Processing Edible Fats WARREN H.GOSS Pillsbury Mills, Inc., Minneapolis 2, Minn. T h e most significant development in the domestic edible oil industry in recent years has been an enormous increase in the production and utilization of soybean oil. In thus expanding its operations, the soybean industry constructed many modern mills: a large proportion of these employ solvent extraction and have introduced additional practices which now are being adopted by other oilseed industries. Several commercial processes have been developed for separating glycerides into fractions; these include crystallization, distillation of fatty acids, molecular distillation, and liquid-liquid extraction. Liquid-liquid extraction has proved especially veisatile and is employed in several distinctly different processes to accomplish a variety of purposes--such as the recovery of valuable minor constituents, the removal of objectionable principles, and the separation of drying from nondrying components. Outstanding among recent advances in the technology of edible fats are progress toward overcoming the tendency toward flavor reversion in soybean oil; improvement of the stability of animal fats by incorporating powerful antioxidants: addition to shortenings of emulsifiers possessing specific properties : and the introduction of shortenings mixed with such materials as dried eggs and dried milk in the form of a dry powder.
F
ATS and oils constitute a major and vital portion of the American diet. Those of vegetable origin, moreover, are coproduced with large quantities of protei@ meal; supplies of meal determine to a considerable degree the amount of meat, dairy products, and other foods of animal origin available for our tables. The technology of oilseed processing and refining edible oils is advancing constantly, perhaps not as spect,acularly as the sciences of destruction, but nevertheless at such a pace that a n appraisal of the latest developments finds an appropriate place in a symposium of this type.
MAJOR CHANGES IN SUPPLIES From a world-wide viewpoint, the outstanding recent developments concern the restoration of prewar sources. As these yield larger and larger supplies, international trade in edible fats and oils is being resumed, and millions of fat-starved humans are beginning t o receive diets at least slightly improved over the meager rations on which they have barely subsisted for many miserable years. Domestically, the major change actually is not a change at all but rather a continuance of the dominant role played by soybean oil in our economy, a development originally due t o government efforts t o stimulate production and thereby to meet wartime requirements. Those who felt that the tremendous increase in supplies of soybean oil was temporary have found otherwise. The problem of quality control, however, is more exacting in the case of soybean oil than with many other edible oils. Another important change which actually occurred in another industry has produced its effects in edible oils-namely, the shortage of linseed oil for use in the manufacture of protective coatings. Principal reason for this shift is the cessation of imports of linseed from Argentina, and the result has been a marked expansion in the consumption of soybean oil for technical purposes, notably the
preparation of alkyd resins. This diversion from usual channels probably augurs well for the future of domestic oils in the paint, varnish, and allied industries, and it has created a pronounced effect on the edible oil markets. There are many other economic aspects of the current fats and oils situation which deserve discussion, but the preceding are those which have exerted the greatest influence on technological developments. SOLVENT EXTRACTION
Because it was comparatively young, the American soybean industry of 15 or 20 years ago possessed more modern and efficient machinery than its competitors. By pursuing a progressive program of research, it has maintained t h a t advantage. I n the middle and latter thirties, several soybean processors imported German extraction equipment ( T ) , which proved tremendously successful and stimulated American fabricators to develop equivalent systems. These, too, have proved highly satisfactory. Each year has brought new improvements in extraction equipment and operating know-how. Perhaps the first important step of this kind was the addition of toasting apparatus for enhancing the value of the protein in the residual meal. This and the greater efficiency of solvent extraction are largely responsible for a steady expansion of solvent processing in the soybean industry and the gradual decline in the proportion of succeeding soybean crops processed by pressure methods. Although there are many reasons why the oilseed processing industry is converting to solvent extraction wherever possible, the principal motive is t o attain a larger margin in price between raw materials and finished producta. T h e comparison between Solvent extraction and pressing in this respect is particularly striking in the case of soybeans; the advantage of the former is in the recovery of 95 to 98% of the oil, whereas pressing results in a recovery of only 75 to 80%. Obtaining the maximum possible yield of oil is important, for oil sells for about five times the price of the residual meal. I n the field of solvent extraction, the greatest interest now is focused on recent and current efforts t o process other oilseeds b y this more efficient procedure. There are two general methods used for applying extraction-namely, removal of all the oil by the solvent method; and pressing to remove p a r t of the oil, f d lowed by extraction t o finish the job. The fast method is well suited to soybeans but its appli’cation to seeds of higher oil content is not so satisfactory. Many seeds contain 50% or more of oil, and in these extreme cases i t is n o s t difficult t o remove all the oil by the action of solvents. Extraction proceeds readily until 2 or 3% of oil is left; recovering the remeinder presents a real problem. The oil-containing cells appear to be insufficiently ground by the preliminary milling t o which the seeds are subjected. Perhaps there are other reasons, too, but the last few per cent of lipids resist practically all attempts to remove them by extraction. This is but one of the troubles encountered i n attempts t o process high-oil seeds in one fell swoop by solvent extraction. An even more serious dilemma results from the tendency of such seeds to disintegrate into a h e powder when the oil is removed. The reason for this is easily visualized if one considers what occurs when such oil-rich material is subjected to the action of a fat solvent. If the seed contains 50% oil, for example, the solvent 2241
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removes approximately half of the material comprising the pulverized mixture of cellular constit,uents-that is, oil, protein, carbohydrates, etc. After removal of such a large proportion of soluble matter, the residue is a fluffy, friable, noncoherent sponge which disintegrates readily. When such fragile and easily dispersible marc is encountered in solvent extraction, endless operating troubles ensue. The miscella is loaded with fine suspended solids; the reinoval of these requires enormous facilities for filtmtion. During recovery of the solvent from t,hespent marc, even the gentlest of stirring raises clouds of prot,einaceous dust which is carried with the solvent vapors into the condensers. Ultimately t,hese fine solids are carried throughout the system, causing trouble almost everywhere. They are a particular nuisance in the solvent-wat,er separators where they promote the formation of emulsions which defy all efforts to break them. A simple method of avoiding these and other pitfalls when processing seeds of high oil content has been practiced for many years both in Europe and in the r n i t e d States, although it scems to have been studied and used more widely in Europe. This is the second method previously referred to-namely, forepressing to remove most of the oil and then finishing the operation bp solvent extraction. This combination of two procedures is both unnecessary and impractical in the cabe of soybeans for their oil content is sufficiently low initially to preclude the formation of a fluffy friable marc during extraction. Other seeds, however, can be processed with a minimum production of fines and a maximum yield of oil by first removing the bulk of t,he oil by application of comparatively low pressures. Indeed, much of the oil can be squeezed out by hand if these seeds are properly prepared and cooked. Ry expelling most of the oil prior l o extraction of high-oil seeds, there is produced a solid mat,erial from which the relatively smaller amount of remaining glycerides can be extracted wit,hout yielding a highly porous noncoherent' marc. Instead, a dense and coherent' meal results, and little disintegration occurs. The prepressing so ruptures all the cells and otherwise disintegrates the seed struct'ure t h a t nearly complet,e solution of the oil is achieved during a reasonablc period of contact with the solvent. These concepts may seem elementary, but they appear t'o have received inadequate consideration in many quarters. A number of oil millers contemplating a change to solvent extraction for processing linseed, cottonseed, and similar oleaginous raw materials, however, are awakening to the advantages of pressing prior to extraction, not only because this method affords operating advantages but also because i t results in more economical processing. T h e problem of dusts and fines in solvent extraction has been solved in another manner by a novel processing system; its developers recognized the practical impossibility of completely eliminating fines, Their answer was to utilize equipment designed specifically for handling and controlling fines-namely, a type of centrifuge which separates finely suspended solids from liquids, discharging both continuously. The extract>ionprocess actually operating according to this principle consists of several mixing devices and centrifuges in series, so connected as to provide multistage countercurrent contact between t,he liquid and solids. The seeds are ground t o form a slurry of solids and partial miscella, which is separated in one of the centrifuges. The solids pass onward t o another mixer and centrifuge where they are leached with leaner miscella; the operation is repeated in additional stages until extraction is complete; t'he final contact is with fresh solvent. Solvent extraction is undergoing rapid evolution; trichloi-6ethylene is being employed as a solvent for soybean oil in a t least four small mills, and the major difficult,ies of using this n0nfla.mmable solvent appear to have been overconie. Several radically new extract,ion systems also have been devised and undoubtedly will be introduced to the oilseed processing industry.
Vol. 40. No. 12
.FRACTIONATION OF PATS AND OILS
Separating the undesirable minor constituents from the desirable oil fmctions has long been t,he sole purpose of t,hr various riafining procedures used in the edible oil industry. Thus, fro(% acids have been removed by neutralizing them with alkalies : adsorbents have been employed to take out the pigments; arid st'ea,nidistillation under vacuum has constituted thr usiial prowdure for getting rid of undesirable flavors and cdors. More rcccntly, emphasis has been placed on the separatiori or major components of fat,s and oils in order t o yield two or morv important coproducts, rsthcr than simply eliminating cwtaiii minor constituents. Research in this field, stimulated by the. need for domestic sources of drying oils, hm progressed Ear beyorid this objective and there are established profit)ablc operations based on the fractionation of oils t o produce relat,ively pure fatty substances for use as raw tnaterials in the synthetic chemirals industry. Some of these new techniques are of great intervsi, to producers and refiners of edible oils, particularly the pro liquid-liquid extraction by means of furfural or propane. One of the earliest methods practiced 011 a large scale for fractionating fatty oils was distillation of the falty acids, a venture undertaken during the late thirties. Rectifying columns ( I ) , containing specially designed trays of bubble caps, are used to remove as a n overhead distillate those acids having shorter chain lengths. From mixed soybean fat'ty acids the palmitic (Cle) acid is rcmoved leaving bottoms which are somewhat higher in unsaturation than the original mixture. I n the case of fish oil acids are distilled leaving principally the highly unsaturated acids. The resulting fractions are reconstituted into glycerides or are processed into various useful chemicals, such as alkyd resins, fatty amines, emulsifiers, and other derivatives. A more recent innovation for fract'ionating either oils or fatty acids is the so-called Emersol process for continuous crystallization (8). Components of higher melt,ing point are allowed to crystallize under controlled conditions in a polar solvent and are removed on a continuous vacuum filter. i\ typical application is the separation of oleic and stearic acids. Molecular distillation also has proved a n effective means for segregating certain constituents of natural oils and is being applied commercially for producing vitamin concentrates ( 5 ) . Anot,her procedure, known as the Rehr process, is employed for separating polymers from nonpolymers in partially-bodied drying oils. The preceding fractionating processes, though of great interest to the edible oil industry, find application largely in the fields of industrial and technical oils. Two forms of liquid-liquid extrartion, however, have been developed for fractionating edible oils; both permit the separation of such glyceride3 as soybean, fish, and linseed oils into fractions which are of greater value than t,he s t a r b ing materials. Soybean oil, for example, can be split readily into a superior drying oil and a n excellent food oil; both of these are more valuable than the starting material. The edible portion not only is of higher organoleptic quality, after refining, but also undergoes a considerably smaller loss during processing than does ordinary crude soybean oil. The lower refining losses and grcatcr value of both the products and by-products afforded by fractionation have caused t>heedible oil industry to consider with favor a number of the new methods for segregating glycerides. The first of these processes is furfural extraction which the Pittsburgh Plate Glass Company is operating commercially a t Milnauliee (5'). Furfural a t room temperature is only partially niiscible with most vegetable oils, and the glycerides of unsaturated acids are more soluble than the more saturated ones. The difference in soluhili tp, however, is small. In the case of soybean oil, the iodine number of the oil in solut,ion--that is, of the estract-is only approximately 14 units higher than that of the undissolved portion, or raffinate. By a single batch extraction with furfural, therefore, i t is impossible t o separate soybean oil
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INDUSTRIAL AND ENGINEERING CHEMISTRY
into fractions differing in iodine value by more than about 14 units. This situation is exactly analogous to that encountered in the distillation of a mixture of hydrocarbons such as gasoline. A sharp separation between components cannot be obtained in either case unless a multistage fractionating column is employed and a substantial portion of the extract OP distillate, as the case may be, is returned as reflux. A s commercially operated, the furfural extraction plant consists principally of a tall vertical column filled with packing; inside the column a furfural-rich phase flows downward and a n oilrich phase flows upward. Furfural, being the heavier liquid, is introduced a t the top and the oil is fed at some point intermediate between the top and the bottom. h continuous stream of raffinate, contained in the oil-rich phase, is withdrawn at the top. The extract, or furfural-rich phase, similarly leaves the apparatus at the bottom. After the oil dissolved therein has been separated from the solvent, a part of the extract is reintroduced a t the bottom as reflux. Furfural is recovered from the products by evaporation and is recirculatrd. By varying the relative amounts of selective solvent and oil, as well as the reflux ratio and other factors, it is possible to obtain any desired yields of extract and raffinate. A 50-50 split is not uncommon, but with equal ease the ratio of extract to raffinat,e may be made 10 to 90,90 to 10,30to 70, or any other value. The furfural extraction process has been studied by several other research organizations, particularly by the Northern Regional Research Laboratory, where the advantages of producing reflux by means of a backwash of naphtha have been investigated. Such operation results in extraordinarily efficient fractionation. When glycerides are treated by liquid-liquid extraction, the degree of separation achieved between the two products depends on the solvent ratio-that is, the amount of solvent fed for each unit of oil processed and also on the reflux ratio. There is a definite limit to the extent of segregation attainable in mixed glycerides. The theoretically maximum separation could be calculated for any given oil if its composition were known in terms of both its fatty acid composition and the manner in which the acids are distributed to form triglycerides. The former can be determined readily, but in most oily there is some uncertainty about the latter. Hilditch (6) has pointed out the tendency of natural oils and fats to be formed with a so-called maximum distribution. According to this concept, the proportion of glycerides each containing three different acyl radicals approaches the maximum theoretically possible for any particular mixture of fatty acids present as glycerides. I n other words, there is a minimum content of simple triglycerides containing three identical acyl radicals per molecule. Some natural oils and fats seem t o conform to this rule more closely than others. At least a few appear t o possess a distribution more nearly equal t o that calculated statistically. This latter possibility is known as random distribution and probably does exist in synthetic glycerides produced by the esterification of glycerol with mixed fatty acids. It is possible to calculate the percentage of each glyceride present in a n oil if distribution is assumed to conform to one or the other of these rules. The results are quite different in the two cases. These calculated percentages of various glycerides possessing different degrees of unsaturation can be employed t o calculate, in turn, the theoretically maximum difference t h a t might be achieved between the extract and raffinate by fractionating a particular oil. I n other words, i t is possible to estimate how much fractionation could be obtained in a hypothetical liquidliquid extraction column t h a t is 1 0 0 ~ efficient. o I n the case of soybean oil, this calculated maximum separability depends on the assumption made as to glyceride distribution and on the respective yields of extract and raffinate. Roughly, however, the maximum difference is 70 iodine number units. In actual practice, differences of 30 t o 50 or 55 units are obtained. If the free acids or their methyl esters are fractionated, instead
2249
of the mixed glycerides, both the actual and the theoretically maximum degrees of separation are much higher; the latter is about 130 units. The most important applications of the furfural extraction process in the vegetable oil industry have been the fractionation of linseed and soybean oils. Processing soybean oil is of particular interest to edible oil refiners because the resulting raffinate is considerably lower in iodine value than the original oil. M o r s over, i t has shown less tendency, after refining, t o develop reverted flavors. It is possible that further perfection of this or some other means of fractionation will provide a t least one solution to the problem of reversion in soybean oil. The other process that has attracted much attention for segregating glycerides by liquid-liquid extraction is t h a t employing propane as the selective solvent, as developed by the &I. W. Kellogg Company ( 2 ) . Propane possesses unique solvent properties when heated nearly to its critical temperature (97' '2.); under these conditions it is only partially miscible with vegetable oils and similar materials with which i t is entirely miscible a t lower temperatures. Furthermore, the saturated components tend to be more soluble than the unsaturated glycerides. The solubility relations in the critical region are the reverse of those observed with the solvents usually employed. The analogy between liquid-liquid extractioii and distillation was pointed out in the case of furfural, which solvent has a higher specific gravity than do vegetable oils. To make a strict comparison under such conditions, i t is necessary to visualize a distillation column working upside down, for the extract is withdrawn and refluxed at the bottom. With propane, however, the solvent is lighter than the oil, and the extraction column operates in an upright position with reflux returned at the top. Propane is less selective than furfural toward unsaturation but it exhibits other advantages. It possesses excellent selectivity for effecting removal of certain minor constituents, such as free acids, pigments, phosphatides, and sterols. The technique appears promising for decolorizing industrial fats, particularly grease and tallow and for recovering vitamins from such sources as fish oils and liver oils. Its high volatility makes its complete removal from the products relativelv easy. The Solexol process can be applied t o soybean oil in an interesting manner. A preliminary extraction separates the oil from pigments and phospholipids. The bulk of the oil, approximately 98.5% of the original volume, then may be re-extracted to segregate i t into drying and edible fractions in any desired proportions. Finally, there is recovered a small fraction containing a high concentration of sterols. One of the chief virtues of the propane process is its versatility. It is difficult t o predict the fields in which i t will find greatest utility, but one of them probably will be its application for removing free acids, color bodies, and the other undesirable constituents of crude edible oils. Removal can be accomplished under mild processing conditions, and thus will be avoided some of the damage done in the usual refining operations by t h e relatively drastic treatments now employed.
REFINING PRACTICES Changes in the practices employed in edible oil refineries do not occur overnight as the industry cannot afford a rapid rate of obsolescence. Nearly all refineries now use a continuous system of neutralization which has replaced the older methods conducted batchwise in refining kettles. A recent innovation, now in commercial operation, is the use of soda ash instead of lye for neutralization. Over-all losses appear to be lower because of the lesser tendency of the soda ash t o saponify the glycerides, but i t is necessary to finish this stage of the refining by a treatment with lye t o complete the removal of free acids and highly colored substances. I n the business of refining edible oils, t h e oil itself is a valuable material, and every effort is made t o manufacture a finished
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INDUSTRIAL AND ENGINEERING CHEMISTRY
product with a minimum loss of glycerides. The centrifugal methods of neutralization now in use represent a n enormous advance over the older kettle-refining process because they yield a considerably higher proportion of neutral oil. I n other Fords, less oil is lost in the form of soapstocli which sells for a comparatively low price. This has proved important from the standpoint not only of realizing the greatest possible financial return from the operation, but also of providing consumers of edible oil ample supplies during the recent years of scarcity. Progress has been made, too, in deodorization which for many years mas carried out by steam distillation of the more volatile constituents of the oil, batchwise, at elevated temperatures and under a high vacuum. I n several more recent installations the oil is scrubbed countercurrently with superheated steam in a vertical column, under a high vacuum. Refiners still are debating the merits and possibilities of this method. I t s development has coincided with intensive research on deodorization, however, and marked improvements have resulted thereby in the quality of t h e finished oils. Many of the latest developments in refining still are classed as trade secrets, especially the numerous improvements in technique t h a t have been devised to adapt existing facilities and practices to the handling of the larger proportions of soybean oil now being processed. Progress has been significant particularly in the technology of hydrogenation and in the control of this reaction to yield the proper isomers of oleic, linoleic, and other fatty acids. REVERSION OF SOYBEAN OIL The reversion phenomenon, referred t,o earlier, has received more intense study by the refining industry during recent years than any other single problem. T h e Soybean Research Council has recognized the importance of solving reversion and has spurred the entire industry to greater efforts by acting as a coordinator of the research being conducted on the subject by many industrial laboratories and research institutions. Besides the experimental work sponsored by the leading refiners, intensive studies are being conducted by the IYorthern Regional Research Laboratory, the Vniversity of Pittsburgh, and other public research institutions. All these groups have been participating in an annual conference where current research is discussed and plans are made for coordinating the industry’s attack on the problem. Experts on reversion recognize t h a t the undesirable flavors and odors are due to many constituents of soybean oil, but there is a difference of opinion as to which should receive consideration as the primary cause. One school of thought places the blame largely on linolenic acid, and there is a wealth of sound experimental results to support this view. Another group feels t h a t unsaponifiable constituents are the chief culprits. Still another opinion is that the phosphatides and possibly other nitrogenous substances are the precursors of revcr sion. The phosphatide thvory has received particular credence by German refiners who, long ago, developed a technology based on thorough removal of lecithin for the purpose of minimizing reversion (4). Examination of the German technology has shown it to be effective a t minimizing reversion in liquid oils, b u t i t seems to be inadeqiiate when applied to the production of hydrogenated fats from soybean oil. This probably accounts, a t least in part, for the fact t h a t soybean oil has bcen consumed in Germany and elsewhere in Europe principally as a liquid oil; it is mixed with other hardened oils to produce margarine and similar edible products. The requirements of Smerican consumers, however, malie i t necessary t o harden most of the soybean oil processed into edible products, so the German remedy is not a complete solution of the reversion problem in the United States. One of the plausible explanations of why linolcnic acid may contribute to reversion has been advanced by Lemon and his coworkers ( 9 ) at the Ontario Research Foundation. They pointed
Vol. 40, No. 12
out that the addition of hydrogen to linolenic arid ran result in the formation of several isomers and that one of these, isolinoleic acid, develops reverted flavors on standing. On the basis of this information, progress has been made toward minimizing reversion by selecting catalytic conditions employed during hydrogenation which are conducive to the formation of a minimum amount of this product. Daubert and associates (11) more recently have made what appears to be a substantial contribution to our knowledge of reversion by showing that one of the products responsihle for the poor organoleptic properties of soybean oil is a-heptenal, and a mechanism has been postulated by which the substance could be produced through degradation of linolenic acid. This development 17-as the result of an intensive laboratory study of a large quantity of distillate obtained from the deodorization of reverted soybean oil, and effortsare being made t o identify other constituents of this material. The role of unsaponifiable matter in contributing to reversion has been explored by bIattil (It?), who reported the creation of typically reverted soybean flavors in cottonseed and peanut oils by adding t o them small amounts of the unsaponifiahle constituents of soybean oil. Such rapid progress is being made towards solution of the reversion problem t h a t the entire subject requires revielv every few months. Its complete solution would be worth many millions of dollars per year to the soybean industry inasmuch as soyhcan oil has been traded for many years a t prices approximately 10ycbelow those of competing oils.
ANTIOXIDANTS Since the time when vegetable shortenings became a n important product in American markets, animal fats have suffered competitively, partly because of their lover resistance t o rancidification. T o overcome this deficiency the packing industry and other research organizations have worked intensi.i.ely on the development of antioxidants which Fill prevent lard from becoming rancid during storage and use, and several effective ones have been developed. Many of these are not in use as yet because thorough pharmacological tests must be conducted t o ensure that the incorporation of such substances into foods will not have undesirable nutritional effects. This entire field was reviewed thoroughly in a recent bulletin by Lundberg (IO). Tocopherol and lecithin have been used extensively for stabilizing lard; the former was incorporated in a t least some cases simply by adding hardened vegetable oils. These two antioxidants bear the approval of the Bureau of Animal Industry, and the use of others has been permitted comparatively recently. These include gum guaiac and nordihydroguaiaretic acid (NDG-4). Propyl and lauryl gallates also appear destined for commercial use as stabilizers for animal fats. The research on antioxidants has yielded a great deal of fundamental information on the mechanism of fat oxidation and the causes therefor. Of particular interest is the role of synergists, such as citric acid, xhose presence greatly enhances the effective ness of the antioxidant itself. There is a general belief that these materials function through their ability t o minimize the catalytic effect of metals present as traces in the fats. As a result of improvements in refining and stabilization, much of the lard now available is far superior to t h a t produced a few years ago; it is regaining considerable of the consumer preference t h a t was lost t o vegetable shortenings during the past 15 or 20 years. DEVELOPMENTS IN SHORTENING During the thirties, a few shortenings appeared on the market which were described as high-ratio products because they contained emulsifying agents which permitted the use of a high ratio of sugar t o flour and other components in cake doughs, sweet
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
goods, and other bakery products. These emulsifiers originally were glyceromonostearate and similar partial esters of glycerol. The advantages of such shortenings were recognized at once, but their extensive use was retarded during the war because of restrictions on the use of glycerol. Subsequently, however, other types of emulsifiers have been made available, including esters of sorbitol and polymers of ethylene oxide. Some of these are so potent t h a t their incorporation into shortenings renders the product vastly superior for many purposes. The proportion of shortenings manufactured containing emulsifiers has increased tremendously during the past year, although i t is impossible to state exactly what percentage actually is of the high-ratio type. The result of this development has been a tremendous improvement in the quality of baked goods and other products which require the use of shortening. Another accomplishment which has achieved prominence in the edible fat field is the production of dry powdered shortenings containing fat, milk, sometimes eggs, and other materials which can act as carriers of the fat. There are many advantages t o such a product, particularly in the manufacture of premixed goods, for the dry powder is far easier to handle during manufacturing operations than is the plastic shortening itself. CONCLUSIONS
These have been some of the most recent developments in the field of edible oils, and they can serve as barometers t o indicate future trends. I n the oilseed processing industry, economic reasons probably will compel further shifting to solvent extraction. I n edible oil refineries, i t is believed t h a t necessity will prove the mother of invention and t h a t a full and satisfactory cure will be devised for soybean oil’s organoleptic deficiencies. The same
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motivating force obviously will stimulate continued improvements and innovations in the manufacture of shortenings. There will be other developments, many of which surely will be of a n unexpected nature and produce far-reaching effects in the food business. This is a safe prediction to make because all branches of the edible oil industry have awakened to the necessity of conducting fundamental chemical research. The number and magnitude of the research programs being devoted to fats, oils, and oilseeds have increased manyfold; such a progressive attitude prevailing throiighout the industry cannot fail to accelerate progress. LITERATURE CITED
Anon., Chem. Eng., 55,146-9,(1946). Anon., New York, The M. W. Kellogg Co., 1947. Gloyer, Stewart W.,IND.ENG.CKEM.,40,228-36 (1948). Goss, Warren H., “German Oilseed Industry,” Washington, D. C., Hobart Pub. Co.,1947. Hickman, K. C. D., and Mees, G. C., IND.ENQ.CHEM.,38, 28-9 (1946). Hilditoh, T. P., “Chemical Constitution of Natural Fats,” New York, John Wiley & Sons, 1944. Kenyon, Richard L., Kruse, N. F., and Clark, S. P., IND.ENQ. CHEM.,40,186-94(1948). Kistler, R. E., Muokerheide, V. J., and Myers, L. D., Oil 62 Soap, 23,146-50(1946). Lemon, H. W., Can. J. Research, 25F, 34-43 (1947);Lips, H. J., Lemon, H. W., and Grant, G. A.,Ibid., p. 44-50. Lundberg, Walter O., Hormel Inst., Univ. of Minn., Pub. No. 20,1947. Martin, C. J., Sohepartz, A,, and Daubert, B. F., preliminary report t o Am. Oi1,Chemists Soc., Oct. 20, 1947. Mattil, Karl F., J. Am. Oil Chemists SOC.,24,243-6 (1947). RECEIVED May 19, 1948. 0
rozen Food Industry CLIFFORD F. EVERS National Association of Frozen Food Packers, Washington, D. C. T h e freezing of foods as a means of preservation is primitive in origin but the frozen food industry is a comparatively recent development. Today many food chemists and technologists consider quick freezing the best method of food preservation. Education is one of the major problems confronting the producers, distributors, retailers, and consumers of frozen foods. Chemists and chemical engineers must play a n important part in the development of this industry if it i s to find the answers to the many problems to be solved. These include the improvement of processing operations and plant sanitation: a profitable utilization of waste material : research on enzyme inactivation, oxidation of pigments and catecholtannins, denaturization of proteins, rancidity of fats, and syneresis of gels: and the development of cbjective methods for determining quality and fill of container.
I
N T H E early stages of evolution man learned either by ac-
cident or experience to provide against famine and starvation through the storage of foodstuffs a t harvest. Primitive man kept food in natural caves and later, with the discovery of fire, learned t h a t meat fire-cooked usually lasted longer and tasted better than raw flesh from wild boar and game. Many hundreds of years later salt came into use as a preservative for foods. Probably in its earliest form, sodium chloride served more to hide the disagreeable flavor of already decaying food than to prevent food
spoilage. Smoking or curing of food then came into practice and still later the dehydration or drying of fruits, grains, and vegetables. Canning or preservation by heat sterilization followed. Although canning may change color, flavor, and texture of foods it is, nevertheless, a n excellent means of food preservation. It is a n interesting fact that not one method of food preservation has ever been discarded but all have been improved continually through experimentation down through the ages. DEVELOPMENT
Freezing as a method of food preservation also has been improved. The fist refrigerators were the natural caves where man hid some of his food in the cool dryness of volcanic caverns. As the science of refrigeration advanced, man transcribed from nature the idea t h a t if cold above the freezing point of water could keep foodstuffs in edible condition for several days or longer, then more intense cold or temperatures below the freezing point of water should maintain foodstuffs for a n indefinite period in good condition. Slow freezing came into use about 1865 with the artificial freeeing of fish and poultry; this was followed by the freezing of meat about 1880 and of small fruits for remanufacture about 1905. T h e commercial freezing of vegetables and fruits for table use is of much more recent origin; i t was started in 1929 and is usually considered as being the beginning of quick-freezing. In the
