Meat Co-Products

DENG-CHENG LIU National Chung-Hsing University, Taichung, Taiwan HERBERT W. OCKERMAN The Ohio State University, Columbus, Ohio

I. INTRODUCTION II. CLASSIFICATION, PRODUCTION, AND UTILIZATION III. NUTRITIONAL VALUES IV. UTILIZATION OF BLOOD A. Isolation of Blood B. Removal of Heme from Red Blood Cells C. Usage of Blood Plasma in Food D. Medicinal and Pharmaceutical Usage of Blood V. UTILIZATION OF HIDES AND SKINS A. Stacking of Hides and Skins B. Processing of Leather from Hides and Skins C. Gelatin from Hides and Skins D. Uses of Gelatin in the Food and Pharmaceutical Industry E. Hides and Skins for Food and Sausage Casing F. Medicinal and Pharmaceutical Usage of Hides and Skins VI. UTILIZATION OF BONE A. Gelatin from Bone B. Liquid Extraction from Bone C. Mechanically Separated Meat from Bone D. Medicinal and Pharmaceutical Usage of Bone VII. UTILIZATION OF GLANDS AND ORGANS A. Glands and Organs as Food B. Medicinal and Pharmaceutical Usage of Glands and Skins VIII. UTILIZATION OF EDIBLE TALLOW AND LARD IX. THE PROCESSING AND UTILIZATION OF MEAT EXTRACT X. CONCLUSION REFERENCES

I. INTRODUCTION Meat co-products are produced by slaughterers, processors, wholesalers, retailers and renderers. Traditional markets for edible meat co-products have gradually been disap- pearing because of concerns about health and economic returns. In response to these problems, meat processors have directed marketing and research efforts toward inedible applications—for example, pet foods, pharmaceuticals, cosmetics, and animal feeds. The literature indicates that co-products (including organs, fat or lard, skin, feet, abdominal and intestinal contents, bone and blood) of cattle, pigs, and lambs represent 66.0%, 52.0%, and 68.0% of the live weight, respectively. Over 50.0% of animal co-products are not suitable for human or animal consumption due to unusual physical and chemical characteristics (1). A valuable source of potential revenue is lost and the cost of disposal of these products incurred by the meat industry is increased if meat co-products are not efficiently utilized. The USDA Economic Research Service announced that the portion of gross farm economic income from animal co-products is 11.4% for beef and 7.5% for pork for 1986 (2). The cost of live animals often exceeds the selling price of their carcasses and the value of the co-products must pay the expense of slaughter and generate the profit for the meat-slaughtering operation. Bengtsson and Holmqvist have suggested that 7% to 12% of the income from slaughter results from the sale of co-products (3). In addition to economic loss, nonutilization of meat products would create serious environ- mental pollution of water and air. However, with efficient utilization, meat co-products can be important and result in profits for meat processors. The modern livestock industry in the past has been an effective utilizer of co-products and it has often been stated that all of the pig is used except the squeal.

II. CLASSIFICATION, PRODUCTION, AND UTILIZATION

The U.S. meat industry considers everything produced by or from the animal, except dressed meat, as a co-product. Therefore, animal co-products in the United States are divided into two divisions, edible and inedible. In U.S. terminology, offal means slaughter co-products and includes all of the animal that is not a part of the carcass. Variety meats are the wholesale edible co-products that are segregated, chilled, and processed under sanitary conditions and that are inspected by the U.S. Meat Inspection Service. In some areas of the world, and to different degrees, blood is also utilized as an edible product for humans. In Downloaded by [Iowa State University] at 01:21 13 May 2015 the United States, meat trimmings from the head are described as edible offal or edible co-product items, and edible fats are fats obtained during slaughter, such as caul fat surrounding the rumen or stomach, and cutting fat, which is back fat or pork leaf fat, or rumen fat. In English commercial slaughterhouse practice the offal is divided into red (heart, liver, lungs, head, tongue, and tail) and white (fat), set of guts and bladder, set of tripe and four feet and trimmings (4). The English Food Standard Committee also separated offal into two categories (5):

List A. Items that may be used in cooked or uncooked products from mammalian species; contain tissues such as diaphragm (skirt, cattle only), head meat (ox cheek, cattle only; bath chip, pig only), heart, kidney, liver, pancreas, tail meat, thymus, and tongue and avian parts such as heart and liver.

List B. Items that may not be used in uncooked products; contain portions of mammalian species such as blood, blood plasma, brain, feet, large intestines, small intestines, lungs, esophagus meat, rectum, spinal cord, stomach (non- ruminant), first stomach (tripe, after cooking), second stomach (tripe, after cooking), fourth stomach, testicles, and udder and parts of avian species such as gizzard and neck.

The evaluated quantities of co-products from pork, beef, and sheep are shown in Table 1. The yield of edible meat co-product from animals ranges from 6.7% of the carcass weight for pork and the world production of edible co-products from pig in 1996 is shown in Table 2. A total of 5,655.5 thousand metric tons of pork edible co-products were produced in 1996, and data in Table 2 show that the largest part of the production of pork co-products is from Asia (50.4%) and the second from Europe (37.1%). Asia and Europe are also the two major consumers of meat co-products including beef and lamb (1). Usage of meat co-products often require treatment by the following steps: collection, washing, trimming, chilling, packaging, and cooling. Acceptance of these products depends on factors such as acceptability, regulatory requirements, nutrition, economics, and competitive products. Although customs, culture, and religion often act as major factors when a meat co-product is utilized as an ingredient in meat products, regulatory requirements also are important factors because many countries already had some food regulations on the policy of food safety and quality. An example of an USDA requirement is that mechanically separated meat and variety meats must be specifically identified by showing them as ingredient on labels. If frankfurters and bologna are made with heart meat or poultry mechanically separated meat as an ingredient, it must be listed. A detailed list of potential uses and preparations of meat co-products are listed in Table 3.

Table 1 Percentage of Marketing Live Weight of By-products from Various Species (hog, cattle, and sheep)

Hog Cattle Sheep

Item Percent Kilogram Percent Kilogram Percent Kilogram Downloaded by [Iowa State University] at 01:21 13 May 2015 Marketing live weight 100.0 600.0 60.0 Carcass 77.5 77.5 63.0 378.0 62.5 37.5 Bone 17.0 17.0 16.0 96.0 18.0 10.8 Blood 3.0 3.0 3.0 18.0 4.0 2.4 Fatty tissue 3.0 3.0 4.0 24.0 3.0 1.8 Hide or skin 6.0 6.0 6.0 36.0 15.0 9.0 Organs 7.0 7.0 16.0 96.0 10.0 6.0 Head 5.9 5.9 Viscera (chest and abdomen) 10.0 10.0 16.0 96.0 11.0 6.6 Feet 2.0 2.0 2.0 12.0 2.0 1.2 Tail 0.1 0.1 0.1 6.0 Brain 0.1 0.1 0.1 6.0 0.26 0.156

Source: From Refs 1, 3, 80, 81, 82, 83, and 84.

Table 2 World Production of Edible Co-products from Pigs, 1996 (thousand metric tons)

Country Carcass wt. Productiona Percentage

World 77,985 5225.0 100.0 Asia 42,534 2849.8 50.4 China 40,000 2680.0 47.4 Japan 1,264 84.7 1.5 Taiwan 1,270 85.1 1.5 North America 9,005 603.3 10.7 U.S.A. 7,765 520.2 9.2 Canada 1,240 83.1 1.5 South America 1,560 104.5 1.8 Brazil 1,560 104.5 1.8 Europe 16,269 1090.0 19.3 Germany 3,085 206.7 3.7 France 2,193 146.9 2.6 Spain 2,180 146.1 2.6 Russia 1,679 112.5 2.0 Netherlands 1,619 108.5 1.9 Poland 1,600 107.2 1.9 Denmark 1,528 102.4 1.8 Italy 1,355 90.8 1.6 Belgium-Luxemburg 1,030 69.0 1.2 European Union 15,043 1007.9 17.8

a Based on 6.7% of carcass weight. Source: National Pork Producers Council (NPPC), pork facts, 1997/1998, USA (85).

III. NUTRITIONAL VALUES Edible meat co-products contain many essential nutrients. Some edible meat co-products often are used as medical cures because they contain special nutrients such as amino acids, hormones, minerals, vitamins, or fatty acids. Except for blood, many meat co-products have higher levels of moisture than meat. Examples would be lung, kidney, brain, spleen, and tripe. Some organ meats such as liver and kidney contain a higher level of carbohy- drates than other meat material; pork tail has the highest fat and the lowest moisture level

Downloaded by [Iowa State University] at 01:21 13 May 2015 of all the meat co-products. Liver, beef tail, ears, and feet have the closest protein level when compared with lean meat tissue but a large amount of collagen is found in the ears and feet (6,7). The lowest protein level of meat co-products is found in the brain, in chit- terlings, and in the fatty tissue. USDA (1983, 1986) states that mechanically deboned beef and pork are required to contain at least 14% protein and a maximum of 30% fat (2,8). The amino acid composition of meat co-products is different from that of lean tissue due to the high amounts of connective tissue; this results in a larger amount of proline, hy- droxyproline, and glycine and a lower level of tryptophan and tyrosine for co-products such as ears, feet, lungs, stomach, and tripe (9). The vitamin content of organ meats is usually greater than that of lean meat tissue. Kidney and liver contain the highest amounts of ri- boflavin (1.697 to 3.630 mg/100g) and have 5 to 10 times more than lean meat. Liver is the best source of niacin, vitamin B12, B6, folacin, ascorbic acid and vitamin A. Kidney also is a good source of vitamin B6, B12, and folacin. A 100 g serving of liver from pork and beef contributes 450% to 1100% of the RDA for vitamin A, 65% of the RDA for vitamin B6,

Table 3 The Potential Uses and Preparation of Edible Meat Co-products

Kind Storage and preparation Methods of usage

Beef and veal Liver Frozen, fresh, or refrigerate Braised, broiled, fry, loaf, patty, Whole, sliced, or grind and sausage Kidney Fresh or refrigerate Broiled, cooked in liquid, and Whole or sliced braised Heart Frozen, fresh, or refrigerate Braised, cooked in liquid Whole or sliced Brains Frozen, fresh, or refrigerate Broiled, braised, and cooked in Whole liquid Tongue Fresh, refrigerate, smoked, or Cooked in liquid pickled Tripe Fresh, refrigerate, Fry, broiled, and cooked in precooked, pickled, or soak liquid before use Sweetbread Frozen, fresh, or refrigerate Fry, broiled, braised, and cooked Whole in liquid Oxtail Frozen, fresh, or refrigerate Cooked in liquid Intestine (small and large) Fresh or refrigerate Sausage casing Remove manure, soaking, washing, and salting before use Cheek and head Frozen, fresh, or refrigerate Cooked sausage, stew, soup, and trimmings bouillon Udder Frozen, fresh, or refrigerate Boiled, fried, smoked, and salted Skin Fresh or refrigerate Gelatin Feet Frozen, fresh, or refrigerate Jelly Fat Frozen, fresh, or refrigerate Shortening, drippings and chewing gum Blood Frozen or refrigerate Black pudding, sausage, blood, and barley loaf Bone Frozen, fresh, or refrigerate Gelatin, soup, jellied products, and refining sugar Pork Downloaded by [Iowa State University] at 01:21 13 May 2015 Liver Frozen, fresh, or refrigerate Braised, broiled, fry, loaf, patty, Whole, sliced, or grind and sausage Kidney Fresh or refrigerate Broiled, cooked in liquid, Whole or sliced braised, soup, grill, and stew Heart Frozen, fresh, or refrigerate Braised, cooked in liquid, Whole, sliced luncheon meat, patty, loaf, and sausage ingredient Brains Frozen, fresh, or refrigerate Broiled, braised and cooked in Whole liquid, poach, and scramble Tongue Fresh, refrigerate, smoked, or Cooked in liquid, cured, sausage pickled ingredient, salad, and jelly Stomach Fresh, refrigerate, or Broiled and cooked in liquid, precooked sausage container, and sausage ingredient

Table 3 Continued

Kind Storage and preparation Methods of usage

Spleen Frozen, fresh, or refrigerate Fry, pie, melt, and blood sausage Whole Tail Frozen, fresh, or refrigerate Cooked in salt liquid Intestine (small and large) Fresh or refrigerate Sausage casing Remove manure, soaking, washing, and salting before use Cheek and head Frozen, fresh, or refrigerate Cooked sausage trimmings Ear Frozen, fresh, or refrigerate Smoked and salted, stew with feet Skin Fresh or refrigerate Gelatin Feet Frozen, fresh, or refrigerate Jelly, pickled, cook in liquid, boiled, fried Fat Frozen, fresh, or refrigerate Shortening, lard Blood Frozen or refrigerate Black pudding, sausage, blood and barley loaf Bone Frozen, fresh, or refrigerate Gelatin, soup, jellied products, and rendered shortening, mechanically deboned tissue Lung Frozen, fresh, or refrigerate Blood preparation and pet food Lamb Liver Frozen, fresh, or refrigerate Braised, broiled, fry, loaf, patty, Whole, sliced, or grind and sausage Kidney Fresh or refrigerate Broiled, cooked in liquid, Whole or sliced braised, fried, stew, and soup Heart Frozen, fresh, or refrigerate Braised, cooked in liquid, Whole or sliced roasted, stuff, luncheon meat, patty, loaf, and sausage ingredient Brains Frozen, fresh, or refrigerate Broiled, braised and cooked in Whole liquid, poach, and fried Tongue Fresh or refrigerate Boiled, stew, jelly, grilled, and cooked in liquid Downloaded by [Iowa State University] at 01:21 13 May 2015 Stomach Fresh or refrigerate Honeycomb tripe and container for haggis Sweetbread Frozen, fresh, or refrigerate Fry, broiled, braised, poach with Whole sauce, cream and cooked in liquid Spleen Frozen, fresh, or refrigerate Pie, melt, blood sausage ingredient, and variety meat Intestine (small and large) Fresh or refrigerate Sausage casing Remove manure, soaking, washing, and salting before use Cheek and head Frozen, fresh, or refrigerate Cooked sausage, stew, and soup trimmings Testicles Frozen, fresh, or refrigerate Fried Lungs Fresh or refrigerate Haggis, pet food Feet Frozen, fresh, or refrigerate Jelly

Table 3 Continued

Kind Storage and preparation Methods of usage

Fat Frozen, fresh, or refrigerate Shortening, drippings, sweets, oleomargarine, and chewing gum Blood Frozen or refrigerate Black pudding, sausage, blood and barley loaf Bone Frozen, fresh, or refrigerate Gelatin, soup, jelly, and mechanically deboned tissue

Source: From Refs. 1, 82, and 86.

3700% of the RDA for vitamin B12, and 37% of the RDA for ascorbic acid. In addition to supplying vitamins, lamb kidney, pork liver, lungs, and spleen are often act an excellent source of iron. The copper content is the greatest in the livers of beef, lamb, and veal. They contribute 90% to 350% of the RDA for copper (2 mg/day). Livers also contain the highest amount of manganese (0.128 to 0.344 mg/100 g). However, the highest level of phosphorus (393 to 558 mg/100 g) and potassium (360 to 433 mg/100 g) are found in thymus and sweetbread when compared with all meat co-products. With the exception of brain, kidney, lungs, spleen, and ears, most other co-products contain sodium at or below the levels found in lean tissue. Among the raw material, mechanically deboned meat has the highest calcium content (315 to 485 mg/100 g). Many organ meats contain more polyunsaturated fatty acid than does lean tissue. Brain, chitterling, heart, kidney, liver, and lung have the lowest level for monounsaturated fatty acids and the highest amount of polyunsaturated fatty acid. In addition to higher levels of cholesterol (260 to 410 mg/100 g), which are three to five times higher than those of lean meat, large quantities of phospholipid also are found in these meat organs. Brain is the highest in cholesterol (1352 to 2195 mg/100 g) and also has the highest amount of phospholipid when compared with other meat co-products (10). Based on these data, USDA- USDHHS recommended limiting the quantity of cholesterol and the amount of these co- products in the diet because of health-related concerns (11). A high-cholesterol content in many organ meat and the possible accumulation of pesticides, residues of drugs, and toxic heavy metal contribute to the recommendation for limited consumption. Downloaded by [Iowa State University] at 01:21 13 May 2015 IV. UTILIZATION OF BLOOD Animal blood has a high level of protein and heme iron and is an important animal co-product. In Europe, animal blood has been used in making blood sausages, blood pudding, bis- cuits, and bread for a long time. And in Asia, it also has been used in blood curd, blood cake, and blood yogurt-like blood pudding (12). It is also used in nonfood systems such as in fertilizer, feedstuffs, and binders. The Meat Inspection Act stated that blood is approved for food use when removed by bleeding of an animal that has been inspected and passed for use in meat food products. Basically, blood is usually sterile in a healthy animal and is high (17.0% to 18.0%) in protein that is reasonably well balanced in amino acid composition. Blood is a significant part of the animal’s mass (2.4% to 8.0% of the animal’s live weight) and the average percentage of blood that can be recovered from pigs, cattle, and lambs is 3.0% to 4.0%, 3.0% to 4.0% and 3.5% to 4.0%, respectively. Because use of blood in meat processing results in the final product being dark and often unpalatable, and because

plasma has a more desirable color and functional properties, plasma is the portion of blood that is of great interest.

A. Isolation of Blood Plasma has been widely used in the meat industry because of its excellent functional properties (13). Plasma contains one-third of the total blood protein, and red blood cells contain the other two-thirds (14). On a large-scale processing of edible whole blood, it is separated into two constituents: plasma (60% to 80%) and red cells (20% to 40%). The plasma consisting of 7.0% to 8.0% protein and 91% water, is cooled, frozen or dried. The red cells, consisting of 34% to 38% protein and 62% water, is dried to form a meal or the heme group is removed to obtain globin. Anticoagulants (0.2% sodium citrate or citric acid or 10.0 gram of a mixture of phosphates—22.0% Na2HPO4, 22.0% Na4P2O7, 16.0% Na2H2P2O7 and 40.0% NaCl per liter of blood) are normally used in collecting whole blood and, are in- jected via a hollow knife if a vacuum transport system is adopted. Continuous blood-separation equipment is used and the separation of the fractions is accomplished with a high- speed centrifuge or separator. After separation, the plasma is frozen or spray dried at low temperature in order to maintain its solubility and functional ability. To freeze blood plasma, it is normally placed on a vertical rotating drum that has a temperature of between 10°C (14°F) and 40°C (40°F) and then the frozen plasma is scraped from the surface in the form of a flake. When blood is dried, great care must be taken to prevent denatura- tion of the protein because this lowers the quality of the dried fraction. Concentration is the first step for the blood plasma drying process in most plants and generally is accomplished by membrane filtration and evaporation. The drying process of the concentrated plasma is finished by a spray drying system or a fluidized bed drying system. A dried blood plasma can be produced with 96.4% protein and 2.4% moisture by this processing technique.

B. Removal of Heme from Red Blood Cells Heme derived from animal blood is a valuable source of organic iron, which may be used as a supplement in foods (15). Heme pigment can be used as a red colorant for food and is used in Chinese semi-dried sausage (16). Several methods have, therefore, been developed to remove the heme group from hemoglobin of red blood cells. These include an acid-acetone method (17), hydrogen peroxide decoloration (18), and decoloration with carboxy methyl cellulose (NaCMC) (19) and sodium alginate (20). With these methods, the globin Downloaded by [Iowa State University] at 01:21 13 May 2015 and heme can be easily separated and recovered.

C. Usage of Blood Plasma in Food Blood in food is used as an emulsifier, stabilizer, clarifier, color additive, and nutritional component. Most blood is used in livestock feed in the form of blood meal and used as a protein supplement, milk substitute, lysine supplement, or vitamin stabilizer and is an excellent source of most of the trace minerals. Blood plasma has gel-forming ability because it contains 60.0% albumin and is the best water and fat binder of the blood fraction. Plasma gels appear very similar to cooked egg whites and plasma forms gel at protein concentra- tions of 4.0% to 5.0% and that its gel strength increases with increasing concentration (21). Cooked ham with the addition of 1.5% and 3.0% frozen blood plasma and hot dog with 2.7% were more satisfactory in color than the control samples (22). In addition to gel forming, blood plasmas also has excellent foaming capacity (22–25). For this reason, blood

plasma can be used to replace egg whites in the baking industry. Nielsen recently indicated that the application of transglutaminase (TGase) from animal blood and organs or microbes to products in the meat industry is one of the most investigated applications in food processing (26–38). Blood factor XIII is a transglutaminase that occurs as a enzymogen in plasma, placenta, and platelets. The reaction catalyzed by Ca2 dependent factor XIIIa involves the formation of a -(-glutamyl)-lysyl bond between an acyle donor (glutaminyl residue) and an acyl acceptor (lysyl residue) of the proteins fibrin and fibronectin, fibrin and actin, myosin and fibronectin and myosin and actin (39). Therefore, this enzyme cat- alyzes conversion of soluble proteins to insoluble high-molecular polymers through formation of covalent cross-links (31,40). Transglutaminase extracted from bovine blood at first for improving the binding ability of fresh meat products at chilling temperature and showed how myosin was cross-linked by TGase in 1983 (27). An important property of the TGase reaction was documented when cross-linking between myosin and proteins (soy, casein and gluten) commonly used in meat processing was found (30). Moreover, the restructured meat products without heating, and decreased with salt and phosphates can be made by the addition of TGase from animal blood (28,32,33,41,42).

D. Medicinal and Pharmaceutical Usage of Blood Blood can be separated into several fractions that have therapeutic properties. Liquid plasma is the largest fraction (63.0%) and consists of albumin (3.5%), globulin, and fibrinogen (4.0%). In the laboratory, many blood products are used as a nutrient for tissue culture media, as a necessary ingredient in blood agar and peptones for microbial use. Glyc- erophosphates, albumins, globulins, sphingomyelins, and catalase are also used for biological assay. Many blood components such as fibrinogen, fibrinolysin, serotonin, ka- likrenins, immunoglobulins, and plasminogen are isolated and used in the chemical or medical aid. Purified bovine albumin is used to help replenish blood or fluid loss in animals, in testing for the Rh factor in human, as a stabilizer for vaccines, and in antibiotic sensitivity tests. Pork-blood fibrin extract is used as a source of amino acids, which are incorporated into parenteral solutions for nourishing some surgical patients. Superoxide dismutase (SOD) is an enzyme attending a series of reactions of superoxide radical and transfering it into water and oxygen to protect cell membranes of the animal body from serious damage by oxidation (43). SOD can be extracted from cattle blood for curing osteoarthritis, is- chemia, and in anti-inflammatory treatment and so forth (44–48). Crude SOD from porcine blood exhibited a higher activity (1570 unit/mg), and the results are similar to the bovine Downloaded by [Iowa State University] at 01:21 13 May 2015 erythrocyte SOD (49). A thin firm can be made from fibrinogen and used to control bleeding in surgery and also can be used as a spray or oral drug for gastric and intestine hemor- rhages (50). Otherwise, the citrate-saline treated fibrinogen from porcine blood is an effective hemostat in animal surgery (51). Industrial uses of blood includes uses as an adhesive and film former in paper, ply- wood, fiber, plastic and the glue industry. Also used as a spray adjuncts with insecticides and fungicides and as a stabilizer in cosmetic base formulations. It also finds use as a foaming agent in fire extinguishers.

V. UTILIZATION OF HIDES AND SKINS

Animal hides and skins have been utilized for shelter, clothing, and weapons and as food containers by humans since prehistoric times. The hides and skins contain a very notable

portion, 4.0% to 11.0% (e.g., cattle: 5.1%–8.5%, average: 7.0%; sheep: 11.0%–11.7%; swine: 3.0%–8.0%), of the weight of the live animal and generally are one of the most valuable animal co-products. Examples of finished product from cattle hide co-products, hog skin co-products, and sheep pelts co-products are the following: cattle cured and tanned hides—shoes, bags, belting, rawhide, athletic equipment; cattle corium layer—picking bands, textile shuttle holders and passers, reformed sausage casing, and cosmetic products; calf skin—lightweight leather, gloves, drum heads, and fabric trimmings; pig skin— sausage, edible gelatin, glue, gloves, belts, shoes; sheep slats (skin after wool or fleece is removed)—shoes and slippers, hat sweat bands, fancy shoes, gloves, sporting goods, diplo- mas; sheep pelts (wool or fleece left on)—heavy coat material, moutons, and shearlings.

A. Stacking of Hides and Skins After hides and skins are removed from any animal, they should be quickly cured to stop bacterial and enzymatic decomposition or spoilage. There are four basic treatment for preserving these hides and skins: air drying, salt-pack curing, mixer curing, and raceway curing; salt-curing is commonly used to treat these raw materials. The quality of cured hides and skins are usually evaluated by measuring the moisture and salt content of the hides. The moisture level of the hides are generally maintained from 40% to 48% to result in good condition during storage or shipping. Some chemicals or insecticides such as sodium sulfite, acetic acid, white arsentic (As2O3), sodium silicofluoride (Na2SiF6), 1,2,3,4,5,6-hex- achlorocyclohexane (Lindane; C6H6Cl6), 1,4-dichlorobenzene (C6H4Cl2), and pyrethrum, are often used to help protect against insect damage or for short-term preservation before tanning.

B. Processing of Leather from Hides and Skins A general description of leather production can be found in the reports of Hague and Ock- erman and Hansen and a summary is given of the processing (1,52). The cured hides should be stored in a cooled and well-ventilated tanner’s hide house when they arrive at the tannery. The first step of tanning is grading and sorting the hides into packs of uniform size, weight, and type of hide. The next step is soaking, and this means that enough moisture needs to be added to the cured hides for the succeeding tanning operations. The soaking of hides is finished in half-round cylindrical vats in which the hides are placed with water, wetting agents, and disinfectants; the hides are stirred in this

Downloaded by [Iowa State University] at 01:21 13 May 2015 solution by a dip-paddle wheel for 8 to 20 hours in order to let the hides reabsorb the needed water. A washing step after soaking removes the remaining dirt, manure, salt, and blood from the hides. The unhairing procedure is the next step; originally it was carried out by a process known as sweating, in which the hides were placed in the previously described paddle vats or mixer with an unhairing agent in a warm environment. The most common chemical de- pilatory agents are a saturated solution of calcium hydroxide [Ca (OH)2] and sodium sul- fide (NaS) or sodium sulfydrate (NaHS) or milk of lime. Some hides, such as sheepskins and pigskins, contain a large quantity of fat and it is often desirable to reduce this to approximately 3.0% on a dry-weight basis; this process is sometime done by a hydraulic press to remove fat prior to continuation of the tanning process. “Bating” is used to remove the alkaline unhairing chemicals and other nonleather substances in the pelt structure and is performed in a large wooden drum. Bating makes the hide softer, less harsh, and cleaner. The next step is “picking,” which places the pelts in an acid. The hides need to have a low

pH in order to accept the tanning materials, such as chrome. The major purpose of tanning is to convert the collagen fibers of the skin into a stable non-rotting leather. “Chrome tanning” is the most popular method of tanning today because it can be finished quickly and desirable physical and chemical properties can be produced. After tanning, the next procedure is “setting,” whose purpose is to lower the moisture content, smooth the grain, and remove wrinkles from the hide. Splitting and shaving follow and the purpose of these two steps is to obtain a uniform thickness of the leather desired for its ultimate use. The desired color of leather can be produced by a “dyeing” operation. The aim of coloring is not only to produce the right strength and shade of color but to produce a color that will resist fading and can be dry-cleaned or washed. “Fatliquoring” is used to adjust the firmness or softness of the leather by lubricating the fibers after coloring, and it also can increase the tensile strength of the leather. “Setting out” is accomplished to smooth and stretch the leather and to compress and squeeze out the excess moisture and grease. The purpose of drying is to remove all but equilibrium moisture, and after drying the skin should contain 10% to 12% moisture. The popular drying technique is called “pasting” in which the hides are actually pasted to large stainless steel or glass plates. After drying the leather is hard and fairly unworkable, and the final user always requires varying degrees of softness; additional moisture is applied by shower-like nozzles and this procedure is called “conditioning” or “wetting back.” “Buffing” is necessary to improve the appearance of the leather and to reduce any blemishes by light mechanical sanding. The next process is “finishing,” which is the application of film foaming materials that provide abrasion and stain resistance, enhance the color, and make the leather easy to care for. After the finishing, it must be dried in a long heating tunnel with steam-heated air. If a smooth grain surface or a various grain texture is needed on the leather, this can be accomplished by “platining,” which is obtained by pressing (300 ton/in2) for a few seconds. The final step is “grading” and it is dependent on temper, uniformity of thickness and color, and defects of the leather. The average total time of the processing of leather from raw skins or hides is 4 weeks. Leather is sold by the area; therefore, the hide needs be measured by a planimeter to cal- culate the total area of the piece of leather, then grouped into batches of four to five hides, rolled into a bundle, covered with paper, and packed in a wooden box for shipping.

C. Gelatin from Hides and Skins

Downloaded by [Iowa State University] at 01:21 13 May 2015 Gelatin is produced by controlled hydrolysis of a water-insoluble collagen that belongs to a water-soluble, hydrophilic, derived colloidal protein. Gelatin is made from fresh, feder- ally inspected raw materials (hide or bone) that are in an edible condition. The conversion of collagen to gelatin involves the breaking of hydrogen bonds that stabilize the triple-coil helix and transform it into the random coil configuration of gelatin. There are three basic types of new chains: alpha-chain, beta-chain, and gamma-chain in gelatin. A single gelatin has several molecular weights and this determines its characteristics, such as colloidal dis- persion in water, viscosity, adhesiveness, and gel strength. The tissues that contain large quantities of collagen that are commercially available as a co-product are usually hides, skins, and bones; therefore, they are a major raw material source for the manufacturing of gelatin. A summary of the general description of gelatin production as described by Hinterwaldner is given as follows (53). The processing of gelatin from hide and skin consists of three major steps: The first step is the elimination of noncollagenous material from the raw material. This is followed

by controlled hydrolysis of collagen to gelatin, and the final step is recovery and drying of the final extracted product. Generally, a collagen stock will be used to extract gelatin by combinations of an alkaline procedure, an acid procedure, and high-pressure steam extraction. The alkaline procedure is the most widely used commercial system for the processing of collagen to gelatin. A saturated solution of calcium hydroxide made by the addition of lime is used in this procedure and its usage in approximately 10% of the weight of the stock. This procedure causes the noncollagen compounds such as keratin, globulin, mu- copolysaccharides, elastin, mucins, and albumins to be changed to more soluble products, and some of the fat is converted into polar compounds that can be removed easily by washing. After the liming of the hides, the collagen fibers are swollen and the internal cohesion of each fiber is decreased. The next step is washing and neutralization; the collagen is washed by cold running water for 1 to 2 days, and the pH of collagen is lowered and the lime is removed. By washing with dilute hydrochloric acid (HCl) or sulfuric acid (H2 SO4) until the collagen is limp, the collagen stock should have a pH between 5.0 and 8.0 and is ready to be extracted. Extraction is normally started at 54° to 60°C for 3 to 5 hours and is continued up to boiling. The highest quality product is obtained at the lower extraction temperature, but yield is increased at higher temperatures. The liquid extract needs be filtered to remove small particles; sometimes, activated carbon is also added to decolorize the gelatin solution. Generally, the extract obtained from higher temperatures needs to be vacuum evaporated in a pan so that a sufficient concentration and gel strength can be obtained when cooled. After concentrating, the gelatin is dried by many drying methods such as a cooled drying tunnel, drum drying, and spray drying. Another extraction procedure for gelatin is acid processing and it is usually applied to pig skin or bone. Pigskins are first washed to remove salt from salted skin and to remove extraneous matter and/or blood. Since pigskin often contains 8.0% to 15.0% fat, pre-extraction of this lipid material is necessary before the acid extraction procedure. This is done by heating in hot water (55°–60°C), two to three times, stirring for 4 to 6 hours, and then washing in 40° to 55°C water. After washing and removal of fat, the skins are soaked in a 5.0% inorganic acid (such as hydrochloric acid, sulfuric acid, or phosphoric acid), which results in a pH of approximately 4.0. This pH causes the collagen to swell and a great deal of solubilization to occur. After 10 to 72 hours of soaking, the acid is then drained and the collagen is washed to raise the pH of the skin to approximately 4.0 to 5.0. At this pH the native collagen is still swollen. After acid treatment, the collagen stock is extracted at a lower starting temperature than cow hides and the procedure is almost the same as the al-

Downloaded by [Iowa State University] at 01:21 13 May 2015 kaline treatment. However, the gelatin produced from pigskins has a higher gel strength and better clarity and color than alkaline-treated cattle hide products and it also should be recognized that alkaline- and acid-precursor produced gelatin are two different classes of gelatin. Two grades of gelatin may be extracted; Class A, which is a high grade, with relatively undamaged molecular material, and Class B, which is extracted by harsh means and consequently has a range of molecular weights and altered properties. All gelatins are soluble and are able to form gels on cooling from hot solution and thus it is an important food additive.

D. Uses of Gelatin in the Food and Pharmaceutical Industry

Gelatin is added to a wide range of foods as well as forming the major constituent of con- fectionery jellies and aspics (54). Its major use is still the production of gel desserts because

of its melt-in-the-mouth properties, but it is also added to a range of meat products, in par- ticular to meat pies as a jelly component. Gelatin also has been used extensively as a stabilizer for frozen dairy products and other frozen desserts. High-bloom gelatin is added as a protective colloid to ice cream, yoghurt, and cream pies. The gelatin is thought to inhibit ice crystal growth and lactose recrystallization during storage. Approximately 6.5% of the total production of gelatin is used in the pharmaceutical industry, with the largest proportion used for capsule manufacturing (55). Gelatin also can be used as a binding and compounding agent in the manufacture of medicated tablets and pastilles. It is used as an important ingredient in many specialized protective dressings such as zinc gelatin or Unna’s paste for the treatment of ulcerated varicose veins. A hemostatics sponge is formed when a sterile solution of gelatin is whipped into a foam, rendered insoluble by treatment with formaldehyde, and then dried; it can be used as an absorbable sponge in surgery and also to implant a drug or antibiotic directly into a specific area. Gelatin is used as a plasma expander for blood in cases of very severe shock and injury due to its protein character. Gelatin is an excellent emulsifier and stabilizing agent for many emulsions and foam; therefore, it is also used in cosmetic products, flocculation agents, and printing applications such as carbon printing, silk screen printing, and photogravure printing.

E. Hides and Skins for Food and Sausage Casing

Extraction of gelatin from animal skins and hides can be used for food. The raw material can also be rendered for lard. In the United States and some Asian countries, the pork skin is immersed in a swelling agent, boiled, dried, and then fried to make a snack food (56–58). The collagen of hides and skins also has a role as an emulsifier in meat products because of its hydrophobic nature: it can bind large quantities of fat. This can be an advantage, and it has been suggested that collagen may act as an adhesive between fatty and lean particles and many absorb excess fat. Therefore, collagen is a useful additive or filler for meat products. The collagen also can be extracted from cattle hides to make collagen sausage used in the meat industry (59). Collagen casing products were developed in Germany in the 1920s but only gained popularity in the United States in the 1960s. Regenerated collagen casings are made using extrusion techniques. Collagen casing manufacturing processes do not convert collagen to a soluble product as does the gelatin extraction process; instead, they result in a much more

Downloaded by [Iowa State University] at 01:21 13 May 2015 fibrillar product that retains a relatively high degree of the native collagen fiber. The extracted collagen product is suspended in an aqueous solvent and converted to an acid- swollen gel or dough that is produced by the alkaline extraction process and is then extruded either by the wet or the dry process. During extrusion the collagen fibers tend to be aligned parallel to the axis of the tube emerging from the extruder. In the wet process, the extruder contains an internal disc that forces the following gel against the sides of the extruder casing. In the dry process the extruder contains twin counter-rotating serrated sur- faces. The combination of fiber length and extruder design produces a weave-angle of cross-hatched collagen fibers. The tube of extruded collagen is then passed through a concentrated salt solution and a chamber of ammonia to precipitate the collagen. The swollen gel contracts to produce a film of reasonable strength that can be improved by the addition of plasticisers such as glycerin. The tube is then dried to a 10.0% to 15.0% water content and pleated so that a 15.0 m length of casing is contracted to 18.0 to 20.0 cm.

F. Medicinal and Pharmaceutical Usage of Hides and Skins An extracted collagen product can assist in stimulating blood clotting during surgery. Pork skin is similar to human skin and can be converted into dressing that can be used for burn or skin-ulcer patients. Pork skin used as a dressing needs to be treated by a series of procedures: cut into strips or into a patch, shaved of hair, split to 0.2 to 0.5 mm thickness, cleansed, sanitized, and packaged. It can be used for skin grafting. When used for skin grafting it is removed from the carcass within 24 hours (60). Gelatin produced from hog skin is also used for coating pills and making capsules in the pharmaceutical industry.

VI. UTILIZATION OF BONE

Eleven percent of pork carcasses, 15% of beef carcasses, and 16% of lamb carcasses is composed of bone, and these values would be higher if adhering meat is included. In addition to the attached lean, the amount of marrow in a bone can also contribute to the yield of mechanically deboned products (61,62). The marrow can average 4.0% to 6.0% of the carcass weight. For centuries bones have been used to make soup and gelatin. In recent years the meat industry have attempted to get more meat from bone and new separation techniques have been utilized for this purpose. The mechanical deboning or separation technique produces tissue that at times has been called mechanically separated beef, pork, or lamb, mechanically deboned beef, pork, or lamb, and mechanically removed meat. Me- chanically deboned or separated meat is now approved for use in meat products (mixed or used alone) in many countries. In 1978, mechanically separated red meat was approved for use in the red meat industry in the United States.

A. Gelatin from Bone

Ossein is normally produced from bone for gelatin extraction, and at first the bones must be pretreated by cooking at 80° to 95°C to remove adhering meat, gristle, and fat. The bones are then washed several times to get them clean. Next the bones are washed in dilute hydrochloric acid to remove minerals. In general the final ash of the ossein is from 1.0% to 2.0%. The clean ossein is then rapidly dried in hot convection air-drying ovens to an 8.0% to 10.0% moisture level. The products are stored in moisture-proof bags and processed into gelatin within 6 months. The ossein is processed through liming, deliming, washing, and

Downloaded by [Iowa State University] at 01:21 13 May 2015 gelatin extraction. The drying of gelatin is similar to the previously described process for gelatin extracted from hide or skin.

B. Liquid Extraction from Bone

In Asia, for many years chicken bones have been extracted and used as a special flavoring ingredient for meal cooking. In this process, crushed bones are cooked with water for 8 to 12 hours. The product is cooled and the fat is skimmed from the liquid. The liquid contains approximately 5.0% solids. Currently, processing time is reduced to 1.5 to 2.0 hours by using a high-pressure extraction system (4 to 6 kg/cm2 or 57 to 85 lb/in2). This technique yields 66.0% liquid extract, which contains approximately 10% solids, and it can be vacuum concentrated to 60.0% solids. Nine percent salt is added to stabilize the product. These extracted products have been used as a soup base, in noodle products, sauce, stew, and cur- ries as well as in processed hams and sausages.

C. Mechanically Separated Meat from Bone

The technique for muscle separation was developed for the fishery industry in the 1940s and was next applied in the poultry industry because fish and poultry bones have some sim- ilarities. The structure of mechanically deboned red meat is a finally ground, paste-like product in which the myofibrils are heavily fragmented. The majority of mechanically separated meat comes from the adhering meat and some of the bone marrow and small quantities of powdered bone is also contained in the final products (63). An average of 30.0% mechanically separated meat based on commercial bone weight is the expected yield for beef, pork, and lamb bone. It is estimated that an average of 6.5 kg of mechanically separated meat could be obtained from a beef carcass and 1.5 kg could be obtained from a pork carcass. The vertebral column, ribs, and sternum would be economi- cally suitable for mechanical separation because of large quantities of high protein matter such as meat tissue and marrow that are contained in these tissues. Mechanically separated meat has at least as good an emulsifying capacity and water-holding capacity, and slightly higher emulsion stability, than hand-deboned products (64). Mechanically separated red meat may be added to ground-beef patties; comminuted fresh, smoked, and cooked sausage-type products; stews, sauces, spreads, and similar products; and even to chunked and formed products. Normally, if mechanically separated red meat is incorporated into products at high levels, the flavor and overall acceptability scores will be reduced, the color becomes darker, and the tenderness and juiciness scores are higher. For these reasons, the practical level of incorporation of mechanically separated meat is usually limited. A 5.0% to 20.0% level in beef patties, hamburger, ground beef, fabricated beef, and a 10.0% to 40.0% level in sausage emulsions have been suggested by the meat industry. Many countries already have regulations on products with mechanically separated red meat. In the United States of America, mechanically separated red meat is not allowed to be use in beef patties, baby food, ground beef, meat pies, and hamburger, and 20.0% is considered to be the maximum level in sausage emulsion (65). In Denmark, if mechanically separated red meat is used at levels of more than 2.0%, this has to be declared on the label. In Australia, a statement of edible mechanically deboned beef or mutton and the maximum calcium and moisture level and minimum protein level must be labeled on the exported products.

D. Medicinal and Pharmaceutical Usage of Bone

Downloaded by [Iowa State University] at 01:21 13 May 2015 Specially processed xiphoid or xiphisternal cartilage from the breastbone cartilage of young cattle is used by plastic surgeons to replace facial bone. Red bone marrow is used to treat patients who have a low red blood cell count. Bone meal is also a nutritional source of calcium and phosphorus in the diet.

VII. UTILIZATION OF GLANDS AND ORGANS

A. Glands and Organs as Food

Animal organs and glands offer various levels of nutritionally attractive contents and have a wide variety of flavor and textures in a range of foods (66). Therefore, they are highly prized and are as valuable as carcass meat in parts of the world, specially in southeast Asia. The glands and organs that are generally recognized as having some use as human foods depends on species; for example, all species: brain, heart, kidney, liver, lung, spleen and

tongue; bovine: pancreas and udder; porcine: stomach and uterus; ovine and bovine: reumen, reticulum, omasum, and absomasum; ovine and porcine: testes and thymus. Brain, nervous system, and spinal cord are usually prepared for the table rather than for use in manufactured medicine. They are blanched to firm the tissue before cooking because of the soft texture. The pia mater and arachnoid meninges, which is a skin collagenous connective tissue, are peeled off-the brain before cooking. Heart meat is generally regarded as relatively tough (66) and this is possibly due to the nature of the cardiac muscle. Hearts are used as table meats: whole hearts can be roasted or braised, sliced heart meat is grilled or braised (67). Heart meat is also often used as an ingredient in processed meat. Kidneys generally are removed from the adipose capsule, which keeps the kidney between the muscle of the loin and the peritoneum but is still covered by a fibrous capsule. This capsule must be removed and the ureter and blood vessel also need be trimmed before the kidneys are prepared for cooking. Kidneys are used whole or sliced and generally broiled, grilled, or braised. Liver is the most widely used edible organ (68) and is used in many styles of processed meats such as liver sausage and paste. Livers from lamb, veal, and young cattle are prepared for the table because they have a lighter flavor and texture, which is preferred in the United States and Europe. But consumers in southeast Asia prefer livers from pigs. Liv- ers are used sliced and generally fried, braised, or broiled. Pig, calf, and lamb lungs are mainly used to make stuffing and some types of sausages and processed meats (67). The ruminant stomachs from cattle and lamb are composed of four compartments: the rumen, reticulum, abomasum, and omnivore stomach. The rumen and reticulum are the most widely consumed parts of the ruminant stomach. They are generally processed at the place of collection by washing, scalding, and bleaching. They are suitable for poaching or braising, or used in sausage and processed meat, or can be sewn to form casing and stuffed. Pig stomachs are composed mainly of smooth muscle and collagenous connective tissue. They are cleaned and scalded to remove the mucosa lining; they are also suitable for braising and are sometimes used as casing for sausage. Animal intestines are used as food by boiling in some countries. Animal intestines are used for pet food, meat meal, tallow, or fertilizer, but certainly the important economic use of these products is in the production of sausage casing. Animal intestines, when removed from the carcass, are highly microbiologically contaminated. They are fragile and

Downloaded by [Iowa State University] at 01:21 13 May 2015 therefore cleaning must be performed immediately after slaughter of the animals. Animal casings come in a wide variety of different shapes and sizes and the preference for a par- ticular type of casing varies tremendously from country to country. When casings are manufactured the following procedures are used: removal of the viscera, separation of the ruf- fle fat from the intestines, stripping the manure, sometimes (often not used today) fermenting the casings, breaking the inner mucosa membrane and separating it from the casing, removal of all strings, soaking and removing the blood, salting and packaging—described by Ockeman and Hansen (1). The thymus glands are available only from young animals (lamb and calf). The glands are covered by a capsule of fibrous connective tissue that penetrates the gland and divides it into lobules, and the connective tissue and fat will be increased with the age of the animals. The thymus glands from lamb and calf are blanched to firm the tissue and peeled from the capsule before cooking. They are sliced and cooked by frying or stewing.

The tongues are removed from the carcasses and generally include a small portion of the trachea, larynx, hyoid bones, associated muscle, and salivary glands. An epithelial mu- cous membrane covering the tongue is removed by a knife before cooking. The tongues are used fresh or salted and are usually boiled or braised. Udders are available only from bovines and the main body is connective tissue and secretory epithelium. Udders are sliced and washed to remove the milk and cooked by frying or boiling. Spleens are minced and used in pie, flavoring, and melt in the United Kingdom but used as variety meat in processed meat in the United States. Uteri are available only from nonpregnant pigs and are collected for human consumption. Fresh pig uteri are generally poached or boiled.

B. Medicinal and Pharmaceutical Usage of Glands and Organs

Animal glands and organs have been consumed since recorded history. Some have been used in medicine for their curing powers in some countries (such as China, India, and Japan). These glands are called endocrine glands and secrete hormones, or enzymes that regulate body metabolism. These include the liver, lungs, pituitary, thyroid, pancreas, stomach, parathyroid, adrenal, kidney, corpus luteum, ovary and follicle. The glands are collected only from healthy animals and locating the glands requires experience because some of the glands are often small and are often encased in other tissue. Different animals have different glands that are important, and their function is dependent on the species, sex, and age of the animals. The best method of preserving most glands and stoping autolysis and bacterial growth is by quick freezing. Before freezing, the glands must be cleaned and trimmed from surrounding fat and connective tissue. They are then put on waxed paper and kept at 18°C or less. When the glands arrive at the pharmaceutical plant, they are again inspected, then chopped and mixed with different solutions for extraction or placed in a vacuum drier for the drying process. If the dried gland contains too much fat, solutions such as gasoline, light petroleum, ethylene dichloride, benzene, and acetone are used to remove the fat. After drying and defatting, the glands or extracts are milled to a powder form and dispensed as capsules, tablets, or injections or utilized as a dilute liquid. They are tested for safety and potency prior to sale. The adrenal gland consist of two parts, an outer cortex and an inner medulla that secretes at least 20 steroids that are essential for life maintenance. Corticosteroids from the

Downloaded by [Iowa State University] at 01:21 13 May 2015 adrenal cortex regulate the body’s utilization of nutrients such as fat, carbohydrate, water, nitrogen, and minerals. Extracted adrenal cortical steroids from cattle, pigs, or sheep are used as anti-neoplastic and anti-inflammatory agents and for treatment of shock and asthma. Epinephrine and norepinephrine can be extracted from the adrenal medullas of cattle, pig, and sheep and are used to arrest hemorrhaging, shrink blood vessels, prolong the effects of local anesthetics, stimulate heart action, and overcome shock. Brains, nervous systems, and spinal cords are a source of cholesterol, which is the raw material for the synthesis of vitamin D3, and steroid pharmaceuticals and is used as an emulsifier in cosmetics. Some materials can be isolated from the hypothalamus of the brain for this purpose. For example, thromboplastin is used as a blood coagulant in surgery, kephalin is prepared to assist in clotting of blood, and lecithin is useful as an emulsifier and antioxidant. The pineal gland is located in the brain cavity behind and above the pituitary. The hormone melatonin extracted from the pineal gland is being evaluated for the treatment of schizophrenia, mental and physical development problems, and mental retardation. The

pituitary gland is located at the base of the brain and is made up of an anterior and a posterior lobe with separate functions. Hormones such as growth-promoting hormone (GH), thyroid-stimulating hormone (TSH), mammary-stimulating hormone, gonad-stimulating hormones, adrenal-cortex-stimulating hormone (ATCH) (extracted from an anterior of the pituitary), antidiuretic hormone (ADH), and oxytocin hormone (produced from a posterior of pituitary) are used to control growth and metabolism and regulate the activity of other endocrine glands. ACTH is the most commercially extracted hormone from the pituitary and is used as a treatment for rheumatism, arthritis, eye inflammation, and multiple myeloma. Bile consists of bile acid, bile pigment, fatty acids, phospholipids, proteins, cholesterol, and other substances and can be obtained from the gallbladder. It is used for treating digestive disorders, constipation, and bile tract disorders and increasing the secretory activity of the liver, and it is also useful in some fat-digestion disorders. Bile can be purchased as dry or liquid extract preparations from cattle or hogs. Some ingredients of bile, such as prednisone, prednisolone, pregesterone, hydeoxycholic acid, chenodeoxycholic acid and dehydrocholic acid, and cortisone, can be extracted individually and used in the medicinal and pharmaceutical areas. Gallstones are reported to have some mystical aphrodisiac value and are very expensive because they are available in extremely small quantities. They are usually used as ornaments to make necklaces and pendants. Liver is the biggest gland in animals; it will usually average about 5 kg when obtained from market-weight cattle and approximately 1.4 kg from market-weight pigs. Liver extract is produced by extracting raw ground livers with slightly acidified hot water. The stock is concentrated to a paste under vacuum at low temperature and is used as a raw material by the pharmaceutical industry. Liver extract and desiccated liver can be obtained from pork and beef and have long been used as a source of vitamin B12, as a nutritional supplement used in treating various types of anemia, and as an enrichment medium in bacterial numeration (69,70). Heparin can be extracted from the liver as well as the lungs and mucosa (inner) lining of the small intestines. It is used as an anticoagulant to prolong the clotting time of blood; it is used to thin the blood (raise the viscosity) and to dissolve, prevent, or retard blood clotting during surgery and in organ transplants. By using the Scott method 10.2 g of crude heparin can be extracted from 540 g of porcine lung but its activity is not as good as that from commercial products (71). The crude heparin prepared from hog lungs by the alkaline ammonium sulfate method can be com- bined with a Sephadex G-50 column for chromatography and purification. The purity and

Downloaded by [Iowa State University] at 01:21 13 May 2015 activity of the heparin can be improved by this method and was acceptable when compared with commercial products (72,73). Progesterone and estrogens can be extracted from pork ovaries and may be used to treat some reproductive problems, such as functional uterine bleeding, abnormalities of the menstrual cycle, and threatened abortion, and are used in the treatment of breast and prostate cancer. Relaxin, a hormone from pregnant sow ovaries, often is used during childbirth. The pancreas has internal and external sections. The internal section secretes insulin, which regulates sugar metabolism, and the external section secretes chymotrypsin, trypsin, lipase and amylase into the small intestine to assist in digestion of fat, protein, and starch. Insulin is produced by specialized cells in the pancreas called islets of Langerhan and can be extracted from the pancreas by first grinding the hard-frozen gland in acetone and alco- hol; then, the crude insulin is salted out and purified. Insulin is used in the treatment of di- abetes. Glucagon extracted from the cells of the pancreas is used to increase blood sugar

and to treat insulin overdose or low blood sugar caused by alcoholism. Chymotrypsin and trypsin are used to remove dead tissue and improve healing after surgery or injury; chymotrypsin also has been used to facilitate cataract-extraction eye surgery. Animal intestines (sheep and calves) are also used for the manufacture of cat-gut, an internal surgical sutures. It is produced by several steps and twisted into one, two, or three strands and then cut, dried, polished, and sterilized. The pork and beef mucosa lining of the small intestines can be collected during the machining of casings, and it is either preserved in a raw state or processed into a dry powder prior to shipment to heparin manufacturers.

VIII. UTILIZATION OF EDIBLE TALLOW AND LARD Animal fats are co-products of the meat packing industry, making supplies of fat available for the preparation of meat for sale or for processed meat products. The major edible animal fats are lard and tallow (74). Lard is defined as the fat rendered from clean, sound edible tissues of hogs in good health at the time of slaughter. Rendered pork fat include ba- con skins and fleshed skin cheek meat trimmings, sweet pickle fat, and fats obtained from skimming the rendering tanks. Tallow is hard fat rendered from fatty tissues of cattle or sheep that is removed during processing of beef or sheep. Lard and edible tallow are obtained by dry or wet rendering (75). In the wet rendering process, the fatty tissues are heated in the presence of water, generally at a low temperature, and prime steam lard is obtained; its quality is better than that of the products from dry rendering. Low-quality lard and almost all of the inedible tallow and greases are produced by dry rendering. Rendered lard is used as an edible fat without being subjected to any post-rendering procedure. Due to consumer demand, lard and tallow now are often subjected to hydrogenation, bleaching, and deodorizing treatments before their utilization in food (76). Traditionally, tallow and lard has been used as a deep fat frying medium. However, this use of tallow or lard fried french fries in the fast-food service is changing due to consumer health demands (76). A pouring tallow-oil shortening has been developed for this purpose and resulted in a product where less fat is absorbed. Tallow and lard also have been used in margarine and shortening. Some edible lards are used in sausages or emulsified products.

IX. THE PROCESSING AND UTILIZATION OF MEAT EXTRACT Meat extract was first produced in France in the eighteenth and nineteenth centuries by al-

Downloaded by [Iowa State University] at 01:21 13 May 2015 coholic extraction (77). The early procedure for manufacturing meat extract included removing the meat from the bones and trimming away the fat; then, the fat-free meat was hashed. The freshly hashed meat was then exposed to clear water and cooked at low temperature (less than 90°C) for extraction. Meat extract is defined as the products obtained by extracting fresh meat with boiling water, removing fat, and concentrating the liquid by evaporation (78). Meat extract should contain more than 75% total solid matter, 8.0% nitrogen, and less than 0.6% fat. The processing procedure for meat extract is summarized as follows (79). Meat stock can be produced from edible meat co-products (e.g., meat trimmings, and mechanically separated meat) that are pressed or soaked in water, or cooked, or obtained from corned beef; then the liquid is skimmed to remove fat and filtered to remove the fines and coagulated protein. The remaining liquid is concentrated under vacuum and later in an open pan to produce meat extract. The concentration of meat stock can be performed by using an evaporator: steam is fed through the line to sterilize the equipment followed by a cold

water rinse. The stock is reduced in volume until it contains approximately 45.0% to 50.0% solids. The state of the art today accomplishes evaporation in a vacuum (70 cm) evaporator operated at a temperature of 70° to 75°C and producing a product of final concentration of 80% solids. This final product should have a natural color (brown or light brown), odor, and flavor and no bitterness. Meat extract is used for making soups, stews, sauces, casseroles, pot pies, canned meat, bouillon cubes, instant bouillon, and gravies. Meat extract is also an excellent flavoring material in a noodle soup mix, onion soup mix, and chip dip. When meat extract is used as an ingredient in other meat products, it should be listed as “flavorings” in the ingredient statement in the appropriate “order of predominance” position.

X. CONCLUSION Meat producers have, for a long time, efficiently used meat co-products in processing into either edible or inedible products. Today, with increasing concerns about health and envi- ronmental protection, many new techniques, operating procedures, and research have been developed to permit more efficient processing and utilization of these co-products. The utilization needs become significantly stronger due to competition. This is important because increasing profit and decreasing the cost is required in the future for the meat industry to remain viable. These contributions and efforts are also necessary for the meat industries to change in an innovative manner and to widen the opportunities to utilize meat co-products. However, the saying “the packer uses everything but the squeal” has always existed in the meat industry and will continue to influence the utilization of meat co-products.

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