Poultry meat quality [617677]

Poultry meat quality
D.L. FLETCHER
Department of Poultry Science, University of Georgia, Athens, GA 30602 USA,
e-mail: fletcher @uga.edu
The two most important quality attributes for poultry meat are appearance and
texture. Appearance is critical for both the consumers’ initial selection of the product
as well as for final product satisfaction. Texture is the single most important sensory
property affecting final quality assessment. Appearance quality attributes include
skin colour, meat colour, cooked meat pinkness, and appearance defects such as
bruises and haemorrhages. Since appearance is so critical for consumer selection,
poultry producers go to great lengths to produce products with the appropriate
colour for a particular market and to avoid appearance defects which will negatively
effect product selection or price. Historically, meat tenderness was primarily
associated with live bird quality factors such as breed, sex, or age. However, modern
production practices produce highly uniform young birds in which the major
problems associated with meat texture are the result of processing errors or early
deboning. Although other quality issues such as juiciness and flavour are important,
they are more a function of product preparation and infrequent, but acute,
production or processing errors which are usually easily corrected or avoided. An
understanding of the major issues contributing to poultry colour and meat
tenderness is critical to producing uniform quality products.
Keywords: meat quality; meat colour; meat tenderness; discolouration, toughness
Introduction
The major poultry meat quality attributes are appearance, texture, juiciness, flavour, and
functionality. Of these, the most important have traditionally been appearance and texture
since they most influence consumers’ initial selection and ultimate satisfaction with
traditional poultry meat products. Although juiciness and flavour are extremely important,
except for isolated defects they are most often more a function of preparation than of the
product itself. With the increasing trends in further processing, meat functionality and all
of the sensory quality attributes have increased in relative importance. Complex products
such as sausages, marinated fillets, breaded products, fully cooked heat-and-serve items,
frozen entrees, and complete dinners require an understanding of the contribution of
poultry meat to these products as well as their influence on sensory properties of the food.
Functional properties such as water holding capacity are critical for successful product
formulation. A basic understanding of the live production and processing factors that
influence these poultry meat quality attributes, especially colour and texture, is necessary
to produce consistently high quality poultry products.
0 World’s Poultry Science Association 2002
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Although the scientific literature has a considerable amount of information on the
subjects of poultry processing and poultry meat quality, there has been, up to recently, a
shortage of comprehensive source books on the subject. For many years, the only text
book in this area was Poultry Products Technology first published in 1966, by George
Mountney. This was a good college text and resource book during the first two editions,
however, by the third edition (Mountney and Parkhurst, 1995) it was no longer current or
relevant to the modem processing industry. Stadelman, Olson, Shemwell, and Pasch,
published Egg and Poultry-Meat Processing in 1988. This also was a good introductory
text, but generally lacked depth, was not a good general reference book, and was not
widely accepted. In 1989, a book, entitled Processing of Poultry was published. This
book, edited by G.C. Mead, was an excellent resource book with chapters authored by
outstanding individuals in their area. However, this book was written from the European
perspective and has begun to show its age.
In the late 1990s and early 2000, Elsevier International (Khan, 2000) published the
Poultry Production Guide in a series of installments, which included chapters on the
poultry market and product quality. In the past year, two new books have reached the
market, both of which are current and have excellent chapters relative to poultry
processing and meat quality issues. The first is Poultry Meat Processing, edited by A.R.
Sams (2001) and the second Poultry Products Processing: An Industry Guide, written by
S. Barbut (2002).
Appearance
Of all the quality attributes, appearance is the most critical for the selection of many food
commodities, including poultry products. Consumers most often select or reject a product
based solely on its appearance. Appearance is also critical for final product evaluation
since it often affects other sensory properties. One of the major contributing components
of appearance is colour. Colour has long been known to be a major selection criterion for
fresh poultry and meat products as well as for final product satisfaction.
For poultry meat products, colour is important for skin, meat, and bone. Skin colour is
most critical for the marketing of fresh whole birds or parts. Meat colour is most important
both for the selection of deboned and skinless raw meat as well as being critical for the
final evaluation of many cooked products. Pink or red appearance of cooked poultry meat
is generally associated with undercooking and is highly undesirable. Dark or black bones
are also considered to be a defect in fully cooked products. Bone darkening is primarily
associated with frozen products prior to cooking. Other visual defects are associated with
bruises, haemorrhages, blood pooling, or any number of other possible discolourations.
SKIN COLOUR
Market studies in the early 1960’s clearly showed pronounced regional differences in
consumers preferences for fresh whole broilers based solely on skin colour (Raskopf et al.,
1961; Courtenay and Branson, 1962; Davis, 1963; Heffner et al., 1964). These studies
showed that consumers generally prefer broiler skin colours ranging from white, to pale
yellow, to deeply pigmented based on traditional regional supplies. In 1987, Marion and
Peterson showed that skin colour still influenced consumers’ attitudes towards fresh
poultry. Thus consumers tend to favour skin colours which were traditionally available
and which were based on local feeding practices as well as genetic stock. In modern
markets, consumers still tend to favour their traditional market forms. In the Eastern
United States, deeply pigmented birds are the most desired; in the South-eastern US,
moderately pigmented birds are preferred; in the North-western US, pale skin colour is
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preferred; in the United Kingdom, consumers prefer a white, non-pigmented skin. Similar
differences in colour preferences exist all over the world, and are based primarily on
historical and regional supplies, traditional genetic stock (ability of some breeds to deposit
carotenoid pigments in the skin), and availability of carotenoid containing feedstuffs.
Because of its market impact, much is known about the factors affecting skin
pigmentation. As early as 1915, researchers recognized the principal pigment involved in
the colouration of egg yolks and tissues of poultry (Palmer, 1915). Pigmentation, or the
deposition of pigments in the skin of the bird, depends upon the genetic capability of the
bird, dietary source of pigments, health of the bird, and processing. A review of the many
factors affecting poultry pigmentation was published by Fletcher (1989) and the state of
the art for pigmenting poultry products was published in symposium form (Sunde, 1992;
Hencken, 1992; Hamilton, 1992; Fletcher, 1992; Williams, 1992). A summary of the major
factors affecting skin pigmentation are presented in Table 1. Broilers must have the
genetic ability to deposit carotenoid pigments in the epidermis. With the exception of the
Cornish breed, English Class birds lack this genetic ability to deposit carotenoid pigments in the skin thus these birds have a white appearance regardless of diet or other factors.
Those birds that have the genetic disposition to deposit the carotenoid pigments in the skin
must also have the pigments supplied in the diet. For this reason, numerous studies have
been conducted to evaluate the skin pigmenting properties of a variety of both natural and
synthetic sources. Diseases, particularly coccidiosis, have been shown to have dramatic
negative effects on pigmentation. Flock health is critical to uniform pigment absorption
and deposition. Since the carotenoid pigments are deposited in the epidermis, care must
also be exercised in processing not to remove this layer by over-scalding or damaging the
skin during picking.
Table 1 Summary of factors affecting poultry skin pigmentation (Fletcher, 1989).
Factor
Feed sources
Xanthophyll
concentrates and
exotic sources
Feed additives
Xanthophyll stability and biological availability
Management and processing Examples
alfalfa, barley, corn gluten meal, grass meals, millet, milo, oats, wheat, yellow corn
algae, bacterial by products, beehive pollen, broccoli, citrus sludge, clover, cow
manure, crawfish waste, kenaf, lake weed, lettuce, leucaena leaf meal, lobster shell,
marigold extract, marigold meal, paprika extract, peanut leaf meal, seaweed, shrimp
waste, soybean oil soapstock, sweet potato vine meal, tomato, yeast and synthetically
produced xanthophylls such as beta-apo-8’-carotenaI and canthaxanthin anticoccidial drugs, antioxidants
(BHT, vitamin E, etc.), fish oils and fish meals,
growth promotants, meat scraps, trace mineral, vitamins (specially as antioxidants
such a E, or negative effects of too much A)
antioxidants, biological availability (absorption), biological deposition (genetic),
chemical form (free or esterified), colouring capacity, storage time, temperature
breed and strain(genetic ability to deposit xanthophylls in skin), disease and health,
environment, housing type, scalding, sex
With the increase in further processing of poultry and changing markets with increased
cut up, deboned meat, and fully cooked products, the relative importance of skin colour
has decreased in recent years, primarily in North America and Western Europe. The
predominance of skinless raw products as well as further processing has reduced demand
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Haem pigments –
Pre-slaughter factors for whole birds and skin-on parts. The increased trend for further processing, which
includes numerous breaded or coated products, has also resulted in a requirement by
further processors to remove the epidermal layer of skin during scalding so as to increase
coating adherence to the underlying dermal layer of the skin during further processing and
cooking. The epidermal layer, also known as the cuticle, is loosened at scald water
temperatures above 54°C and is removed during picking leaving only the underlying
dermal layer of skin. Thus even in areas which may prefer a yellow skinned bird, further
processing demands for removing the epidermis has resulted in decreased economic
incentives to maintain high carotenoid levels in the feed.
myoglobin, haemoglobin, cytochrome C and their derivatives, presence of ligands
complexing with haem pigments genetics (new and fast growing strains), feed (e.g. mouldy feed), feed withdrawal,
hauling and handling, stress, heat and cold stress, preslaughter gaseous environment
of the bird MEAT COLOUR
Colour of raw poultry meat is critical for consumer selection while colour of the cooked
meat is critical for final evaluation. Colours which differ from the expected pale tan to
pink raw meat or from the tan to grey cooked meat will result in consumer rejection of the
product. This is especially true with the appearance of pinkness in fully cooked meat; a
major defect in poultry meat products. A recent survey indicated that approximately 7% of
skinless-boneless breast fillets, packaged 4 fillets to a pack, had one or more fillets which
were noticeably different from the other 3 fillets in the same package (Fletcher, 1999a). In
a survey of five commercial broiler processing plants, breast meat colours were found to
have a wide range with lightness values (lightness value ranges from 43.1 to 48.8 using the
CIELAB colour description system) which had a strong negative correlation to muscle pH
(Fletcher, 1999b). These results indicate that significant variations in breast meat colour
exist and are present at the retail level. In a later study, Fletcher et al. (2000) showed that
variations in raw breast meat colour are sufficient to cause variations in cooked product
appearance.
Mugler and Cunningham (1972) reviewed many of the factors affecting poultry meat
colour. Such factors as bird sex, age, strain, processing procedures, chemical exposure,
cooking temperature, irradiation, and freezing conditions were all shown to affect poultry
meat colour. In recent years additional factors have also been identified as affecting
poultry meat colour. Maga (I 994) reviewed the primary factors influencing pink
discolouration in cooked white meat (pork and poultry). This review stressed the nature
and reactions of the major meat pigment, myoglobin, as well as effects of nitrates and
nitrites, ovens and environmental gasses (primarily carbon monoxide and nitric oxide),
age, sex, and strain of animal, scalding temperature, irradiation, cooking temperature,
storage, canning, processing additives, pre-slaughter conditions, haemachromes, and
cytochrome C reactions on final meat colour. Froning (1995) presented the most recent
review on many of these factors affecting poultry meat colour and those major factors are
summarized in Table 2.
Slaughter
Chilling
Further processing Table 2 Factors influencing poultry meat colour (from Froning, 1995).
stunning techniques, presence of nitrates, additives and pH (e.g. salt, phosphates,
etc.), end point cooking temperatures, reducing conditions, washing surimi-like
processing, irradiation I
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Stress immediately prior to and during slaughter have been shown to affect meat colour.
Antemortem temperature stress and excitement just prior to slaughter has been shown to
affect turkey meat colour (Froning et al., 1978; Babji et al., 1982; Ngoka and Froning,
1982). Walker and Fletcher (1993) reported that epinephrine injections just prior to
slaughter, to simulate severe antemortem stress, resulted in darker breast meat due in part
to both a higher muscle pH and increased haemoglobin content of the meat. Northcutt et
al. (1 994) reported that thermal preconditioning and heat shock in chicken resulted in
breast meat that appeared pale, soft, and exudative, similar to a condition found in pork.
Electrical stunning at high currents (greater than 100 mA) was shown to increase blood
spots in broiler chicken breast meat by Veerkamp (1987). However, other than for
haemorrhaging effects on meat appearance, comparisons of low and high current stunning
appears to have little direct effect on broiler breast meat colour (Papinaho and Fletcher,
1995; Craig and Fletcher, 1997). Gas stunning or gas killing has been shown to affect
breast meat colour. Mohan Raj et al. (1990) reported that broiler breast muscles from
argon killed birds were less dark than those killed conventionally or killed with carbon
dioxide. Fleming et al. (1991a) found that stunning with carbon dioxide resulted in
significantly less red breast and thigh meat compared to electrically stunned turkeys. Maki
and Froning (1987) showed that electrical stimulation resulted in redder raw breast meat
but lighter cooked breast meat than non-stimulated controls. Froning and Uijttenboogaart
(1988) reported that postmortem electrical stimulation resulted in darker broiler breast
meat. However, Owens and Sams (1997) reported no effects of electrical stunning on
turkey breast meat colour.
The effect of chilling and leaching of haem pigments on poultry meat colour is not clear.
Fleming et al. (1991b) reported no effect of immersion versus air chilling on broiler breast
or thigh muscle colour or haem content. However, Boulianne and King (1 995) attributed
pale boneless broiler breast fillets to loss of haem pigments during storage in ice slush
tanks. Yang and Chen (1993) found that lightness and redness values of ground breast and
thigh meat decrease with storage.
The major contributing factors to poultry meat colour are myoglobin content, chemical
state of the haem structure, and meat pH. Myoglobin content has been shown to be
primarily related to species, muscle, and age of the animal. Muscle pH has been shown to
be primarily related to the biochemical state of the muscle at time of slaughter and
following rigor mortis development. Both of these factors contribute to meat colour and
the occurrence of meat colour defects.
The relationship of animal species, muscle type, and animal age on meat myoglobin
content and visual colour was presented by Miller (1994). White meat from 8 week old
poultry had the lowest myoglobin content (0.01 mg myoglobin/g meat) compared to 26
week male poultry white meat (0.10 mg/g), young turkey white meat (0.12 mg/g), 8 week
poultry dark meat (0.40 mg/g), 26 week male poultry dark meat (1 SO mg/g), 24 week
male turkey dark meat (1 SO mg/g) and compared to 5 month old pork (.30 mg/g), young
lamb (2.50 mg/g), dark meat fish species (5.3 to 24.4 mg/g), white meat fish species (0.30
to 1.0 mg/g), 3 year old beef (4.60 mg/g), and old beef (16 to 20 mg/g).
Because of the importance of both fresh and processed meat colour, the biochemistry of
the haem pigments and their reactions that affect meat colour are extremely well
documented in the general meat science literature. Bodwell and McClain (1978) present a
comprehensive coverage of the myoglobin reactions associated with fresh meat colour and
cooking. The various ionic and covalent complexes of both the ferrous and ferric state of
the haem with oxygen and other compounds to form the basic meat colour variations from
the purplish red of deoxygenated myoglobin to the bright red of oxymyoglobin to the
brown/gray of metmyglobin are well established. Bard and Townsend (1978) discuss
numerous haem reactions involved in meat curing. The reactions with various nitrogen
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compounds and heat to form stable nitrosyl haemachrome complexes produce the
desirable pink colour of cured red meats or the undesirable pinkness of some poultry
products. A series of research reports by Ahn and Maurer (1990a, 1990b, and 1990c)
presented a comprehensive coverage of the complex haem reactions that affect turkey
breast meat colour. This series of papers clearly illustrates the complexity of the numerous
potential compounds and their effects on turkey meat colour. Their work also illustrated
the pronounced effect of muscle pH on the formation of these complexes.
PXE- AND DFD-LIKE CONDITIONS IN POULTRY MEAT
Muscle pH and meat colour have consistently been reported to be highly correlated,
especially when wide ranges of meat colour are examined. This is especially true when
referring to meat as being either PSE-like or DFD-like in which pH is strongly related to
these extreme conditions. This is an important distinction since several scientists have not
found consistent relationships between colour and pH in “normal” or unselected
populations of breast meat. Since negative data is seldom published, the literature may
have a bias toward publishing only positive data in regards to these relationships.
Therefore, it may be important to emphasize that the breast meat colour and pH
correlations may be more prevalent in studies where wide ranges of breast meat colour
were purposely selected.
Higher muscle pH is associated with darker meat while lower muscle pH values are
associated with lighter meat. In the extremes, high pH meat is often characterized as being
dark, firm, and dry (DFD-like) and the lighter meat as being pale, soft, and exudative
(PSE-like). Both DFD-like and PSE-like meat have been associated with poor functional
properties, or at the very least, have been considered major contributing factors to product
variation. Several researchers have demonstrated this significant relationship between raw
breast meat colour and raw meat pH (Barbut, 1993; Boulianne and King, 1995 and 1998;
Allen et al., 1997; Fletcher, 1999b).
The effect of pH on meat colour is complex. One effect, as noted earlier, is that many of
the haem-associated reactions are pH dependent. In addition, muscle pH affects the water
binding nature of the proteins and therefore directly affects the physical structure of the
meat and its light reflecting properties (Briskey, 1964). Also, pH affects enzymatic activity
of the mitochondria1 system thereby altering the oxygen availability for haem reactivity
(Ashmore et al., 1972 and Cornforth and Egbert, 1985).
Muscle pH has been associated with numerous other meat quality attributes including
tenderness, water hold capacity, cook loss, juiciness, and microbial stability (shelf life).
Allen et al. (1 997 and 1998) showed that variations in breast meat colour, presumably due
primarily to pH effects, significantly affect breast meat shelf life, odour development,
moisture pick-up during marination, drip loss, water holding capacity, and cook loss.
Although the differences in poultry breast colour exist, and these differences are related
to differences in muscle pH, there are some contradictions in the literatures as to what
extent colour can be directly related to a loss of meat functionality based solely upon
colour discrimination. Barbut (1997) reported that the occurrence of pale, soft, exudative
(PSE) meat in broiler chickens ranged from 0% to 28% in 7 different flocks. Woelfel et al.
(1998) examined the incidence of pale, soft and exudative chicken meat in a commercial
plant and reported that approximately 37% of 175 1 commercial broiler fillets examined
could be classified as being pale and could be expected to exhibit poor water holding
capacity. Mallia et al. (2000) reported that in Canada, broiler carcasses with dark breast
fillets are often condemned for cyanosis although the dark, firm and dry (DFD-like)
condition may be due to other causes such as ascites or emaciation. Qiao et al. (2001)
reported that selected breast meat samples in the very light, normal, and very dark ranges
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were associated with significant differences in meat functionality.
Research has been conducted to better define factors contributing to DFD- and PSE-like
conditions as well as methods to identify breed or strains that may be more prone to
producing poor quality meat. Many of these projects, including stress, have been
previously discussed. Qiao et al. (2002) reported that broiler breast meat with wide
variations in lightness between very pale to very dark had significant differences in
chemical composition. The authors concluded that although short term stress may
contribute the most to breast meat colour variation, the compositional difference indicates
that long term or genetic factors may create a predisposition to carcasses being either
extremely light or dark. In an effort to determine if birds can be tested for a predisposition
to colour variation, halothane has been used to detect turkeys prone to developing PSE
meat (Wheeler et ul., 1999; Owens et al., 2000b, Owens et al., 2000~). These results
indicated that halothane is only a limited predictor of PSE meat in turkey.
There appears to be little disagreement that DFD- and PSE-like conditions do occur in
poultry breast meat and that these defects are related, at least in part, to difference that
contributes to a colour difference, from extremes in darkness to lightness. However, from
the articles reviewed, there appears to be a difference among researchers as to how much
difference in absolute lightness values is necessary to describe meat that has reduced
functional properties. Extreme differences in lightness values have been correlated with
differences in functional properties, but arbitrary lightness cut-off values have yet to be
established which can clearly differentiate meat functionality.
VISUAL DEFECTS
Visual defects are those factors that can dramatically affect the appearance of the carcass
or meat but may not be only associated with the pigments, physical, or chemical property
of the skin or meat. The most important visual defects are those associated with bruising
and haemorrhages. The discolouration of muscle tissue due to bruising or due to the
accumulation of blood in the tissue due to haemorrhages negatively affect product
appearance. If severe enough, bruises and haemorrhages can result in product
condemnation or product rejection by the consumer.
Bruising is due to physical trauma (without laceration) resulting in capillary rupture and
haemorrhaging (escape of blood from the circulatory system) of blood into the
surrounding tissue. Initially a bruise will impart a red discolouration to the damaged
tissues but will begin to darken to a blue-black discolouration and finally to green and
possibly yellow as the haem compounds degrade. Haemorrhaging refers directly to any
capillary or blood vessel rupture resulting in blood pooling in the meat or below the skin.
Therefore, bruises are due to aging of capillary haemorrhaging in the tissue due to physical
trauma whereas haemorrhages refer simply to any blood accumulation.
Because bruises are a major source of condemnation and downgrading (Bilgili, 1990)
efforts to reduce or control their incidence have been identified. Factors identified to affect
bruising include breedstrain, sex, housing density, feathering, bird size and age, season,
light intensity, litter conditions, housing ventilation, disease, mycotoxins, vitamins, stress,
holding conditions, unloading, hanging, stunning, killing, and picking. Tung et al. (1971)
reported that feed aflatoxins can result in capillary fragility and increased incidences of
haemorrhages. Wu et al. (1 994) found that corn containing Fusarium monilijiorme resulted
in significantly darker and more red turkey breast meat. As presented earlier, electrical
stunning has been implicated in contributing to increased haemorrhaging and blood
spotting in meat. However, it is often difficult to completely separate haemorrhaging from
meat colour issues.
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COLOUR CHANGES OVER TIME
A phenomenon associated with both broiler skin and meat colour is that the absolute
colour has noted to change over time, especially during storage. Since early changes
would not affect product appearance in the display case, little practical problems were
associated with these gradual changes, except in rare cases of long term storage issues.
However, with the increased concern with the relationship between breast meat colour and
functional properties of the meat, interest in the use of machine vision and computer aided
sorting devices have been receiving considerable interest in recent years.
Breast meat colour, measured both on the day of processing and following 24 hours
holding have been shown by numerous authors to be different (Alvarado and Sams, 2000;
Bihan-Duval et al., 1999; Mallia et al., 2000; Owens et ul., 2000a; Owens et al., 2000b;
Owens et al., 2000c; Owens and Sams, 2000; Qiao et al., 2001). In a series of studies, the
effect of both short term (0 to 12 hours) and long term (1 to 7 days) on both soft and hard
scalded broiler skin and on intact and packaged breast fillets, were studied. Results show
that both skin and meat colour values change dramatically for the first several hours after
processing, and continuously, but at a slower rate, through 7 days of storage (Petracci and
Fletcher, 2002). Additional research has clearly shown that breast meat sample thickness
and background colour can also dramatically affect instrumental colour readings (Bianchi
and Fletcher, 2002). The results from these two studies clearly indicate that machine
vision systems used in processing plants to sort carcasses or meat based on colour need to
consider the post-mortem time, sample thickness, and background (belt) material effects
on calibration of such systems.
COLOUR MEASUREMENT
The science of food colourimetry is well established and many resources are available
describing various methods of colour measurement of a wide variety of foods using both
subjective and objective measurement systems. Reflectance colourimetry is one the most
widely used colour measurement systems used in food science. However, such methods
were not designed to be optimal to measure the colour of opaque materials, such as meat
where much of the light is either transmitted or absorbed as opposed to be reflected to the
detector. However, systems to measure the colour or reflectivity of such materials are not
readily available for meat colour determination. Unfortunately, the basis for much of the
previous discussion of meat colour is based on the use of reflectance colour measurement.
Although this may not invalidate these studies, some caution should be exercised in over
interpreting the impact of the method of colour measurement in predicting biochemical
properties of the meat.
Texture
Texture is probably the single most critical quality factor associated with the consumers’
ultimate satisfaction with a poultry meat product. The two major contributors to poultry
meat tenderness are the maturity of the connective tissues and contractile state of the
myofibrillar proteins. The first, maturity of the connective tissue involves the chemical
cross bonding of the collagen in the muscle. Since collagen cross-linking increases with
age, meat is generally tougher from older animals. The second factor, the contractile state
of the myofibrillar proteins, is primarily a function of the rate and severity of rigor mortis
development.
As the modern broiler industry developed and began to dominate the chicken meat
market, the issue of age related toughness (connective tissue cross-linking) has virtually
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disappeared. Except for spent hen and older bird utilization, or for specialty markets such
as for capons, age related connective tissue toughness is not a major factor in broiler meat
quality since the market age of broilers is less than 7 to 8 weeks of age.
The myofibrillar protein impacts on ultimate meat tenderness are primarily a function of
the biochemical predisposition of the muscle at the time of slaughter, the rate and severity
of rigor mortis development, and the physical handling of the carcass and muscle during
rigor development. With traditional broiler industry production practices, processing, and
the predominant marketing of whole carcasses the negative impact of the myofibrillar
protein reactions were not thought to have a major impact on meat quality. Shrimpton
(1960) concluded that,
“….if tough flesh is found on the carcasses of broilers, its presence is likely to be caused
by adverse conditions during the life of the bird. The toughness may also be
accentuated by bad practice in the packing station, but the changes associated with rigor
seem likely to play only a small part in the development of toughness in the muscle of
young chicken.”
However, in recent years with the dramatic increase in cut up, deboned meat, and further
processed products, the demands are placed on the slaughter plant to cut up and debone the
carcasses as fast as possible. If the carcass is cut-up into parts, or more importantly, if the
breast meat is removed from the carcass prior to the completion of rigor mortis, the
muscles will contract unimpeded by the normal skeletal restraint, the muscle fibres will
contract and shorten the muscle, and the resulting meat will be less tender.
Although the predominant marketing of young broilers minimizes age associated
toughness, the economic incentive to cut-up and debone broilers earlier in the processing
scheme has resulted in an increased incidence of tough broiler breast meat. During the past
20 years, intensive research efforts have been focused on determining the live bird and
processing factors which affect breast meat tenderness. The ultimate goal has been to
develop slaughter methods which would allow for acceleration of post-mortem rigor
mortis such that carcasses could be cut-up and deboned as soon after slaughter as possible.
ACCELERATED PROCESSING
It has long been established that poultry must be allowed a postmortem aging period
prior to cut-up and deboning, cooking, or freezing to avoid adverse toughening, especially
in the breast meat (Koonz et al., 1954). A plethora of recent data suggests that a minimum
of 4 hours aging is required to allow the breast muscles sufficient time to complete rigor
development and to allow subsequent removal from the carcass without excessive
toughening.
The concept of accelerated processing is based on the rapid depletion of muscle
glycogen and ATP stores as fast after slaughter as possible. Once the muscle loses the
ability to generate ATP, rigor contractions cease and the muscle can be released from
skeletal restraint with less adverse toughening. The major factors affecting rigor
development and accelerated processing are antemortem handling, electrical stunning, gas
stunning, and electrical stimulation. LIVE BIRD HANDLING AND STRESS
Feed withdrawal, environment, and struggle prior
to slaughter have been shown to
affect muscle glycogen stores in the muscle at time of slaughter. Birds with higher muscle
glycogen content at slaughter have lower final muscle pH and lower shear values than
birds with lower muscle glycogen (Mellor et al., 1958). Increasing feed withdrawal times
have been shown to decrease breast muscle glycogen stores (Murray and Rosenberg,
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1953; Kotula and Wang, 1994). The later authors also reported that increasing feed
withdrawal also reduced initial breast muscle pH values, but had little effect on terminal
muscle pH, and resulted in higher breast meat shear values.
Ante-mortem stress, including heat stress (Simpson and Goodwin, 1975; Lee et al.,
1976; Babji et al. 1982), epinephrine injections (Wood and Richards, 1975; Fletcher,
1991), as well as struggle (Ma and Addis, 1973; Lee et al., 1979; Ngoka and Froning,
1982; Papinaho et al., 1995), have been shown to accelerate glycogen depletion, increase
the rate of pH decline, and possibly result in tougher meat. Although ante-mortem
handling, feed withdrawal, and stress affect muscle glycogen content at time of slaughter
and therefore the rate and severity of rigor as well as ultimate muscle pH, the effect on
accelerated processing and final meat tenderness is still not well defined.
STUNNING AND SLAUGHTER
Electrical stunning has been shown to result in more tender breast meat and altered
postmortem rigor development. Lee et al. (1979) showed that stunned birds had higher
ATP, lower lactate, and higher pH values than non-stunned birds and concluded that
stunning inhibited metabolism and delayed the onset of rigor. Kim et al. (1988) concluded
that stunning indirectly delayed post-mortem glycolysis primarily through a suspension of
ante-mortem struggle. Research directly comparing electrical stunning and ante-mortem
struggle showed that the early delay in rigor attributed to electrical stunning was indeed
due more to a suppression of ante-mortem struggle than to any direct effects of electrical
stunning on muscle metabolism (Papinaho et al., 1995). Comparisons between high
current stunning, as recommended in Europe, and low voltage stunning, as commonly
used in the North America, showed that high current stunning resulted in a more
pronounced effect on early rigor delay than low voltage stunning (Papinaho and Fletcher,
1995; Papinaho and Fletcher, 1996; Craig and Fletcher, 1997). These differences in
muscle glycogen stores and breast muscle pH during early rigor development, however,
do not affect ultimate muscle pH, tenderness values, or meat quality.
In Europe, electrical stunning has been under intense scrutiny for both animal welfare
and meat quality issues for the past 15 years. The use of high current stunning to insure
humane slaughter is also associated with increased carcass damage and lower meat
quality. Although gas stunning has been evaluated since the 1950’s (Kotula et al., 1957)
possible application for humane slaughter and meat quality improvements have led to
renewed interest in gas as a possible method for both stunning and killing of poultry. To
this end, intensive research into the use of argon and carbon dioxide gas killing systems
has been conducted in the United Kingdom. In addition to humane slaughter benefits,
improvements in reduced carcass damage and improved meat quality were reported.
Specifically, killing birds in a gas environment appeared to result in accelerated rigor such
that the breast meat could be harvested earlier without adverse toughening (Mohan Raj et
al., 1990; Mohan Raj et al., 1991). These authors reported that gas killing resulted in lower
initial muscle pH, more tender meat, faster post-mortem rigor development, and early
harvesting of tender breast meat compared to electrically stunned birds.
Evaluations and comparisons of conventional and gas killing in the United States have
been less encouraging relative to accelerated processing. Poole and Fletcher (1 998)
compared gas killing to both high current and low voltage stunned and conventionally
killed broilers. Their results indicated that gas killing only showed a meat quality advantage when compared to high current stunning. The authors concluded that at least
part of the rigor accelerating influence of gas stunning previously reported by the UK
researchers was made in comparison to high current stunning which is now known to
delay early rigor development.
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Poultry meat quality: D.L. Fletcher
ELECTRICAL STIMULATION
Electrical stimulation has been used to accelerate rigor development and enhance red
meat quality. Li et al. (1993) reviewed the use of electrical stimulation in poultry. Due to
numerous variations in the electrical stimulation systems studied, results have been
variable and inconclusive. Although most researchers agree that electrical stimulation
accelerates early rigor development, the magnitude of such effects and its subsequent
applicability for commercial utilization is still in question.
Researchers at Texas A&M University however have conducted numerous experimental
trials as well as industry prototype systems and have concluded that electrical stimulation
does indeed allow for earlier deboning of broiler breast meat (Birkhold et al., 1992; Sams,
1994; Sams, 1995, Zocchi and Sams, 1996). A number of such systems are now in use in
the commercial poultry industry in Brazil and North America.
It is interesting that electrical stunning delays rigor development while electrical
stimulation accelerates rigor development. A comparison of both high and low current
stunning followed by electrical stimulation shows that electrical stimulation is most
effective following high current stunning and had little effect following low voltage
stunning (Craig et al., 1998). These results might explain some of the inconsistency in
previous results evaluating electrical stimulation. COMBINATION TREATMENTS
Clatfelter and Webb
( 1987) reported that a combination of high temperature
conditioning and electrical stimulation could be used to produce tender early deboned
breast meat. Sams (1990) reported that both high temperature conditioning and electrical
stimulation had no individual effects on early deboned breast meat, but when used in
combination, they resulted in more tender breast meat. Walker et al. (1994) compared
various combinations of high and low voltage electrical stimulation, high temperature
conditioning, and muscle tensioning on broiler breast meat tenderness and concluded that
only high voltage electrical stimulation with muscle tensioning had a significant positive
effect on muscle tenderness.
It appears that no one single rigor acceleration procedure works as well as combinations
of treatments. Current evaluations of commercial electrical stimulation systems, extended
chilling, and interactions with stunning and gas killing systems are making progress
towards making accelerated processing a reality.
Conclusion
Traditionally, poultry quality issues have focused primarily on the appearance of both the
carcass and meat and the tenderness of the meat. The dramatic changes in the market
forms for poultry over the past 30 years, from a predominantly whole bird commodity to
the modem highly diversified industry focused on cut up, deboned meat, and ready-to-eat
further processed products has also resulted in a change of our quality expectations.
Although the basic issues of appearance and texture are still critical quality issues, the
specifics and relative degree of importance has evolved with the changes in market
products. As the market continues to evolve, we can expect traditional quality issues to
continue to evolve as well as the identification of new quality parameters. Also, during this
time, we have seen a definite shift from a more traditional concept of market based quality,
affecting price and preference, to a more production oriented definition of quality based on
statistical control and product uniformity.
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Poultry meat quality: D.L. Fletcher
References
ALLEN, C.D., RUSSELL, S.M. and FLETCHER, D.L. (1997) The relationship of broiler breast meat color
and pH to shelf-life and odor development. Poultry Sci. 76: 1042-1046.
ALLEN, C.D., FLETCHER, D.L., NORTHCUTT, J.K. and RUSSELL, S.M. (1998) The relationship of
broiler breast color to meat quality and shelf-life. Poultry Sci. 76: 1042-1046.
ALVARADO, C.Z. and SAMS,A.R. (2000) Rigor mortis development in turkey breast muscle and the effect of
electrical stunning. Poultry Sci. 79: 1694.1698.
ASHMORE, C.R., PARKER, W. and DOERR, L. (1 972) Respiration of mitochondria isolated from dark-
cutting beef postmortem changes. J. Anim. Sci. 34: 46-48.
AHN, D.U. and MAURER, A.J. (l990a) Poultry meat color: Kinds of heme pigments and concentrations of the
ligands. Poultry Sci. 69: 157-165.
AHN, D.U. and MAURER, A.J. (1990b) Poultry meat color: Heme-complex-forming ligands and color of
cooked turkey breast meat. Poultry Sci. 69: 1769.1774.
AHN, D.U. and MAURER, A.J. (1990~) Poultry meat color: pH and the heme-complex forming reaction.
Poultry Sci. 69: 2040-2050.
BABJI, AS., FRONING, G.W. and NGOKA, D.A. (1982) The effect of pre-slaughter environmental
temperature in the presence of electrolyte treatment on turkey meat quality. Poultry Sci. 61: 2385-2389.
BARBUT, S. (1 993) Color measurements for evaluating the pale soft exudative ( PSE) occurrence in turkey
meat. Food Res. Int. 26: 39-43.
BARBUT, S. (1 997) Problem of pale soft exudative meat in broiler chickens. British Poultry Sci. 38 (4): 355-
358.
BARBUT, S. (2002) Poultry Products Processing: An Industry Guide. CRC Press LLC, Boca Raton, Florida
3343 I, USA.
BARD, J. and TOWNSEND, W.E. (1978) Cured meats. In, “The science of meat and meat products,” Ed.
PRICE, J. F. and SCHWEIGERT, B. S., Food and Nutrition Press, Inc., Connecticut, pages 452-483.
BIANCHI, M. and FLETCHER, D.L. (2002) Effects of thickness and background color on poultry meat color
measurements. Proc. International Poultry Scient$c Forum, Atlanta, GA, January 14-15, 2002, Abstract No.
164.
BIHAN-DUVAL, E., MILLET, N. and REMIGNON, H. (1999) Broiler meat quality: Effect of selection for
increased carcass quality and estimates of genetic parameters. Poultry Sci. 78: 822-826.
BILGILI, S.F. (1990) Broiler quality: grades are posted. Broiler Ind. 53(1): 32-40.
BIRKHOLD, S.G., JANKY, D.M. and SAMS, A.R. (1992) Tenderization of early-harvested broiler breast
fillets by high-voltage post-mortem electrical stimulation and muscle tensioning. Poultry Sci. 71: 2 106-21 12.
BODWELL, C.E. and McCLAIN, P.E. (1978) Chemistry of animal tissues. In, “The science of meat and meat
products,” Ed. PRICE, J. F. and SCHWEIGERT, B. S., Food and Nutrition Press, lnc., Connecticut, pages 78-
207.
BOULIANNE, M. and KING, A.J. (1 995) Biochemical and color characteristics of skinless boneless pale
chicken breast. Poultry Sci. 74: 1693-1698.
BOULIANNE, M. and KING, A.J. (1998) Meat color and biochemical characteristics of unacceptable dark-
colored broiler chicken carcasses. Journal of Food Sci. 63(5): 759-762.
BKISKEY, E.J. (1 964) Etiological status and associated studies of pale, soft, exudative porcine musculature.
Adv. Food Res. 13: 89- 178.
CLATFELTER, K.A. and WEBB, J.E. (1987) Method for eliminating aging step in poultry processing. US.
Patent No. 4,675,947. June 30, 1987.
CORNFORTH, D.P. and EGBERT, W.R. (1985) Effect of rotenone and pH on the color of pre-rigor muscle.
J. Food Sci. 50: 34-35, 44.
COURTENAY, H.V. and BRANSON, R.E. (1962) Consumers image of broilers, Bulletin 989, Texas
Agricultural Experiment Station.
CRAIG, E.W. and FLETCHER, D.L. (1997) A comparison of high current and low voltage electrical stunning
systems on broiler breast rigor development and meat quality. Poultry Sci. 76: 1178- 11 81.
CRAIG, E.W., FLETCHER, D.L. and PAPINAHO, P.A. (1998) The effects of ante-mortem electrical
stunning and postmortem electrical stimulation on biochemical and textural properties of broiler breast meat.
Poultry Sci. (In Press).
D,4VIS, B.H. (1963) How do consumers react to broiler pigmentation, Broiler Business, July, 1963.
FLETCHER, D.L. (1989) Factors influencing pigmentation in poultry. CRC Critical Reviews in Poultqt
FLETCHER, D.L. (1991) Ante mortem factors related to meat quality. Quality of Poultry Products: I. Poultry
FLETCHER, D.L. (1 992) Methodology for achieving pigment specifications. Poultry Sci. 71: 733-743.
FLETCHER, D.L. (1999a) Color Variation in Commercially Packaged Broiler Breast Fillets. J. Appl. Poulrry Biology 2(2): 149.170.
Meat. Proceedings of the 10th European Symposium on the Quality of Poultry Meat, page 11-19.
Res. 8: 67-69.
142 World’s Poultry Science Journal, Vol. 58, June 2002

Poultry meat quality: D.L. Fletcher
FLETCHER, D.L. (1999b) Broiler Breast Meat Color Variation, pH, and Texture. Poultry Sci. 78: 1323-1 327.
FLETCHER, D.L., QIAO, M. and SMITH, D.P. (2000) The relationship of raw broiler breast meat color and
FLEMING, B.K., FRONING, G.W., BECK, M.M. and SOSNICKI, A.A. (1991a) The effect of carbon
FLEMING, B.K., FRONING, G.W. and YANG, T.S. (1991 b). Haem pigment levels in chicken broilers chilled
FRONING, G.W. (1995) Color of poultry meat. Poultry and Avian Biology Reviews 6(1): 83-93.
FRONING, G.W., BABJI, A.S. and MATHER, F.B. (1978) The effect of pre-slaughter temperature, stress,
struggle and anesthetization on color and textural characteristics of turkey muscle. Poultry Sci. 57: 630-633.
FRONING, G.W. and ULJTTENBOOGAART, T.G. (1988) Effect of post-mortem electrical stimulation on
color, texture, pH, and cooking loss of hot and cold deboned chicken broiler breast meat. Poultty Sci. 67:
1536-1 544.
HAMILTON, P.B. (1 992) The use of high-performance liquid chromatography for studying pigmentation.
Poultry Sci. 71: 718-724.
HEFFNER, J., ROY, E.P., DAVIS, B.H. and HILTON, W.B. (1964) Consumer preference for broiler
pigmentation in New Orleans, Louisiana, Bulletin 586, Louisiana Agricultural Experiment Station.
HENCKEN, H. (1992) Chemical and physiological behavior of feed carotenoids and their effects on
pigmentation. Poultry Sci. 71: 71 1-717.
KHAN, N., Editor (2001) The Poultry Production Guide. Elsevier International, Doetinchem, The Netherlands.
KIM, J.W., FLETCHER, D.L. and CAMPION, D.R. (1988) Research Note: The effect of electrical stunning
and hot boning on broiler breast meat characteristics. Poultry Sci. 67: 674-676.
KOONZ, C.H., DARROW, M.I. and ESSARY, E.O. (1954) Factors influencing tenderness of principal
muscles composing the poultry carcass. Food Technol. 8: 97- 100.
KOTULA, A.W., DREWNIAK, E.E. and DAVIS, L.L. (1957) Effect of carbon dioxide immobilization on the
bleeding of chickens. Poultry Sci. 36: 585-589.
KOTULA, K.L. and WANG, Y. (1994) Characterization of broiler meat quality factors as influenced by feed
withdrawal time. J. Appl. Poultry Res. 3: 103- 110.
LEE, Y.B., HARGUS, G.L., HAGBERG, E.C. and FORSYTHE, R.H. (1976) Effect of antemortem
environmental temperatures on postmortem glycolysis and tenderness in excised broiler breast muscle. J.
Food Sci. 41: 1466.1469.
LEE, Y.B., HARGUS, G.L., WEBB, J.E., RICKANSRUD, D.A. and HAGBERG, E.C. (1979) Effect of
electrical stunning on post-mortem biochemical changes and tenderness in broiler breast muscle. J. Food Sci.
44: 1121-1128.
LI, Y., SIEBENMORGEN, T.J. and GRIFFIS, C.L. (1993) Electrical stimulation in poultry: A review and
evaluation. Poultry Sci. 72: 7-22.
MA, R.T-I. and ADDIS, P.B. (1973) The association of struggle during ex-sanguination to glycolysis, protein
solubility and shear in turkey pectoralis muscle. J. Food Sci. 38: 995-997.
MAGA, J.A. (1994) Pink discoloration in cooked white meat. Food Reviews International, lO(3): 273-286.
MAK1.A. and FRONING, G.W. (1987) Effect of post-mortem electrical stimulation on quality of turkey meat. pH to cooked meat color and pH. Poultry Sci. 79: 784-788.
dioxide as a pre-slaughter stunning method for turkeys. Poulfry Sci. 70: 2201-2206.
in ice slush and air. Poultry Sci. 70: 2197-2200.
Poultry Sci. 66: 1155-1157.
MALLIA. J.G.. BARBUT. S.. VAILLANCOURT. .I.-P.. MARTIN. S.W. and MCEWEN, S.A. (2000) I_ I ,I ,~
Roaster breast meat condemned for cyanosis: A dark firm’dry-like condition? Poultry Sci. 79: 908-912.
brands of broilers in grocery stores, Poultry Sci. 66: 1174-1179. MARION, J.E. and PETERSON, R.A. (1987) Composition, pigmentation, and yield by parts of different
MEAD, G.C., Editor (1989) Processing of Poulrry. Elsevier Science Publishers Ltd. Essex IG11 8JU, England.
MELLOR, D.B., STRINGER, P.A. and MOUNTNEY, G.J. (1958) The influence of glycogen on the
MILLER, R.K. ( 1994) Quality characteristics. In, ”Muscle Foods; Meat, Poultry, and Seafood Technology ”,
MOHAN RAJ, A.B., GREY, T.C., AUDSELY, A.R. and GREGORY, N.G. (1990) Effect of electrical and
MOHAN RAJ, A.B., GREY, T.C. and GREGORY, N.G. (1991) Effect of early filleting on the texture of
MOUNTNEY, G.J. (1966) Poultry Products Technology. The AVI Publishing Co., Wesport, Connecticut, USA.
MOUNTNEY, G.J. and PARKHUST, C.R. (1995) Poultry Products Technology: Third Edition. Food Products
MUGLER, D.J. and CUNNINGHAM, F.E. (1972) Factors affecting poultry meat color – A review. World’s
MURRAY, H.C. and ROSENBERG, M.M. (1953) Studies on blood sugar and glycogen levels in chickens.
NGOKA, D.A. and FRONING, G.W. (1982) Effect of free struggle and pre-slaughter excitement on color of tenderness of broiler meat. Poultry Sci. 37: 1028-1034.
Ed. Kinsman, D.M., Kotula, A.W. and Breidenstein. Chapman & Hall, New York, pages 296-332.
gaseous stunning on the carcase and meat quality of broilers. Br. Poultry Sci. 31: 725-733.
breast muscle of broilers stunned with argon-induced anoxia. B,: Poultry Sci. 32: 3 19-325.
Press, The Haworth Press, Inc., Binghampton, NY 13904 USA.
Poultry Science Journal 28(4): 400-406.
Poultry Sci. 32: 805-8 I I.
turkey breast muscles. Poultry Sci. 61: 2291-2293.
World’s Poultry Science Journal, Vol. 58, June 2002 143

Poultry meat quality: D.L. Fletcher
NORTHCUTT, J.K., FOEGEDING, E.A. and EDENS, F.W. (1994) Water holding properties of thermally
preconditioned chicken breast and leg meat. Poultry Sci. 73: 308-3 16.
OWENS, C.M., HIRSCHLER, E.M., MCKEE, S.R., MARTINEZ-DAWSON, R. and SAMS, A.R. (2000a)
The characterization and incidence of pale, soft, exudative turkey meat in a commercial plant. Poultry Sci. 79:
OWENS, C.M., MATTHEWS, N.S. and SAMS, A.R. (2000b) The use of halothane gas to identify turkeys
prone to developing pale, exudative meat when transported before slaughter. Poultry Sci. 79: 789-795.
OWENS, C.M., MCKEE, S.R. and MATTHEWS, N.S. and SAMS, A.R. (2000~) The development of pale,
exudative meat in two genetic lines of turkeys subjected to heat stress and its prediction by halothane
screening. Poultry Sci. 79: 430-435.
OWENS, C.M. and SAMS, A.R. (1 997) Muscle metabolism and meat quality of pectoralis from turkeys treated
with postmortem electrical stimulation. Poultry Sci. 76: 1047- 105 1.
OWENS, C.M. and SAMS, A.R. (2000) The influence of transportation on turkey meat quality. Poultry Sci. 79:
1204-1207.
PALMER, L.S. (1915) Xanthophyll, the principal natural yellow pigment of the egg yolk, body fat, and blood
serum of the hen. The physiological relation of the pigment to the Xanthophyll of plants. The Journal oj
13iological Chemistry 23: 261-279.
PAPINAHO, P.A. and FLETCHER, D.L. (I 995) Effect of stunning amperage on broiler breast muscle rigor
development and meat quality. Poultry Sci. 74: 1527-1532.
PAPINAHO, P.A. and FLETCHER, D.L. (I 996) The effect of stunning amperage and deboning time on early
rigor development and breast meat quality of broilers. Poultry Sci. 75: 672-676.
PAPINAHO, P.A., FLETCHER, D.L. and BUHR, R.J. (1 995) Effect of electrical stunning amperage and
perimortem struggle on broiler breast rigor development and quality. Poultry Sci. 74: 1533-1539.
PETRACCI, M. and FLETCHER, D.L. (2002) Broiler skin and meat color changes during storage. Poultry
Sci. (In press)
POOLE, G.H. and FLETCHER, D.L. (1998) Comparison of a modified atmosphere stunning-killing system
to conventional electrical stunning and killing on selected broiler breast muscle rigor development and meat
quality attributes. Poultry Sci. 77: 342-347.
QL40, M., FLETCHER, D.L., SMITH, D.P. and NORTHCUTT, J.K. (2001) The effect of broiler breast
meat color on ph, moisture, water-holding capacity, and emulsification capacity. Poultry Sci. 80: 676-680.
Q1.40, M., FLETCHER, D.L., NORTHCUTT, J.K. and SMITH, D.P. (2002) The relationship between raw
broiler breast meat color and composition. Poultry Sci. (Accepted and In Press).
RASKOPF, B.D., KIDD, I.H. and GOFF, O.E. (1961) Effects of diets containing milo on broilers, Tennessee
Agr. Exp. Sta. Bul. No. 324.
SAMS, A.R. (1990) Electrical stimulation and high temperature conditioning of broiler carcasses. Poultry Sci.
SAMS, A.R. (1994) Electrical stimulation at commercial line speeds. Broiler Ind. 57(12): 18-23.
SAMS, A.R. (1 995) Electrical stimulation at commercial line speeds – an update. Broiler Ind. 58( 11): 20-23.
SAMS, A.R., Editor (2001) Podfry Meat Processing. CRC Press LLC, Boca Raton, Florida 3343 I, USA.
SHRIMPTON, D.H. (1960) Some causes of toughness in broilers (young roasting chickens) 1. Packing station
procedure, its influence on the chemical changes associated with rigor mortis and on the tenderness of the
flesh. BI: Poultry Sci. 1: 101-110.
SIMPSON, M.D. and GOODWIN, T.L. (1975) Tenderness of broilers as affected by processing plants and
seasons of the year. Poultry Sci. 54: 275-279.
STADELMAN, W.J., OLSON, V.M., SHEMWELL, G.A. and PASCH, S. (1988) Egg and Poultry Meat
Processing. Ellis Honvood Ltd., Chichester, England.
SUNDE, M.L. (1992) Introduction to the symposium; The scientific way to pigment poultry products. Poultry
Sci. 71: 709-710.
TUNG, H.T., SMITH, J.W. and HAMILTON, P.B. (1971) Aflatoxicosis and bruising in the chicken. Poultry
VEERKAMP, C.H. (1987) Stunning and killing broilers. Proc. 8th European Symp. on Poultry Meat Quality,
Budapest, Hungary, pp 121-126.
WALKER, J.M. and FLETCHER, D.L. (1993) Effect of ante-mortem epinephrine injections on broiler breast
meat color, pH, and haem concentration. Poultry Sci. 72(Suppl. 1): 138.
WALKER, L.T., BIRKHOLD, S.G., KANG, IS. and SAMS, A.R. (1994) A comparison of treatments for
reducing the toughness of early-harvested broiler pectoralis. Poultry Sci. 73: 464-467.
WHEELER, B.R., MCKEE, S.R., MATHEWS, N.S., MILLER, R.K. and SAMS, A.R. (1999) A halothane
lest to detect turkeys prone to developing pale, soft, and exudative meat. Poultry Sci. 78: 1634-1638.
WILLIAMS, W.D. (1992) Origin and impact of color on consumer preference for food. Poultry Sci. 71: 744-
746.
WOELFEL, R.L., OWENS, C.M., HIRSCHLER, E.M. and SAMS, A.R. (1998) The incidence and
characterization of pale, soft and exudative chicken meat in a commercial plant. Poultry Sci. 77(Suppl. 1): 62. 553-558.
69: 1781-1786.
Sci. 50: 795-800.
144 World's Poultry Science Journal, Vol. 58, June 2002

Poultry meat quality: D. L. Fletcher
WOOD, D.F. and RICHARDS, J.F. (1975) Effect of pre-slaughter epinephrine injection on post mortem
WU, W., JEROME, D. and NAGARAJ, R. (1994) Increased redness in turkey breast muscle induced by
YANG, C.C. and CHEN, T.C. (1993) Effects of refrigerated storage, pH adjustment, and marinade on color of
ZOCCHI, C. and SAMS, A.R. (1996) The use of electrical stimulation and extended aging times to reduce the aspects of chicken broiler pectoralis muscle. Poultry Sci. 54: 520-527.
Fusarial culture materials. Poultry Sci. 73: 33 1-335.
raw and microwave cooked chicken meat. Poultry Sri. 72: 355-362.
aging needed to achieve maximum tenderness in broiler breast fillets. Poultry Sci. 7S(Suppl. 1): 21.
World’s Poultry Science Journal, Vol. 58, June 2002 145