffins and Derivatives as Heat Sensitizers for Rubber Latices- Correction
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In this article IIND. ENG. CHEM.,34, 1106 (1942)l cerium oxide was incorrectly designated in We tabulation of compounds that produced no gelling, Group IV. It should have been written CeOa. ARTHURWILLIAM CAMPBELL
