Download Muscle Fiber Types in Broilers and Their Relationship to Meat

Muscle Fiber Types in Broilers and Their Relationship to Meat Quality
by Shelly McKee, Ph.D.
Department of Poultry Science
Aubum University
Introduction
Because of the emphasis on value-added products, the poultry industry
has become focused on muscle yield characteristics. To meet the demands of
the industry, genetic selection has been concentrated on growth parameters in
meat producing lines. In the past 25 years, the production time required to
produce a 4-4.5 pound bird has been reduce to 5-6 weeks compared to 12
weeks in genetically unimproved lines. While vast improvements in growth traits
have been observed, these improvements have not been without consequence
to other performance traits particularly in regards to disease susceptibility,
skeletal muscle cell structure, metabolism and meat quality. Changes in muscle
cell function and/or structure may predispose birds to stress related muscular
damage which may manifest as meat quality defects. Many of the meat quality
problems noted today are more evident because of the market shift from whole
birds to further processed products. These problems include poor cohesiveness,
poor water holding capacity, poor texture, pale color development and meat
toughness (McKee and Sams, 1997; Sosniki and Wilson, 1991). Perhaps future
genetic selection decisions will recognize the importance of processing and meat
quality relative to the economic tradeoff associated with growth and performance
traits.
To understand the underlying biochemical mechanisms that relate to meat
quality, the inherent qualities of the muscle fibers should be discussed. Muscles
are made up of individual muscle fibers of different sizes, different numerical
densities, and different biochemical and physiological characteristics.
Differences in muscle fibers give rise to different muscle colors and biochemical
potential. Color differences in muscle fibers have been recognized for several
centuries. However, it was not until 1874 that differences were observed in the
contraction rate of muscle fibers based on muscle fiber color (Pearson and
Young, 1989). Specifically, it was noted that "red" muscle maintained slower
contractions that were sustained for a longer period of time compared to the
"white" muscles. It was later realized that muscle fibers are not distinctively "red
or white", but are a heterogeneous mixture of the two. These inherent differences
in muscle composition are related to the varying functions of muscle and the
need to provide skeletal support and movement. Thus, all skeletal muscle
contains varying degrees of both "red and white" muscle.
Although the descriptors "red and white" provide a relatively easy distinction
between the two fiber types, the metabolic differences between the various
muscle fiber types is much more complex and therefore not adequately
described by differences in color. Peter et aL (1972) classified muscle as type 1,
IIA or liB based on speed of contraction, oxidative capacity and glycolytic
metabolism. Type I muscle can be characterized as slow-contracting, oxidative
in metabolism and "red" in color (Lawrie, 1991). Type II fibers are generally
characterizedas fast-contracting,predominatelyglycolyticin metabolismand
'%vhite"in color;however,furtherdistinctionsnotedby Peteret al. (1972)
recognizedtype IIA fibersas havingmixedoxidative-glycolytic
capacitywhereas
type liB fiberswere primarilyglycolytic.Becausetype II fibershave less
oxidativemetabolismin comparisonto type I fibers, type II fibersor "white"
musclehave generallyless myoglobinand fewer mitochondriabut a higher
glycogencontent. Notonly doestype II muscle(white)have less myoglobin,but
the musclealso has fewer capillariessupplyingblood. The levelsof metabolic
enzyme and ATPase activityalsodifferamongfibertypes. Differencesin muscle
metabolismbetweenthe variousfibertypes will influencepost-mortem
metabolism,and ultimately,the functionalpropertiesof meat.
Chicken skeletalmusclecan befurther dividedintofive distinctmusclefiber
types. There is the type I slow-contracting
"red" fibers,type IIA and liB fastcontracting"white"fibers, and a type Ilia and IIIB whichare slow,tonic
"intermediate"fibers (Table 1). In chicken,type I musclefibers are found in the
soleusmusclethat requiresa sustainedlevelof activityfor activitiessuchas
walkingand standing(Hnik et al., 1985). Type IIA fibersare foundin muscles
that are fast-movingand repetitivein action;therefore,they do notfatigueas
easilyas type liB glycolytic.Type IIA fibersare foundin musclessuchas the
sartorius(red). Type liB musclefibersare fast-contractingbut are moreeasily
fatigued in comparisonto bothtype I and type IIA musclefibers. Type liB fibers
have higherlevelsof ATP and glycogenand are foundprimarilyin pectoral
muscle,posteriorlatisimusdorsiand to some degree in the satorius(white).
Type Ilia and IIIB slow-tonicfibersare notfound in mammalsbut are found in
musclessuchas the plantarisand anteriorlatissimusdorsiof the avian species.
These musclesremaincontractedmuchof the time becausetheirfunctionisto
keep the birds'wingsbackagainstthe body(Goldspinkand Yang, 1999).
As birdsage, the cross-sectionalarea of the musclefiber
increasesin size (Table 2) (Dransfieldand Sosnicki,1999). Musclefibersfrom
fast growinglinesof chickenshave largerfiber diametersthan slowgrowinglines
and largerfiber diametersare oftenassociatedwithan increasednumberof giant
fibers (Essen-Gustavasson,1993). These types of fibersare also seen among
stress-susceptiblepigsthat displayrapidglycogenolysisand lactateproductionin
responseto a particularstress(Essen-Gustavasson,193). Poor meat quality
characteristicssuchas higherdrip loss,paler color,and poortexturehave been
observedin porkwithan increasednumberof giantfibers. Regardlessof the
presenceof giantfibers,swinehavingmorewhite type II fiberstend to be more
stresssusceptiblethan swinewithalternativefibertype distributions.Poultry
musclenaturallyhas a predominanceof type II fibers whichare associatedwith
stresssusceptibilityand poormeat qualityin othermeat producinganimals.
Degenerative muscle and meat quality issues
Because chicken skeletal muscle differs in fiber type, biochemistry, and
overallfunctionfrom otheranimals,it is not surprisingthat differencesalso exist
in meat quality. In domesticchickenand turkey, breedingprogramsare selecting
for rapidgrowthtraitsand heavierbreastmuscling.These selectivetraits
influence muscle fiber type that may potentiallyaffect meat quality. In studies of
turkeys, there was a correlation between body weight, muscle weight, and fiber
size (Mahon, et al., 1999). At market age, Type I "red" fibers of the leg are
smaller in diameter compared to type IIA and liB fibers of the pectoralis (Mahon
et al., 1999). In addition, it has been shown that while the increase in size of
muscles such as the medial lateral adductor and gastrocnemius were
proportional to body weight, the pectoralissuperficialis was proportionately larger
and exhibited a more rapid increase in fiber size (Wilson, et al., 1990).
Chickens and turkeys have proportionally more type II "fast-contracting" fibers
thereby influencing rigor mortis development and their susceptibility to stress.
Rigor morris completion normally takes 4-6 hr in chicken and 6-8 hr in turkeys.
However, there has been an increase in the susceptibility of chickens and turkey
to rapid glycolysis leading to the development of pale, soft, and exudative (PSE)
meat. In these stress susceptible birds, ultimate pH values can be observed as
earlier as 20 minutes post-mortem. This condition is similar to the PSE meat
found in swine. Because the muscles reach a low pH while the carcass
temperatures are still high, extensive protein denaturation can occur altering the
functionality of these proteins in further processed products. In swine, this
condition is due to a point mutation in the ryanodine receptor caused by the
selection for heavier leaner muscling. Pigs susceptible to this condition have
more type II anaerobic fibers than other non-susceptible breeds. Moreover, beef
muscles having a much higher ratio of type I to type II muscle fibers rarely exhibit
PSE meat characteristics.
Chilling temperatures of poultry can influence the rate glycolysis and
ultimate meat quality. Minimal pH changes have been associated with protein
denaturation; specifically, Offer (1991) reported a drop in pH by I unit increased
protein denaturation 12 times. McKee and Sams (1998) found that chilling
temperature and rates significantly influenced turkey meat quality. Particularly,
meat from turkey carcasses chilled at high temperatures had higher drip loss,
paler color, higher cook loss and was tougher than turkey carcasses chilled at
lower temperatures (Table 3). This study suggested that rapid chilling may
offset some of the potential detrimental PSE like effect of rapid glycolyzing lines
of birds, particularly those that are fast growing.
Muscle histology from turkeys selected for rapid growth, show that the width
of the muscle fiber exceeds that of the connective tissue leading to a loss of
muscle integrity or focal myopathy (Sosnicki and Wilson, 1991). Aside from the
biochemical changes occurring in PSE type muscle, focal myopathy may also
influence the final cohesiveness and juiciness of further processed products
(Sosnicki and Wilson, 1991). Furthermore, muscle degeneration is characterized
by focal necrosis, proliferation of fat and connective tissue associated with the
endomysium, perimysium, and hypercontraction of muscle fibers.
Hypercontraction of muscle fibers is associated with toughening of the pectoralis
superficialis; although, hypercontracted muscle can also be associated with leg
muscle or red type fibers (Grey et al., 1986).
Cold shortening, meat tendemess and fiber type
Even though hypercontractionisassociatedwithtougheningof degenerative
type II muscle fibers; in general, muscles having predominately non-degenera,.;ve
type II muscle tend to be more tender than "red" or type I fibers. One reason for
the difference in toughening between type I and type II muscle fibers appears to
be associated with the difference in susceptibility to cold shortening. This may be
attributed to the increased susceptibility to cold shortening in "red" fibers
because calcium recapture is not as efficient in "red" muscle. Calcium promotes
muscle contraction, and calcium uptake is regulated by the sarcoplasmic
reticulum which is not as well developed in "red" muscle in comparison to type II
"white" muscle. Similar conclusions were made by Smulders et al. (1990) who
suggested that the higher the degree of oxidative fibers the greater the
propensity for meat toughening. Furthermore, direct relationships have been
drawn between type liB fiber content and meat tendemess (Totland, et al., 1988).
Other factors such as the fiber diameter, fiber number per section, the presence
of connective tissue and fat influence meat tenderness as well.
Effect of electrical stimulation on different fiber types
Although cold shortening occursto a lesserdegree in poultry in comparisonto
meat animals having more "red" fibers, poultry is usually deboned earlier in the
processing scheme compared to other meat producing animals. Rigor mortis is
not fully resolved in chickens until 4-6 hours post-mortem; however, in
commercial practice, the muscle may be deboned as earlier as 1 to 2 hours.
Without the anchor of the skeletal frame, pre-rigor poultry muscle is free to
contract. Therefore, cold shortening of poultry muscle can occur resulting in
meat toughening. Electrical stimulation is commonly used in beef to hasten rigor
mortis resolution and prevent toughening due to cold shortening. Depending on
the voltage used for the stimulation, the mode of action for tenderization can be
different. Lower voltages tend to exercise the muscle depleting ATP and
preventing cold shortening. Alternatively, higher voltages may disrupt muscle
integrity thereby tenderizing the meat.
Electrical stimulation is also used to a lesser degree in poultry to achieve the
same effect. In 1794, Benjamin Franklin was the first to find that electrical
stimulation tenderized turkey flesh (Lawrie, 1991). Because of the different
levels of glycogen and ATP among type I and type II fibers, there is a difference
in the way the muscle will respond to electrical stimulation. A study comparing
meat characteristics of duck pectoralis (red muscle fiber) to broiler pectoralis
muscle found that electrical stimulation was more effective in the broiler
pectoralis compared to the duck (Owens et al., 1997). It has been suggested
that electrical stimulation could possibly intensify the PSE type condition by
hastening rigor development, but this has not been the case. Studies in both
turkey and pork have shown that electrical stimulation does not necessarily
promote pale color, poor water holding capacity or poor texture in meat as one
might expect (Alvarado and Sams, 1999).
Meat palatability and functional characteristics in relation to fiber type
Unlike other meat animals, fat in poultry in deposited primarily under the skin;
therefore, poultry meat does not contain the intramuscular fat deposits such as
those found in beef, swine, or lamb. Poultry white meat is generally very lean
having as low asl.3% fat that is attributed to triglycerides found in the cell
membranes of the muscle. Poultry "red" meat such as the thigh and drum have
about 7.3% fat (Mountney, 1989). In swine, histochemical stainings indicated
that type I fiber and type IIA contain more neutral lipids in comparison to type liB
"white" fibers. Furthermore, it was noted that pig muscles with higher oxidative
capacity and higher triglyceride content rated higher in sensory evaluations than
other muscles ( Essen-Gustavsson and Fjelkner-Modig, 1985).
There are differences in the sensory characteristics of poultry "white" and
"red" meat. Poultry thigh and drum have higher cooking losses compared to
breast meat. Poultry thighs and drums have more type I fibers, more fat and
more connective tissue. Meat with higher percentage of fat will have higher
cooking loss because of the percentage of fat lost during cooking. Also, there is
proportionately less functional protein available for water binding. Because
poultry thigh and drum have more oxidative type fibers, they also have more
myoglobin and mitochrondia. The myoglobin is a heme protein containing iron.
Poultry drum and thighs have a stronger flavor in comparison to the breast
muscle which is largely attributed iron content of the muscle. The higher level of
fat in the dark meat may also enhance the perceived juiciness of the meat.
In general, poultry meat is a source of highly functional proteins that lend to
the cohesiveness and juiciness of further processed products. Some of the
advantages of using poultry meat in further processed products, include the
leanness of the meat, the relatively low amount of connective tissue, and high
availability of functional meat proteins. Other meat sources such as beef, pork
and lamb must be trimmed of excess fat and tendons or sinews. These meat
quality characteristics are directly related to the fiber type of the different
muscles.
Literature Cited
AIvarado,C. Z., and A. R. Sams, 1999. Rigormortisdevelopmentin turkey
breastmuscle and the effect of electricalstimulation.PoultrySci. 78:210.
Essen-Gustavsson,B., 1993. Pork Quality: Genetic and Metabolic Factors. E.
Puolanneand D. I. Demeyer, (Ed.), p. 140-159. CABI Publishing,
Wallingford,UK:
I
Essen-Gustavsson,B. and S. Fjelkner-Modig,1985. Skeletal muscle
characteristicsin differentbreedsof pigs in relationto sensorypropertiesof
meat. MeatSci. 13:33-47.
Dransfield,E. and A. A. Sosnicki,1999. Relationshipbetweenmuscle growth
and poultrymeat quality. PoultrySci. 78:743-746.
Hnik, P., R. Vejsada, D. F. Goldspink,S. Kasicki,and I. Krekule,1985.
Quantitativeevaluationof electromyogramactivityin rat extensorand flexor
musclesimmobilizedat differentlengths. ExperimentalNeurology88:515-528.
Goldspink,G. and S. ¥. ¥ang, 1999. PoultryMeat Science: PoultryScience
SymposiumVolume25. R.I. Richardsonand G.C. Mead, (Ed.), p. 3-18. CABI
Publishing,Wallingford,UK.
Grey, T. C., N. M. Griffiths,J. M. Jones and D. Robinson,1986. A studyof some
factors influencingthe tendernessof turkey breastmeat. Lebensm.Wiss.
Technol. 19:412-414.
Lawrie, R.A., 1991. Pages 125-131 in: Meat Science, 5thedition. Pergamon
Press,Oxford, England.
Mahon, M., 1999. PoultryMeat Science: PoultryScience SymposiumVolume
25. R.I. Richardsonand G.C. Mead, (Ed.), p. 19-64. CABI Publishing,
Wallingford,UK.
McKee, S. R. and A. R. Sams. 1997. The effect of seasonalheat stresson rigor
developmentand the incidenceof pale, exudativeturkeymeat. Poultry
Sci. 76:1616-1620.
McKee, S. R. and A. R. Sams, 1998. Rigormortisdevelopmentat elevated
temperaturesinducespale exduativeturkeymeat characteristics.Poultry
Sci. 77:i69-174.
Mountney,G. J., 1989. Pages 53-56 in: PoultryProductsTechnology,2 nd
edition. Food ProductsPress, New York, N¥.
Owens, C. M., C. Zocchi, and A. R. Sams, 1997. Rigor mortisdevelopment,
calpastatin activity, and tenderness in pectoralis from electrically stimulated
broiler chickens and ducks. Poultry Sci. 76:49 (Suppl. 1) (Abstr.).
Pearson, A.M. and R.B. Young, 1989. Pages 248-260 in: Muscle and Meat
Biochemistry. Academic Press, Inc., San Diego, CA.
Peter, J. B., R. J. Bamard, V. R. Edgerton, C. A. Gillespie and K. E. Stempel,
1972. Metabolic profiles of three fiber types of skeletal muscle in guinea pigs
and rabbits. Biochem. 11:2627.
Re'mignon, H., G. Marche', and F. H. Ri chard, 1993. Conse-quences de la
selection sur la vitesse de croissance sur lesproprie'te's des fibres musculaires
chez le poulet. Pages5965in: Proceedings of the Xl European Symposium on
the Quality of Poultry Meat. Vol 1. Tours, France.
Smulders, F. J. M., B. B. Marsh, D. R. Swartz, R. L. Russell and M. E. Hoenecke,
1990. Beef tenderness and sarcomere length. Meat Sci. 28:349-363.
Sosnicki, A.A. and B. W. Wilson, 1991. Pathology of turkey skeletal muscle:
implications for the poultry industry. Food Structure 10:317-326.
Sturkie, P.D., 1986. Pages 77-78 in: Avian Physiology, 4thedition. SpringerVerlag New York, Inc., New York, NY.
Totland, G. K., H. Kryvi and E. Slinde, 1988. Composition of muscle fibre types
and connective tissue in bovine M. semitendinosus and its relation to
tenderness. Meat Sci. 23:303-315.
Whiting, R.C. and J.F. Richards, 1978. Calcium uptake and ATPase activity by
sarcoplasmic reticulum of red and white poultry muscles. J. Food Sci. 43:662665.
Wilson, B.W., P.S. Nieberg and R.J. Buhr, 1990. Turkey muscle growth and
focal myopathy. Poultry Sci. 69:1553-1562.
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TABLE 3. Physicalparametersof Pectoralis musclesfromturkey carcassesheld
at 0, 20, and 40 C for4 h post-mortem(McKee and Sams, 1997).
Post-mortemTemperatureTreatments
Pooled
Physical Parameters
SEM
0C
20 C
40 C
Drip loss(%)1
0.18
0.01a
0.05a
1.88b
Cook loss(%)
0.71
24.05a
26.99a'b
28.86b
Shear value (kg/g)
0.30
7.31a
7.43a
9.69b
Sarcomere lencjth2
0.20
1.89a
1.87a
1.79b
a'bMeans(n=12 per mean) withineach rowwithdifferentsuperscriptsare
significantlydifferent(P<.05)o
124h post-mortem.
24 h post-mortem.