AUTOXIDATION of FATS and OILS 545 Unique Antioxidant, Called Sesamol

Autoxidation of Fats and other off-flavors and odors; the senses of taste and smell can detect autoxicla- tive deterioration quite readily. Fats in the early stages of autoxidation are Oils edible, but unpalatable. Thereafter the degree of unpalatability increases until C. E. Swift, F. G. Dollear the odor and flavor become so repulsive that the fat cannot be eaten. Nutritional tests indicate that autoxidation reduces or destroys the food value of fats. For example, the vitamin Products that contain fats and oils E content of vegetable oils and the turn rancid and deteriorate in other vitamin A content of fish oils are re- ways when they arc exposed to air. The duced, if not entirely destroyed, during action^ known as autoxidation, imparts autoxidation. Furthermore, the fatty disagreeable flavors and odors to fats acid components of fats that are most and foods containing them. For a long essential in the diet are the first to be time baffled investigators spent a vast attacked during autoxidation. Rancid amount of effort trying to find ways to fat in diets adversely affects the body's prevent autoxidation. Specifically, the utilization of vitamins from other basic problem was the mechanism of sources. Finally, there is some evidence autoxidation—how oxygen attacks a that autoxidized fat may exert a toxic fat. On that point the investigators action. made several discoveries in 1943. They have developed moderately efí'cctive NATURAL AXTIOXIDANTS, substances methods of preventing rancidification, that tend to prevent autoxidation, are and believe now that the solution of present in small amounts in most vege- the problem is in sight. table fats. Their importance has been It is important to prevent autoxida- realized for a very long time. For in- tion because fat and fat-containing stance, the American Indians added foods valued at several billion dollars oak-bark extracts to the fat of bears to are produced and marketed annually. keep the fat from spoiling. Some nat- The oil, meat, fishery, dairy, and bak- ural antioxidants have been isolated re- ery industries suffer serious losses from cently from the fats in which they occur autoxidation of their products. and their chemical structures have Rancidification was an important been determined. A number of fats and economic and military problem during oils contain the same natural antioxi- the First and Second World Wars, al- dant; some contain one not yet found though many modern scientific prac- in any other fat or oil. Fats and oils also tices reduced the frequency of its difí'er very markedly in the amounts of occurrence. Measures that were mod- natural antioxidants originally present erately effective in preserving civilian in them. foods availed little for food that had to The most common antioxidant is be transported long distances and vitamin E, or tocopherol. Generally stored in unfavorable climates. speaking, vegetable fats contain appre- In different fats, and under different ciable amounts of tocopherols, while conditions, autoxidation produces tal- animal fats contain them in very low lowy, painty, burned, fishy, grassy, and concentrations. Sesame oil contains a 544 AUTOXIDATION OF FATS AND OILS 545 unique antioxidant, called sesamol. The tocopherols, which are only Crude cottonseed oil contains a differ- moderately active as compared with ent antioxidant, gossypol. certain antioxidants, have some ad- vantages. They impart no color, odor, BESIDES NATURAL antioxidants, fats or flavor to fats. During the autoxida- and oils generally contain phosphatidcs, tion of fats that contain tocopherols, complex substances that sometimes act red substances, known as chroman-5, as an antioxidant and sometimes also 6-quinones, are produced, but the color enhance the activity of other anti- formed is usually not objectionable. oxidants present. A substance which Because the tocopherols are not soluble has practically no antioxidant activity, in water and are relatively stable to but which increases the activity of a heat, they generally arc carried over true antioxidant, is called a synergist. into finished food products, as, for ex- Unfortunately, both the antioxidants ample, baked goods, such as piecrust and synergists are sometimes partly or or cakes. Finally, the antioxygenic wholly removed from crude fats and activity of a tocopherol may be greatly oils during the refining process to which increased when any of a number of they must be subjected to rid them of synergists is used to increase its activity. objectionable coloring matter and ila- These properties indicate that the toco- vorous or odorous constituents. A re- pherols are singularly well adapted to fined fat or oil may, therefore, require their role as natural antioxidants. the addition of antioxidants to increase Several effective antioxidants and its stability. antioxidant combinations have been When refining is carefully carried suggested for use in artificially stabiliz- out, however, most of the natural anti- ing fats. Only a few are important. oxidant remains in the refined oil. The addition of antioxidants to foods Under such conditions, there may be is subject to Federal regulations. Their no advantage in adding more antioxi- acceptability must be established by dant, for it has been found that there is toxicological and nutritional tests be- an optimum concentration for these fore their addition is permitted. A long substances in any fat or oil. It is still time may elapse between the labora- possible, however, to add synergists to tory discovery and the commercial assist the natural antioxidants in pro- utilization of an antioxidant. tecting the fat. Sometimes, of course, it is advantageous to add both antioxi- MANY INVESTIGATIONS of the effect dants and synergists. of various antioxidants on fat stability The phosphatides and certain other have provided a great deal of informa- compounds form effective synergist- tion on the properties of antioxidants. antioxidant combinations with natural Most compounds with appreciable tocopherols. The manner in which antioxygenic activity belong to the synergists act to increase the activity of phenols, a group of complex substances antioxidants has been investigated, but including the natural tocopherols— is not clearly understood. Phosphoric gum guaiac obtained from a tropical acid, which forms an effective syner- tree and nordihydroguaiaretic acid ob- gist-antioxidant combination with tained from the creosotebush of the tocopherol, apparently is capable of southwestern United States—and the regenerating tocopherol that has been synthetic substance known as hydro- oxidized. It has been shown that toco- quinonc. pherols in the presence of a synergist Adding phenolic antioxidants to are depleted at a retarded rate during vegetable fats which already contain autoxidation. One present theory as- natural tocopherols improves the sta- sumes that the antioxidants are con- bility of the fat only slightly. On the tinuously regenerated at the expense of other hand, addition of the phenolic the synergists. antioxidants to fats naturally lacking in 546 1950-19 5 1 YEARBOOK OF AGRICULTURE antioxidants, such as animal fats, im- and fat-containing foods. Care is taken proves stability appreciably. Moreover, to minimize exposure to light, heat, a relatively large group of synergists and air (oxygen) and contamination can greatly enhance the antioxygenic with metallic pro-oxidants, or promot- activity of the phenolic antioxidants. ers of autoxidation, such as copper and The eircctive members of this group iron. These precautions call for atten- include citric, ascorbic, gallic^ and tion to the design of equipment, to the phosphoric acids and the phosphatidcs, materials from which the (equipment especially the commercial lecithins, is fabricated, to packaging iTiaterials, such as the soybean, peanut, and rape- and to nuoK^rous other details. If suit- seed lecithins. able precautions are observed, many Propyl gállate, a chemical com- fats, particularly vegetable fats, are pound that acts synergistically with sufficiently stable for most uses with- tocopherols, is particularly effective in out added antioxidants. vegetable fats. It is one of the few com- A large portion of commercially im- jDOunds that are both phenolic antioxi- portant liquid vegetable oils are hydro- dants and synergists. Animal fats and genated, or hardened, to produce plas- fish oils can be eíTectively stabilized by tic fats like shortening and oleomar- the addition of phenolic antioxidants, garine. Although the main objective and even more effectively by syncrgist- of liydrogenation is to produce plastic antioxidant combinations. The anti- fats, hyclrogenated fats are generally oxidants approved for use, subject to many times more stable than the un- change and wdth certain limiting re- hardened oils from which they are strictions, an^ the tocopherols, gum produced. guaiac, nordihydroguaiaretic acid, bu- Lard and other animal fats are the tylated hydroxyanisole, thiodipropi- main ones that require stabilization onic acid, thiopropionic; acid plus di- with antioxidants. Much of the lard laurylthiodipropionate, and propyl marketed today is stabilized with ap- gállate, also the lecithins, and citric and proved antioxidant-syncrgist combina- phosphoric acids, which are synergists. tions selected from those we have The addition of natural food sub- mentioned. stances is permissible, but generally An appreciable quantity of fat is only mildly effective. marketed in the form of animal-vege- There are several other

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