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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
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present era, many food chemists and technologists consider refrigeration, especially quick-freezing, as preservation a t its best. However, food freezing as an industry is in its infancy and is beset with all the problems and perils of the young and growing. Frozen foods, packaged in consumer size cartons, constitute t h e largest portion of the quick-freezing industry as it exist,s today. Yet this part of the industry grew slowly after an unspectacular birth during the depression years. A skeptical pennysaving public was slow to accept frozen foods, with good reason, for there was many a sad consumer experience with poor quality cold storage merchandise that had been frozen not, as quality products but only to remove fresh produce of questionable quality from a n already glut'ted market. This early mistake \vas repeated during the recent' war years with the same detrimental effects to the freezing industry. The industry learns its lessons the hard way, for education was then and is now a major problem confronting producers, distributors, retailers, and consumers of frozen foods. I n any system of education first things must come first and so the basic need of the industry is education wit,hin its own group. There are numerous packers of quality frozen foods, but not enough, and even the best packers should be looking continually for ways to improve their products. A few packers do have a research and technical staff for this purpose. However, more packers producing better products d l make for a bigger and be,tter industry. Apparently t,his idea as yet has not been accepted wholeheartedly by the industry, since it has no definite industrywide plan for education and research. I t is usually difficult to convince hardheaded businessmen that money for research and education can and will benefit their individual or collective industries either with savings in production cost or increases in product, sales. I n fact, some facets of the industry with a firm grip on the know-how have a selfish motive in not wanting others in the industry t o know too much about the right way of doing a bett,er job. This is just another sign of infancy, for all adult members of any group realize that knoxledge as common property benefits not only the group, but the individual.
PROGRESS It has been estimated that about 5 billion pounds of foods are being frozen in the United States annually. Unfortunately, the industry does not have any detailed statistics on the annual production of frozen fish, meat, poultry, or precooked foods. However, the total 1947 pack of frozen fruits, berries, and vegetablw amounted to approximately 693,000,000 pounds: of this approximately 37y0\\as in retail Containers. If the latter figurr is interpreted t o indicate an annual per capita consumption of fruits, berries, and vegetables of less than 2 pounds, it is evident that the industry's potential is still great. €Io\\- far the industry will go or how fast i t will progress is something that no one can foretell, but since freezing is a n excellent method of food preservation, there is every reason to believe that the industry has a great future. Expansion within the industry can take place only by educating all concerned. It is obvious that if the packer knows what to do and how t o do it, he d l be able to produce a better quality product. Likewise if the distributors and retailers know how to handle frozen foods, they will be able to offer the consumer a better quality product. Last but not least the housewife must be taught how to use frozen foods because a perfect product, mishandled by a n uninformed homemaker will rcsult in consumer dissatisfaction.
PROBLEMS The industry is in need of technical advice and development to improve its products and its proccssing techniques but has done tittle to support such work. Government agencies have been
Vol. 40, No. 12
interested but have not accomplished much toward the development of frozen foods. Probably bhe greatest, amount of progress made t,o date can be attributed to the work of the State Expcriment Stations a t universities and colleges. It is hoped that schools will continue to train more nien and women to be food technologists a%d that more food technologists will spwialize in the field of frozen foods. Food technology is a broad term; it involves those u-ith scientific training who make practical application of their knowledge to the food industry. Many manufacturers feel that the only scient'ifically trained person needed in the frozen food industry is a refrigerating engineer whereas freezing is only the last step in the processing of frozen foods. It' is true that a refrigerating engineer is probably the best trained person to solve problems concerned with the refrigerated warehousing, shipping, arid dispensing of frozen foods as well as improved methods of freezing. However, the greater share of the engineering problems fall into a category other than refrigeration. Chemical engineers have and must play a n important part in the devclopmcnt of this industry if i t is to find the answers to many of its problems. PREPARATION
Vegetables such as peas and lima beans are harvested by cutting the entire plant at approximately ground level. The cut vines are fed through a viner in which rotating paddles beat the peas and beans out of their pods. There is much bruising during t.he threshing process and consequently deterioration is exceedingly rapid after threshing. I n addition to bruising during viriing the peas and lima beans are covered XTith vine juice which is an excellent medium for the growth of bacteria; hence rapid dclerioration through bacterial action also takes place. If the vincr currently in use cannot be improved then the engineer should swing his thoughts to some other method for removing the peas and beans from their pods. X vacuum treatment to burst the pods has been suggested but the method and equipment, have not been developed. The fluming of a product through and around a processing plant is an excellent means of conveying provided the product is not in a st,ate or condition where the leaching of soluble solids can take place. Fluming a product such as fres!i raw asparagus would actually serve as a washer to remove sand and grit and probably do no harm to the product,; yet instances have been noted where frozen food packers have flumed blanched cut corn several hundred feet. It is obvious that such handling of sweet corn will wash out a large quantity of sugars and vitamins from the product. Sanitation also is a major factor in t,he hmdling of foods and if mechanical means are used, the engineer must develop suitable cleaning methods as well as adequate equipment. All vegetables must, be blanched promptly after harvesting in order to stop objectionable enzjmie action which causes serious losses of their natural sugars, flavor, and vitamins. Under present day practice, the blanching process is conducted through the use of hot water or steam. Here again, considerable loss is due to the leaching of soluble solids and nutricnts. I n general, these losses during steam blanching are much less than during blanching in boiling water. Either t.reatment means losses which should be lessened if not entirely eliminated. Electronic blanching niay be the answer and from experiment,s made to date it appears to offer definite possibilities. Vegetables, as they come from the blancher arc hot and if allowed to remain hot will lose color, flavor, and vitamin C rapidly. Therefore, i t is imperative that they be cooled directly as they come from the blancher. Since the usual method of cooling is by sprays or by fluming in water, there is additional leaching. This will still be a problem even when electronic blanching is introduced commercially unless a waterless cooling method also is developed. Peas and lima beans are two important frozen vegetables, and
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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each may be quality graded for maturity by brine flotation and separation. It is almost standard practice to brine-separate peas but only in recent years are a few packers using a similar process on lima beans. Brine separation is far from being a sharp cutoff for peas of desirable maturity from those t h a t are overmature. Quality graders require constant attention and the services of a good operator. Even so, there are times when the separators just will not work. The specific gravity of vegetables cannot be controlled but machines could be improved or other means devised to separate overmature products from those 'of desired maturity.
undesirable toughening such as occurs in precooked frozen crustacean products after a few months in frozen storage. I n certain other types of food, denaturization of protein due to freezing is the cause of drip, since after defrosting the protein is no longer able to hold the same amount of cellular fluids. Cntil more is known about the fundamentals of these changes there is little that can be accomplished to avoid or overcome them. Trial and error methods can be used but they are costly and unsatisfactory.
€ REEZING
The colloidal chemical changes in frozen foods are profound, yet they are not well understood. Syneresis is a n obstacle in the way of freezing many types of gels or flour-liquid combinations. Research on the colloidal properties of foods is of particular importance in connection with the preparation and freezing of precooked foods. The frozen food industry has made little progress in the field of efficient economical plant sanitation or the profitable utilization of waste materials. These are two broad fields t h a t offer many problems for the chemical engineer to investigate and study. Problems exist also in the field of pure sciences; enzyme inactivation, oxidation of pigments and catechol-tannins, denaturization of proteins, rancidity of fats, and syneresis of gels require further study and practical application to industrial situations.
T h e blanching of vegetables preparatory to freezing inactivates catalase and a considerable portion of the other enzymes SO that enzyme actions are reduced greatly during subsequent freezing and storage. Fruits usually are not heated, hence enzyme actions often result in a n undesirable frozen product; even et low temperatures freezing does not inactivate any of the common enzymes. The actions of enzymes and enzyme inhibitors are not understood too Fell b u t i t is known that unless certain enzymes are inactivated the frozen product will develop off-flavors and there will be loss of color and vitamins. A study of the enzymes themselves would provide more information on how t o retard their activity. Peaches darken rapidly after peeling because of a n enzymatic oxidation of the catechol-tannins which this fruit contains. The browning effect may be the result of an interaction of a polyphenol oxidase with oxygen and a suitable substrate, forming hydroxyquinone which undergoes some sort of a polymerization to yield brown pigments. This is a plausible explanation although not certain. One of the most outstanding contributions to the progress of the industry was the discovery t h a t ascorbic acid retarded this reaction. Ascorbic acid has been referred to as a n antioxidant. Although ascorbic acid prevents oxidative changes, it does not act in the manner ascribed by chemists to t h a t group of compounds known as antioxidants. Actually, when ascorbic acid prevents oxidation in food products it acts as a reducing agent rather than as a n antioxidant. The Food and Drug Administration refers to ascorbic acid as a preservative, but sui-ely it is not something that prevents the product from decaying. STORAGE
Other fruits also darken or discolor during freezing storage. Covering the fruit with syrup retards but does not prevent oxidation. Sliced apples darken rapidly as do cherries. Strawberries often discolor and some varieties even turn purple. Blackberries not only discolor but become sour to the taste. Little is known about any of these reactions, or why they occur, or what can be done to truly prevent them. During freezing storage the fats of poultry, meats, fish, and shellfish hydrolyze slowly to form free fatty acids and at the same time they may oxidize and become rancid. These chemical actions are rapid in pork sausage and oily fish; t h e frozen products will show signs of rancidity after 2 month's storage at 0' F. Pork sausage is much less stable at frozen temperatures than ordinary pork because of the fact that oxidation of the fatty acids is accelerated by the salt added as a seasoning agent. Some recent studies made by a fisheries laboratory and a leading manufacturer of vitamin C, indicate t h a t the storage life of mackerel and salmon may be extended another month or two by dipping the fish, prior to freezing, in a solution containing ascorbic acid. This is a step in the right direction but industry should be supporting much more extensive research. There is no doubt that if ascorbic acid will aid in retarding rancidity i t will tend to prevent the rusting of fish also as the fatty acids of fish are highly unsaturated and oxidize rapidly causing the fish to turn brown. Denaturization of protein is a basic research problem relating t o most types of frozen foods. In some cases it is the cause of a n
CHEMICAL AND ENGINEERING
PACKAGING
Another problem to be solved is proper packaging for frozen foods. The ideal carton or container would be highly moistureand vaporproof and would not taint the product with any odor or flavor; i t would have eye appeal, would be capable of machine handling and could be easily opened by the housewife. There are other requirements but these specifications give some idea of what is desirable and needed.
CONCLUSIONS
It is axiomatic that the frozen food industry needs assistance from all branches of the science of chemistry. T h a t includes the analytical field, as little has been done to develop objective methods for determining quality and fill of container. Present grading techniques rely on human interpretations of typical light yellow color, practically free from defects, and reasonably tender. Standards for grades would have considerably more value and acceptance if color could be determined and defined by its wave length, and if defects and maturity could be determined by reliable and accurate analytical methods. To say t h a t a container must be as full as practicable has little meaning whereas t o say that a container must contain sufficient product t o occupy a certain minimum percentage of its cubic capacity has a meaning that can be verified once a suitable method for determining fill of container is established. During the recent war years the quality of frozen foods was not good at all times. I n most instances the poor quality of nierchandise could be traced to new and inexperienced packers who, through lack of the know-how, had not done a good job. However, there were instances of just plain cutting corners and putting quantity ahead of quality. Top quality must be maintained or the frozen food industry will not survive. Objective methods for determining quality would do much to improve existing quality and help keep poor quality merchandise off the market. Education is still one of the major problems of the frozen food industry and the know-how is needed from the time the seed is planted until the finished product is consumed in the home. The industry is in its infancy and in need of technical advice and development to improve its products and its processing techniques. RECEIVED A4pril27, 1948.
