FLAVORS IN FOOD FATS H . E . Robinson and H . C. Black SWIFT
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COMPANY, CRIFAGO, ILL.
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fIE importmce of food fa& as a dietary staple 16pmbsbly not popularly appreciated. In ad~tiontofurnibhingarelativelylarge Emaunt of the daily caloric requirements of moat people, food fats m of major importance from a flavor standpoint. Some food fstsme used to enhance the flavorof pastries, bread, and biscuits; others serve to add flavor to actual products in which they are found; still another group of food fats are carriers for other f l a v o ~in that they are themselves quite bland. Since one of the main principles of good nutrition is that food must be appetizing and appealing in taste, i t is easy to recognize the contribution of food fats to eating pleasures. Butter, margarine, alive oil, oleo oil, and openkettle rendered, dry-rendered, and prime steam lard may be called the “flwarful” food fats. Moat prominent among the gmup of “invisible” food fats are those which m eaten 89 part of roasts, chops, steaks, etc. There is little doubt that they contribute flavor to the appetitt! apped of these foods. Cream seems to add apprecishly to the flavor of milk. At any rate, t,here is E marked diRerenoe in the flavor of skim milk and whole milk which is in favor of the latter. It sews prohshlc that the fats which are nsturally oontained within cereals, f N h , and vegetables do not particularly influence th* taste of those products. Sdad oils, shortenings, and bland lard comprise a group of fats which &re, at least during n a m d holding periods. odorless and flavorless. Salad oils sre processed from cottonseed oil. peanut oil, myhean oil, and corn oil. Shortenings are formulated from: (a) all hydrogenated mest fats or vegetable oils, (b) blends of meat fats and vegetable oils, and (c) blends of hydrogenated fats with unhardened frits or oils, either from vegetable or meat sources. Fmm the standpoint of domestic economy the most prominent vegetable oils are soybe=. cottonseed. and msnut. h e n t h the prodkctian of &bean o i has slightly exceeded that of eottoneeed ail which bas $ways been B leader in the p s t In times of normd world trade tremendous tonnages of palm, enconut, and other less well-known vegetnble ails are imported into this oountry for processing into varions types of food fats. The odorleas and flavorless characteristics of the above-named gmup of fats are- achieved only through the usual commercial praotices of re5ning. bleaching, and deodorizing. In the raw state, with the exception of those products which were grouped with the flavorful fats, they ail hnve charaoteristie and, to American palates, undesirable flavors and odors. These flavor and odor matsrialsmapparentlynot part of the glyceride struoture, hut are due to foreirm inerrdients orinnstins? in the fruit. huskq. or seed.
Pilot-Plant Deodorizer for Edible Fate and Oil!
$rum which each oil WBS expressed. All glyoerides whose fat acids consist of B. or higher are considered to be free of Aavc The characteristio and natural flavor of butter appears to I highly hutyrie in nature, blended with diacetyl, acetylmeth2 carbinol, and vsrjous butyric, caproic, esprylic, and capric e ters and other short chain fatty acids. The flsvor of butter BI margarine are also markedly iduenced by the nature of the em^ sion into which they are formed during processing. This fact. can be readily demonstrated hy E separation of butter fst and r emulsification in which the same flavors do not again preva The addition ofedt to these pmduets slso ex& B marked effec trnqalt4
hiittrr n r r n n w d n r hna a rnnoh 1m.s riaririnrl R a ~ i r r r
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Most margarines today are prepared from bland, deodorized vegetable oils. In some states formulation is based on deodorized combinations of vegetable oils, beef fats, and lard. In either instance the characteristic flavor of these products is furnished chiefly by pasteurized, cultured skim milk. The chigf flavoring substances produced in these cultures are diacetyl and acetylmethylcarbinol. The organisms involved are Streptococcus lactis, Streptococcus cilrovorus, and Streptococcus paracitrovorus. It seems probable that the chief difference between the flavor eomponents of butter and margarine is the presence, due to hydrolysis in butter, of short-chain fatty acids and their esters. RANCIDITY
While it is relatively easy to produce odorless and flavorless salad oils and shortenings, it is difficult to maintain this condition when the products are stored or held at elevated temperatures for long periods, ranging from a few weeks in some instances to several months in others. The principal changes involved come about through the processes of rancidity and reversion. The combination of oxygen with odorless and flavorless food fats tends to produce a number of degradation products which are eharacterized by undesirable flavors and odors. The predominant flavor, according to Powick (8),is due to heptylic aldehyde. Everyone who has had occasion to use food fats is well able to distinguish those flavors and odors which are termed “rancid”. There are several ways of avoiding or delaying the onset of the oxidative process on food fats. Recently the Meat Inspection Division of the Food Distribution Administration approved the use of nordihydroguaiaretic acid, lecithin, and tocopherols for shortening products containing meat fats. I n 1940 the Bureau of Animal Industry, Meat Inspection Division, approved gum guaiac as the first edible antioxidant. While these antioxidants are valuable in varying degree in delaying the onset of rancidity in meat fat shortening or shortenings containing meat fats, they are of limited value with products made exclusively from vegetable oils. It seems probable that the field of edible antioxidants will be considerably extended during the next few years. One of the chief advances made possible by the use o‘f antioxidants has been the production of a bland lard which has a relatively high keeping quality. In years past, lard was not processed through the steps of refining, bleaching, and deodorizing because any one of these treatments lowers the keeping quality of the product to such an extent that it cannot be marketed successfully. The use of an antioxidant has now made possible the production of a bland lard which possesses the characteristic properties of other fully processed shortenings. Flavor in meat fats as they are originally expressed or rendered in the raw state is quite different from that of vegetable oils in the raw state previously rated as undesirable. Many consumers believe that the unaltered flavor of lard is desirable for certain cooking and baking purposes. The same is true to a lesser degree of the beef fab, oleo oil, oleo stearin, and tallow. However, the introduction since World War I of hundreds of millions of pounds of the bland processed vegetable oils has apparently led the American housewife to demand this characteristic in any all-purpose shortening material. In the case of lard, as in one other which will be pointed out later, the question of the flavor of a fat and its stability to rancidity has been of tremendous economic importance to American agriculture. There is little doubt but that the demand for bland shortenings has had an effect upon consumer acceptance of the old style lards. The successful introduction of bland lard shortening holds great possibilities for regaining the popular demand for this fatty food and thus improving the agricultural economic position of this commodity. REVERSION
Another effect of storage upon odors and flavors of food fats is typified by the phenomenon termed “reversion”. At present the
Vol. 37, No. 3
reversion of soybean oil h a s probably the greatest economic importance. Reversion is, in many instances, a misnomer since it $ends to indicate that a fat which has been made bland will revert to the odor and flavor which it carried before processing. Actually the reverted flavor in soybean oil, lard, or tallow is not particularly characteristic of that fat in the undeodorized state. The reverted flavor of soybean oil is often termed, “grassy” or “beany”, progressing to “fishy”. The reverted flavor of lard is not characteristic of the original taqte and odor of this product when first rendered. The reversion of fish oil has some of the original characteristics of the undeodorized product but is still not the same flavor or odor, Tallow may be considered to revert to a flavor which is more nearly that of the original product in the raw state. Corn oil tends to revert after a time to a flavor which is undesirable and not characteristic of the original undeodorized product. Even cottonseed and peanut oils tend to revert to less desirable flavors after long periods. Fish oil has been prevented from becoming an important factor in the edible oil field because of its tendency to revert. Soybean oil has, over the past several years, averaged approximately one cent per pound lower in price than cottonseed oil. From chemical and physical characteristics other than the tendency to revert there would be no justification for such a price differential. Therefore, we have another instance in which the significanceof a flavor factor in a food fat lowers the return to agriculture from a farm product. There is little published material on the factors which are fundamentally concerned in reversion. Apparently the quantity of material which produces these reverted flavors apd odors is in the range of only a few parts per million. Attempts so far, and there have been many, to isolate these flavor materials have been unsuccessful. It is known that hydrogenation of fats and oils is of some value in delaying reversion. It might also be mentioned in this connection that the reverted flavor of hydrogenated products is not the same as the reverted flavor of deodorized unhydrogenated fats and oils. Temperature as well as time is a factor in promoting reversion. I t has not been clearly established whether the presence of oxygen is essential. Some experiments have tended to show that reversion takes place in the presence of very small amounts of oxygen, such as in the storage of hydrogenated soybean oil under nitrogen or other inert gases. ?3!bwever, in this instance it was probable that some traces of dissolved or occluded oxygen were present. DIETARY EFFECTS O F RANCID FATS
The available literature concerning the deleterious effects of rapcid fats in the diet is limited and inconclusive. There is little doubt that ingestion of rancid fats is detrimental to health, but whether the effect is direct or indirect has not been answered. The chief criticism of most of the research is that one cannot determine whether the ill effects resulted directly from a possible toxicity of the end products of rancidification or indirectly from the destruction by oxidation of various essential nutrients in the diet. The direct toxicity effects have received little attention. Gyorgy et al. (6) observed some toxic effects which they ascribed t o the oxidation products of linoleic acid.‘ Some products of such oxidation may be absorbed in the intestines; for example, it has been shown that heptaldehyde is readily absorbed (2). If harmful products are absorbed, it must be to a minor extent; for it has been demonstrated that, when they are administered parenterally, they exhibit Ear greater toxicity than when taken orally (5). Much more thought has been directed toward the indirect effects produced by the destruction of various essential factors. It, has been suggested that, on the basis of their chemical structures, the following dietary essentials could conceivably be destroyed by oxidation: vitamins A, D, and E, carotene, pantothenic acid, pyridoxine, biotin, ascorbic acid, and the essential unsaturated fatty acids (I). Of these, only pantothenic acid and pyridoxine have not been studied from this point of view; all the
March, 1945
INDUSTRIAL AND ENGINEERING CHEMISTRY
"them have been ahown Lo hc miore or less eonrglctely datroyed in rancid fats. The substance or substances in rancid fat thst cause destruetion are unknown. Steenboek'Y group loend that vitamin A is not destroyed by oxidized gly~.wl, glyceric Raid, glycerakiehyde, allyl alcohol, atmight-chain aldehyd-, methyl ketones with sown to twelve carbons, or decomposition products formed by the commercial hydrogenation o f fats (fi). Thc components which c511se tkcdertruction " w e not removed bystezm distillation or by extraction with alcohol (6). Evans and Burr have concentrated tho vitamin-E-destroying factor of rancid iirts in dhe unsaponiGable portion (4).Sumner eoiieluded that the iiitemadiatw oi fatty wid peroxidation wem the active agents but. not. the peroxides themselves (9). The loss of activity of vitnniiii A &ppe&m to be associated wit.h the rapid furniat,ion ol peroxiilcs immediately following the induction period. It h s s been suggested that destruction of I i m k i c acid and other essential fat %ids m&ybe an important factor. The feeding of midized fats hss resulted in skin changes in rat8 (10) and in dogs ( I l ) which werc Suggestive 01 linoleic acid deficiency, but io much mom awere form. However, i t ha4 been shown that st she end of its induction period a fat still retains approximately 90%
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01 its original linoleic arid, and some of the acid is still present when the peroxide value liar gone w high BS 500 (7). I n conclusion it must bo said thst the flavom or the absence 01 flavors in food fats are 01 p&mmouot nuttitiond und economiq importance. There is little doubt that fortune awaits the chem ist or group of chemical research woiken who &pe able to sulw suecessiully the little known problem of reversion. LITERATURE CITED
( I ) Burr, G . 0.. and I h r a e ~R. , 15.. Phusiol.Rna..23,256-78 (19431 ( 2 ) Clark, W.G . . Pmc. Soc. E m l l . Bioi. Med.. 40.502-4 11938).
f.,Tomnielii. R., Oaicigsid, It. P.. and Brown, J. B J . E z p l l . M a d . , 76,413-20 (1942) (0) Lense. I:. J.. Lease, J. 0.. Weber. J., and Steenboak. H., 4 Nwtr
