FATTY ACIDS FEED SUPPLEMENTS GLUE AND GELATIN FOAM STABILIZERS FERTILIZERS ADHESIVE TEXTILES LEATHER GLYCEROL
MEAT
Only 6 0 % of the animal is meat. The rest goes into by-products, some of which are shown above
H. E. ROBINSON, W . M. URBAIN, and H. H. YOUNG Research Laboratories, Swift & Co., Chicago, III.
PROTEIN BY-PRODUCTS OF THE MEAT P A C K I N G INDUSTRY
I EC ANNIVERSARY
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FEATURE
I HE USE OF MEAT as food for man is prehistoric. Methods for preparing, curing, and preserving meat likewise are old. Yet the science and technology applied to the processing of meat, meat products, and byproducts, were relatively slow in development. While certain important developments representing isolated efforts such as the refrigerator car, chrome tannage, the disassembly line for carcass dressing, etc., provided the industry with
INDUSTRIAL AND ENGINEERING CHEMISTRY
highly significant methods, organized technical research in the current sense was not used until about 1900. Why then has it been only the past 50 or 60 years that an organized research approach has been used? Several answers can be given, but two are easily recognized : 1. Disposal of inedible residues from the dressing of meat animals presented no particular problem. Large volumes of such "waste" were not accumulated until the development of the refrigerator
car made possible centralization of slaughter. The rendering industry converting animal waste products into fertilizer and fatty products solved this disposal problem. 2. Perhaps the major reason for applying scientific research to byproduct utilization has been the highly competitive nature of the meat packing industry. Today there are over 4000 independent processors of meat products, each being competitive with the other. As only about 60% of the live animal weight is meat, it appeared logical that by-product values could be enhanced to yield greater earnings. The growth of a profitable rendering industry proved this fact by taking animal waste for little more than the hauling cost, and converting it to glue, fertilizer, fatty acids, and glycerol. Although good value was obtained from meat and meat products by efficiently carrying out age-old processes, by-products in general required new processes to yield a better value. Numerous other factors outside the meat industry simultaneously exerted considerable pressure. Among these were the growth of the mineral fertilizer, soap, petroleum, and plastic industries. With a rapidly increasing population, not only of human beings but also of livestock, the meat industry had no alternative but to develop new and better methods for processing byproducts. Thus, a vigorous research program is now getting under way.
development of surface active agents, emulsions, accelerators, and other additives have been accepted eagerly by the tanner but time is still the bottleneck and time is expensive in modern industry. Chrome tanning, first patented in 1879, has not changed fundamentally. Improvements made and those still being studied are designed primarily to cut the processing time— e.g., the change from a dry salt cure to a brine cure for hides, cutting days from the processing time. If other reactions such as liming, washing, bating, tanning, and drying could be accelerated proportionately, the cost of leather manufacture would be reduced sharply. As in all industries, improvements do not come always from one's own research effort. Thanks to the chemical industry we now have chromium complexes with fatty acids and their fluoro derivatives which make it possible for leather products to shed water, oil, and soil alike. And they are amenable to cleaning techniques! This coupled with a host of new plastics and resins has made it possible for a new garment leather industry to offer a wide variety of colors and finishes, in addition to improved wearing qualities. Keratins
Leather Hides, Skins, and Wool
This group comprises those byproducts which are probably the oldest in use. The centuries old art of tanning hides and skins to form leather is most remarkable because it uses a complex series of chemical and physical reactions— the nature of which is still not fully understood. The preservation of hide substances by reaction with unsaturated fats, vegetable bark extracts, or heavy metal salts have been critically examined only during the past half century and have led to the synthesis of several new chemical derivatives (syntans), now being used in the leather industry. The tanning industry like others which use protein raw material has been plagued by the colloidal nature of the parent substance. Such material does not lend itself to instantaneous reactions because it depends upon diffusion, hydration, presence of powerful buffers, and other timeconsuming factors. Advances in the
This group of proteins, also known as sclero or protective proteins, possesses a physical form which has dictated their use. Wool, hair, fur, or feathers have in common a fibrous nature and an appreciable resistance to deterioration. This has defined well their use in textiles, upholstery, insulation, and felts of all kinds. Other members of this group which are chemically but not physically similar are hoofs and horns. These, too, were used originally for their physical characteristics as in buttons, combs, knife handles, and other novelties now replaced by cheaper resins which are readily molded rather than carved or shaped. Advances in felts and nonwoven fabrics coupled with the wide variety of resin emulsions available have aided in the formation of fibrous bonded sheet material offering improved characteristics for upholstery, air filters, and insulation. Another peculiar characteristic of keratin proteins is their amino acid composi-
tion. This is reflected in using keratin hydrolyzates as foam stabilizers in air-entrained concrete and foam-type fire extinguishers. Also they offer the most potent hydrolyzates for retarding the rate at which plaster of Paris sets. Glue and Gelatin
These two derivatives from the parent collagen protein found in skin and bones have been processed for centuries. Many changes during the last half century have cut hours if not days from the processing schedules. The engineering principle of turbulent agitation within a vacuum evaporator has all but eliminated the conventional refrigerated chilling belt and wind tunnel as a practical drying apparatus. Concentration to a high solids liquor, previously limited to 5 to 1 5 % solids with increase in viscosity, can now be raised to 35 to 50% solids without the loss in viscosity so prevalent in film-type concentrators. This resulted in the development of continuous dryers operating at elevated temperatures without fusion of the drying film. Numerous chemicals which prevent gelation have been developed to make a complete line of adhesives from cold liquid animal glue. In the other direction gelation accelerators have improved gelatin desserts and related confections. Newly developed hygroscopic agents or humectants have increased the variety of thermoplastic protein gels. Simultaneous with improvements made in the manufacture of these protein derivatives there has been developed new derivatives and new fields of use. Increased knowledge of the physical and colloidal chemistry of these proteins has effectively opened a new group of protective colloids useful in many processes from gun powder to paper manufacture. Many newly available polymerizable monomeric acids have been attached to the protein molecule and then polymerized to form industrially important compounds. Animal glue, formerly used entirely as adhesives, is now used equally for its colloidal properties. Livestock and Poultry Feeds
Cooked meat by-products used in livestock and poultry feeds are much VOL. 50, NO. 4
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APRIL
1958
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Leather tanning is a big business today. Pictured above are incoming hides as received by the tannery. Before this, they were salted and allowed to cure for 30 days. During cure, the hides are usually treated with a fungicide such as Dow's Dowicide for protection. Next step is unhairing
older than the modern animal feed industry. The latter was started when it became apparent that chemical fertilizers were here to stay. While the return of animal refuse to the soil will never be entirely eliminated, we must face the fact that synthetic urea or even liquid ammonia is much cheaper than dried protein on the basis of nitrogen or ammonia equivalent. Hence the introduction of Chilean nitrates, German or American potash, and Idaho and Florida phosphate rock has made the need for new outlets for protein by-products inevitable. Diversion of protein concentrates from plant to animal feeding was no great discovery but thanks to tremendous advance in other fields of science, feed formulation has become an important part of the by-product industry. Identification of the essential amino acids, vitamins and minerals plus some of their syntheses, coupled with progress in animal genetics, husbandry, and veterinary medicine as well as the discovery and application of antibiotics to feeding has been accomplished all within this half century. In addition to these contributions from our universities and industrial research laboratories much has been learned about the effect of processing on protein quality and its availability to the animal. All these developments made it possible to maintain an adequate livestock supply in spite of a sky rocketing population growth 44 A
and a gradual decrease in the arable land available for agriculture. A most dramatic example is in the poultry industry where the pounds of feed required to effect a one pound gain has been reduced about 50%. Blood From the. start as in fertilizer, blood can now be processed to yield a far better return. Cooked dried blood, although an excellent feed supplement, has more value if its ability to coagulate with heat could be retained or if it could be separated into its fractions of fibrin, corpuscles, and serum. Developments in low cost spray-drying techniques and equipment have aided in producing commercially dried blood which is soluble, coagulable, and suitable for plywood adhesive production without drying in shallow pans under a stream of cool air. Also modern centrifuging equipment can now separate whole blood into corpuscle paste and plasma proteins both of which serve as raw materials for the highly specialized pharmaceutical industry. The future of proteins has never been brighter, because new compounds, ever increasing in number, react readily with proteins under conditions which do not destroy the large protein molecules themselves. The general outlook for future use of protein by-products in the current trends is
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1. Continuous development of new products and/or new uses 2. Application of automation to the many chemical and physical changes used in processing these by-product materials Almost all native animal proteins are fibrous in nature except those maintained in aqueous solution. These fibers whether found in meat tissue, skin, organs, intestines, or as protective hair, feathers, fur, or wool have properties not found in any other substances. Their response to changes in pH, humidity, organic reagents, biologically active agents such as enzymes, mold, and bacteria, to say nothing of radiation, are profound. Irrespective of their physical form or source, native proteins have not and probably will not be synthesized on a basis that will compete with agricultural production. Therefore, any modification which will make them useful as a new product or in a process cannot help but enhance their value. With respect to more traditional protein by-products such as gelatin, glue, leather, and wool it can be expected that new processes will be developed. The methods from the past periods of time are best suited to batch-type operations. To secure the advantages of automation and other modern techniques, more inline processing will be needed. Process changes avoiding hold-up time are indicated. As automation involves expensive conversion from batch units to continuous machinery its economy is predicated upon sufficiently large volume to support the investment. This entails in many instances, new procedures or even standards for the commodities so processed. For example, it is posssible that the meat-packing plant may prepare for the leather industry hides and skins fully dehaired, dried, degreased, and otherwise substantially free from nonleather-forming materials. The mechanical removal of wool from sheep pelts has been realized but before maximum benefits of automation can be effected depilating agents must be developed. In conclusion, these goals, and our goals they must be, cannot be achieved without intensive research, not only in chemistry and engineering but also in many other fields of scientific endeavor.
