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CHAPTER 16
Problems and solutions in deboning poultry meat A. Sams Department of Poultry Science, Texas A&M University, College Station, TX 77843-2472, USA
INTRODUCTION The trend in consumption and production of poultry meat has progressed from whole carcasses, through cut-up parts, to boneless meat. This trend stems from the consumer’s demand and willingness to pay for the convenience and minimal waste associated with boneless meat. However, along with the willingness to pay a premium price comes a demand for maximum quality and consistency. As a result, processors are under extreme pressure in the production of boneless breast meat for not only quality and uniformity, but also for efficiency. This chapter explores the limitations of the harvesting of boneless meat and the problems associated with them. Also, current and future technologies directed at reducing or eliminating these limitations are presented. The limitations in the production of boneless meat are two main categories. Probably the most important from the consumer’s standpoint are the sensory properties of the meat, particularly tenderness. This has been the focus of the majority of the research in meat harvesting. Also, appearance is an emerging consideration as more boneless, skinless meat is displayed in retail display. Second, meat yield is equally important to the processor because of both the high profit on the product and its impact on production efficiency.
SENSORY PROPERTIES Rigor Mortis Development For the purpose of understanding the death process and its effect on meat quality, the muscle can be thought of as an aggregate of individual muscle cells, with each of these cells undergoing its own response to the environment and death. As the animal dies due to loss of blood and the resulting anoxia, the muscle cells continue to respire, producing and consuming adenosine triphosphate (ATP), the primary currency of cellular energy. As cellular oxygen is © CAB International 1999. Poultry Meat Science (eds R.I. Richardson and G.C. Mead)
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depleted, the cell depends almost solely on anaerobic metabolism for the production of its needed ATP. As glycogen is depleted and lactic acid, the end product of anaerobic metabolism, accumulates, due to the lack of blood flow to remove it, sarcoplasmic pH decreases to a level that inhibits further glycolysis and ATP production ceases. However, ATP consumption continues, most importantly in the role of ATP as a plasticizer to dissociate actin and myosin, maintaining muscle extensibility. When the ATP concentration falls to a critical level [1 µmol g−1 (Hamm, 1982)] and there is insufficient ATP to dissociate all of the actin and myosin, they begin to remain complexed as actomyosin and the onset phase of rigor mortis begins. These complexes continue to accumulate until the ATP concentration reaches about 0.1 µmol g−1 at which rigor is developed. In this state, rigor mortis has developed, the muscle is not extensible (cannot ‘relax’) and becomes stiff. The stiffness of a muscle in rigor mortis is a function of the extent of myofibrillar overlap of thick and thin filaments, which is determined by the strength of the opposing muscle groups (Cason et al., 1997), the presence of skeletal attachments (Stewart et al., 1984), the presence of external restraints (Papa and Fletcher, 1988) and temperature (Smith et al., 1969; Lee and Rickansrud, 1978; Bilgili et al., 1989; Dunn et al., 1995). All these factors serve to prevent or increase myofibrillar overlap, sarcomere shortening and contraction that can occur during rigor mortis development. Opposing muscles, skeletal attachments and external restraints are all various forms of resistance to filament overlap and sarcomere shortening. Temperature has its primary effect through ‘cold shortening’, a phenomenon involving calcium leaking from the sarcoplasmic reticulum when ATP is present, initiating a contraction. Although ‘heat shortening’ is a possibility if prerigor meat is cooked, its effect on tenderness depends on the rate of heating and the condition of the meat before cooking (de Fremery and Pool, 1960; Khan, 1971; Lawrie, 1991). In addition to the effect of sarcomere shortening on toughness via filament overlap, it also increases water loss which can further increase toughness (Honikel et al., 1968; Dunn et al., 1993).
Tenderness The impact of rigor mortis development on boneless poultry meat tenderness has been studied for many years. Lowe (1948) and de Fremery and Pool (1960) provided early reports that poultry meat harvested before the development of rigor mortis was objectionably tough. Therefore, the research objective became to determine the time course of rigor mortis development in an attempt to determine the earliest possible time at which the meat could be deboned without causing toughness. de Fremery and Pool (1960) measured the time course of rigor mortis development according to biochemical changes and the loss of extensibility and determined that the onset of rigor mortis occurred between 2.5 and 4 h post-mortem. Kijowski et al. (1982) reported that chicken breast muscle ATP concentration declined to its minimum value by 2 h postmortem whereas lactic acid levels required between 4 and 8 h post-mortem to
Problems and solutions in deboning poultry meat reach their ultimate plateau. Lyon et al. (1985) reported that breast muscle pH reached its ultimate level (5.59) by 2 h post-mortem and that meat deboned after 4 h of refrigerated post-mortem ageing was not significantly toughened. Dawson et al. (1987) reported that meat deboned after 3.3 h post-mortem was not significantly toughened. Together, these reports suggest that different metabolic indices have different abilities to predict rigor mortis development and resulting meat tenderness. This was later reinforced by Stewart et al. (1984) and Sams and Janky (1986) who reported that the relationship between muscle pH at the time of excision is not significantly (P > 0.05) correlated to the tenderness of the resulting meat. Stewart et al. (1984), Lyon et al. (1985) and Dawson et al. (1987) all reported that at some time between 2 and 4 h post-mortem was the critical period after which deboning did not cause toughening. This was taken by the poultry industry as a working indication of rigor mortis completion and it adopted recommendations to store intact carcasses at refrigerated temperatures (< 4°C) for at least 4 h prior to deboning. For logistical reasons, such as shift changes, many processors store the carcasses or breast halves for 8—12 h. It should be noted that this minimum ageing time evolved as the time needed to prevent any statistically detectable change in shear value. This is not to say that it is the minimum time needed to produce meat that would be considered ‘tender’ to consumers. It is also important to note that there is variation around a mean shear value that can cause a considerable percentage of the fillets to be tough, despite a mean that would indicate acceptable tenderness (Young, 1997). It may therefore be necessary to report shear data as frequency distributions rather than simple means with a pooled variance. Although most of the research on ageing poultry meat has been done using shear value as an indication of tenderness, there have also been reports on the sensory responses. However, the results of these studies have been generally consistent with those using shear values (Simpson and Goodwin, 1974; Lyon and Lyon, 1990a, b, 1991). This work has been instrumental in developing target shear values that would be considered tender by consumers. Because shear values are easier to measure for routine quality control uses, they are usually the method of choice provided some appropriate target is available. A 10-blade Allo-Kramer shear compression value of 8 kg g−1 has been widely used as the threshold between tough and tender broiler breast meat. However, Sams and Hirschler (1994) and other cooperative research between ours and five other laboratories suggest that identical meat preparation and shearing procedures can produce quite different shear results. To address this issue, Lyon and Lyon (1990a, b, 1991) used several shearing methods and reported ranges of shear values that corresponded to the various sensory tenderness responses. It is therefore important to a processor desiring a particular level of tenderness to establish the level for the target consumers using consistent methodology. Furthermore, the tough/tender threshold differs between people, cultures and geographic regions of the world. In some parts of the world, broiler breast meat that is aged under refrigeration before deboning is considered too tender/soft by consumers. Slightly toughening the meat by abbreviating the ageing period is an easy way to toughen the meat.
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Appearance Although texture is the primary sensory attribute affected by accelerated harvesting of broiler breast meat, other characteristics such as appearance also need to be considered. The visibility of breast meat has greatly increased with the skin removed and with its use in loaf/roll-type delicatessen items. Two common appearance problems are haemorrhages, with the associated yield losses from trimming, and cellular-based discoloration (paleness) that is generalized throughout the muscle. The haemorrhaging problem is much greater in Europe and is thought to be primarily due to high electrical stunning amperages before slaughter (Veerkamp and de Vries, 1983; Gregory and Wilkins, 1989a, b, 1993). Unfortunately, such amperages are required for poultry slaughter in some countries. Innovative stunning methods, such as high frequency stunning (Gregory et al., 1991; Gregory and Wilkins, 1993), constant current stunning (Rawles et al., 1995a, b) and gas stunning (Raj et al., 1990) are being studied to reduce this problem. As for the generalized, cellular-based discoloration, the use of electrical stunning has been reported to lighten (van Hoof, 1979) and darken (Ngoka and Froning, 1982) poultry meat. Electrical stunning amperage (Papinaho and Fletcher, 1995), electrical stunning duration (Young et al., 1996), gas stunning with CO2 or argon (Raj et al., 1990, 1997; Kang and Sams, 1995; Sams and Dzuik, 1995) or ageing prior to harvest (Owens and Sams, 1997) do not seem to affect fresh broiler meat colour. However, meat colour lightens with preslaughter heat stress (McKee and Sams, 1997), inadequate chilling (McKee and Sams, 1998) and ageing after harvest (Sams and Dzuik, 1995).
MEAT YIELD Although ageing is practically a universal practice among poultry processors producing boneless meat, there is little documentation regarding its effect on product yield and, therefore, the cost of the practice. In an effort to determine this cost for the purpose of providing justification for its elimination, we have recently conducted a survey of the cost of ageing in a commercial plant (Hirschler and Sams, 1998). The results of this survey indicated that deboning breast fillets at 2 h post-mortem would increase meat yield by 3.4% compared to deboning at 11 h post-mortem (9 h of ageing), but only if the deboning was manual. This gain in meat yield was due to a combination of reduced drip loss occurring during ageing and a softening of the muscle during ageing that caused it to tear on harvesting. This tearing left some residual meat on the skeleton during deboning. The mechanism for the softening of muscle tissue probably involves post-mortem myofibrillar proteolysis (Etherington et al., 1987; Birkhold and Sams, 1995; Walker et al., 1995; McKee et al., 1997) or weakening of the connective tissue network (Stanton and Light, 1987, 1988; Nishimura et al., 1995). The cost analysis of the ageing period indicated that, although labor was a substantial cost, drip loss and reduced meat yield were the largest expenses
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that could be saved by eliminating the ageing period before deboning. As an example, the test plant processed 1.3 million broilers per week. The labour cost that could be saved by the elimination of ageing was approximately US$ 210,000 annually. It was determined that the cooler space was inconsequential as it was small relative to the overall space in the plant and would be readily used for another purpose. This also negated the energy savings from eliminating ageing. However, it was estimated that using the processing volume, bird size and meat yields measured in the study, the plant would produce an additional 45,000 kg of boneless breast meat per week. At US$ 2.2 kg−1, this added yield would multiply to US$ 5,200,000 in additional revenue for this single plant each year. Clearly, ageing is an expensive process with the majority of the costs being associated with the loss in meat yield, not labor and energy. The additional revenue gained should justify any capital outlay needed for implementing technologies to eliminate ageing.
TECHNIQUES TO ACCELERATE MEAT HARVESTING The extreme costs of ageing meat on the carcass prior to harvest have made the reduction/elimination of this processing step the target of much research. Many techniques have been evaluated over the years, all directed at the primary limitation to reducing ageing. These technologies either accelerate rigor mortis development, to prevent the toughness that would result from harvesting too early, or attempt to tenderize the meat that was toughened by deboning without sufficient ageing. Yet another technique simply attempts to reduce some of the costs involved in the ageing process. Although some of these technologies are in various stages of commercial implementation, ageing is still practised by most processors producing boneless meat.
Electrical Stimulation to Prevent Toughness Post-mortem electrical stimulation (ES) of meat carcasses was first commercially used by the red meat industry. This technique pulses electricity through a carcass immediately after death, causing generalized muscle contractions throughout the carcass. These contractions serve to exercise the muscles using up stored energy and can therefore affect the rate of rigor mortis development. Cross (1979) reviewed three theories by which post-mortem ES may tenderize meat. First, ES accelerates ATP depletion, resulting in the prevention of cold shortening and improved tenderness. Secondly, ES hastens the decline of post-mortem pH while muscle temperatures are still high, enhancing the possible action of endogenous proteases responsible for tenderization during the ageing process. Finally, ES tenderizes meat by inducing physical disruption of muscle fibres. Many methods of using ES with poultry, with varying degrees of effectiveness, have been reported in the literature and were reviewed by Li et al. (1993). ES systems that use ‘low’ amperages of 0—200 mA per bird induce
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contractions, exercise the muscle and accelerate rigor mortis development. Although rigor is accelerated and the toughening of the resulting meat is significantly reduced, it is not reduced to a sufficient degree to allow the elimination of ageing. These systems only allow some abbreviation of the ageing period and the meat is tough or only ‘slightly tender’ (Thompson et al., 1987; Lyon et al., 1989; Sams, 1990; Lyon and Dickens, 1993). These systems are in commercial use in the USA but are usually used in combination with other techniques such as extended chilling. ES systems using ‘high’ amperages of 350—500 mA per bird induce such forceful contractions that the muscle not only exercises, but tears itself. Birkhold and Sams (1995) presented transmission electron micrographs of ES-treated muscle in which the myofilaments were torn and contracture bands had formed. This physical disruption tenderizes the meat and the rigor mortis acceleration from the exercising prevents toughening. The combination of these two mechanisms has generally made high amperage ES more effective at reducing the need for the ageing period. Whereas low amperage ES results in statistically significant reduction in toughness, high amperage ES results in sufficient reduction in the toughening to produce meat with a shear value that would be considered ‘slightly to moderately tender’ to consumers (< 8 kg g−1) (Birkhold et al., 1992; Birkhold and Sams, 1993). Both low and high amperage electrical stimulation systems have been commercially implemented to some degree and a commercially available high amperage ES device was recently introduced by a USA manufacturer. Although most of the published research on ES has been conducted using immersion chilling, we recently evaluated its effect when using a simulated air-chilling system (Skarovsky and Sams, 1997 unpublished data). Because air chilling can have slower muscle cooling rates, there is a potential for the accelerated metabolism to deplete ATP and/or create a low pH/high temperature environment which may increase heat shortening of sarcomeres and proteolytic activity, all of which may affect tenderness. The results suggested that, when followed by air chilling, high amperage ES accelerated post-mortem metabolism, reducing the need for ageing by up to 50%, but increased drip loss.
Gas Stunning to Prevent Toughness Gas stunning has been reported to affect harvested meat in two ways. First, it reduces the incidence of haemorrhaging on the surface of the pectoralis and therefore improves the appearance of the fillet (Raj et al., 1990; Hirschler and Sams, 1993; Kang and Sams, 1995). However, stunning with CO2 or argon has been shown to have no effect on the more generalized, cellular-based colour measured by L-value (Raj et al., 1990; 1997; Sams and Dzuik, 1995). Second, gas stunning has been reported to cause anoxia, accelerating post-mortem pH decline and rigor mortis development and reducing the ageing needed before harvesting fillets (Raj and Gregory, 1991; Raj et al., 1991; 1997; Raj, 1994). These effects are observed when using an atmosphere of less than 2% oxygen
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with air displacement by either argon (Ar) or a mixture of Ar and CO2. However, it appears as though using high concentrations of CO2 to create this anoxia prevents the metabolic acceleration, probably because of the anaesthetic effect of the CO2 (Sams and Dzuik, 1995; Kang and Sams, 1995). However, research suggests that the benefit from gas stunning largely depends on electric stunning to which it is compared (Craig and Fletcher, 1995). The higher amperage (90—120 mA per bird) electric stunning used in Europe causes more carcass damage and slows rigor mortis development. The lower amperage (10—30 mA per bird) electric stunning used in the USA causes very little damage (if done properly) and has little if any delaying effect on rigor mortis development.
Chemical and Physical Methods of Tenderization Instead of attempting to accelerate metabolism to reduce the need for ageing, other studies have attempted to correct the toughness developed when meat was harvested without sufficient ageing. Lyon and Hamm (1986) harvested broiler breast fillets within 40 min of death and treated them with blade tenderization and a combination of NaCl and polyphosphates. Their results indicated that the treatments involving the phosphates produced meat with a tenderness equivalent to ageing 24 h before harvest. However, such extensive treatments may not be acceptable for markets demanding minimally processed fillets. Restraining the wings during rigor mortis development to reduce sarcomere shortening also has been reported to reduce the toughening associated with early-harvested fillets (Birkhold et al., 1992; Birkhold and Sams, 1993; Lyon and Dickens, 1993), but not to a sufficient degree to produce acceptably tender meat and thereby completely eliminate the need for ageing. A final physical method was the use of a belt flattener to apply pressure to the fillets and reduce their height (Lyon et al., 1992). Flattening reduced shear values but not enough to cause the fillets to be tender.
Extended Ageing after Harvesting Because of the extremely rapid pace and variations in poultry meat processing, the industry generally operates under the minimum guideline of 4—6 h of ageing before deboning. As previously stated, this is to prevent toughening. The resolution of rigor mortis, the physical and biochemical degradation of the muscle ultrastructure responsible for toughness, was not considered in developing this guideline because processors cannot always predict the destiny of their product. McKee et al. (1997) reported that if meat was deboned immediately after chilling without any ageing and then stored for 71 h at 2°C, it achieved shear value of 8 kg g−1 or less, a tenderness level considered ‘slightly to moderately tender’ by consumers (Lyon and Lyon, 1990b). However, in addition to uncertain product destiny, processors in the USA are increasingly demanding ‘maximum’ tenderness and not simply ‘acceptable’
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tenderness. This may not be the case in some other countries where the population prefers slightly tougher meat.
Extended Chilling to Reduce Ageing Costs A final approach to reducing the cost of ageing meat on the carcass prior to harvesting is to extend the chilling time to include the ageing period. This process, called extended chilling, would eliminate the labour involved in transferring the carcasses into a separate area/container. If done with immersion chilling, extended chilling would reduce the drip loss associated with ageing. However, excessive evaporative loss can already be a problem for air chilling and extending the chilling time would only increase this loss. Another limitation of extended chilling is the additional plant and chiller space needed to contain four or more hours of production. Also, although drip loss may be reduced with extended immersion chilling, it would not reduce the loss in meat yield resulting from muscle softening occurring during ageing.
REFERENCES Bilgili, S.F., Egbert, W.R. and Huffman, D.L. (1989) Effect of postmortem aging temperature on sarcomere length and tenderness of broiler pectoralis major. Poultry Science 68, 1588—1591. Birkhold, S.G. and Sams, A.R. (1993) Fragmentation, tenderness and post-mortem metabolism of early-harvested broiler breast fillets from carcasses treated with electrical stimulation and muscle tensioning. Poultry Science 72, 577—582. Birkhold, S.G. and Sams, A.R. (1995) Comparative ultrastructure of pectoralis fibers from electrically stimulated and muscle-tensioned broiler carcasses. Poultry Science 74, 194—200. 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 Science 71, 2106—2112. Cason, J.A., Lyon, C.E. and Papa, C.M. (1997) Effect of muscle opposition during rigor on development of broiler breast meat tenderness. Poultry Science 76, 785—787. Craig, E.W. and D.L. Fletcher (1995) A comparison of European (EC) and US electrical stunning systems of broiler carcass and meat quality. Poultry Science 74 (Suppl. 1), 30. Cross, H.R. (1979) Effects of electrical stimulation on meat tissue and muscle properties: a review. Journal of Food Science 44, 509—512, 514, 523. Dawson, P.L., Janky, D.M., Dukes, M.G., Thompson, L.D. and Woodward, S.A. (1987) Effect of post-mortem boning time during simulated commercial processing on the tenderness of broiler breast meat. Poultry Science 66, 1331—1333. de Fremery, R. and Pool, M.F. (1960) Biochemistry of chicken muscle as related to rigor mortis and tenderization. Food Research 25, 73—87. de Fremery, R. and Pool, M.F. (1963) The influence of post-mortem glycolysis on poultry tenderness. Journal of Food Science 28, 173—176. Dunn, A.A., Kilpatrick, D.J. and Gault, N.F.S. (1993) Effect of post-mortem temperature on chicken M. pectoralis major: muscle shortening and cooked meat tenderness. British Poultry Science 34, 689—697.
Problems and solutions in deboning poultry meat Dunn, A.A., Kilpatrick, D.J. and Gault, N.F.S. (1995) Contribution of rigor shortening and cold shortening to variability in the texture of Pectoralis major muscle from commercially-processed broilers. British Poultry Science 36, 401—413. Dzuik, C.S. and Sams, A.R. (1996) Rigor mortis, toughness and color development in breast fillets from broilers treated with argon-induced anoxia and post-mortem electrical stimulation. Poultry Science 75, 21. Etherington, D.J., Taylor, M.A.J. and Dransfield, E. (1987) Conditioning of meat from different species. Relationship between tenderising and the levels of cathepsin B, cathepsin L, calpain I, calpain II and β-glucuronidase. Meat Science 20, 1—18. Gregory, N.G. and Wilkins, L.J. (1989a) Effect of ventricular fibrillation at stunning and ineffective bleeding on carcass quality defects in broiler chickens. British Poultry Science 30, 825—829. Gregory, N.G. and Wilkins, L.J. (1989b) Effect of stunning current on carcass quality in chickens. Veterinary Record 124, 530—532. Gregory, N.G. and Wilkins, L.J. (1993) Causes of downgrading. Broiler Industry 56 (4), 42—45. Gregory, N.G., Wilkins, L.J. and Wotton, S.B. (1991) Effect of electrical stunning frequency on ventricular fibrillation, downgrading and broken bones in broilers, hens and quails. British Veterinary Journal 147, 71—77. Hamm, R. (1982) Post mortem changes in muscle with regard to processing of hot-boned beef. Food Technology 36 (11), 105—115. Hirschler, E.M. and Sams, A.R. (1993) Comparison of carbon dioxide and electricity for the preslaughter stunning of broilers. Poultry Science 72, 143. Hirschler, E.M. and Sams, A.R. (1998) Commercial-scale electrical stimulation of poultry: the effects on tenderness, breast meat yield and production costs. Journal of Applied Poultry Research 7, 99—103. Honikel, K.O., Kim, C.J., Hamm, R. and Roncales, P. (1968) Sarcomere shortening of prerigor muscles and its influence on drip loss. Meat Science 16, 267—282. Kang, I.S. and Sams, A.R. (1995) Rigor mortis development and meat quality in broilers stunned with electricity, stunned with carbon dioxide, or killed with carbon dioxide. Poultry Science 74, 79. Khan, A.W. (1971) Effect of temperature during postmortem glycolysis and dephosphorylation of high energy phosphates on poultry meat tenderness. Journal of Food Science 36, 120—121. Kijowski, J., Niewiarowicz, A. and Kujawska-Biernat, B. (1982) Biochemical and technological characteristics of hot chicken meat. Journal of Food Technology 17, 553—560. Lawrie, R. (1991) Meat Science, 5th edn. Pergammon Press, Elmsford, NY, pp. 206—207. Lee, Y.B. and Rickansrud, D.A. (1978) Effect of temperature on shortening in chicken muscle. Journal of Food Science 43, 1614—1615 Li, Y., Siebenmorgen, T.J. and Griffin, C.L. (1993) Electrical stimulation in poultry: a review and evaluation. Poultry Science 72, 7—22. Lowe, B. (1948) Factors affecting the palatability of poultry with emphasis on the histological post-mortem changes. Advances in Food Research 1, 203—256. Lyon, C.E. and Dickens, J.A. (1993) Effects of electric treatments and wing restraints on the rate of post-mortem biochemical changes and objective texture of broiler pectoralis major muscles deboned after chilling. Poultry Science 72, 1577—1583. Lyon, B.G. and Hamm, D. (1986) Effects of mechanical tenderization with sodium chloride and polyphosphates on sensory attributes and shear values of hotstripped broiler breast meat. Poultry Science 65, 1702—1707. Lyon, B.G. and Lyon, C.E. (1990a) Texture profile of broiler pectoralis major as influenced by post-mortem deboning time and heat method. Poultry Science 69, 329—340.
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A. Sams Lyon, C.E. and Lyon, B.G. (1990b). The relationship of objective shear values and sensory tests to changes in tenderness of broiler breast meat. Poultry Science 69, 1420— 1427. Lyon, B.G. and Lyon, C.E. (1991) Shear value ranges by Instron Warner—Bratzler and single-blade Allo-Kramer devices that correspond to sensory tenderness. Poultry Science 70, 188—191. Lyon, C.E., Hamm, D. and Thomson, J.E. (1985) pH and tenderness of broiler breast meat deboned at various times after chilling. Poultry Science 64, 307—310. Lyon, C.E., Davis, C.E., Dickens, J.A., Papa, C.M. and Reagan, J.O. (1989) Effects of electrical stimulation on the post-mortem biochemical changes and objective texture of broiler pectoralis muscle. Poultry Science 68, 249—257. Lyon, C.E., Silvers, S.H. and Robach, M.C. (1992) Effects of a physical treatment applied immediately after chilling on the structure of muscle fiber and the texture of cooked broiler breast meat. Journal of Applied Poultry Research 1, 300—304. McKee, S.R. and Sams, A.R. (1997) The effect of seasonal heat stress on rigor development and the incidence of pale, exudative turkey meat. Poultry Science 76, 1616—1622. McKee, S.R. and Sams, A.R. (1998) Development at elevated temperatures induces pale exudative turkey meat characteristics. Poultry Science 77, 169—174. McKee, S.R., Hirschler, E.M. and Sams, A.R. (1997) Physical and biochemical effects associated with tenderization of broiler breast fillets during aging after pre-rigor deboning. Journal of Food Science 62, 959—962. Ngoka, D.A. and Froning, G.W. (1982) Effect of free struggle and preslaughter excitement on color of turkey breast muscles. Poultry Science 61, 2291—2293. Nishimura, T., Hattori, A. and Takahashi, K. (1995) Structural weakening of intramuscular connective tissue during conditioning of beef. Meat Science 39, 127— 133. Owens, C.M. and Sams, A.R. (1997) Muscle metabolism and meat quality of pectoralis from turkeys treated with postmortem electrical stimulation. Poultry Science 76, 1047—1052. Papa, C.M. and Fletcher, D.L. (1988) Effect of wing restraint on postmortem muscle shortening and the textural quality of broiler breast meat. Poultry Science 67, 275— 279. Papinaho, P.A. and Fletcher, D.L. (1995) Effect of stunning amperage on broiler breast muscle rigor development and meat quality. Poultry Science 74, 1527—1532. Raj, A.B.M. (1994) Effect of stunning method, carcase chilling temperature and filleting time on the texture of turkey breast meat. British Poultry Science 35, 77—89. Raj, A.B.M. and Gregory, N.G. (1991) Effect of argon stunning, rapid filleting and early filleting on texture of broiler breast meat. British Poultry Science 32, 741—746. Raj, A.B.M., Grey, T.C., Audsley, A.R. and Gregory, N.G. (1990) Effect of electrical and gaseous stunning on the carcass and meat quality of broilers. British Poultry Science 31, 725—733. Raj, A.B.M., Grey, T.C. and Gregory, N.G. (1991) Effect of early filleting on the texture of breast muscle of broilers stunned with argon-induced anoxia. British Poultry Science 32, 319—325. Raj, A.B.M., Wilkins, L.J., Richardson, R.I., Johnson, S.P. and Wotton, S.B. (1997) Carcase and meat quality in broilers either killed with a gas mixture or stunned with an electric current under commercial processing conditions. British Poultry Science 38, 169—174. Rawles, D., Marcy, J. and Hulet, M. (1995a) Constant current stunning of market weight broilers. Journal of Applied Poultry Research 4, 109—116.
Problems and solutions in deboning poultry meat Rawles, D., Marcy, J. and Hulet, M. (1995b) Constant current stunning of market weight turkeys. Journal of Applied Poultry Research 4, 117—126. Sams, A.R. (1990) Electrical stimulation and high temperature conditioning of broiler carcasses. Poultry Science 69, 1781—1786. Sams, A.R. and Dzuik, C.S. (1995) Gas stunning and post-mortem electrical stimulation of broiler chickens. In: Briz, C.P. (ed.) Proceedings of the XIIth European Symposium on the Quality of Poultry Meat. Zaragosa, Spain, pp. 307—314. Sams, A.R. and Hirschler, E.M. (1994) A reevaluation of the toughness/tenderness threshold shear value as affected by cooking method, deboning time and laboratory. Poultry Science 73 (Suppl. 1), 159. Sams, A.R. and Janky, D.M. (1986) The influence of brine-chilling on tenderness of hot-boned chill-boned and age-boned broiler breast fillets. Poultry Science 65, 1316—1321. Simpson, M.D. and Goodwin, T.L. (1974) Comparison between shear values and taste panel scores for predicting tenderness of broilers. Poultry Science 53, 2042—2046. Smith, M.C. Jr, Judge, M.D.and Stadelman, W.J. (1969) A ‘cold shortening’ effect in avian muscle. Journal of Food Science 34, 42—46. Stanton, C. and Light, N. (1987) The effects of conditioning on meat collagen: part 1. evidence for gross in situ proteolysis. Meat Science 21, 249—265. Stanton, C. and Light, N. (1988) The effects of conditioning on meat collagen: part 2. direct biochemical evidence for proteolytic damage in insoluble perimysial collagen after conditioning. Meat Science 23, 179—199. Stewart, M.K., Fletcher, D.L., Hamm, D. and Thomson, J.E. (1984) The influence of hot boning broiler breast muscle on pH decline and toughening. Poultry Science 63, 1935—1939. Thompson, L.D., Janky, M.D. and Woodward, S.A. (1987) Tenderness and physical characteristics of broiler breast fillets harvested at various times from post-mortem electrically stimulated carcasses. Poultry Science 66, 1158—1167. Veerkamp, C.H. and de Vries, A.W. (1983) Influence of electrical stunning on quality aspects of broilers. In: Eikelenboom, G. (ed.) Stunning of Animals for Slaughter. Martinus Nijhoff, Boston, MA, pp. 197—212. Van Hoof, J. (1979) Influence of ante- and peri-mortem factors on biochemical and physical characteristics of turkey breast muscle. Veterinary Quarterly 1, 29—36. Walker, L.T., Shackelford, S.D., Birkhold, S.G. and Sams, A.R. (1995) Biochemical and structural effects of rigor mortis-accelerating treatments in broiler pectoralis. Poultry Science 74, 176—186. Young, L.L. (1997) Effect of post-chill deboning on tenderness of broiler breast fillets. Journal of Applied Poultry Research 6, 174—179. Young, L.L., Northcutt, J.K. and Lyon, C.E. (1996) Effect of stunning time and polyphosphates on quality of cooked chicken breast meat. Poultry Science 75, 677— 681.
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