Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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outlined, may be removed during the holding period.

Packaging assists in preventing weight loss, freezer

burn, and the onset of rancidity. (See Freezing: Stor-

age of Frozen Foods.)

Refrigerated Transport

0011 In theory there should be few problems in the storage

or transport of chilled or frozen products, especially

in the case of meat or meat-based products, since:

0012 Cooling, chilling and, where applicable, freezing

and tempering have been completed so that re-

frigerated transport equipment has merely to insu-

late the product from sources of ambient heat

0013 The product is insulated by primary and second-

ary packaging

0014 There is no respiratory heat load such as occurs

with some fruits and vegetables.

Retail Display

0015 With the introduction of the European Community

(EC) Food Hygiene Regulations, the temperature of

chilled foods in the EC has to be kept at or below



C. This requires much more stringent control than

bulk storage since the displayed products have to be

accessible and hence are potentially exposed to a

warm atmosphere. A high intensity of lighting can

lead to a further rise in temperature due to a ‘green-

house’ effect inside transparent packaging.

0016 Similar conditions apply to frozen foods, but these

are more likely to be cartoned in opaque material

with entrapped air, which acts as an insulator. It is

also a fact that it is much more difficult to check and

hence legislate on the temperature of frozen foods.

Domestic Storage

0017 As with retail display cabinets, domestic refrigerators

have minimal reserve capacity for chilling, freezing,

or tempering. Therefore the addition of substantial

amounts of a product which is above the set storage

temperature will affect that of the existing contents.

An awareness of the necessity to maintain the cold

chain from the retailer to domestic refrigerator is

paramount. While it has been demonstrated that

meat which has been repeatedly frozen and thawed

under controlled conditions suffers minimal deterior-

ation, such a practice cannot be recommended wher-

ever precise control cannot be guaranteed.

Refrigeration Plant Selection

0018 The first priority in plant selection is to quantify the

refrigeration duty. To do so requires a knowledge of

the thermal properties of the product under consider-

ation, such as: (1) initial and final temperatures; (2)

heat capacity above and below freezing; (3) latent

heat of freezing; and (4) effective chilling or freezing

time between specified initial and final temperatures.

(See Freezing: Operations.)

0019Recognition has to be taken of the fact that the

maximum rate of product heat output (which occurs

in the early stage of chilling or freezing) may be two

or three times the average. To the load is added the

heat due to: (1) leakage through insulation into the

refrigerated space; (2) leakage of ambient air through

door openings; (3) electrical input such as lights, fans,

or fork-lift trucks; (4) metabolic heat from personnel.

0020Having estimated the total refrigeration load, a

decision is taken on the type of refrigeration equip-

ment to be installed. In the majority of cases this will

be mechanical refrigeration using ammonia or a

fluorocarbon as the refrigerant. Where production is

seasonal, it may be more economical to use an ex-

pendable refrigerant such as liquid nitrogen or carbon

dioxide.

Moisture Control

0021Freezing per se is an effective means of preservation as

it makes moisture unavailable for microbial growth

by its conversion to ice. However, other means of

moisture control have been devised that enable prod-

ucts to be stored at temperatures above the freezing

point of water. These include curing, several methods

of dehydration, including freeze-drying, intermediate-

moisture technology, and high-pressure processing.

Curing

0022Salting as a means of meat preservation has been

practiced for 3000 years and contamination of salt

by potassium nitrate probably led to the development

of modern cured meats, since it led to characteristic

and acceptable effects on color and flavor. Thus, al-

though heavily salted products are not now available,

having been supplanted by more acceptable preserva-

tion procedures, cured pork and to some extent

poultry, beef, and fish products have established

niches in the marketplace, though the relatively low

levels of salt now present (usually < 4%) are more for

flavor than preservation.

0023To cure meat, salt (sodium chloride) and nitrite

must be present and other ingredients may be used

during processing to accelerate curing, stabilize color

(e.g., ascorbic acid), modify flavor (e.g., sugars) and

texture, and reduce shrinkage (e.g., polyphosphates).

0024Several methods may be used to incorporate

the curing ingredients into the meat, the object being

to achieve uniform distribution. In comminuted

3774 MEAT/Preservation

products, such as sausages, the cure ingredients (in

the dry form or as a concentrated solution) are in-

corporated into the product during mixing or com-

minution.

0025 For whole sides or muscles the oldest technique is

dry-curing. Here, the dry-curing agents (salts) were

rubbed over the surface of the meat, the meat then

being placed on a shelf or in a box to cure. For large

muscles or cuts the process needed to be repeated

several times and it may have taken up to 80 days to

get uniform distribution in, for example, the top of

the hind leg.

0026 Another method which is still practiced for a few

specialty products involves immersing the cuts or

sides in concentrated brine, usually at 3–7



C, and

allowing the brine slowly to diffuse through the

meat. This method is also very time-consuming and

care must be taken to insure microbial spoilage does

not occur during curing.

0027 The curing procedure can be considerably shortened

by injection of brine into the meat to achieve

rapid, uniform distribution. Three such methods are:

(1) artery pumping, in which brine is pumped directly

into the intact vascular system; (2) stitch pumping, in

which brine is injected (through a hollow needle) into

various parts of the meat, especially the thickest parts

and those near to joints; and (3) multiple injection, in

which brine is injected simultaneously and automatic-

ally through a series of hollow needles which have a

number of evenly spaced holes along their length.

Another modern method is the ‘tumbling’ or ‘massa-

ging’ of meat pieces in rotating drums. In the presence

of about 0–6% of their weight of salt the physical

interactions of the meat pieces draw out salt-soluble

protein which, on subsequent heating, gels to bind the

pieces together in ‘reformed’ hams. Tumbling can

shorten the curing period to 24 h or less. Tumbling

may be carried out under vacuum to eliminate prob-

lems caused by dissolved air.

0028 A typical traditional brine contains 25–30%

sodium chloride and 3–4% sodium or potassium

nitrate and specific salt-tolerant bacteria capable

of reducing the nitrate to nitrite. In modern cures,

nitrite may be added directly at a concentration of

200 p.p.m. or less. In most countries there are strict

limits on the level of nitrite permitted in meats (usu-

ally 200 p.p.m.) and addition of nitrite directly, rather

than relying on nitrate reduction in situ, insures such

limits are not breached.

Dehydration

0029 That dehydration can preserve meat has been known

for over 5000 years and simple drying procedures are

still used today in some parts of the world. In these

processes, strips of lean meat are exposed to the sun,

e.g. pemmican manufactured by North American

Indians, or a combination of light salting and drying

is used as in the preparation of charqui (South

America) or biltong (South Africa). (See Drying:

Theory of Air-drying; Drying: Drying Using Natural

Radiation.)

0030Hot-air drying has been used in the past to prepare

dehydrated meat for the armed forces, but has not

been manufactured successfully for domestic con-

sumption. Due to case hardening, raw meat cannot

be successfully dehydrated and the need for a high

surface-area-to-volume ratio has limited its use to

cooked, minced meat. A typical procedure involves

cooking the meat in thin slices, mincing (0.3–0.8 cm

in diameter) and drying under controlled conditions.

The temperatures that can be tolerated without caus-

ing unacceptable damage to the meat depend on both

the residual water and fat contents. A typical regime

that lowers the moisture content to about 5% in

about 5 h involves an air speed of 3 m s

1

, a tempera-

ture of 60



C, a relative humidity of 40%, and a tray

loading of about 10 kg m

2

. Vacuum drying has been

unsuccessfully tried to improve the quality of dehy-

drated meat. A successful technique for both raw and

cooked meat is freeze dehydration. In this process the

product remains frozen throughout the drying cycle

and thus the water (ice) is sublimed from the meat. At

a vacuum pressure of 1.0–1.5 mmHg, temperatures

up to 43



C can be tolerated with no thawing. The

rate of freeze-drying is limited by the rate of heat

transfer to the product for sublimation and several

methods have been developed to increase the rate,

including the use of microwave or radiant (infrared)

energy. Freeze-drying is an expensive processing pro-

cedure and freeze-dried meats (containing about 2%

moisture) are usually only used in such foods as dehy-

drated soup mixes and specialty products for

campers, the military, and space agencies. (See Freeze-

drying: The Basic Process.)

0031Dehydrated meats need to be rehydrated prior to

consumption and, to address this step, with all its

attendant problems, and evolve a technology suitable

for developing countries, intermediate-moisture meats

have been formulated. With intermediate-moisture

foods the object is to lower the water activity to a

level at which bacteria will not grow, but without

lowering the water content to a point where the

product becomes unpalatable. This involves mixing

the meat with suitable humectants, such as sugars,

salts, polyols, and amino acids, to lower the water

activity to about 0.85 whilst keeping the moisture

content at 20–50%. Under these conditions bacteria

will be inhibited, but molds and yeasts may prolifer-

ate and thus an antimycotic such as sorbate or

propionate is often incorporated at a concentration

MEAT/Preservation 3775

of 0.1–0.3%. (See Intermediate-moisture Foods;

Water Activity.)

0032 For minced products, such as semimoist pet foods

and Chinese pork, the equilibration is easily achieved

by batch-mixing. In the production of semimoist pet

food, the mixture is subsequently shaped and formed

in a cooker-extruder. For whole meats two techniques

are available: (1) desorption processing, in which the

meat pieces are soaked in an infusing solution of high

osmotic pressure so that, after equilibration, the meat

has the desired water activity (equilibration is nor-

mally aided by heating, which has the additional

benefit of inactivating enzymes); and (2) absorption

processing, in which freeze-dried meat is equilibrated

with the infusing solution to the appropriate water

activity. Though this latter method allows close con-

trol of water activity, the cost is prohibitive for all but

the most specialized uses (e.g., space flights).

Other Preservation Techniques

0033 Although temperature reduction and moisture con-

trol are the most commercially important methods of

meat preservation, other techniques may have im-

portant niches in the marketplace. For example, fer-

mented meat products, in which specific bacteria,

such as selected Lactobacillus strains, are encouraged

to grow and reduce the pH of the meat to levels

inhibitory to the growth of spoilage organisms, are

well established in many parts of the world. This

technology is often combined with partial dehydra-

tion to enhance shelf-life. Though not commonly

made in the UK, European varieties include French

saucisson sec, German Dauerwurst and Rohwurst

and Italian crudi stagionati. In modern processes a

starter culture is used to initiate two fermentations –

the conversion of nitrate to nitrite (by micrococci)

and of carbohydrates to lactic acid by lactobacilli.

Fermentation ceases after 3–7 days under high (e.g.,



C) temperatures and humidities (e.g., 95%). The

product is then dried at lower temperatures and hu-

midities to moisture contents in the range 30–35%.

This takes several weeks (usually 3–7) and the prod-

uct is then matured for several months. The combin-

ation of low pH (about 4.5), lactic acid, low water

activity, and residual nitrite gives a shelf-life from

6 months to over 2 years, provided the whole process

has been controlled and managed correctly. (See

Lactic Acid Bacteria.)

0034 The use of chemical preservatives in meat is

not widely practiced (except for cured/fermented

products), but sulfur dioxide is permitted in some

countries for certain products. Thus ‘English’-style

sausages may contain up to 450 p.p.m. of this com-

pound, usually added in the form of a salt such as

metabisulfite.

0035High-temperature preservation (canning) of meat

and meat products is also well established and, al-

though certain cured products may only require a

pasteurization regime, others are heated under the

more severe regimes necessary for low-acid foods.

(See Canning: Principles.)

0036In the 1940s, ionizing radiation was advocated as

a method of meat preservation and after very exten-

sive trials it was permitted in most countries under

certain conditions. Thus, in 1991 in the EC pas-

teurizing doses of g-rays up to 5 kGy were permitted

for poultry. (See Irradiation of Foods: Basic Prin-

ciples; Legal and Consumer Aspects.) More recently,

high pressures ( 400 MPa) have been used to extend

the shelf-life of cured meats. However, this technol-

ogy has less potential for uncured products, although

the technology is developing rapidly.

Chemical, Physical, and Microbiological

Implications of Preservation

Chilling and Freezing

0037The physical dimensions of postrigor meat are un-

affected by both chilling and freezing but fluid (drip)

is exuded from both chilled and frozen products. The

amount expressed is far greater in frozen-thawed

meat and some evidence suggests the amount in-

creases as the freezing rate decreases.

0038In frozen meat, bacterial growth usually ceases,

but yeasts and molds may continue to grow down

to about 5



C. In chilled meat, psychrotrophic

bacteria become the dominant species, mainly

Pseudomonas, Achromobacter, Micrococcus, Lacto-

bacillus, Streptococcus, Leuconostoc, Pediococcus,

Flavobacterium, and Proteus spp. Of these, during

storage in air, Pseudomonas spp. are the most import-

ant since they give rise to slime and off-odor forma-

tion at levels of 10

–10

2

. The time for this to

occur depends on several factors (especially tempera-

ture, relative humidity, and initial load) but meat kept

in retail packs at a relative humidity of 99.3% usually

spoils after 5–10 days at 1



C. If meat is stored under

elevated levels of carbon dioxide the growth of Pseu-

domonas spp. is inhibited and Lactobacillus spp.

become dominant. Such meat can be kept for several

weeks at chill temperatures with little evidence of

spoilage.

0039Chemical changes take place during storage of

fresh meat and some, such as those due to enzymatic

proteolysis, may be favorable, leading as they do

to increased tenderness. The major deteriorative

changes are oxidative in nature, leading to the forma-

tion of the undesirable brown methemoproteins and

rancidity. The formation of methemoproteins is

3776 MEAT/Preservation

important in both chilled and frozen meat but

lipid oxidation leading to rancidity is usually only

important in frozen meats. This oxidation is respon-

sible for recommending maximum shelf-lives of 4

months for pork and poultry and 6 months for beef

and lamb at 18



C. (See Oxidation of Food Com-

ponents.)

Cured Products

0040 Nitrite is essential for the development of the pink-

red color of cured meats and has the further import-

ant attribute of being a very effective inhibitor of

Clostridium botulinum. The pink-red color is due to

nitric oxide, from nitrite, binding to the iron atom

of hemoprotein (myoglobin and hemoglobin) at the

sixth coordination site; there is still controversy

regarding the mechanism involved in the formation

of this nitrosyl pigment. In the presence of light and

oxygen (air), nitric oxide can be liberated from the

hematin and the color fades as the oxidized methe-

moprotein forms. Thus, cured meats should be stored

in the absence of oxygen and/or light if an extended

shelf-life is required. Although cured meats are eaten

uncooked (e.g., Parma Iberian ham), many are cooked

prior to consumption, either by the consumer, e.g.,

bacon, or by the manufacturer to be sold as cooked,

ready-to-eat meats (e.g., boiled or roast ham). The red

pigment formed on heating is relatively stable in the

presence of light and oxygen and is believed to be a

complex of free hematin and either one (pentacoordi-

nated) or, less likely, two (hexacoordinated) mol-

ecules of nitric oxide.

Dehydrated Meats

0041 Hot-air-dried meats are invariably shriveled and

are virtually impossible to rehydrate to typical ‘full-

moisture’ products. Freeze-dried meats retain the

shape and color of the original meat pieces and the

porous structure does rehydrate more satisfactorily

than hot-air-dried products. Intermediate-moisture

meats have the physical characteristics of their fresh-

meat counterparts.

0042 Unless partial rehydration inadvertently occurs,

dehydrated meats are not susceptible to microbial

spoilage and can be kept for several weeks at elevated

temperatures. The factors limiting their shelf-life

are chemical in nature, mainly lipid (or sorbate)

oxidation, and/or nonenzymatic browning. With

freeze-dried meats, nonenzymatic browning involv-

ing glucose and glucose-6-phosphate (with protein)

occurs, as also, in the presence of oxygen, does oxi-

dation of the hemoproteins to yellow bile pigments.

Some fat oxidation due to residual lipolytic activity

may also occur. In intermediate-moisture meats,

browning involving reactions between sorbate or

lipid oxidation products and protein occurs, as also

does oxidation of the hemoproteins. However, a re-

action occurring in intermediate-moisture meats, but

not fully dried meats, is hydrolytic degradation of

collagen. Anaerobic storage of intermediate-moisture

meats inhibits all these reactions, except for the

breakdown (hydrolysis) of collagen. (See Browning:

Nonenzymatic.)

See also: Drying: Theory of Air-drying; Drying Using

Natural Radiation; Freeze-drying: The Basic Process;

Freezing: Principles; Operations; Storage of Frozen

Foods; Irradiation of Foods: Basic Principles; Legal and

Consumer Aspects; Lactic Acid Bacteria; Legislation:

Additives; Oxidation of Food Components;

Preservation of Food; Spoilage: Chemical and

Enzymatic Spoilage; Bacterial Spoilage; Molds in

Spoilage; Yeasts in Spoilage

Further Reading

Diestre A and Monfort JM (1998) Meat Science, 49, sup-

plementary issue.

Lawrie RA (1998) Lawrie’s Meat Science, 6th edn. Cam-

bridge: Woodhead.

Ledward DA (1981) Intermediate moisture meats. In:

Lawrie RA (ed.) Development in Meat Science, vol. 2,

pp. 159–194. London: Applied Science.

Ledward DA (1998) High pressure processing of meat and

fish. In: Autio K (ed.) Fresh Novel Foods by High Pres-

sure, pp. 165–175. Helsinki, Finland: VTT Biotechnol-

ogy & Food Research.

Ranken MD (2000) Handbook of Meat Product Technol-

ogy. Oxford: Blackwell Science.

Wilson NRP (1981) Meat and Meat Products – Factors

Affecting Quality Control, pp. 138–163. London:

Applied Science.

Eating Quality

I Lebert, S Rousset, A Lebert and R Talon, National

Institute of Agronomic Research, France

Background

0001Meat eating quality refers to microbiological safety,

shelf-life, sensory properties, nutritive values, and

healthiness. Safety is the priority, but sensory qualities

must also satisfy the consumer. The acceptability of

the final product is often influenced by the pro-

cessing of the raw material. The hygienic and sensory

MEAT/Eating Quality 3777

qualities (texture, juiciness, flavor, and color) are par-

ticularly important. The control of the quality must

therefore be implemented from the entry of the live

animal into the meat chain. Initial carcass chilling is

particularly important, and its effects on beef quality

are listed in Table 1.

0002 Consumers are becoming more sensitive to issues

of safety, hygienic, and sensory qualities, and these

issues are discussed in this article.

Microbiology of Meat

0003 The microbiological quality of meat carcasses is

highly dependent on the processing conditions: most

important are the temperature and time of storage

and distribution, which largely determine the number

and spread of contamination during slaughter and

processing (Figure 1).

0004 During slaughter and dressing, the three major

sources of contamination are: (1) the skin of the

animal, which is mainly contaminated by spoilage

flora such as staphylococci, micrococci, pseudomo-

nads, yeasts, and molds; (2) fecal contamination

during evisceration, which, if little care is taken,

could happen by bursting of the intestinal tract; then

Salmonella, Escherichia coli, enterococci, and Clos-

tridium perfringens can be detected in meat; (3)

contamination by direct contact or cross-contamin-

ation between dirty and clean surfaces. Staphylococci

are the main concern, since they are widely distrib-

uted, and contamination may arise from both animal

and human sources. Airborne particles and aerosols

also contribute to the dissemination of microor-

ganisms.

0005 Under good hygienic conditions, dressed carcasses

may have typical surface aerobic bacterial counts of

–10

2

for beef, 10

–10

bacteria cm

2

for

sheep, and 10

–10

bacteria cm

2

for pig carcasses.

0006 Once the temperature at the surface of the carcass

has fallen below 10



C, growth of mesophilic bacteria

no longer occurs, and a psychrotrophic flora (Pseudo-

monas, Acinetobacter, Psychrobacter, Lactobacillus,

Brochothrix thermosphacta, Shewanella putrefaciens,

some genera in the family Enterobacteriaceae)

gradually displaces the micrococci and coliforms,

which are commonly found on freshly dressed

carcasses.

0007Two bacterial flora can be found on meat products:

a pathogenic flora (Salmonella spp., Clostridium

spp., Yersinia enterocolitica, Staphylococcus aureus,

Listeria monocytogenes) that causes foodborne dis-

eases and a spoilage flora (Pseudomonas spp., lacto-

bacilli, staphylococci, micrococci, B. thermosphacta)

that limits the storage of the product.

Pathogenic Flora

0008Epidemiology Public health authorities need to be

informed about the nature and magnitude of food-

borne illnesses and their epidemiology for the early

detection of outbreaks, planning, evaluation of any

disease, and policy implementation. Foodborne dis-

ease cases are significantly underestimated because of

the weakness in foodborne disease surveillance and of

the variation in reporting systems between countries.

As a consequence, it has been estimated that the

reported incidence of foodborne diseases represents

less than 10%, perhaps even less than 1%, of the

actual incidence.

0009Foodborne outbreaks occur in most, if not all,

countries (Table 2). Salmonella spp. cause 84.5% of

all outbreaks (Salmonella enteritidis, 50.9%); S. aur-

eus, 3.5%; Clostridium botulinum, 1.1%; Bacillus

cereus, 1.0%; and unknown agents, 9.5%. Sporadic

cases have been associated with Escherichia coli,

Campylobacter jejuni, L. monocytogenes, Y. entero-

colitica, Aeromonas hydrophila, Shigella, Vibrio

parahaemolyticus. The main factors affecting the

growth of these pathogenic bacteria are the tempera-

ture, pH, and water activity (Table 3).

0010The most frequently identified foods associated

with outbreaks are eggs and egg products (25.4%),

meat and meat products (23.4%), and confectionery,

cakes, pastries, puddings, desserts, and icecream

(17%). Fish and shellfish, milk and dairy products,

and poultry and poultry products were each impli-

cated in less than 5% of the outbreaks.

0011Main pathogenic bacteria As mentioned above, Sal-

monella spp. cause 84.5% of all outbreaks, and many

foods of animal origin, particularly beef and pork,

have often been identified as vehicles in outbreaks

of salmonellosis. Salmonella are transferred to meat

surfaces from the intestinal contents and from feces

contaminating hair, skin, and feet of animals. Consid-

erable contamination of pig carcasses occurs during

scalding and dehairing. Later, bacteria can be trans-

ferred from carcass to carcass and from contaminated

carcasses to knives, work surfaces, and the hands of

meat handlers. Minced pork and sausages, as well as

tbl0001 Table 1 Beef chilling: effect of increasing time, temperature,

air velocity, and humidity on quality

Time Temperature Air velocity Humidity

Microbiological quality  þ 

Tenderness þþ 00

Appearance   þ

Weight loss þþ þ 

þ, increase; , decrease; 0, no effect.

3778 MEAT/Eating Quality

PigCattle, sheep

Other animals carrying

pathogenic organisms

Feed

Contaminated

environment

Points with little contamination

Points with serious contamination

CCP1 Effective control point

CCP2 Not effectively controllable

Listeria

Salmonella

Clostridium perfringens

Staphylococccus aureus

group D Streptococci

Yersinia enterocolitica

Staphylococci

Micrococci

Pseudomonas

Moulds

Pseudomonas

Psychrobacter

Lactobacillus

Brochothrix thermosphacta

Shewanella putrefaciens

Psychrotrophic enterobacteria

Food-borne pathogens

Yeasts

Spoilage microorganisms

Moulds

Yeasts

Farm animal

Slaughter

Transport

Lairage

CCP2

Washing

Eviscerating

Dehiding

CCP2

Scalding

Flaming

Polishing

Dehairing

Eviscerating

CCP2

Chilling

Packaging

Cutting and Deboning

Transport

CCP1

CCP2

Acinetobacter

fig0001 Figure 1 Causes of contamination from live animal to store.

tbl0002 Table 2 Cases of foodborne diseases in 1997 and 1998

Date Locations Numberof cases Bacteria Associated foods

1997 Australia 650 (three deaths) Salmonella Different food in many foodborne outbreaks

Russia 12 (one death) C. botulinum Fish

Finland 200 Salmonella Pig

USA 745 (one death) Salmonella Stuffed ham

1998 Argentina 9 C. botulinum Matambre (meat specialty from Argentina)

Japan 1142 Salmonella Unknown origin

USA 316 V. parahaemolyticus Oysters

Algeria 1400 (17 deaths) C. botulinum Spoiled chicken

USA 100 (20 deaths) L. monocytogenes Hot dogs

USA 165 Shigella Interhuman?

Canada 130 Salmonella Turkey meat

France 300 Salmonella Egg/egg product 52%, meat/meat product/chicken 24%,

other foods 24%

France 68 C. perfringens meat/meat product/chicken 40%, other foods 60%

France 155 S. aureus Meat/meat product/chicken 15%, milk/milk product 24%,

other foods 61%

France 139 Unidentified Meat/meat product/chicken 14%, other foods 86%

MEAT/Eating Quality 3779

inadequately cooked meat, are frequently implicated

in salmonellosis. Salmonella are widespread in

poultry, especially turkey and chicken carcasses, and

are transferred to the meat from the intestinal tract or

from fecal material on feet and feathers. Cross-

contamination is a particular problem in which the

critical steps include defeathering, evisceration, and

chilling. The major recent change in the epidemiology

of Salmonella concerns the emergence of S. enteritidis

and S. typhimurium. These bacteria, first studied in

the USA and UK, are now reported in many industri-

alized countries. The factors that may contribute to

their emergence are the microbial adaptation and

dissemination of the pathogen through increasing

global distribution of food and international travel,

the increasing susceptible populations as well as life-

style changes leading to an increase in food-service

establishments and food outlets combined with

inadequate knowledge of food-handling.

0012 S. aureus is ubiquitous and occurs on the skin of

most warm-blooded animals, including all food

animals. The organism is resistant to drying and

may colonize food-processing equipment that may

be wet and difficult to clean. Meat and meat products

are frequently incriminated in staphylococcal food

poisoning, but cases have arisen in egg products,

sandwich fillings, milk, and dairy products. Foods

that require considerable handling during prepar-

ation and that are kept at slightly elevated tempera-

tures after preparation (20–40



C) are frequently

involved in staphylococcal food poisoning. Human

intoxication is caused by ingesting the enterotoxins

produced in the food by some strains of S. aureus,

usually because the food has not been kept hot

enough (60



C or above) or cold enough (7.2



Cor

below). The toxin is a highly heat-stable protein. The

toxin is produced when S. aureus populations exceed

per gram. A toxin dose of about 1.0 mm produces

symptoms of intoxication.

0013The incidence of C. botulinum in meats appears to

be low, but its presence has been demonstrated in

sufficient large surveys of pork. Botulism in man

results most often from eating improperly stored

foods in which C. botulinum has multiplied and pro-

duced toxin.

0014C. perfringens is part of the normal flora of the

intestinal tract of animals, including man, and is

found in a large variety of foods. In raw meat, a few

vegetative cells may be found deep in muscle tissue

after slaughter, and more cells are found in meat from

fatigued animals. The presence of spores on the sur-

face of recently slaughtered carcasses is the result of

fecal contamination. Care is needed with foods made

of several ingredients such as meat pies, cooked

meats, and poultry products, because spores may

survive cooking.

0015Other pathogenic bacteria causing sporadic cases

Undercooked or raw ground beef has been implicated

in nearly all documented outbreaks of E. coli

O157:H7 and in other sporadic cases. E. coli is a

normal inhabitant of the intestine of all animals, in-

cluding humans. Currently, there are four recognized

classes of enterovirulent E. coli that cause gastroen-

teritis in humans. The enterohemorrhagic strain, des-

ignated E. coli serotype O157:H7, is a rare variety of

E. coli that produces large quantities of one or two

toxins that cause severe damage to the lining of the

intestine. These toxins are closely related to the toxin

produced by Shigella dysenteriae.

0016C. jejuni frequently contaminates raw chicken.

Surveys show that 20–100% of retail chickens are

contaminated. This is not entirely surprising, since

many healthy chickens have these bacteria in their

intestinal tracts. Raw milk is also a source of infec-

tions. The bacteria are often carried by healthy cattle

and by flies on farms. However, properly cooking

chicken or pasteurizing milk kills the bacteria. Cam-

pylobacters can be isolated from freshly slaughtered

red-meat carcasses, but in smaller numbers than on

poultry. This bacterium is recognized as an important

enteric pathogen. Recent surveys have shown that

C. jejuni is the leading cause of bacterial diarrhea in

the USA, causing more illness than Shigella spp. and

Salmonella spp. combined.

0017L. monocytogenes has been associated with foods

such as raw milk, cheeses (particularly soft-ripened

varieties), raw vegetables, but also fermented raw-

meat sausages, raw and cooked poultry, all types of

tbl0003 Table 3 Minimal and maximal temperature (T), pH and water

activity (a

) values for the growth of some pathogenic bacteria

(ICMSF, 1996)

Organisms T (



C) pH a

Bacillus cereus 4–55 5–8.8 >0.93

Vibrio parahaemolyticus 5–43 4.8–11 >0.94

Escherichia coli 7–45 4.4–9.0 >0.95

Campylobacter jejuni 32–45 4.9–9 >0.987

Yersinia enterocolitica 1–42 4.2–9;6 >0.97

Listeria monocytogenes 0–45 4.4–9.4 >0.92

Aeromonas hydrophila 0–45 4.5–NR >0.97

Salmonella spp. 5.2–46.2 3.8–9.5 >0.94

Shigella spp. 7.9–45 5–9.2 >0.978

Staphylococcus aureus 7–48 4–10 >0.83

Clostridium perfringens 12–50 5.5–9 >0.93

Clostridium botulinum

A & B 10–50 4.7–9 >0.93

Non proteolytic, C & D 5–NR 4.7–9 >0.95

E 3.3–15–30 4.7–9 >0.97

F 4–NR 4.7–9 >0.95

NR: not reported.

3780 MEAT/Eating Quality

raw meats, and raw and smoked fish. Its ability to

grow at temperatures as low as 3



C permits multipli-

cation in refrigerated foods. The contamination of

meat and meat products can be due to fecal contamin-

ation during slaughter, presence on clean and unclean

sections in slaughterhouses, and contaminated

ground and processed meats: 10–80% of contamin-

ated samples contain less than 10–100 CFU g

1

L. monocytogenes is a ubiquitous bacteria found in

soil, silage, and other environmental sources, and is

present in the intestines of 1–10% of humans.

L. monocytogenes is quite hardy and resists the dele-

terious effects of freezing, drying, and heat.

0018 Y. enterocolitica has been recovered from a wide

variety of animals, foods, and water. Pigs seem to be

the principal reservoir of bioserotypes pathogenic to

humans, but the exact cause of the food contamin-

ation is unknown.

0019 Aeromonas spp. are ubiquitous and are also asso-

ciated with foods of animal origin (raw meats,

poultry, and milk). A. hydrophila grows rapidly in a

refrigerated environment and can increase its number

10–1000-fold in meat and fish samples over 1 week of

refrigerated storage.

0020 Among several environments (Table 4), the home is

where the pathogens are frequently identified (13%),

with 46% of the outbreaks occurring in people eating

at home largely due to mishandling of food products

(Table 4). The consumer must take care when hand-

ling food at home, and recommendations have been

given by The National Advisory Committee on

Microbiological Criteria for Foods to prevent the

contamination of food products by foodborne patho-

gens (Table 5).

Spoilage Flora

0021Without exception, there is a loss in microbial quality

in meat products following slaughter and manufac-

ture (Table 6). Microorganisms cause deterioration in

appearance, texture, flavor, odor, or safety of the

product. The first detectable sign of spoilage is usu-

ally an off-odor, which is slightly sour or putrid. The

odors are caused by bacterial metabolic end products,

as they accumulate, the color of meat may change to a

gray or green color, while the texture changes due to

the destruction of proteins and lipids. Spoilage may

occur slowly in the refrigerator and more rapidly at

higher temperatures.

0022On meat held under aerobic conditions, spoilage is

often related to the growth of Pseudomonas and

occurs when the Pseudomonas counts exceed about

CFU cm

2

. Because of their psychotrophic char-

acteristics, Pseudomonas species have a marked ad-

vantage in growth rate compared with other genera,

and this advantage tends to increase with decreasing

temperature. Pseudomonas is less tolerant to reduced

water activity than lactobacilli and B. thermosphacta,

so these organisms may become dominant in the drier

parts of the carcass. Acinetobacter may become

dominant in high pH meat.

0023Vacuum packaging is used to prolong the storage

life of fresh meat (for 21–28 days at 0–1



C) and

tbl0004 Table 4 Results of foodborne disease surveillance

Place of contamination or mishandling Identified outbreaks when

people eat foodproducts

Factors contributing to outbreaks

Entering the food chain at the farm (50%) Homes (46%) Temperature abuse, inadequate cooling, and

improper cooking (44%)Restaurants/hotels (15%)

Mishandling Catered events (8%) Contaminated or toxic raw products (16%)

Restaurants (22%) Medical-care facilities (6%) Contamination by personnel or equipment (15%)

Homes (13%) Canteens (6%) Lack of hygiene in processing, preparing, and

handling (10%)

Catering establishments (7%) Schools (5%) Cross-contamination (4%)

tbl0005 Table 5 Recommendations of safe food preparation

Wash hands and utensils before handling food, especially after handling raw foods

Reheat all foods thoroughly (above an internal temperature of 74



Keep hot food hot (above 63



Keep cold foods cold (below 4



Thoroughly cook meat, poultry, and seafood, and adequately heat frozen or refrigerated foods

Chill foods rapidly in shallow containers

Keep raw and cooked foods separate, especially when shopping, preparing, cooking, and storing these products

Wrap and cover foods in the refrigerator

Keep the refrigerator temperature between 1 and 4



MEAT/Eating Quality 3781

restricts the growth of Pseudomonas so that Lacto-

bacillus or B. thermosphacta becomes the dominant

flora. In most cases, Lactobacillus can grow more

rapidly than B. thermosphacta, but B. thermosphacta

dominates in fatty meat with a high pH.

0024 The deterioration of the food occurs progressively

during the storage and results from the activity of

the microorganism in the food. To avoid these

changes, preservative techniques can be applied to

inactivate the microorganism: by heat or irradiation;

and to inhibit growth: by chilling or freezing, drying,

curing with salt, vacuum or gas packaging, acidifying,

or by adding preservatives. Consequently, in dried

cured meat product, the pathogenic and spoilage

flora are inhibited by drying and salting, whereas

in dried sausage, the main inhibiting factors are

drying and acidification. Eventually, the cumulative

effects of the changes reach a point of consumer

rejection due to unacceptable quality expectations

and perception.

Acceptability and Sensory Properties of

Meat

0025 In order to determine the characteristics of food prod-

ucts and their acceptability, food manufacturers need

two kinds of information: how much people like their

products overall and the sensory characteristics of

the products. Hedonic liking tests are carried out

by consumer panels and usually ask a question of

overall acceptability and ask for comments about

the characteristics which consumers like or dislike.

At least 60 consumers are generally included in such

surveys because of the large range of their hedonic

responses. Retailed sensory characteristics are not

asked of consumers because they usually use only a

limited vocabulary to describe the food. Qualitative

and quantitative sensory descriptions are reserved for

a trained panel composed of 12 assessors. Their work

is to generate sensory attributes, to give accurate

definition of these terms, and to assess the intensity

of each attribute for each product. Sensory and he-

donic guidelines which are reviewed regularly and

published by standards organizations include: ISO

(International Organization for Standardization),

AFNOR (Association Franc¸aise de Normalisation),

AMSA (American Meat Science Association), DIN

(Deutsches Institut fu

r Normung), BSI (British Stand-

ards Institution), UNI (Ente Nazionale Italiano di

Unificazione), AENOR (Asociacio

n Espan

ola de

Normalizacio

n y Certificacio

n), and ASTM (Ameri-

can Society for Testing and Materials). Data are ana-

lyzed using multivariate statistical techniques, such as

preference mapping, which are used to relate sensory

and acceptability data in order to understand the

acceptance or rejection criteria.

Factors Affecting Consumer Acceptability for Meat

0026Many experiments have shown that acceptability

varies widely among consumers. A large number of

factors can influence meat acceptability (Table 7),

which is related to the product sensory characteris-

tics: flavor, toughness, and appearance. For most

consumers, food flavor seems to be the most import-

ant acceptability criterion before texture and appear-

ance. However, in beef, tenderness is probably the

most studied characteristic because its variation is

wider than that in flavor. If beef is tough, other sens-

ory properties become less important, and as meat

tenderness increases, the overall acceptability to the

consumer generally increases. For beef, tenderness is

a major criterion of acceptability and toughness a

criterion of reject. However, for poultry, firm meat

may be preferred. Appreciation of the right level of

tenderness thus depends on the product and on the

individual or groups of consumers. This fact suggests

that the sensory expectancies are variable for various

meat products.

tbl0007 Table 7 Factors influencing the acceptability of meat products

Sensory characteristics ofmeat Type of meat products Sensitivityof consumer Foodhabits of consumer

Flavor Species Olfactory Gender

Texture Cut Gustatory Age

Appearance Fat Custom

tbl0006 Table 6 Type of spoilage caused by spoilage bacteria in meat

Frequency Bacteria Spoilage

High Pseudomonas Green color, slimy

Acinetobacter Putrid

Enterobacteria Gas, green color (Proteus)

Flavobacterium Putrid

Brochothrix Green color, cheesy odor

Lactobacilli Green color, sour

Medium Bacillus Putrid odor, brown color

Alcaligenes Putrid

Streptococcus Sour

Aeromonas Putrid, gas

Clostridium Putrid, gas, green color

Shewanella Putrid, green color

Rare Pediococcus Green color, sour

Kurthia Putrid

3782 MEAT/Eating Quality

0027 Appearance of meat also determines acceptance.

Many consumers do not want to eat meat with too

much visible fat because they consider it harmful to

health that dominates over any contribution to flavor.

Exudates or off-colors serve as indicators of unsafe

products to consumers. Consumers also use color to

determine when meat has been cooked sufficiently,

essentially as a predictor of flavor and texture.

0028 Acceptability depends on the product and the con-

text, and consumers’ preferences may be based on

different sensory characteristics: for example, some

for its tenderness and some for its grilled meat aroma.

Some individuals are very much taste- and smell-

oriented, while others divide their attention among

multiple sensory inputs. Moreover, what one person

likes, another may dislike. Some consumers prefer

higher-salt/higher-fat restructured steaks, and others

prefer and actively seek out lower-salt/lower-fat

steaks. Olfactory and gustatory sensitivity can also

play a role in interindividual differences in liking.

0029 Meat acceptability depends strongly on the food

habits of consumers. Consumers generally like what

they know. For example, in New Zealand, consumers

eat much lamb and find the specific flavor of lamb

attractive, whereas American people appear not to

because they are more used to consuming pork and

beef. In an inter-European country study on consumer

preferences for dry-cured hams, most of the French

and Italian consumers preferred Italian home-style

Parma and Bayonne hams, whereas Spanish people

preferred Iberian hams. These differences in liking are

attributed to the different sensory traits among the

different types of ham. Parma and Bayonne have a

pink red color, salty taste, and fresh meat flavor,

whereas the Iberian hams are generally soft, purplish,

slightly sweet, and bitter with a strong, rancid, blue

cheese and mushroom aroma.

0030 Most consumers eat meat because it has desirable

sensory properties. Many of the sensory attributes

depend on the species and cut of meat, which deter-

mines to a large extent the cooking method.

Main Factors Affecting the Sensory Characteristics

of Meat

0031 Sensory properties have been used to study meats

from different origins (species, age, sex, rearing con-

ditions of animals), to monitor processes (aging dur-

ation, electrical stimulation, mincing), and to

compare products. Such qualitative and quantitative

descriptions, without any hedonic connotation, are

carried out by a panel of trained panelists.

0032 Texture Sensory profiles of texture describe in

detail the different stages of its perception (Table 8).

The surface texture is evaluated, followed by an

impression of the first bite or mastication stage and

then the characteristics of the residual or swallowing

stage. Surface properties are smoothness/roughness,

surface moisture, or a granular appearance. During

the mastication stage, the degree to which the sample

returns to its original form (springiness/elasticity), the

tenderness/hardness, the fatty perception, and the

moisture release (juiciness) can be evaluated.

0033Tenderness is the opposite of toughness or resist-

ance to rupture during chewing. Meat tenderness

depends largely on the amount and status of the

connective tissue and myofibers. The connective

tissue is composed mainly by collagen, of which its

quantity, quality, and distribution in muscle contrib-

ute to the specific character of meat tenderness. The

extent of aging (chill storage) increases, whilst a con-

tracted state of the myofibrils decreases tenderness.

Collagen content imposes the cooking method of

muscles. When the collagen content is low, the muscle

can be grilled quickly at high temperature to avoid

myofibrillar toughness. However, if meat is rich in

collagen, a long cooking in a wet atmosphere and at

a moderate temperature is essential to solubilize the

collagen and to reduce mechanical resistance.

0034Juiciness is related to the perception of water re-

leased from meat during chewing and to the intra-

muscle fat content, which has a stimulant effect on

salivation.

0035The residual texture stage depends on the number

of chews to prepare the sample for swallowing, the

fibrousness of the connective tissue, the denseness,

the bolus formation, the ease of swallowing, and

how much and what is remaining in the mouth

tbl0008Table 8 Texture attributes at different stages of mastication

Stage of perception Attribute

First stage: surface perception Granular

Rough

Moist

Mid stage: during mastication Tender/hard

Springy/elastic

Cohesive

Moisture release

Moisture absorption

Juicy

Gristle

Stringy

Fibrous

Particle size and shape

Sticky

Greasy

Final stage: residual perception Number of chews

Mouth coating

Ease of swallowing

Residual particles

Source: Bett KB (1993) Measuring sensory properties of meat in the

laboratory. Food Technology 47: 121–127.

MEAT/Eating Quality 3783