15.Meat and Meat Products

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    15

    Meat and Meat Products

    YOULING L. XIONG and WILLIAM BENJY MIKEL

    University of Kentucky, Lexington, Kentucky

    I. INTRODUCTION

    II. EXPORT AND IMPORT

    III. CANNED MEATS

    IV. FROZEN MEATS

    V. COOKED REFRIGERATED MEATS

    VI. DRY-PRESERVED MEATS

    VII. CURED MEATS

    A. Ingredients and Functions

    B. Hams

    C. Bacon

    VIII. SAUSAGES

    A. IngredientsB. Fresh Sausages

    C. Cured Sausages

    D. Fermented Sausages

    IX. LUNCHEON MEATS

    X. PREPARED DINNER MEATS

    REFERENCES

    I. INTRODUCTIONMeat and meat products, referred to here as red meats or postmortem muscles from mam-

    malian species (beef, veal, pork, and lamb/mutton), are an important component in the

    American diet. Despite the surge in poultry product consumption in the past two decades,

    red meats, with a current annual production totaling about 20 million metric tons (or 53 kg

    consumed per capita), remain to have a dominant market share in all muscle foods pro-

    duced in the United States (American Meat Institute [AMI], 1999). Today, meat and meat

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    Figure 1 Examples of processed and prepared meat and meat-based products. (This is an illustra-tive example only. The use or illustration of a trade name does not mean that the authors and their af-

    filiation endorse the product.)

    Table 1 Meat and Meat Products by Variety

    Meats Processing/characteristic Example

    Canned meats

    Frozen meats

    Dry-preserved

    meats

    Cured meats

    Sausages

    Dinner meats

    Luncheon meats

    Retort to sterilize; fully cooked;

    cured or noncured; metal or

    plastic containers

    Cooked or raw; most microwav-

    able; include home-meal-re-

    placement items; breakfast

    items

    Low water activity; cured;

    refrigeration not required

    Cured with nitrite/nitrate, salt

    and adjuncts by injection or

    dry rub

    Fresh, cured, or fermented; com-

    minuted or emulsified; spicedPrepared meals (HMR); pumped

    products; battered/breaded

    meats; precooked or raw;

    frozen or refrigerated

    Deli meats; lunchables; fully

    cooked and ready to consume;

    restructured meats

    Ham; pork luncheon meat;

    corned beef; beef stew; beef

    in chili sauce

    Breaded boneless pork cutlet;

    pork sausage; meat loaf; beef

    stew and steaks; deli pouch;

    meatball;

    Beef jerky; pastrami

    Hams; bacon; jowl; most deli

    meats

    Bratwurst; frankfurters; salami;

    pepperoniSteak with vegetables; barbecue

    smoked pork; seasoned pork

    roast

    Sliced ham; bologna, and

    salami; ham and cheese; head

    cheese

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    products available in the marketplace are no longer limited to the traditional items; in the

    past few years, numerous new items of processed meats, particularly those in the form of

    convenience foods, have emerged. Many of the products are fully cooked and ready to

    consume, whereas others are portion-controlled and case-ready, to be cooked in a mi-

    crowave or conveniently heated in an oven at home. These products are widely distributed

    at retail and deli markets, and in a typical large food store, over 100 meat items can be read-ily found. Figure 1shows examples of meats that are sold in grocery stores. Despite the

    great variety, meat products can be divided into seven groups based on their product char-

    acteristics and the general processing procedures required (Table 1).

    Postmortem muscle that has gone through major physical or chemical alterations is

    generally consideredprocessed meat. Thus, in a broad sense, meat processing may include

    protein extraction, chemical and enzymatic treatments, massaging or tumbling, curing,

    stuffing, canning, smoking, and other related preliminary preparations, such as meat parti-

    cle size reduction and mixing of meat with various additives. It is noteworthy that simple

    handling of fresh meat in retail stores and in homes (e.g., cutting, grinding, and packaging)is generally excluded from the definition of meat processing.

    II. EXPORT AND IMPORT

    Today, food production and merchandise have become a globalized enterprise. This has al-

    lowed the United States to export or import greater amounts of fresh and processed meats.

    Despite the large U.S. trade deficit in textiles, electronics, and a number of other economic

    sectors, U.S. agriculture maintains its trade surplus with foreign countries. For examples,

    through July of fiscal 1999, U.S. agriculture exported $41.0 billion worth of commodities,in contrast to $31.6 billion imported goods during the same period (United States Depart-

    ment of Agriculture [USDA], 1999). Among the leading commodities that contribute to the

    trade surplus are meats and meat products, whose 1.7 million-ton exports amount to a $3.7

    billion value, versus $2.5 billion for imports. The surplus, however, is expected to decrease

    as a result of the U.S. dollar strength and relatively low prices of domestic meat and meat

    products.

    Countries that lead in exporting fresh chilled and frozen meat and meat products to

    the United States include Canada (451 106 tons), Australia (209 106 tons), and New

    Zealand (183 106 tons), whereas those that contribute to most of the U.S. import tonnageof further processed meats are Denmark (50 106 tons, about 40% are canned pork), Ar-

    gentina (37 106 tons, all are processed beef products), and Uruguay (23 106 tons, with

    10% canned beef products) (USDA, 1998). Table 2compares U.S. exports and imports of

    meats by product type, and the changes that occurred from 1990 to 1996.

    III. CANNED MEATS

    Canning is a thermal process that employs heat (steam) to sterilize the food material placed

    in a sealed container. Thus, canning produces shelf-stable meat products that can be con-veniently consumed in outdoor activities or situations where refrigeration is not readily

    available. The annual production of canned meats (including poultry) has stayed at about 1

    billion pounds in recent years (Pearson and Gillett, 1996). Pasta with meat, chili, and

    canned hams represent about 70% of total canned meat products produced in the United

    States. Vienna sausage, canned luncheon meat, and meat spread are some other major

    forms of canned meats. The internal temperature of canned meat products must reach

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    Table 2 United States Meat Exports and Imports by Type of Products (in th

    Beef and veal Por

    Fresh Lamb, Fresh,

    chilled, mutton, chilled, Hams

    and and and andYear frozen Canned Prepared/preserved goat frozen bacon Canned

    Imports

    1990 699.3 57.6 10.9 19.1 233.5 31.5

    1996 640.7 53.4 13.6 33.1 183.6 55.2

    Exports

    1990 339.9 7.8 2.5 66.8 10.1 1.0

    1996 596.9 14.6 2.5 267.4 25.6 5.3

    Source: USDA Agricultural statistics, 1998.

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    121C to achieve commercial sterility. However, this severe heat treatment may adversely

    affect the product flavor, texture, and color. Therefore, an increased number of cannedmeats are now only pasteurized to an internal temperature between 65 and 75C. In a typ-

    ical pasteurization process, canned meat is cooked in water at about 80C for several hours,

    or steam pasteurized. It is desirable to keep the temperature difference between the heating

    medium and meat to a minimum to minimize cooking losses and jelly formation. All

    canned pasteurized meats must be cured to comply with federal regulations. They must be

    labeled PerishableKeep Under Refrigeration. Thus, canned pasteurized meat products

    require refrigeration during distribution and storage.

    Meat canning is similar to fruit and vegetable canning in processing operations. Pre-

    treated and prepared meat, which may contain various ingredients, is packed into cans vary-ing in size and shape, e.g., pullman, round sanitary, pear-shaped, and oblong. Most cans

    used for meat are made of thin sheets of steel coated with a thin film of tin to prevent rust-

    ing. An enamel consisting of sulfur-resistant resins is formed on the surface of tin to pre-

    vent corrosion of metal due to interaction with sulfur compounds produced from meat.

    Plastic cans, such as semi-rigid retortable bowls and trays, have also been developed in

    recent years. Although the products are not exactly canned, they are processed in the

    same manner as metal-canned meats. Plastic can-like containers (e.g., D-shaped) made of

    nylon, surlyn, and other ethylene/vinylacetate copolymers are used for producing cook-

    in hams that receive pasteurizing treatments (Fig. 2). Vacuum-sealed cans are either ster-ilized or pasteurized in retorts, and are subsequently cooled, labeled, and marketed.

    IV. FROZEN MEATS

    Frozen meat and meat products make up a major sector of the meat industry; with the in-

    creased consumer demand for convenient foods, production of this group of meats has con-

    Figure 2 Pork ham processed (pasteurized) in a plastic can (left) and beef stew processed insemirigid retortable plastic bowls.

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    tinued to grow in recent years. Freezing as a means of preserving meat became known fol-

    lowing the development of efficient mechanical refrigeration during the 19th century; how-

    ever, the freezing technology was not fully commercialized in the meat industry until the

    1960s, during which decade there was a rapid growth in home freezers and refrigerators.

    The availability of efficient freezing systems has greatly facilitated meat exportation

    as well as importation (Table 2).Domestically, it has enabled meat producers and proces-sors to market various convenient, packaged, and prepared foods (e.g., the so-called home

    meal replacements that have entered the market in the past few years) at the retail level. The

    freezing process involves placing meats in a cold room, typically18 to20C. Water in

    the product exposed to the freezing temperatures will transform into ice. Due to the pres-

    ence of various water-soluble and hydrophilic compounds, ice crystals actually do not form

    until the temperature of meat reaches a few degrees below 0C.

    Quality of frozen meat and meat products is influenced by many factors. The rate of

    freezing has a profound effect on meat tenderness and drip loss. In general, fast freezing is

    conducive to the formation of small ice crystals that are located intracellularly and causelittle physical damage to meat components. On the other hand, a slow freezing process fa-

    vors large ice crystals to form, extracelluarly, which results in disruption of muscle cells

    and causes exudation (Fennema, 1975). In almost all commercial meat plants, forced air

    circulation (blast freezing) is used to achieve rapid freezing. Blast freezing may operate on

    either a batch or a continuous basis and normally employs20 to40C cold air. Air with

    higher velocity allows a greater heat transfer coefficient, and hence, a more rapid temper-

    ature drop in meat. To avoid thaw rigor, beef and lamb must have gone through rigor mor-

    tis prior to freezing. To initiate early onset of rigor, thereby preventing thaw rigor, electri-

    cal stimulation can be employed.To prevent quality loss due to protein denaturation, cryoprotectants are often in-

    cluded in the formulation of meat products. Among them, Polydextrose, polyphosphate,

    and to a lesser extent, sorbitol, are used. Packaging is another important factor affecting the

    shelf-life of frozen meats. Large, wholesale meat cuts are often vacuum sealed to prevent

    lipid oxidation and formation of metmyoglobin. For retail meats, cooked or raw, films with

    low water permeability and adequate mechanical strength, e.g., Sarlyn, are required. To

    prevent the products from being exposed to light, thereby eliminating oxidation catalyzed

    by light-sensitive compounds, nontransparent outside cardboard-type packages are com-

    monly used.There are various kinds of frozen, cooked meat products in todays food market. A

    quick survey has shown many specific items manufactured by different companies, e.g.,

    entree items: breaded boneless pork cutlet; country fried beef steaks; meat loaf; beef pot

    roast; and corn dog (batter-dipped wieners on a stick); dinner items: gravy and sliced beef;

    tomato sauce and meat loaf; steak and gravy; noodles with beef stew; steak with mushroom

    gravy; meat loaf in gravy; deli pouches (cheese burgers inside); croissant pockets; stuffed

    sandwiches (beef, ham, pepperoni); and meatballs in sauce with pasta (Fig.3). Most of

    these meats are packaged with side dish items, such as green beans, tomatoes, carrots,

    mashed potatoes, onions, macaroni and cheese, and others, and are microwavable.

    V. COOKED REFRIGERATED MEATS

    This group includes various kinds of ready-to-consume products, many of which are sand-

    wich-type prepared meats and belong to the HMR category (discussed later). Side dish

    items are normally included in the same package and the product needs only to be warmed

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    either with a microwave or conventional oven before serving. In some cases, flavor and

    freshness appearance may be a problem. For example, a precooked porkchop may develop

    warmed-over-flavor upon reheating, rendering the product unacceptable. To enhance prod-

    uct shelf-stability, antioxidants and specific flavor ingredients are often included.

    VI. DRY-PRESERVED MEATS

    Drying of meat is a very old process that was originally used to preserve meat, namely,to keep the meat at ambient temperature for an extended period of time. Historically, sun-

    drying was the only drying method, but today hot air-drying is prevalent commercially. Al-

    ternatively, freeze-drying is done, but because of its prohibitively high costs, it is restricted

    to some specialty products that require rapid rehydration. The most well-known dried

    meats are beef jerkies and dried meat bits as a soup base.

    Dried meats prepared in the United States are cooked before drying. The usual pro-

    cess is to cut meat into slices and then cook, mince, or cut it into small cubes to provide a

    large surface-to-volume ratio, and dry it. Precooking is important not just because of food

    safety, but also because it facilitates the removal of a large amount of water from meat fol-lowing protein aggregation. For beef jerkies, marination is a required extra pretreatment:

    meat slices are marinated (e.g., in teriyaki soy sauce, brown sugar, liquid smoke, black and

    red pepper, and other seasonings) before cooking and drying. During the drying process,

    meat undergoes extensive physical and chemical changes. Conventional air-drying in-

    volves the extraction of almost all of indigenous water in muscle. The process is funda-

    mentally a diffusion of water to the meat surface, which is driven by the difference in wa-

    ter vapor partial pressure between the air and the meat surface. Both continuous belt oven

    and fluidized bed driers are used to dry meat. The removal of water from the muscle cells

    as well as between muscle fibers results in stronger hydrophobic interactions of the my-ofibrils, thereby hardening the texture of meat for desirable chewiness.

    VII. CURED MEATS

    Curing of meat refers to treatment of fresh meat with salt, nitrite or nitrate compounds, and

    adjuncts for the purpose of preservation and obtaining desirable color and flavor. It is not

    Figure 3 Cooked frozen meat products: croissant pockets with ham, cheddar, and selected veg-

    etables (left), and beef steak with peas and mashed potato (right).

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    known where and when the use of curing first began, but some evidence suggests that

    around 3000 B.C. the Chinese began using salt that was contaminated with nitrate to pre-

    serve meat. Many cured meat products are available in the current food market. They in-

    clude traditional pork products such as ham and bacon, and to a lesser extent, beef products

    such as corned beef. More recently, a number of new cured meats have been developed,

    with most belonging to the restructured and sliced deli meat category. This section will con-centrate on ham and bacon because both not only are popular products in the cured meat

    category, but are also of a long tradition, have unique characteristics, and involve some spe-

    cial processing technologies.

    A. Ingredients and Functions

    1. Curing Agents

    Salt in the form of NaCl is commonly used in cured meats. Occasionally, KCl is used to re-

    place or partially substitute for NaCl to alleviate its potential adverse effect on health of thehumans. The main functions of salt, other than providing flavor, are solubilizing proteins,

    dehydration, and altering osmotic pressure so as to inhibit bacterial growth and subsequent

    spoilage. Salt can be applied to meat directly in its dry crystal form, or dissolved in solu-

    tion (pickle) before incorporation into meat. Although salt is an indispensable ingredient in

    cured products, the true curing agent is nitrite (NO2) or nitrate (NO3). Nitrate was origi-

    nally approved for color fixation in cured meats, but now it has largely been replaced by ni-

    trite. This is because nitrate is reduced to nitrite either by organisms or by reducing com-

    pounds before the actual curing process begins, and because direct application of nitrite can

    be more easily controlled. In the United States, the use of nitrate is now restricted to dry-cured products, such as country cured hams and dry sausages.

    Nitrite (or nitrate) is a multifunctional compound. It induces and stabilizes the pink-

    ish color of lean meat, contributes to the characteristic flavor of cured meat, inhibits the

    growth of spoilage and pathogenic microorganisms (especially Clostridium botulinum),

    and retards development of oxidative rancidity. The level of nitrite or nitrate allowed in

    cured meats, both ingoing and residual, is strictly regulated by the USDA. For instance, the

    maximum level of ingoing NaNO2 in pumped bacon is 120 ppm, and the residual level (in

    the finished product) shall not exceed 40 ppm. Establishment of nitrite regulation is based

    on the concern that nitrite can form nitrosamines by reacting with secondary amines incooked cured meat as well as in the intestines of the human body. In response to consumer

    concern, an increased number of meat processors are now reducing the nitrite level in cured

    products. A recent survey showed that residual nitrite levels in cured meats (ham, bacon,

    wiener, and bologna) produced in the United States average about 10 ppm, which repre-

    sents only 10% of the recorded levels in cured meats two decades ago (Cassens, 1997).

    The pinkish red color characteristic of cooked cured meats results largely from the

    reaction of the heme group in myoglobin with nitric oxide forming the nitrosylmyoglobin

    pigment. Nitric oxide is derived from nitrite in the presence of reducing compounds such

    as erythorbic acid. Part of nitrite dissolved in water can form nitrous acid (HNO2). Undera reducing condition, nitrous acid decomposes to nitric oxide. When nitric oxide binds to

    the heme iron, it changes the electron distribution or resonance of the heme structure,

    thereby producing a pinkish color. Under heating conditions, nitrosylmyoglobin is con-

    verted to the more stable forms, i.e., nitrosylhemochromogen and dinitrosylhemochrome.

    The concerns with possible carcinogenic effect of residual nitrite present in cured

    meats have prompted researchers to search for alternative curing methods. One of the pos-

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    sible methods was the so-called nitrite-free curing (OBoyle et al., 1990). In this curing sys-

    tem, the three major functions of nitritecolor fixation, antimicrobial activity (antibo-

    tulism in particular), and inhibition of oxidative rancidityare conferred through the use

    of combined materials. Dinitrosylhemochrome is presynthesized by reacting nitric oxide

    gas with hemin extracted from beef red blood cells, an abundant animal by-product. Dini-

    trosylhemochrome is not very stable, so the pigment is microencapsulated with carbohy-drate-based encapsulating agents to prevent it from direct contact with air. To reproduce the

    antioxidative activity of nitrite, antioxidants such as ascorbate, tripolyphosphate, and vari-

    ous phenolics (TBHQ, BHA, etc.) are added to the nitrite-free mixture. In addition, an-

    timicrobial agents, such as sorbate, sodium hypophosphite, methyl fumarate, and sodium

    lactate, are also used. The mixture is blended with meat in sausage production. Frankfurters

    and wieners manufactured using the nitrite-free curing system cannot be distinguished from

    products made by the traditional nitrite-cured method.

    2. Curing Adjuncts

    Reducing compounds are added in meat-curing mixtures to hasten color development via

    converting nitrite to nitric oxide, and ferric iron of the heme to ferrous iron. The most com-

    monly used reducing agent is sodium ascorbate (vitamin C), or its isomer, erythorbate,

    which is less expensive and more stable. Muscle itself also contains endogenous reductants

    and enzymatic reducing activity, but the reducing power of these factors is relatively small.

    In addition to reducing metmyoglobin (Fe3) to myoglobin (Fe2), and nitrite to nitric ox-

    ide, ascorbate (or erythorbate) also serves as an antioxidant to stabilize both color and fla-

    vor, and to decrease the formation of nitrosamines.

    Another curing adjunct is phosphate, usually sodium pyrophosphate, tripolyphos-

    phate, and hexametaphosphate, that can be used individually or in various combinations. In

    either case, the total addition cannot exceed 0.5% of the meat product weight as regulated

    by the USDA. Phosphates do not directly enter the curing reactions; they are added mainly

    to increase water-holding capacity of muscle, thereby reducing shrinkage of finished prod-

    ucts. Phosphates are also effective antioxidants and can retard rancidity development.

    However, because nitrite and ascorbate are stronger antioxidants, the antioxidative effect

    by phosphates may not be significant in cured meats. Because phosphates are corrosive

    (they bind with metal ions), the equipment used must be made of stainless steel or plastic,

    or metal with a plastic coating.

    B. Hams

    Hams can be separated into two groups: bone-in hams (processed using the whole pork

    legs) and boneless hams (made from deboned pork meat). The latter type also belongs to

    the deli meat group and therefore will be further discussed later. A typical ham is cured with

    a mixture consisting of salt, sugar, sodium nitrite, sodium erythorbate, and sodium

    tripolyphosphate. Occasionally, corn syrup in lieu of sugar is utilized. Hams can be cured

    by two fundamental methods: dry curing and pickle (wet) curing. In dry curing, the curingingredients are applied to fresh pork leg by rubbing without the addition of water. Thus, the

    curing ingredients, particularly salt, draw enough water from the meat due to the osmotic

    pressure gradient to form a brine, which serves to transport the curing ingredients into the

    meat through diffusion. This curing method is obviously labor-intensive and distribution of

    the curing ingredients is not efficient. Furthermore, dry-cured meats are often too salty and

    may be unacceptable to many consumers. Therefore, except for country ham, commercial

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    processing of hams is now accomplished mostly by pickle injection. Dry curing is also still

    used for fatty cuts, such as fat backs, clear plates, and jowls.

    1. Dry Curing

    Country hams are prepared using dry curing methods. Country hams are not cooked but

    must be free of Trichinae and have a salt content in the finished product of at least 4%, andshrink a minimum of 18% during processing. The flavor and appearance of country hams

    distinctly differ from common pickle-cured hams. Country hams are salty, somewhat dry,

    and rather hard products with a rich flavor. They are primarily produced in the southern re-

    gions of the United States, including the states of Kentucky, Virginia, North Carolina, Ten-

    nessee, Georgia, and Missouri.

    Most commercial country ham processors rely on added nitrite or nitrate for curing.

    However, a small percentage of processors do not add nitrate or nitrite and still make highly

    flavored and well-colored country hams. Salt and seasoning may be contaminated with ni-

    trate or nitrite and produce the color and flavor characteristic of country hams. The curingmixture is divided into three equal portions, which are applied by rubbing around the en-

    tire cut immediately, and 7 and 14 days later, respectively. It is important to make sure that

    the flesh surface is adequately rubbed with the cure mixture because the cure penetrates into

    the ham through the flesh surface, not the skin surface. For best product quality, country

    hams should be cured under refrigeration conditions with a temperature of 2.2 to 4.4C

    (3640F) and a relative humidity of 70% to 90%. Hams are stacked with overhauling two

    to three times during a 30- to 50-day curing period. The exact curing time depends on the

    size of ham (~2 days/pound).

    Following curing, country hams are held for approximately 20 more days for saltequalization. The equalization room should be maintained at 7.2 to 12.8C (45 to 55F)

    at a relative humidity of 75% to 90% and can be done in the curing room. The hams should

    then be hung by the shank using a string, or placed in stockinette and suspended from a

    rack, and allowed to age for 6 to 9 months but no longer than 12 months. The temperature

    of the aging room is relatively high (21 to 35C) and the humidity relative low (50% to

    60%) to facilitate dehydration and development of firm texture and distinct flavors. It is

    generally believed that both cathepsins (which degrade proteins to small flavor-active pep-

    tides) and lipases (which generates volatile compounds by catalyzing lipid oxidation) are

    involved in the flavor development. Frequently, molds will grow on the surface of countryhams during salt equalization and subsequent aging. These molds are generally unharmful

    and can be removed by wiping with a cloth dampened with edible oil. Finished country

    hams should have a moisture content of 50% to 60% and an average salt content of 4.5%

    to 5.5%.

    There are other types of dry-rubbed hams made in other countries that are more or

    less similar to country hams made in the United States. Examples are Chinese Jinhua ham,

    Italian prosciutto ham, German Black Forest ham, and Spanish serrano ham.

    2. Pickle CuringThis is the most widely used curing method for hams. The method differs from dry curing

    in that the curing mixtures are dissolved in water to form a brine or pickle. Furthermore, ni-

    trite instead of nitrate is used in pickle curing. Among the different ways to incorporate cur-

    ing solution into meat, stitch pumping is by far the most widely used. In a typical commer-

    cial operation, multiple needles are used to inject the curing solution into the ham flesh. The

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    pickle, in the amount of ~10% of the raw pork leg weight, is injected from different sides

    of the leg, allowing a uniform incorporation of the curing ingredients. This amount of

    added solution is usually lost by the time the ham is fully cooked. The amount of residual

    brine after cooking is regulated. If the finished ham does not weigh more than it did before

    cure injection, no label restrictions are imposed. However, if the finished ham is heavier

    than its fresh cut, i.e., the protein fat-free (PFF) value falls below 20.5, then it must be la-beled cooked ham with natural juice (PFF 18.5) or cooked ham with water added

    (PFF17.0) (USDA, 1984).

    C. Bacon

    Similar to ham processing, bacon can be cured by both dry rub and pickle curing. Since

    pork bellies are relatively thin, they do not require a long time to cure before cooking and

    smoking. A typical pork belly requires only 10 to 14 days to cure by dry rub, compared with

    hams, which require several months. Most commercially processed bacon is now cured

    through multi-needle stitch pumping. Finished bacon is usually partially cooked; the final

    internal temperature of the belly reaches only 52 to 56C. Before consumption, bacon

    slices must be fully cooked to ensure a complete destruction of possible pathogenic mi-

    croorganisms and the parasite Trichinae.

    Recently, microwavable bacon has been developed. The process involves frying of

    cured belly for sufficient length to develop the characteristic flavor and texture of cooked

    bacon. The fully cooked bacon is packaged in a special pack designed to enhance mi-

    crowave heating (5 to 10 seconds). Additional procedures may be necessary, including the

    use of binders to minimize moisture loss during heating and texturizing through rollers to

    prevent excessive distortion of the rashers. The product is rather stable, requiring no re-

    frigeration until opened.

    There are several other kinds of bacon, e.g., jowl bacon, beef bacon, and Canadian

    bacon. Canadian bacon, made from pork loin muscle, differs sharply from conventional ba-

    con, which is made from the pork bellies.

    VIII. SAUSAGES

    Sausages are a unique type of comminuted meat products that are usually spiced or

    seasoned to obtain various flavor intensities and profiles. The development of sausages

    was initially driven primarily by economic factors, i.e., it utilizes low-quality meats such

    as trimmings, head and shoulder meat, and edible by-products. Convenience and variety

    are other important reasons why sausages are widely consumed in modern society. In

    the United States, about 4 billion kg of sausage products are produced annually, and the

    per capita consumption is estimated to be 15 kg per year. Based on the product charac-

    teristics and the specific processing method used, sausages can be classified into

    three major groups: fresh sausages, cured sausages, and fermented sausages. A compre-hensive list of sausages produced in the world is provided by Roman et al. (1994). Tech-

    nologically, sausage making consists of several common stepscomminution to reduce

    meat and fat particle size (grinding, mincing, chopping, or flaking), mixing with ingredi-

    ents, stuffing into a specific casing, linking to obtain specific lengths, and finally,

    packaging.

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    A. Ingredients

    1. Raw Meat

    A proper selection of meat ingredients is essential for the production of sausages of uni-

    form quality. Raw meats used for sausages are generally low-valued materials, but they

    must be fresh, i.e., with very low microbial counts. These include cuts high in connectivetissue or fat, tough meat from mature animals, carcass trimmings, mechanically separated

    meat, and edible animal by-products. The function of each selected raw meat ingredient

    may be unique. Meats used for binding should have a sufficiently high protein content and

    the proteins should be readily extracted and form gels during cooking. Skeletal muscle

    from cows, bulls, and sows is an excellent meat binder, whereas high-fat trimmings are

    generally poor binders. There is another group of meats that are included in sausage for-

    mulations to fill the void space in sausages. Filler meats have little or no binding ability,

    and they include offal meats (e.g., tripe, snouts), skin, and partially defatted beef and pork

    tissue.The rapidly increased use of poultry meat in the sausage industry is worth particular

    mentioning. Poultry meat has been blended into pork and beef sausages. The increased use

    of poultry meat in sausage production has resulted mainly from the relatively low cost for

    poultry meat (particularly turkey), and increased consumer demands for light meat,

    which is perceived as more healthy than red meat.

    2. Salt and Nitrite

    Salt is the single most critical nonmeat ingredient. The main form of salt utilized in sausage

    production is sodium chloride. Its principal function is to solubilize and extract the my-ofibrillar proteins needed to form a bind during cooking. Of course, it also imparts flavor

    and has antimicrobial effects. Thus, salt is responsible for the textural characteristics and

    integrity of finished sausage products. Most commercial sausages contain 1.5% to 2.5%

    added salt. Phosphates at a level up to 0.5% in finished products are used to improve wa-

    ter-binding capacity of meat by increasing fiber swelling and solubilizing proteins. Phos-

    phates may also help to stabilize flavor and color in finished product, presumably by se-

    questering transitional metal ions (Fe and Cu), thus reducing oxidation.

    Many sausage products are cured with nitrite. Sodium nitrite is commonly used, al-

    though in certain cases it may be substituted for by potassium nitrite. The maximum levelof nitrite allowed in sausage is 156 ppm. The use of nitrate is more restricted; it can be used

    only in dry and semi-dry, fermented sausages. Nitrite is used in conjunction with the re-

    ducing agent ascorbate or erythorbate, and phosphates.

    3. Water and Extenders

    Water, sometimes together with ice, is added in sausage making to help distribute nonmeat

    ingredients and increase the product yield. In 1988, the USDA implemented a new regula-

    tion to permit water addition to partially substitute for fat in cooked sausages, so long as the

    sum of fat (30% maximum) and added water in the final product does not exceed 40% of

    the product weight. As a result of this regulatory change, numerous new, low-fat sausage

    productsfor example, reduced-fat sausages (25% fat reduction over traditional prod-

    ucts), low-fat or light sausages (contain 10% fat), extra lean sausages (contain

    5% fat), and fat-free sausages (contain1% fat)have been produced. Along with the

    addition of water, nonfat dry milk, whey protein concentrate, sodium caseinate, wheat

    gluten, cereal flours, tapioca dextrin, soy flour, soy protein concentrate, and more recently,

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    polysaccharide gums, at limited levels, are used as extenders or fillers in sausages. The

    terms extender and filler are often used interchangeably. Their main functions are to im-

    prove functional properties related to product texture and flavor, and to aid in meat particle

    binding and water retention.

    4. SeasoningsUnlike most other processed meats, sausages are seasoned products. Different spices and

    flavorings are added in sausages, and their use levels are primarily dictated by product iden-

    tity standards and not by regulations. Spices are aromatic vegetable substances in whole,

    broken, or ground form. Spices may be added as natural spices or spice extracts. In the lat-

    ter case, they must be labeled as flavoring. Flavorings refer to extractives that contain fla-

    vor constituents from fruits, vegetables, herbs, roots, meat, seafood, poultry, eggs, dairy

    products, and other food sources. Flavoring compounds can also be synthesized. A good

    example is monosodium glutamate, which is a potent flavor enhancer. Most flavorings are

    oil-based extracts. Because of their high flavor intensity, they can be more accurately ap-plied in sausage to obtain desired flavor intensity than their natural counterparts (spices).

    Sugars in a variety of formssucrose, dextrose, corn syrup, and so onare most com-

    monly used in sausages. Almost all sausage products contain sugar in one form or another.

    B. Fresh Sausages

    As the word fresh indicates, fresh sausages include a variety of uncooked sausages, such

    as breakfast sausage and sausage patties, whole hog sausage, bratwurst, Italian-style

    sausage, and Polish-style sausage, all of which can have a fat content up to 50% of the rawproduct weight. They are salted but not cured with nitrite, and are generally coarsely ground

    and not emulsified. Fresh smoked sausages such as Kielbasa also belong to this product

    group.

    Fresh sausages are manufactured by grinding meat through plates with holes ranging

    from 0.32 cm (1/8) to 0.95 cm (3/8) in diameter. Particle size reduction is achieved

    through extrusion and cutting in a screw auger operating in a horizontal chamber. The

    ground meat is mixed with salt, seasonings, and other ingredients by blending in a mixer or

    similar equipment. Stuffing is done by extrusion of the batter into casings through a small-

    opening tube called the horn. There are two major types of sausage casingsnatural or syn-thetic. Natural casings are small intestines from hog and sheep. The intestine is inverted and

    thoroughly washed in a dilute chlorine solution (0.5%) followed by water rinsing. Excess

    fat and connective tissue are removed by brushing with a soft brush. Natural casings are

    normally packed in saturated salt solution and stored in a cold room or a freezer. Natural

    casings are denatured upon cooking. Shrinkage of the casing allows it to firm up the

    sausage links. Synthetic casings are made of edible collagen materials or inedible cellulose.

    For fresh sausages, edible casings are always used. After stuffing, sausage is linked to make

    individual links of equal length.

    Because casings contribute a significant cost to sausage products, technology hasbeen developed to manufacture sausages without the use of casings (Frye, 1996). In one

    method (co-extrusion), collagen solution is extruded around an endless rope of sausage

    batter, forming a thin collagen layer on the surface of the sausage. Subsequent treatment

    with a saturated salt solution causes dehydration of collagen and transforms it into a fibrous

    structure or coating. After heating and cooling, a thin invisible film is formed as the result

    of collagen cross-linking, thereby encasing the sausage. Another method (using sintered

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    mold) is based on the principle that myofibrillar proteins extracted to the surface of

    sausage can coagulate upon acidification. The meat batter is extruded into a porous mold.

    When a small amount of acetic acid is pumped through the mold, it lowers the pH and

    causes the proteins on the surface to coagulate, forming a natural skin. Fresh sausages are

    sold uncooked, and require either refrigeration or freezing.

    C. Cured Sausages

    Nitrite-cured sausages are mostly finely chopped and emulsified. The most popular prod-

    ucts in this group are frankfurters and bologna, which account for about 25% and 20% of

    all sausages (including both red meat and poultry) consumed in the United States. Frank-

    furters are prepared in various forms, and those with a relatively large diameter are often

    referred to as wieners. Most frankfurters in the United States are a blend of beef and pork,

    with or without poultry, mildly seasoned with paprika and other spices, and smoked. The

    processing technology for bologna is similar to that for frankfurters; however, bologna ismuch larger in diameter (e.g., ~10 cm compared to less than 2.5 cm for frankfurters) for the

    purpose of sandwich preparation, and the spices used may be different. Many luncheon

    meats with distinctly different standards of identity actually also belong to the cured

    sausage category.

    In a typical cured sausage processing, the mixture of meat and ingredients is finely

    chopped and emulsified. Frequently, mixing and chopping are done simultaneously in a

    bowl chopper where a series of vertically positioned rotating knives cut through meat that

    is forced to move with the horizontally positioned rotating bowl. The chopping process cre-

    ates sufficient shear to comminute meat and fat into fine particulates. Because myofibrillarproteins are extracted in the presence of added salt and phosphate during chopping, they

    will form coatings on the surface of the fat droplets and produce protein matrices sur-

    rounding the emulsified fat particles, thereby reducing the surface tension. Some sausage

    manufacturers use a separate emulsifier to produce fine emulsions after the meat is already

    chopped. However, with a good chopping machine, a separate emulsifier is often found un-

    necessary. The finely chopped meat system is completely stabilized during cooking, where

    three-dimensional gel structures are formed and fat particles are imbedded in the gel ma-

    trices. Most cured sausages are also smoked.

    One of the most critical factors in the production of emulsified meats is the tempera-ture of meat batters during chopping. This temperature should be maintained low enough

    to prevent emulsion collapse, but not too low to keep fat soft. It varies depending on type

    of fat added or meat used. For most frankfurter emulsions, a chopping temperature of about

    10 to 12C is desirable. Due to friction between the high-velocity rotating blades and

    meat particles, a 10C temperature rise in meat batters is not uncommon. To prevent heat

    rise during chopping, ice is used to replace water in the product formulation. Finely

    chopped sausages are stuffed mostly in synthetic casings. Therefore, after cooking, casings

    are removed by peeling prior to vacuum packaging. Natural casings described above are

    also used for certain finely chopped products, and they are not removed after cooking.

    D. Fermented Sausages

    The first use of fermentation in meat is lost in the mists of antiquity but may date back to

    the Babylonian culture around 1500 B.C. Fermented sausages can be divided into two main

    groups based on the processing procedure and product characteristics: dry and semi-dry.

    For both groups, lactic acid is produced; thus, meat is fermented. Dry and semi-dry

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    sausages, as their names imply, differ in moisture content, which averages between 30% to

    40% and 40% to 50%, respectively. Of the different fermented meat products produced do-

    mestically or imported, pepperoni and salami are two of the most popular items, with pep-

    peroni alone amounting to 180 million kg consumed annually (Hinkens et al., 1996).

    The most crucial processing step in sausage fermentation is to timely lower the pH of

    fresh meat (which averages about 5.6 to 5.8 post rigor) so as to curtail the growth ofspoilage microorganisms The final pH of fermented sausages typically ranges from 4.8 to

    5.2, depending on tanginess, firmness, and other product characteristics desired. Lactic acid

    bacteria, which produce lactic acid through glycolysis, can be introduced into meat either

    by chance inoculation (natural fermentation) or by inoculating a starter culture. In natu-

    ral fermentation, lactic bacteria are inoculated by chance from the processing environment

    (e.g., processing equipment). Sometimes, a portion of already fermented meat from a pre-

    vious batch is added to a new batch to start fermentation. This procedure, called back-

    slopping, reduces the incubation time for the bacteria to reach a productive level. Natural

    fermentation has been used for centuries but it has many obvious disadvantages. The fer-mentation usually takes a long time (e.g., more than one week). The population and type of

    lactic acid bacteria in fresh meat are difficult to control. If the initial population of lactic

    bacteria is small and the meat pH cannot be rapidly lowered, spoilage microorganisms will

    predominate and the product will fail. Moreover, pathogens can grow well in meat when

    the pH is not sufficiently low, especially when they do not have to compete with lactic bac-

    teria. Many lactic bacteria from chance inoculation are heterofermentative, i.e., in addition

    to producing lactic acid, they also produce acetic acid, alcohol, gas, etc. Because different

    bacteria species may be introduced each time, batch-to-batch variability in product flavor,

    acidity, and textural characteristics can be very high.Today, almost all commercial production of fermented sausages is done by using se-

    lected starter cultures. Starter cultures are available in two forms: frozen concentrate and

    lyophilized dry powder. Starter cultures available commercially are typically blends of two

    or more different microorganisms and sometimes different strains of the same microor-

    ganism. The most commonly used microorganisms areLactobacillus, Pediococcus, Lacto-

    coccus (all three are homofermentative), andMicrococcus (used to reduce nitrate to nitrite).

    Specific examples areL. plantarum, P. acidilactici, andL. lactis sub sp. lactis.

    Fermented sausages are salted and cured, and both nitrate and nitrite can be used. Salt

    is needed to facilitate dehydration and impart flavor. Fermented sausages are usually heav-ily spiced, making the product particularly palatable. Organic acidulants, such as encapsu-

    lated glucono-delta-lactone and lactic acid, are sometimes mixed with fresh meat at the be-

    ginning of fermentation. They are used to quickly establish an acidic environment that will

    stimulate the growth of lactic acid bacteria and inhibit spoilage microorganisms. In fact, dry

    or semi-dry sausages can be produced by direct acidification with proper acidulants such

    as lactic acid and glucono-delta-lactone, a slow acid-releasing compound. Sausages pre-

    pared by direct acidification have a characteristic tangy flavor closely resembling that of

    fermented products, and they are most widely used in pepperoni production for pizza top-

    pings. In order to produce lactic acid during fermentation, sugar must be present, whichserves as substrate for glycolytic enzymes inside the bacterial cells. Simple sugars, such as

    sucrose and dextrose, are preferred because they can be readily transported through the bac-

    terial cell wall. The amount of sugar added to dry or semi-dry sausages are typically in the

    range of 0.5% to 2.0%. The lower the desired pH, the more sugar will be needed.

    After ground meat is blended with all ingredients, including the starter culture, the

    mixture is stuffed and subsequently incubated in a closed chamber (sometimes a smoke-

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    house) to allow fermentation to take place. Temperature of the incubator is typically main-

    tained at 21 to 24C with a 75% to 80% relative humidity for dry sausage, and 30 to 37C

    with a 75% to 80% relative humidity for semi-dry sausage. The fermentation time, how-

    ever, is longer for dry sausage (1 to 3 days) than for semi-dry sausage (8 to 20 hours) (Ter-

    rell, 1977). For dry sausage production, the fermented meat is placed in a drying room to

    allow further dehydration and flavor development. As a general recommendation, the tem-perature of the drying room should be controlled to 7 to 13C and the relative humidity to

    70% to 72%. The air of the drying room should be changed periodically to ensure air qual-

    ity and prevent moisture buildup on the surface of sausage. The drying time varies consid-

    erably, depending on the size (diameter) and type of product. Most dry sausages are aged

    for somewhere between 10 days to 3 months. Dry sausages are not cooked, and most are

    not smoked. They do not require refrigeration after manufacture. The low moisture content

    (aw 0.91) and low pH conditions in the sausage are effective to preserve the product.

    Semi-dry sausages, however, are generally cooked to an internal temperature of at least

    68C following fermentation. Semi-dry sausages have a relatively high moisture content(aw ~ 0.95) and hence, require refrigeration to prevent microbial spoilage. Most semi-dry

    sausages are smoked.

    IX. LUNCHEON MEATS

    This group encompasses a broad range of processed meats that are manufactured in the

    form of loaves or slices (Fig. 4). They have been introduced to the retail and convenience

    store or deli markets as consumer demand has grown for ready-to-eat or ready-to-heat prod-

    ucts. Luncheon meats are fully cooked/pasteurized and require refrigeration for storage.Many of the loaves are pre-sliced and packaged for distribution to retail stores. Wholesale

    loaves, typically in the 3 to 5 kg range, are usually sliced in the deli at the time the customer

    purchases them. Because these meat products are sold in the deli section, they are some-

    times referred to as deli meats. Luncheon meats, as the name indicates, are utilized pri-

    marily for lunch sandwich preparation. These products are normally restructured and may

    be cured or uncured with a variety of flavor profiles to meet the demand of ever-changing

    Figure 4 Sliced deli or luncheon meats: restructured ham (left) and pickled loaf (right).

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    consumer makeup. Among the popular luncheon meat items manufactured in the United

    States are sliced ham (e.g., honey ham 98% fat free), bologna- and salami-type loaves, liver

    cheese (wrapped in a layer of pork fat), ham and cheese loaf, and head cheese (made of pork

    snout and tongue meat with added water, salt, gelatin, spices, flavorings, monosodium glu-

    tamate, dextrose, nitrite, etc.). It must be pointed out that the traditional luncheon meats,

    which are high-temperature processed and canned, have lost their true meaning, and shouldbe distinguished from the deli-type meats that are consumed as convenient lunch items.

    There is a great variation in flavor and texture among luncheon meats, and the dif-

    ferences are derived from the specific processing procedures involved as well as the dif-

    ferent formulations employed. For bologna-type luncheon meats, essentially the same meat

    ingredients as for sausages are used, and the same emulsion for making frankfurters can be

    used for luncheon meat loaves. However, luncheon meats often contain also other condi-

    ments to enhance palatability, e.g., pickles, pimentos, and olives. Luncheon meat loaves are

    stuffed into plastic or cellulose bags inside a stainless steel tube that has a 10 to 12 cm in-

    ner diameter. The meat batter is compressed into the tube, capped, and then cooked. Someluncheon meat loaves are prepared by stuffing inside a pan (similar to the bread pan). The

    open top surface is sometimes brushed with a thin layer of syrup to create a brown appear-

    ance after cooking. This type of luncheon meat, after slicing, can easily be used for sand-

    wich preparation.

    A notable processing change that is made by some luncheon meat manufacturers in

    recent years is repasteurization of the fully cooked product after it is sliced. This is to as-

    sure that psychrotrophic pathogens, particularlyListeria monocytogenes, that could be in-

    troduced during slicing and handling are inactivated. Since reheating tends to cause addi-

    tional water loss, it is important that a proper water-binding agent, such as polyphopshateand polysaccharide gums, be included in the product formulation.

    Another group of luncheon food product, referred to as Lunchables, have been de-

    veloped in the past few years, led by Oscar Mayer Foods Division. This type of product is

    sealed in a small plastic package that consists of several compartments. Bite-size meat (e.g.,

    ham, franks, and pepperoni) is placed in one compartment while cheese, cookies, crackers,

    desserts, or other nonmeat items are packed in other compartments (Fig. 5). This new mar-

    keting concept was developed to target children, including elementary school pupils, from

    busy families. It is nevertheless more of an ingenious marketing strategy than it is a true

    processing innovation.

    Figure 5 Lunchables containing ham slices (left) or cooked beef patties (right).

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    X. PREPARED DINNER MEATS

    In the United States today, an estimated 50% of the food dollar is spent on foods prepared

    away from home. This is especially true for double working households that have little time

    to spend on meal preparation. According to the U.S. Department of Commerce, the percent

    of women working outside the home has increased from 42% in 1960 to 70% in 1995.These consumers are looking for options that allow their families to continue to enjoy the

    mealtime experience as a family without the hassle of extended preparation time. Options

    available may include eating out at restaurants, having takeout foods, or purchasing ready

    prepared meals to be reheated at home for the family meal. Taking advantage of this shift

    in consumer attitudes and lifestyle, many processors have developed new products as home

    meal replacements and component meals. In essence, the preparation time is shortened for

    the consumer by preparing the meal at the processing plant.

    Pre-prepared meat items have been available for years, including frozen dinners, sand-

    wiches, pot pies, as mentioned previously. Today, frozen or refrigerated sandwiches arepopular items in many institutional settings and can even be found in convenience vending

    machines. However, in many cases these items tended to lack consumer appeal, which

    prompted meat processors to develop new processing strategies. The first of the renewed

    generation of these products were home meal replacements that emerged a few years ago.

    This concept, similar to frozen dinners, provides all the components of the meal ready for

    the table. Everything, including the meat, vegetables, and other items, are included in the

    package (Fig. 6). The consumer only needs to cook the items or in some cases just reheat in

    a conventional oven or microwave. Although these products have filled a niche, consumers

    are still looking for other options with greater flexibility. This has led to the development ofso-called component meals. These meals allow for an entree, and sometimes a side dish, to

    be prepared at the processing plant and packaged for refrigeration storage until reheated by

    the consumer. This allows even greater flexibility by the consumer to add variety to the meal

    at their own discretion. The sale of prepared refrigerated meals has gained wide popularity

    and is becoming a substantial market force with both the beef and pork industry.

    Another group of prepared products that are gaining sizable market share are battered

    and breaded meats. These types of products (long perfected by the poultry and seafood seg-

    ments of the muscle foods processing industry) are becoming more commonplace in both

    the retail and the food service segments of the marketplace. Technologically, breading con-

    Figure 6 Prepared meat items: home meal replacement (left) and injected pork roast (right).

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    sists of three major steps: predustingapplying a finely ground flour and seasoning mix-

    ture to the raw meat; batteringapplying a flour/seasoning batter of specific consistency

    to the predusted meat; and breadingapplying a flour mixture with a coarser crumb tex-

    ture. Not all three steps may be required, depending on the specific products. Sometimes,

    the raw meat is marinated in water and phosphate solutions before predusting to pick up

    moisture for improved palatability and product yield. The breaded meat can be fried for afew seconds (raw) or up to a few minutes (fully cooked) to help the batter adhere to the

    meat, and the final product is either frozen or refrigerated before marketing.

    Breaded meats are of great interest to the meat industry partly due to profit margins

    available with these items induced by a lower input cost per unit. In addition, this process

    allows for creation of greater product variety. Whether the product is restructured or is

    made from whole muscle, the addition of up to 30% breading allows the processor to meet

    the consumer demand for convenient products while also targeting both the retail and food

    service industries. Many of these products are now being used or evaluated as finger

    foods or appetizers.Another type of product that has gained widespread acceptance is that of enhanced

    products. In essence, these are fresh whole muscle products, both beef and pork, that have

    been subjected to injection or marination to improve sensory acceptability (Fig. 6).These

    products normally are injected with a combination of water, salt, and phosphate with the

    addition of seasoning or flavoring if an ethnic flavor profile is desired. In most cases, the

    products have an addition of less than 10% added ingredients (which are labeled as x% so-

    lution containing ....). This process not only allows the processor to improve the economic

    viability of many lower value meats but also enhances consumer acceptance by reducing

    dissatisfaction with the product that may result from the use of less palatable raw materialsor consumer abuse due to overcooking.

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