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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 BLOODA. Isolation of BloodB. Removal of Heme from Red Blood CellsC. Usage of Blood Plasma in FoodD. Medicinal and Pharmaceutical Usage of Blood

V. UTILIZATION OF HIDES AND SKINSA. Stacking of Hides and SkinsB. Processing of Leather from Hides and SkinsC. Gelatin from Hides and SkinsD. Uses of Gelatin in the Food and Pharmaceutical IndustryE. Hides and Skins for Food and Sausage CasingF. Medicinal and Pharmaceutical Usage of Hides and Skins

VI. UTILIZATION OF BONEA. Gelatin from BoneB. Liquid Extraction from BoneC. Mechanically Separated Meat from BoneD. Medicinal and Pharmaceutical Usage of Bone

VII. UTILIZATION OF GLANDS AND ORGANSA. Glands and Organs as FoodB. 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

Copyright © 2001 by Marcel Dekker, Inc. All Rights Reserved.

I. INTRODUCTION

Meat co-products are produced by slaughterers, processors, wholesalers, retailers andrenderers. Traditional markets for edible meat co-products have gradually been disap-pearing because of concerns about health and economic returns. In response to theseproblems, meat processors have directed marketing and research efforts toward inedibleapplications—for example, pet foods, pharmaceuticals, cosmetics, and animal feeds. Theliterature indicates that co-products (including organs, fat or lard, skin, feet, abdominaland 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 arenot suitable for human or animal consumption due to unusual physical and chemicalcharacteristics (1). A valuable source of potential revenue is lost and the cost of disposalof these products incurred by the meat industry is increased if meat co-products are notefficiently utilized. The USDA Economic Research Service announced that the portion ofgross farm economic income from animal co-products is 11.4% for beef and 7.5% forpork for 1986 (2). The cost of live animals often exceeds the selling price of their car-casses and the value of the co-products must pay the expense of slaughter and generatethe profit for the meat-slaughtering operation. Bengtsson and Holmqvist have suggestedthat 7% to 12% of the income from slaughter results from the sale of co-products (3). Inaddition to economic loss, nonutilization of meat products would create serious environ-mental pollution of water and air. However, with efficient utilization, meat co-productscan be important and result in profits for meat processors. The modern livestock indus-try in the past has been an effective utilizer of co-products and it has often been statedthat 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, exceptdressed meat, as a co-product. Therefore, animal co-products in the United States are di-vided into two divisions, edible and inedible. In U.S. terminology, offal means slaughterco-products and includes all of the animal that is not a part of the carcass. Variety meats arethe wholesale edible co-products that are segregated, chilled, and processed under sanitaryconditions and that are inspected by the U.S. Meat Inspection Service. In some areas of theworld, and to different degrees, blood is also utilized as an edible product for humans. Inthe United States, meat trimmings from the head are described as edible offal or edibleco-product items, and edible fats are fats obtained during slaughter, such as caul fat sur-rounding the rumen or stomach, and cutting fat, which is back fat or pork leaf fat, or rumenfat.

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 andfour feet and trimmings (4). The English Food Standard Committee also separated offalinto two categories (5):

List A. Items that may be used in cooked or uncooked products from mammalianspecies; 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.

582 Liu and Ockerman


List B. Items that may not be used in uncooked products; contain portions ofmammalian 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, aftercooking), fourth stomach, testicles, and udder and parts of avian species suchas 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 isshown in Table 2. A total of 5,655.5 thousand metric tons of pork edible co-productswere produced in 1996, and data in Table 2 show that the largest part of the productionof pork co-products is from Asia (50.4%) and the second from Europe (37.1%). Asiaand Europe are also the two major consumers of meat co-products including beef andlamb (1).

Usage of meat co-products often require treatment by the following steps: collection,washing, trimming, chilling, packaging, and cooling. Acceptance of these products de-pends on factors such as acceptability, regulatory requirements, nutrition, economics, andcompetitive products. Although customs, culture, and religion often act as major factorswhen a meat co-product is utilized as an ingredient in meat products, regulatory require-ments also are important factors because many countries already had some food regulationson the policy of food safety and quality. An example of an USDA requirement is that me-chanically separated meat and variety meats must be specifically identified by showingthem as ingredient on labels. If frankfurters and bologna are made with heart meat or poul-try mechanically separated meat as an ingredient, it must be listed. A detailed list of po-tential uses and preparations of meat co-products are listed in Table 3.

Meat Co-Products 583

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

Marketing live weight 100.0 600.0 60.0Carcass 77.5 77.5 63.0 378.0 62.5 37.5Bone 17.0 17.0 16.0 96.0 18.0 10.8Blood 3.0 3.0 3.0 18.0 4.0 2.4Fatty tissue 3.0 3.0 4.0 24.0 3.0 1.8Hide or skin 6.0 6.0 6.0 36.0 15.0 9.0Organs 7.0 7.0 16.0 96.0 10.0 6.0Head 5.9 5.9Viscera (chest and abdomen) 10.0 10.0 16.0 96.0 11.0 6.6Feet 2.0 2.0 2.0 12.0 2.0 1.2Tail 0.1 0.1 0.1 6.0Brain 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 5225.0 100.0Asia 42,534 2849.8 50.4China 40,000 2680.0 47.4Japan 1,264 84.7 1.5Taiwan 1,270 85.1 1.5North America 9,005 603.3 10.7U.S.A. 7,765 520.2 9.2Canada 1,240 83.1 1.5South America 1,560 104.5 1.8Brazil 1,560 104.5 1.8Europe 16,269 1090.0 19.3Germany 3,085 206.7 3.7France 2,193 146.9 2.6Spain 2,180 146.1 2.6Russia 1,679 112.5 2.0Netherlands 1,619 108.5 1.9Poland 1,600 107.2 1.9Denmark 1,528 102.4 1.8Italy 1,355 90.8 1.6Belgium-Luxemburg 1,030 69.0 1.2European 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-productsoften 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-productshave 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 levelof all the meat co-products. Liver, beef tail, ears, and feet have the closest protein levelwhen compared with lean meat tissue but a large amount of collagen is found in the earsand 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 beefand 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 tissuedue 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 suchas ears, feet, lungs, stomach, and tripe (9). The vitamin content of organ meats is usuallygreater 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 thebest source of niacin, vitamin B12, B6, folacin, ascorbic acid and vitamin A. Kidney also isa good source of vitamin B6, B12, and folacin. A 100 g serving of liver from pork and beefcontributes 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 vealLiver

Kidney

Heart

Brains

Tongue

Tripe

Sweetbread

OxtailIntestine (small and large)

Cheek and headtrimmings

Udder

SkinFeetFat

Blood

Bone

PorkLiver

Kidney

Heart

Brains

Tongue

Stomach

Frozen, fresh, or refrigerateWhole, sliced, or grindFresh or refrigerateWhole or slicedFrozen, fresh, or refrigerateWhole or slicedFrozen, fresh, or refrigerateWholeFresh, refrigerate, smoked, or

pickledFresh, refrigerate,

precooked, pickled, or soakbefore use

Frozen, fresh, or refrigerateWholeFrozen, fresh, or refrigerateFresh or refrigerateRemove manure, soaking,

washing, and salting beforeuse

Frozen, fresh, or refrigerate


Fresh or refrigerateFrozen, fresh, or refrigerateFrozen, fresh, or refrigerate

Frozen or refrigerate


Frozen, fresh, or refrigerateWhole, sliced, or grindFresh or refrigerateWhole or slicedFrozen, fresh, or refrigerateWhole, sliced

Frozen, fresh, or refrigerateWholeFresh, refrigerate, smoked, or

pickledFresh, refrigerate, or

precooked

Braised, broiled, fry, loaf, patty,and sausage

Broiled, cooked in liquid, andbraised

Braised, cooked in liquid

Broiled, braised, and cooked inliquid

Cooked in liquid

Fry, broiled, and cooked inliquid

Fry, broiled, braised, and cookedin liquid

Cooked in liquidSausage casing

Cooked sausage, stew, soup, andbouillon

Boiled, fried, smoked, and salted

GelatinJellyShortening, drippings and

chewing gumBlack pudding, sausage, blood,

and barley loafGelatin, soup, jellied products,

and refining sugar


Broiled, cooked in liquid,braised, soup, grill, and stew

Braised, cooked in liquid,luncheon meat, patty, loaf,and sausage ingredient

Broiled, braised and cooked inliquid, poach, and scramble

Cooked in liquid, cured, sausageingredient, salad, and jelly

Broiled and cooked in liquid,sausage container, andsausage ingredient



Table 3 Continued


Spleen

TailIntestine (small and large)


Ear

SkinFeet

FatBlood

Bone

LungLambLiver

Kidney

Heart

Brains

Tongue

Stomach

Sweetbread

Spleen

Intestine (small and large)


TesticlesLungsFeet

Frozen, fresh, or refrigerateWholeFrozen, fresh, or refrigerateFresh or refrigerateRemove manure, soaking,




Fresh or refrigerateFrozen, fresh, or refrigerate

Frozen, fresh, or refrigerateFrozen or refrigerate



Frozen, fresh, or refrigerateWhole, sliced, or grindFresh or refrigerateWhole or slicedFrozen, fresh, or refrigerateWhole or sliced

Frozen, fresh, or refrigerateWholeFresh or refrigerate

Fresh or refrigerate

Frozen, fresh, or refrigerateWhole


Fresh or refrigerateRemove manure, soaking,



Frozen, fresh, or refrigerateFresh or refrigerateFrozen, fresh, or refrigerate

Fry, pie, melt, and blood sausage

Cooked in salt liquidSausage casing

Cooked sausage

Smoked and salted, stew withfeet

GelatinJelly, pickled, cook in liquid,

boiled, friedShortening, lardBlack pudding, sausage, blood

and barley loafGelatin, soup, jellied products,

and rendered shortening,mechanically deboned tissue

Blood preparation and pet food


Broiled, cooked in liquid,braised, fried, stew, and soup

Braised, cooked in liquid,roasted, stuff, luncheon meat,patty, loaf, and sausageingredient

Broiled, braised and cooked inliquid, poach, and fried

Boiled, stew, jelly, grilled, andcooked in liquid

Honeycomb tripe and containerfor haggis

Fry, broiled, braised, poach withsauce, cream and cooked inliquid

Pie, melt, blood sausageingredient, and variety meat

Sausage casing

Cooked sausage, stew, and soup

FriedHaggis, pet foodJelly


3700% of the RDA for vitamin B12, and 37% of the RDA for ascorbic acid. In addition tosupplying vitamins, lamb kidney, pork liver, lungs, and spleen are often act an excellentsource of iron. The copper content is the greatest in the livers of beef, lamb, and veal. Theycontribute 90% to 350% of the RDA for copper (2 mg/day). Livers also contain the high-est amount of manganese (0.128 to 0.344 mg/100 g). However, the highest level of phos-phorus (393 to 558 mg/100 g) and potassium (360 to 433 mg/100 g) are found in thymusand 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 lev-els found in lean tissue. Among the raw material, mechanically deboned meat has the high-est 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 monounsaturatedfatty acids and the highest amount of polyunsaturated fatty acid. In addition to higher lev-els of cholesterol (260 to 410 mg/100 g), which are three to five times higher than those oflean meat, large quantities of phospholipid also are found in these meat organs. Brain is thehighest in cholesterol (1352 to 2195 mg/100 g) and also has the highest amount of phos-pholipid 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 inmany organ meat and the possible accumulation of pesticides, residues of drugs, and toxicheavy metal contribute to the recommendation for limited consumption.

IV. UTILIZATION OF BLOOD

Animal blood has a high level of protein and heme iron and is an important animal co-prod-uct. 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, bloodcake, and blood yogurt-like blood pudding (12). It is also used in nonfood systems such asin fertilizer, feedstuffs, and binders. The Meat Inspection Act stated that blood is approvedfor food use when removed by bleeding of an animal that has been inspected and passed foruse 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 is3.0% to 4.0%, 3.0% to 4.0% and 3.5% to 4.0%, respectively. Because use of blood in meatprocessing results in the final product being dark and often unpalatable, and because


Table 3 Continued


Fat

Blood

Bone


Frozen or refrigerate


Shortening, drippings, sweets,oleomargarine, and chewinggum

Black pudding, sausage, bloodand barley loaf

Gelatin, soup, jelly, andmechanically deboned tissue

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


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

A. Isolation of Blood

Plasma has been widely used in the meat industry because of its excellent functional prop-erties (13). Plasma contains one-third of the total blood protein, and red blood cells containthe other two-thirds (14). On a large-scale processing of edible whole blood, it is separatedinto two constituents: plasma (60% to 80%) and red cells (20% to 40%). The plasma con-sisting 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 groupis removed to obtain globin. Anticoagulants (0.2% sodium citrate or citric acid or 10.0 gramof a mixture of phosphates—22.0% Na2HPO4, 22.0% Na4P2O7, 16.0% Na2H2P2O7 and40.0% 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-sepa-ration 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 lowtemperature in order to maintain its solubility and functional ability. To freeze bloodplasma, 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 surfacein 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 thefirst step for the blood plasma drying process in most plants and generally is accomplishedby membrane filtration and evaporation. The drying process of the concentrated plasma isfinished by a spray drying system or a fluidized bed drying system. A dried blood plasmacan 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 usedas a supplement in foods (15). Heme pigment can be used as a red colorant for food and isused in Chinese semi-dried sausage (16). Several methods have, therefore, been developedto remove the heme group from hemoglobin of red blood cells. These include an acid-ace-tone method (17), hydrogen peroxide decoloration (18), and decoloration with carboxymethyl cellulose (NaCMC) (19) and sodium alginate (20). With these methods, the globinand 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 nutritionalcomponent. Most blood is used in livestock feed in the form of blood meal and used as aprotein supplement, milk substitute, lysine supplement, or vitamin stabilizer and is an ex-cellent source of most of the trace minerals. Blood plasma has gel-forming ability becauseit contains 60.0% albumin and is the best water and fat binder of the blood fraction. Plasmagels 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 with2.7% were more satisfactory in color than the control samples (22). In addition to gel form-ing, 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 indicatedthat the application of transglutaminase (TGase) from animal blood and organs or microbesto products in the meat industry is one of the most investigated applications in food pro-cessing (26–38). Blood factor XIII is a transglutaminase that occurs as a enzymogen inplasma, placenta, and platelets. The reaction catalyzed by Ca�2 dependent factor XIIIa in-volves the formation of a �-(-glutamyl)-lysyl bond between an acyle donor (glutaminylresidue) and an acyl acceptor (lysyl residue) of the proteins fibrin and fibronectin, fibrinand actin, myosin and fibronectin and myosin and actin (39). Therefore, this enzyme cat-alyzes conversion of soluble proteins to insoluble high-molecular polymers through for-mation of covalent cross-links (31,40). Transglutaminase extracted from bovine blood atfirst for improving the binding ability of fresh meat products at chilling temperature andshowed how myosin was cross-linked by TGase in 1983 (27). An important property of theTGase reaction was documented when cross-linking between myosin and proteins (soy, ca-sein and gluten) commonly used in meat processing was found (30). Moreover, the re-structured meat products without heating, and decreased with salt and phosphates can bemade 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. Liquidplasma is the largest fraction (63.0%) and consists of albumin (3.5%), globulin, and fib-rinogen (4.0%). In the laboratory, many blood products are used as a nutrient for tissue cul-ture media, as a necessary ingredient in blood agar and peptones for microbial use. Glyc-erophosphates, albumins, globulins, sphingomyelins, and catalase are also used forbiological assay. Many blood components such as fibrinogen, fibrinolysin, serotonin, ka-likrenins, immunoglobulins, and plasminogen are isolated and used in the chemical or med-ical aid. Purified bovine albumin is used to help replenish blood or fluid loss in animals, intesting for the Rh factor in human, as a stabilizer for vaccines, and in antibiotic sensitivitytests. Pork-blood fibrin extract is used as a source of amino acids, which are incorporatedinto parenteral solutions for nourishing some surgical patients. Superoxide dismutase(SOD) is an enzyme attending a series of reactions of superoxide radical and transfering itinto water and oxygen to protect cell membranes of the animal body from serious damageby 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 porcineblood exhibited a higher activity (1570 unit/mg), and the results are similar to the bovineerythrocyte SOD (49). A thin firm can be made from fibrinogen and used to control bleed-ing 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 effec-tive 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 insecticidesand fungicides and as a stabilizer in cosmetic base formulations. It also finds use as a foam-ing agent in fire extinguishers.

V. UTILIZATION OF HIDES AND SKINS

Animal hides and skins have been utilized for shelter, clothing, and weapons and as foodcontainers 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 valu-able animal co-products. Examples of finished product from cattle hide co-products, hogskin co-products, and sheep pelts co-products are the following: cattle cured and tannedhides—shoes, bags, belting, rawhide, athletic equipment; cattle corium layer—pickingbands, 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 isremoved)—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 stopbacterial and enzymatic decomposition or spoilage. There are four basic treatment for pre-serving these hides and skins: air drying, salt-pack curing, mixer curing, and raceway cur-ing; salt-curing is commonly used to treat these raw materials. The quality of cured hidesand skins are usually evaluated by measuring the moisture and salt content of the hides. Themoisture level of the hides are generally maintained from 40% to 48% to result in good con-dition 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 beforetanning.

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 housewhen they arrive at the tannery. The first step of tanning is grading and sorting the hidesinto packs of uniform size, weight, and type of hide. The next step is soaking, and thismeans that enough moisture needs to be added to the cured hides for the succeeding tan-ning operations. The soaking of hides is finished in half-round cylindrical vats in which thehides are placed with water, wetting agents, and disinfectants; the hides are stirred in thissolution by a dip-paddle wheel for 8 to 20 hours in order to let the hides reabsorb the neededwater. A washing step after soaking removes the remaining dirt, manure, salt, and bloodfrom the hides.

The unhairing procedure is the next step; originally it was carried out by a processknown as sweating, in which the hides were placed in the previously described paddle vatsor 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 sheepskinsand pigskins, contain a large quantity of fat and it is often desirable to reduce this to ap-proximately 3.0% on a dry-weight basis; this process is sometime done by a hydraulic pressto remove fat prior to continuation of the tanning process. “Bating” is used to remove thealkaline unhairing chemicals and other nonleather substances in the pelt structure and isperformed 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 tanningis to convert the collagen fibers of the skin into a stable non-rotting leather. “Chrome tan-ning” is the most popular method of tanning today because it can be finished quickly anddesirable physical and chemical properties can be produced.

After tanning, the next procedure is “setting,” whose purpose is to lower the moisturecontent, smooth the grain, and remove wrinkles from the hide. Splitting and shaving followand the purpose of these two steps is to obtain a uniform thickness of the leather desired forits ultimate use. The desired color of leather can be produced by a “dyeing” operation. Theaim of coloring is not only to produce the right strength and shade of color but to producea color that will resist fading and can be dry-cleaned or washed. “Fatliquoring” is used toadjust the firmness or softness of the leather by lubricating the fibers after coloring, and italso can increase the tensile strength of the leather. “Setting out” is accomplished to smoothand stretch the leather and to compress and squeeze out the excess moisture and grease. Thepurpose of drying is to remove all but equilibrium moisture, and after drying the skin shouldcontain 10% to 12% moisture. The popular drying technique is called “pasting” in whichthe hides are actually pasted to large stainless steel or glass plates. After drying the leatheris hard and fairly unworkable, and the final user always requires varying degrees of soft-ness; 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 theleather and to reduce any blemishes by light mechanical sanding. The next process is “fin-ishing,” which is the application of film foaming materials that provide abrasion and stainresistance, enhance the color, and make the leather easy to care for. After the finishing, itmust be dried in a long heating tunnel with steam-heated air. If a smooth grain surface or avarious 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 “grad-ing” and it is dependent on temper, uniformity of thickness and color, and defects of theleather.

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

Gelatin is produced by controlled hydrolysis of a water-insoluble collagen that belongs toa 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 conversionof collagen to gelatin involves the breaking of hydrogen bonds that stabilize the triple-coilhelix and transform it into the random coil configuration of gelatin. There are three basictypes of new chains: alpha-chain, beta-chain, and gamma-chain in gelatin. A single gelatinhas 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 availableas a co-product are usually hides, skins, and bones; therefore, they are a major raw mate-rial source for the manufacturing of gelatin. A summary of the general description ofgelatin production as described by Hinterwaldner is given as follows (53).

The processing of gelatin from hide and skin consists of three major steps: The firststep 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 ofthe final extracted product. Generally, a collagen stock will be used to extract gelatin bycombinations of an alkaline procedure, an acid procedure, and high-pressure steam extrac-tion. The alkaline procedure is the most widely used commercial system for the processingof collagen to gelatin. A saturated solution of calcium hydroxide made by the addition oflime 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 wash-ing. After the liming of the hides, the collagen fibers are swollen and the internal cohesionof each fiber is decreased. The next step is washing and neutralization; the collagen iswashed by cold running water for 1 to 2 days, and the pH of collagen is lowered and thelime 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 isready to be extracted. Extraction is normally started at 54° to 60°C for 3 to 5 hours and iscontinued up to boiling. The highest quality product is obtained at the lower extraction tem-perature, but yield is increased at higher temperatures. The liquid extract needs be filteredto remove small particles; sometimes, activated carbon is also added to decolorize thegelatin solution. Generally, the extract obtained from higher temperatures needs to be vac-uum evaporated in a pan so that a sufficient concentration and gel strength can be obtainedwhen cooled. After concentrating, the gelatin is dried by many drying methods such as acooled drying tunnel, drum drying, and spray drying.

Another extraction procedure for gelatin is acid processing and it is usually appliedto pig skin or bone. Pigskins are first washed to remove salt from salted skin and to removeextraneous matter and/or blood. Since pigskin often contains 8.0% to 15.0% fat, pre-ex-traction of this lipid material is necessary before the acid extraction procedure. This is doneby heating in hot water (55°–60°C), two to three times, stirring for 4 to 6 hours, and thenwashing in 40° to 55°C water. After washing and removal of fat, the skins are soaked in a5.0% inorganic acid (such as hydrochloric acid, sulfuric acid, or phosphoric acid), whichresults in a pH of approximately 4.0. This pH causes the collagen to swell and a great dealof solubilization to occur. After 10 to 72 hours of soaking, the acid is then drained and thecollagen is washed to raise the pH of the skin to approximately 4.0 to 5.0. At this pH thenative collagen is still swollen. After acid treatment, the collagen stock is extracted at alower starting temperature than cow hides and the procedure is almost the same as the al-kaline treatment. However, the gelatin produced from pigskins has a higher gel strength andbetter clarity and color than alkaline-treated cattle hide products and it also should be rec-ognized that alkaline- and acid-precursor produced gelatin are two different classes ofgelatin. Two grades of gelatin may be extracted; Class A, which is a high grade, with rela-tively undamaged molecular material, and Class B, which is extracted by harsh means andconsequently has a range of molecular weights and altered properties. All gelatins are sol-uble and are able to form gels on cooling from hot solution and thus it is an important foodadditive.

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 stabi-lizer for frozen dairy products and other frozen desserts. High-bloom gelatin is added as aprotective colloid to ice cream, yoghurt, and cream pies. The gelatin is thought to inhibitice crystal growth and lactose recrystallization during storage.

Approximately 6.5% of the total production of gelatin is used in the pharmaceuticalindustry, with the largest proportion used for capsule manufacturing (55). Gelatin also canbe used as a binding and compounding agent in the manufacture of medicated tablets andpastilles. It is used as an important ingredient in many specialized protective dressings suchas zinc gelatin or Unna’s paste for the treatment of ulcerated varicose veins. A hemostaticssponge is formed when a sterile solution of gelatin is whipped into a foam, rendered insol-uble by treatment with formaldehyde, and then dried; it can be used as an absorbablesponge 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 dueto its protein character. Gelatin is an excellent emulsifier and stabilizing agent for manyemulsions and foam; therefore, it is also used in cosmetic products, flocculation agents, andprinting applications such as carbon printing, silk screen printing, and photogravureprinting.

E. Hides and Skins for Food and Sausage Casing

Extraction of gelatin from animal skins and hides can be used for food. The raw materialcan also be rendered for lard. In the United States and some Asian countries, the pork skinis 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 becauseof its hydrophobic nature: it can bind large quantities of fat. This can be an advantage, andit has been suggested that collagen may act as an adhesive between fatty and lean particlesand many absorb excess fat. Therefore, collagen is a useful additive or filler for meat prod-ucts. The collagen also can be extracted from cattle hides to make collagen sausage used inthe meat industry (59).

Collagen casing products were developed in Germany in the 1920s but only gainedpopularity in the United States in the 1960s. Regenerated collagen casings are made usingextrusion techniques. Collagen casing manufacturing processes do not convert collagen toa soluble product as does the gelatin extraction process; instead, they result in a much morefibrillar product that retains a relatively high degree of the native collagen fiber. The ex-tracted 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 ex-truded either by the wet or the dry process. During extrusion the collagen fibers tend to bealigned parallel to the axis of the tube emerging from the extruder. In the wet process, theextruder contains an internal disc that forces the following gel against the sides of the ex-truder 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 ofcross-hatched collagen fibers. The tube of extruded collagen is then passed through a con-centrated salt solution and a chamber of ammonia to precipitate the collagen. The swollengel contracts to produce a film of reasonable strength that can be improved by the additionof plasticisers such as glycerin. The tube is then dried to a 10.0% to 15.0% water contentand 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. Porkskin is similar to human skin and can be converted into dressing that can be used for burnor skin-ulcer patients. Pork skin used as a dressing needs to be treated by a series of proce-dures: 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 skingrafting it is removed from the carcass within 24 hours (60). Gelatin produced from hogskin 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 iscomposed of bone, and these values would be higher if adhering meat is included. In addi-tion to the attached lean, the amount of marrow in a bone can also contribute to the yield ofmechanically deboned products (61,62). The marrow can average 4.0% to 6.0% of the car-cass weight. For centuries bones have been used to make soup and gelatin. In recent yearsthe meat industry have attempted to get more meat from bone and new separation tech-niques have been utilized for this purpose. The mechanical deboning or separation tech-nique produces tissue that at times has been called mechanically separated beef, pork, orlamb, 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 orused alone) in many countries. In 1978, mechanically separated red meat was approved foruse 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 mustbe pretreated by cooking at 80° to 95°C to remove adhering meat, gristle, and fat. The bonesare then washed several times to get them clean. Next the bones are washed in dilute hy-drochloric acid to remove minerals. In general the final ash of the ossein is from 1.0% to2.0%. 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 intogelatin within 6 months. The ossein is processed through liming, deliming, washing, andgelatin extraction. The drying of gelatin is similar to the previously described process forgelatin 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 flavoringingredient for meal cooking. In this process, crushed bones are cooked with water for 8 to12 hours. The product is cooled and the fat is skimmed from the liquid. The liquid containsapproximately 5.0% solids. Currently, processing time is reduced to 1.5 to 2.0 hours by us-ing a high-pressure extraction system (4 to 6 kg/cm2 or 57 to 85 lb/in2). This techniqueyields 66.0% liquid extract, which contains approximately 10% solids, and it can be vac-uum concentrated to 60.0% solids. Nine percent salt is added to stabilize the product. Theseextracted 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 1940sand 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-likeproduct in which the myofibrils are heavily fragmented. The majority of mechanically sep-arated meat comes from the adhering meat and some of the bone marrow and small quan-tities of powdered bone is also contained in the final products (63).

An average of 30.0% mechanically separated meat based on commercial bone weightis the expected yield for beef, pork, and lamb bone. It is estimated that an average of 6.5 kgof mechanically separated meat could be obtained from a beef carcass and 1.5 kg could beobtained 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 mattersuch as meat tissue and marrow that are contained in these tissues. Mechanically separatedmeat has at least as good an emulsifying capacity and water-holding capacity, and slightlyhigher emulsion stability, than hand-deboned products (64). Mechanically separated redmeat may be added to ground-beef patties; comminuted fresh, smoked, and cookedsausage-type products; stews, sauces, spreads, and similar products; and even to chunkedand formed products. Normally, if mechanically separated red meat is incorporated intoproducts at high levels, the flavor and overall acceptability scores will be reduced, the colorbecomes darker, and the tenderness and juiciness scores are higher. For these reasons, thepractical 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% to40.0% level in sausage emulsions have been suggested by the meat industry. Many coun-tries already have regulations on products with mechanically separated red meat. In theUnited States of America, mechanically separated red meat is not allowed to be use in beefpatties, baby food, ground beef, meat pies, and hamburger, and 20.0% is considered to bethe maximum level in sausage emulsion (65). In Denmark, if mechanically separated redmeat 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 andmoisture level and minimum protein level must be labeled on the exported products.

D. Medicinal and Pharmaceutical Usage of Bone

Specially processed xiphoid or xiphisternal cartilage from the breastbone cartilage ofyoung cattle is used by plastic surgeons to replace facial bone. Red bone marrow is used totreat patients who have a low red blood cell count. Bone meal is also a nutritional source ofcalcium 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 havea wide variety of flavor and textures in a range of foods (66). Therefore, they are highlyprized 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 foodsdepends 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 thanfor use in manufactured medicine. They are blanched to firm the tissue before cooking be-cause of the soft texture. The pia mater and arachnoid meninges, which is a skin collage-nous connective tissue, are peeled off-the brain before cooking.

Heart meat is generally regarded as relatively tough (66) and this is possibly due tothe nature of the cardiac muscle. Hearts are used as table meats: whole hearts can be roastedor braised, sliced heart meat is grilled or braised (67). Heart meat is also often used as aningredient in processed meat.

Kidneys generally are removed from the adipose capsule, which keeps the kidney be-tween 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 beforethe kidneys are prepared for cooking. Kidneys are used whole or sliced and generallybroiled, grilled, or braised.

Liver is the most widely used edible organ (68) and is used in many styles of pro-cessed meats such as liver sausage and paste. Livers from lamb, veal, and young cattle areprepared for the table because they have a lighter flavor and texture, which is preferred inthe 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 ofsausages 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 themost widely consumed parts of the ruminant stomach. They are generally processed at theplace of collection by washing, scalding, and bleaching. They are suitable for poaching orbraising, 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 brais-ing and are sometimes used as casing for sausage.

Animal intestines are used as food by boiling in some countries. Animal intestinesare used for pet food, meat meal, tallow, or fertilizer, but certainly the important economicuse of these products is in the production of sausage casing. Animal intestines, when re-moved from the carcass, are highly microbiologically contaminated. They are fragile andtherefore cleaning must be performed immediately after slaughter of the animals. Animalcasings 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 man-ufactured 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 thecasing, removal of all strings, soaking and removing the blood, salting and packaging—de-scribed by Ockeman and Hansen (1).

The thymus glands are available only from young animals (lamb and calf). Theglands are covered by a capsule of fibrous connective tissue that penetrates the gland anddivides it into lobules, and the connective tissue and fat will be increased with the age ofthe animals. The thymus glands from lamb and calf are blanched to firm the tissue andpeeled from the capsule before cooking. They are sliced and cooked by frying orstewing.



The tongues are removed from the carcasses and generally include a small portion ofthe 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 areused fresh or salted and are usually boiled or braised.

Udders are available only from bovines and the main body is connective tissue andsecretory epithelium. Udders are sliced and washed to remove the milk and cooked by fry-ing or boiling.

Spleens are minced and used in pie, flavoring, and melt in the United Kingdom butused as variety meat in processed meat in the United States.

Uteri are available only from nonpregnant pigs and are collected for human con-sumption. 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 beenused in medicine for their curing powers in some countries (such as China, India, andJapan). These glands are called endocrine glands and secrete hormones, or enzymes thatregulate body metabolism. These include the liver, lungs, pituitary, thyroid, pancreas,stomach, parathyroid, adrenal, kidney, corpus luteum, ovary and follicle. The glands arecollected only from healthy animals and locating the glands requires experience becausesome of the glands are often small and are often encased in other tissue. Different animalshave 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 autolysisand bacterial growth is by quick freezing. Before freezing, the glands must be cleaned andtrimmed from surrounding fat and connective tissue. They are then put on waxed paper andkept at �18°C or less. When the glands arrive at the pharmaceutical plant, they are againinspected, then chopped and mixed with different solutions for extraction or placed in avacuum drier for the drying process. If the dried gland contains too much fat, solutions suchas gasoline, light petroleum, ethylene dichloride, benzene, and acetone are used to removethe fat. After drying and defatting, the glands or extracts are milled to a powder form anddispensed as capsules, tablets, or injections or utilized as a dilute liquid. They are tested forsafety and potency prior to sale.

The adrenal gland consist of two parts, an outer cortex and an inner medulla that se-cretes at least 20 steroids that are essential for life maintenance. Corticosteroids from theadrenal 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 areused as anti-neoplastic and anti-inflammatory agents and for treatment of shock andasthma. Epinephrine and norepinephrine can be extracted from the adrenal medullas of cat-tle, pig, and sheep and are used to arrest hemorrhaging, shrink blood vessels, prolong theeffects of local anesthetics, stimulate heart action, and overcome shock.

Brains, nervous systems, and spinal cords are a source of cholesterol, which is theraw material for the synthesis of vitamin D3, and steroid pharmaceuticals and is used as anemulsifier in cosmetics. Some materials can be isolated from the hypothalamus of the brainfor 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 andantioxidant. 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 treatmentof 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 poste-rior lobe with separate functions. Hormones such as growth-promoting hormone (GH), thy-roid-stimulating hormone (TSH), mammary-stimulating hormone, gonad-stimulating hor-mones, adrenal-cortex-stimulating hormone (ATCH) (extracted from an anterior of thepituitary), antidiuretic hormone (ADH), and oxytocin hormone (produced from a posteriorof pituitary) are used to control growth and metabolism and regulate the activity of otherendocrine glands. ACTH is the most commercially extracted hormone from the pituitaryand is used as a treatment for rheumatism, arthritis, eye inflammation, and multiplemyeloma.

Bile consists of bile acid, bile pigment, fatty acids, phospholipids, proteins, choles-terol, and other substances and can be obtained from the gallbladder. It is used for treatingdigestive disorders, constipation, and bile tract disorders and increasing the secretory ac-tivity of the liver, and it is also useful in some fat-digestion disorders. Bile can be purchasedas dry or liquid extract preparations from cattle or hogs. Some ingredients of bile, such asprednisone, prednisolone, pregesterone, hydeoxycholic acid, chenodeoxycholic acid anddehydrocholic acid, and cortisone, can be extracted individually and used in the medicinaland pharmaceutical areas. Gallstones are reported to have some mystical aphrodisiac valueand are very expensive because they are available in extremely small quantities. They areusually used as ornaments to make necklaces and pendants.

Liver is the biggest gland in animals; it will usually average about 5 kg when obtainedfrom market-weight cattle and approximately 1.4 kg from market-weight pigs. Liver ex-tract is produced by extracting raw ground livers with slightly acidified hot water. Thestock is concentrated to a paste under vacuum at low temperature and is used as a raw ma-terial by the pharmaceutical industry. Liver extract and desiccated liver can be obtainedfrom pork and beef and have long been used as a source of vitamin B12, as a nutritional sup-plement used in treating various types of anemia, and as an enrichment medium in bacte-rial numeration (69,70). Heparin can be extracted from the liver as well as the lungs andmucosa (inner) lining of the small intestines. It is used as an anticoagulant to prolong theclotting time of blood; it is used to thin the blood (raise the viscosity) and to dissolve, pre-vent, 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 ofporcine lung but its activity is not as good as that from commercial products (71). The crudeheparin 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 andactivity of the heparin can be improved by this method and was acceptable when comparedwith commercial products (72,73).

Progesterone and estrogens can be extracted from pork ovaries and may be used totreat some reproductive problems, such as functional uterine bleeding, abnormalities of themenstrual cycle, and threatened abortion, and are used in the treatment of breast andprostate cancer. Relaxin, a hormone from pregnant sow ovaries, often is used duringchildbirth.

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 canbe 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 andtrypsin are used to remove dead tissue and improve healing after surgery or injury; chy-motrypsin also has been used to facilitate cataract-extraction eye surgery.

Animal intestines (sheep and calves) are also used for the manufacture of cat-gut, aninternal surgical sutures. It is produced by several steps and twisted into one, two, or threestrands and then cut, dried, polished, and sterilized. The pork and beef mucosa lining of thesmall intestines can be collected during the machining of casings, and it is either preservedin 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 availablefor the preparation of meat for sale or for processed meat products. The major edible ani-mal fats are lard and tallow (74). Lard is defined as the fat rendered from clean, sound ed-ible 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 fromskimming the rendering tanks. Tallow is hard fat rendered from fatty tissues of cattle orsheep that is removed during processing of beef or sheep. Lard and edible tallow are ob-tained by dry or wet rendering (75). In the wet rendering process, the fatty tissues are heatedin 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 al-most all of the inedible tallow and greases are produced by dry rendering. Rendered lard isused as an edible fat without being subjected to any post-rendering procedure. Due to con-sumer demand, lard and tallow now are often subjected to hydrogenation, bleaching, anddeodorizing treatments before their utilization in food (76). Traditionally, tallow and lardhas been used as a deep fat frying medium. However, this use of tallow or lard fried frenchfries in the fast-food service is changing due to consumer health demands (76). A pouringtallow-oil shortening has been developed for this purpose and resulted in a product whereless fat is absorbed. Tallow and lard also have been used in margarine and shortening. Someedible 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-coholic extraction (77). The early procedure for manufacturing meat extract included re-moving the meat from the bones and trimming away the fat; then, the fat-free meat washashed. The freshly hashed meat was then exposed to clear water and cooked at low tem-perature (less than 90°C) for extraction. Meat extract is defined as the products obtained byextracting fresh meat with boiling water, removing fat, and concentrating the liquid byevaporation (78). Meat extract should contain more than 75% total solid matter, 8.0% ni-trogen, and less than 0.6% fat. The processing procedure for meat extract is summarized asfollows (79).

Meat stock can be produced from edible meat co-products (e.g., meat trimmings, andmechanically separated meat) that are pressed or soaked in water, or cooked, or obtainedfrom corned beef; then the liquid is skimmed to remove fat and filtered to remove the finesand coagulated protein. The remaining liquid is concentrated under vacuum and later in anopen pan to produce meat extract. The concentration of meat stock can be performed by us-ing 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) evapora-tor operated at a temperature of 70° to 75°C and producing a product of final concentrationof 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 ex-tract is also an excellent flavoring material in a noodle soup mix, onion soup mix, and chipdip. When meat extract is used as an ingredient in other meat products, it should be listedas “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 intoeither edible or inedible products. Today, with increasing concerns about health and envi-ronmental protection, many new techniques, operating procedures, and research have beendeveloped to permit more efficient processing and utilization of these co-products. The uti-lization needs become significantly stronger due to competition. This is important becauseincreasing profit and decreasing the cost is required in the future for the meat industry toremain viable. These contributions and efforts are also necessary for the meat industries tochange 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 themeat industry and will continue to influence the utilization of meat co-products.

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Dk1792 ch25

Education

edible meat coproducts

animal coproducts

sale of coproducts

meat processors

meat industry

wholesale edible coproducts

tail meat

meat trimmings