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Effects of Electrical Stunning and Hot Deboning on Broiler Breast Meat Quality
Effects of Electrical Stunning and Hot Deboning on Broiler Breast Meat Quality J. E. THOMSON, C. E. LYON,1 D. HAMM, and J. A. DICKENS Richard B. Russell Agricultural Research Center, Agricultural Research Service, United States Department of Agriculture, P.O. Box 5677, Athens, Georgia 30613 D. L. FLETCHER Department of Poultry Science, University of Georgia, Athens, Georgia 30602
Richard B. Russell Agricutural Research Center, Agricultural Research Service, United States Department of Agriculture, P.O. Box 5677, Athens, Georgia 30613 (Received for publication November 18, 1985) ABSTRACT The effects were determined of electrical stunning prior to death and hot deboning on pH, percent weight loss due to cooking, and objective tenderness of broiler breast meat. Forty-eight live broilers were obtained from a processing plant and transported to the pilot plant facility of the research center. Half the birds were electrically stunned prior to death, and half were not. Birds were processed in the following manner: bled by outside neck cut for 2 min, scalded for 2 min at 53 C, feathers removed, and left pectorialis major immediately removed. The remainder of carcass was eviscerated, head, neck, and feet removed, prechilled, stored for 24 hr at 2 C, and right p. major removed. The pH was taken at the time of muscle removal, the skinless p. major weighed, cooked in water at 88 C to 82 C, cooled, and weighed. A 2.5-cm wide strip was removed to measure objectively tenderness as force to shear. The entire procedure was replicated twice. There was a significant stun by age interaction for pH and percent weight loss due to cooking. Breast meat from birds stunned prior to death exhibited higher pH 20 min postmortem than meat from nonstunned birds. Stunning had no effect on ultimate postmortem pH. Breast meat cooked 20 min postmortem exhibited lower percentage weight loss than meat cooked 24 hr postmortem. The meat cooked 20 min postmortem exhibited significantly higher shear values-it was less tender-than meat cooked 24 hr postmortem. Postmortem aging had a more pronounced effect on objective texture than electrical stunning. (Key words: electrical stunning, hot deboning, pH, tenderness) 1986 Poultry Science 65:1715-1719 INTRODUCTION
Broiler chickens are electrically stunned prior to severing neck blood vessels in commercial slaughtering. The primary justifications for stunning are: 1) immobilization of the bird for effective presentation to the in-line mechanical killing device, 2) humane slaughter considerations, and 3) reduction of struggle and movement during bleeding, which in turn reduces potential carcass damage. Variations in stunning have been studied relative to blood loss (Kotula and Helbacka, 1966; Pollard et al., 1959; Kuenzel and Ingling, 1977; Kuenzel et al., 1978; Kuenzel
1
To whom correspondence should be addressed.
and Walther, 1978), because blood loss may be related to carcass quality and acceptability according to regulatory requirements (Harris and Carter, 1977; Kuenzel and Ingling, 1977). Heath (1984), however, disputed the contention that reduced bleeding is deleterious to meat quality, and recommended not only stunning but also the humane killing of poultry by electrical charge. Goodwin et al. (1961) reported that the variance of shear values among turkey breast muscles as affected by electrical stunning was not significant. Ma and Addis (1973) reported that cooking loss and shear values of breast meat of electrically stunned turkeys were not significantly different from those of unstunned turkeys,
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tions for postmortem holding periods to avoid adverse toughening were 4 hr before cooking (Pool et al., 1959), 3 to 6 hr before freezing (Dawson et al., 1958), and at least 4 hr before deboning (Stewart et al., 1984a; Lyon et al., 1985). The purpose of this study was to determine the effects of electrical stunning and hot deboning on pH, cooking loss, and objective tenderness of broiler breast meat. MATERIALS AND METHODS
Forty-eight live male broiler chickens, 7 weeks old, from the same flock, were obtained from a local processing plant. The birds were transported to the Russell Research Center pilot plant and held in catching crates for no longer than 2.5 hr before slaughter. The experiment was designed so that half (24) of the chickens would be electrically stunned before killing and the remaining chickens (24) would be slaughtered without stunning. The stunning apparatus consisted of four grounded leg shackles, an electrically charged pan of brine isolated from surroundings, and a variable commercial stunning transformer. Stunning was accomplished by applying 55 volts A.C. for 10 sec on a path from the head to the feet. Chickens were removed from the stunning shackles and placed in restraining cones (approximately 20 sec elapsed between stunning and the neck cut). The procedure for killing was a single outside knife cut, severing both the carotid artery and jugular vein on one side of the throat. Bleeding was for 120 sec. Scalding was performed in a commercial type in-line scalder for 2 min at 53 C. Feather removal was in a Gordon-Johnson commercial model C-11 in-line picking machine and required 20 sec. The overhead shackle conveyor was operated in a stop-start mode, and each processing operation was timed with the aid of a stopwatch. Harvesting was accomplished by stripping the left breast muscle (pectoralis major only) from each carcass immediately after defeathering, using the method described by Hamm et al. (1984). Thus left breast muscle harvesting was performed without eviscerating. pH of each raw breast was measured within 15 sec of removal from the carcass by the procedure of Stewart et al. (1984a). Feet, head, and viscera were manually removed from the remainder of each carcass, the carcasses prechilled in 16 C water for 10 min and chilled in slush ice (1 part crushed ice to 6 parts water) for 20 min. Carcass cooling and chilling were with pilot plant chillers that simulate commercial continuous chiller agi-
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but consistent data trends suggested that stunning had beneficial effects. Van Hoof (1979) observed that the shear value of the pectoralis major of unstunned turkeys slaughtered manually at the farm was significantly higher than that of unstunned turkeys slaughtered manually, stunned turkeys slaughtered industrially immediately after transportation, or stunned turkeys slaughtered industrially 24 hr after transportation. In contrast, Boulgakova et al. (1977) observed that electrical stunning created a stress reaction in chickens (hens and broilers), which resulted in a toughening of the meat. The relationship of antemortem and perimortem struggle to meat tenderness has also been studied. Dodge and Stadelman (1960) concluded that struggling did not significantly affect postmortem tenderization of meat aged up to 5 hr. Khan and Nakamura (1970), Froning et al. (1978), and Ngoka et al. (1982) found that minimizing struggle increased tenderness. Grey et al. (1974) determined that the greater the degree of struggle at death, the more rapid the onset of rigor mortis. Because labor, water, and energy are a large proportion of the cost of standard poultry processing, minimizing the input of these resources by process modifications while maintaining quality and wholesomeness of the product can lead to significant economies for the processor and consumer. Hamm (1981, 1982) and Hamm et al. (1984) devised a system of reduced processing, or hot stripping, in which breast and leg meat are removed from poultry carcasses without the conventional eviscerating and chilling stages of standard processing. Both hot deboning and cutting up immediately after slaughter are associated with greater toughness of the breast meat in comparison to standard processing, during which tenderizing occurs in the meat left intact on the carcass as it passes through the extended stages of standard processing and storage (Klose et al., 1971; Treat and Goodwin, 1973; Stewart et al., 1984a; Lyon et al, 1985). Lee et al. (1976) concluded that the toughness of excised breast meat from birds stressed antemortem was attributable primarily to a high initial glycogen level and much less to postmortem glycolysis rate. Stewart et al. (1984b) also reported that toughness of hot deboned breast meat did not appear to be caused by an acceleration of anaerobic glycolysis. Lee et al. (1976) hypothesized that when broiler carcassses are deboned immediately after slaughter, antemortem treatments that lower glycogen in the muscle should enhance meat tenderness. Recommenda-
STUNNING AND HOT DEBONING
dent in both experiments. These data indicate that the effect of stunning is restricted to immediately postmortem, because pH of stunned and nonstunned meat was essentially the same at 24 hr postmortem. Although every effort was made to minimize antemortem stress on the birds, information such as feed and water withdrawal schedules and distance traveled to and time spent at the processing plant was not available. Stewart et al. (1984a) noted that antemortem stress may play an important role in postmortem pH decline, and the large initial pH differences between the two experiments may well be an example of some antemortem factors beyond our control. The ability of electrical stunning to elevate the pH in the early postmortem period could be very important to the functional properties of the breast meat. Froning and Neelakantan (1971) reported that a pH of 5.9 or higher could be used to indicate a prerigor condition in broiler breast meat; meat with a pH of 5.9 was correlated with increased functional properties when compared with postrigor meat with a lower pH. Using this 5.9 pH as a benchmark, and the pH at 20 min postmortem from this study, the breast meat from stunned birds (both experiments) and the unstunned breast meat from Experiment 2 were all prerigor. However, unstunned breast meat from Experiment 1 was already below the 5.9 pH at 20 min postmortem. There was also a stun by age interaction for percent weight loss due to cooking in both exper-
EXPERIMENT1
EXPERIMENT 2
RESULTS AND DISCUSSION
There was a significant stun by age interaction for pH in both experiments (Fig. 1). The most pronounced effect of electrical stunning on pH was in the difference for readings taken within 20 min postmortem. The pH within 20 min for breast meat from stunned birds was higher than meat from nonstunned birds. This trend was evi-
I NO STUN EfffKKXM S£-.tBe
I STUN
2 NO STUN
2 STUN
FIG. 1. The pH of electrically stunned and nonstunned broiler breast muscle at two postmortem times prior to cooking.
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tation. The chillers contained paddles for agitating the carcasses at a rate of 5 rpm. After chilling, the carcasses were removed from the chiller, drained for approximately 3 min, packed in individual polyethylene bags, and stored on wire racks at 2 C for 24 hr in a controlled temperature room at the end of the storage time. The right breast muscle (pectoralis major only) was removed from each carcass. Each breast was cooked in water at 88 C to an internal temperature of 82 C, which required 35 min for breast meat removed from carcasses before evisceration and 45 min for breast meat removed from carcasses after storage. After cooking, all samples were cooled in ice-slush for 15 min. Elapsed time between killing of the bird (end of the 2 min bleeding time) and start of the cooking procedure for the hot deboned left breast meat averaged 20 min. Objective tenderness of the cooked breast meat was measured as maximum force to shear (kg) with a Warner-Bratzler shear press. A strip of the pectoralis major (2.5 cm wide and 7.6 cm long) was cut by placing a metal template on the breast. The template was placed so that the anterior end of the strip originated at the humeral insertion and posterior end at the area of attachment to the keel. Samples were positioned in the press for shearing to occur from the interior to the exterior surface of the strip, and each strip was sheared twice. All shear measurements were made within 3 hr of cooking and cooling, and all samples were at room temperature. Loss of weight during cooking was determined by weighing each breast to the nearest .1 g before cooking and after cooling, and calculation of percentage of loss based on weight before cooking. The experiment was repeated twice (48 birds per time), but as we had no historical background or control of growing conditions, and the time of year was different for the two runs, data were analyzed as separate experiments. All data were analyzed statistically by analysis of variance; statistical differences were noted at P<.05.
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28
24h
I STUN
28.
24h
Z NO STUN
20>
24h
2 STUN
FIG. 2. Percent weight loss due to cooking of electrically stunned and nonstunned broiler breast muscle at two postmortem times.
iments (Fig. 2). In Experiment 1, the lower percent weight loss (20.9%) for the birds that were electrically stunned and then immediately water cooked was responsible for the interaction. Birds that were not electrically stunned, and with cooking started within 20 min, exhibited a loss of 23.68%, whereas the percent weight loss for meat aged 24 hr prior to cooking was essentially the same for both treatments: 25.87 (stunned) and 25.45% (nonstunned). Percent weight losses were greater for all treatments in Experiment 2. Average raw weight of the skinless pectoralis major pieces of Experiment 2 were 85 g for the prerigor samples and 92 g for the postrigor, whereas prerigor samples in Experiment 1 aver-
TABLE 1. Effect of electrical stunning and time postmortem before cooking on objective tenderness of cooked broiler breast meat Warner-Bratzler shear value Treatments
Experiment 1
Experiment 2 (kg)
Stunning Yes No Time postmortem 20 min 24 hr
8.07 a 8.77 a
6.96b 8.22 a
11.44 a 5.00°
10.84a 4.35 b
' Means within a column by treatment and experiment followed by different superscripts are significantly different (P<.05) according to analysis of variance; 48 observations per variable.
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28« I NO STUN EVnUEHT 1 SJL-M1 EWOaCNT 2 S£.-.4tt
aged 94 g and postrigor samples 93 g. These weights indicate that meat removal was fairly uniform across the two aging treatments and would rule out weight differences as a major cause of the increased weight loss for Experiment 2. It may be that the lower ultimate pH of the 24 hr aged samples in Experiment 2 compared with Experiment 1 could account for a corresponding decrease in water-holding capacity of the samples and an increase in percent weight loss. The most evident trend in percent weight loss was that samples cooked 20 min postmortem consistently lost less weight than the samples cooked 24 hr postmortem. This trend was evident in both experiments. There appears to be a beneficial effect on percent weight loss due to electrical stunning, but the differences are not as large nor the patterns as consistent as are the differences due to times postmortem in this study. Breast meat introduced to the water for cooking 20 min postmortem exhibited significantly higher shear values; they were less tender than meat cooked 24 hr postmortem (Table 1). This effect on texture was evident for both experiments. The samples in this study progressed from muscle to a cooked intact meat in approximately 1 hr (20 min postmortem into the water plus 35 or 45 min to fully cook). The heat rise associated with the water cooking procedure was not rapid enough to halt early postmortem biochemical reactions in the muscle and thus prevent toughening. The effect of electrical stunning on objective tenderness is not as well defined as is the postmortem time prior to cooking. Cooked breast meat from broilers that had been stunned prior
STUNNING AND HOT DEBONING
ACKNOWLEDGMENTS
Appreciation is expressed to R. E. Vaughn and W. F. Whitehead for technical assistance and to R. L. Wilson for assistance in statistical analysis. REFERENCES Boulgakova, L. W, N. P. Gorbataya, T. V. Ivanova, V. G. Solovyov, and E. G. Shoumkov, 1977. Stress and meat quality. Proc. Eur. Mtg. Meat Res. Workers B7:10-19. Dawson, L. E., J. A. Davidson, M. Frang, and S. Walters, 1958. The effects of time interval between slaughter and freezing on toughness of fryers. Poultry Sci. 37:231-235. Dodge, J. W, and W. J. Stadelman, 1960. Variability in tenderness due to struggling. Poultry Sci. 39:672-677. Froning, G. W , A. S. Babji, and F. B. Mather, 1978. The effect of preslaughter temperature, stress, struggle, and anesthetization on color and textural characteristics of turkey muscle. Poultry Sci. 57:630-633. Froning, G. W, and S. Neelakantan, 1971. Emulsifying characteristics of pre-rigor and post-rigor poultry muscle. Poultry Sci. 50:839-845. Goodwin, T. L., W. C. Mickelberry, and W J. Stadelman, 1961. The influence of humane slaughter on the tenderness of turkey meat. Poultry Sci. 40:921-924. Grey, T. C , J. M. Jones, and D. S. Robinson, 1974. The influence of death stuggle on the rate of glycolysis in chicken breast muscle. J. Sci. FoodAgric. 25:57-66. Hamm, D., 1981. Unconventional meat harvesting. Poultry Sci. 60(Suppl. 1):1666. (Abstr.) Hamm, D., 1982. A new look at broiler meat harvesting. Broiler Ind. 48(7):38-39.
Hamm, D., C. E. Lyon, F. H. Benoff, J. P. Hudspeth, J. L.Ayres, and L. R. Minear, 1984. Meat yields from hot deboned noneviscerated broilers. Poultry Sci. 63:497-501. Harris, C. E., and T. A. Carter, 1977. Broiler blood losses with manual and mechanical killers. Poultry Sci. 56:1827-1831. Heath, G.B.S., 1984. The slaughter of broiler chickens. World's Poult. Sci. J. 40:151-159. Kahn, A. W, and R. Nakamura, 1970. Effects of pre- and postmortem glycolysis on poultry tenderness. J. Food Sci. 35:266-267. Klose, A. A., R. N. Sayre, and M. F. Pool, 1971. Tenderness changes associated with cutting up poultry shortly after warm evisceration. Poultry Sci. 50:585-591. Kotula, A. W, and N. B. Helbacka, 1966. Blood volume of live chickens and influence of slaughter technique on blood loss. Poultry Sci. 45:684-688. Kuenzel, W. J., and A. L. Ingling, 1977. A comparison of plate and brine stunners, A.C. and D.C. circuits for maximizing bleed-out in processed poultry.Poultry Sci. 56:2087-2090. Kuenzel, W. J., A. L. Ingling, D. M. Denbow, J. H. Walther, and M. M. Schaefer, 1978. Variable frequency stunning and a comparison of two bleed-out time intervals for maximizing blood release in processed poultry. Poultry Sci. 57:449^154. Kuenzei, W J., and J. H. Walther, 1978. Heart beat, blood pressure, respiration, and brain waves of broilers as affected by electrical stunning and bleed-out. Poultry Sci. 57:655-659. Lee, Y. B., G. L. Hargus, E. C. Hagburg, and R. H. Forsythe, 1976. Effect of antemortem environmental temperatures on postmortem glycolysis and tenderness in excised broiler breast muscle. J. Food Sci. 41:14661469. Lyon, C. E., D. Hamm, and J. E. Thomson, 1985. pH and tenderness of broiler breast meat deboned various times after chilling. Poultry Sci. 64:307-310. Ma, R. T.-L., and P. B. Addis, 1973. The association of struggle during exsanguination to glycolysis, protein solubility and shear in turkey pectoralis muscle. J. Food Sci. 38:995-997. Ngoka, D. A., G. W. Froning, S. R. Lowry, and A. S. Babji, 1982. Effects of sex, age, preslaughter factors, and holding conditions on the quality characteristics and chemical composition of turkey breast muscles. Poultry Sci. 61:1996-2003. Pollard, W O., J. L. Heath, and C. J. Wabeck, 1973. The effect of electrical stunning of birds on carcass quality. Poultry Sci. 52:2074.(Abstr.) Pool, M. F., D. de Fremery, A. A. Campbell, and A. A. Klose, 1959. Poultry tenderness II. Influence of processing tenderness of chickens. FoodTechnol. 13:25-29. Stewart, M. K., D. L. Fletcher, D. Hamm, and J. E.Thomson, 1984a. The influence of hot boning broiler breast muscle on pH decline and toughening. Poultry Sci. 63:1935-1939. Stewart, M. K., D. L. Fletcher, D. Hamm, and J. E. Thomson, 1984b. The effect of hot boning broiler breast meat muscle on postmortem pH decline. Poultry Sci. 63:2181-2186. Treat, D. W, andT. L. Goodwin, 1973. Effects of sex, size, and time of cutting on processing yields and tenderness of broilers.Poultry Sci. 52:1348-1353. Van Hoof, J., 1979. Influence of ante- and peri-mortem factors on biochemical and physical characteristics of turkey breast muscle. Vet. Q. 1:29-36.
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to killing was significantly more tender than meat from unstunned broilers in Experiment 2; however, the difference in tenderness due to stunning for Experiment 1 was not statistically significant. The beneficial effect of stunning on tenderness in Experiment 2 may well be related to higher initial pH (20 min, no stun: 6.22) versus lower initial pH for Experiment 1 (5.84). Electrical stunning caused an elevation of pH measured 20 min postmortem, and even though the rise in pH was greater for Experiment 1 (.34 pH units) than for Experiment 2 (.18 pH units), any beneficial effect may have been offset by the low inital pH of 5.84. This observation also illustrates the importance of antemortem factors on product quality. Proper electrical stunning had a postiive effect on the quality of broiler breast meat, but the magnitude was not as pronounced as that of postmortem aging. The elevation of muscle pH and its subsequent alteration of postmortem biochemical reactions may have a significant effect on product quality. Effects of electrical stunning on both the biochemical reactions and microstructure of poultry muscle need to be studied further.
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Richard B. Russell Agricutural Research Center, Agricultural Research Service, United States Department of Agriculture, P.O. Box 5677, Athens, Georgia 30613 (Received for publication November 18, 1985) ABSTRACT The effects were determined of electrical stunning prior to death and hot deboning on pH, percent weight loss due to cooking, and objective tenderness of broiler breast meat. Forty-eight live broilers were obtained from a processing plant and transported to the pilot plant facility of the research center. Half the birds were electrically stunned prior to death, and half were not. Birds were processed in the following manner: bled by outside neck cut for 2 min, scalded for 2 min at 53 C, feathers removed, and left pectorialis major immediately removed. The remainder of carcass was eviscerated, head, neck, and feet removed, prechilled, stored for 24 hr at 2 C, and right p. major removed. The pH was taken at the time of muscle removal, the skinless p. major weighed, cooked in water at 88 C to 82 C, cooled, and weighed. A 2.5-cm wide strip was removed to measure objectively tenderness as force to shear. The entire procedure was replicated twice. There was a significant stun by age interaction for pH and percent weight loss due to cooking. Breast meat from birds stunned prior to death exhibited higher pH 20 min postmortem than meat from nonstunned birds. Stunning had no effect on ultimate postmortem pH. Breast meat cooked 20 min postmortem exhibited lower percentage weight loss than meat cooked 24 hr postmortem. The meat cooked 20 min postmortem exhibited significantly higher shear values-it was less tender-than meat cooked 24 hr postmortem. Postmortem aging had a more pronounced effect on objective texture than electrical stunning. (Key words: electrical stunning, hot deboning, pH, tenderness) 1986 Poultry Science 65:1715-1719 INTRODUCTION
Broiler chickens are electrically stunned prior to severing neck blood vessels in commercial slaughtering. The primary justifications for stunning are: 1) immobilization of the bird for effective presentation to the in-line mechanical killing device, 2) humane slaughter considerations, and 3) reduction of struggle and movement during bleeding, which in turn reduces potential carcass damage. Variations in stunning have been studied relative to blood loss (Kotula and Helbacka, 1966; Pollard et al., 1959; Kuenzel and Ingling, 1977; Kuenzel et al., 1978; Kuenzel
1
To whom correspondence should be addressed.
and Walther, 1978), because blood loss may be related to carcass quality and acceptability according to regulatory requirements (Harris and Carter, 1977; Kuenzel and Ingling, 1977). Heath (1984), however, disputed the contention that reduced bleeding is deleterious to meat quality, and recommended not only stunning but also the humane killing of poultry by electrical charge. Goodwin et al. (1961) reported that the variance of shear values among turkey breast muscles as affected by electrical stunning was not significant. Ma and Addis (1973) reported that cooking loss and shear values of breast meat of electrically stunned turkeys were not significantly different from those of unstunned turkeys,
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tions for postmortem holding periods to avoid adverse toughening were 4 hr before cooking (Pool et al., 1959), 3 to 6 hr before freezing (Dawson et al., 1958), and at least 4 hr before deboning (Stewart et al., 1984a; Lyon et al., 1985). The purpose of this study was to determine the effects of electrical stunning and hot deboning on pH, cooking loss, and objective tenderness of broiler breast meat. MATERIALS AND METHODS
Forty-eight live male broiler chickens, 7 weeks old, from the same flock, were obtained from a local processing plant. The birds were transported to the Russell Research Center pilot plant and held in catching crates for no longer than 2.5 hr before slaughter. The experiment was designed so that half (24) of the chickens would be electrically stunned before killing and the remaining chickens (24) would be slaughtered without stunning. The stunning apparatus consisted of four grounded leg shackles, an electrically charged pan of brine isolated from surroundings, and a variable commercial stunning transformer. Stunning was accomplished by applying 55 volts A.C. for 10 sec on a path from the head to the feet. Chickens were removed from the stunning shackles and placed in restraining cones (approximately 20 sec elapsed between stunning and the neck cut). The procedure for killing was a single outside knife cut, severing both the carotid artery and jugular vein on one side of the throat. Bleeding was for 120 sec. Scalding was performed in a commercial type in-line scalder for 2 min at 53 C. Feather removal was in a Gordon-Johnson commercial model C-11 in-line picking machine and required 20 sec. The overhead shackle conveyor was operated in a stop-start mode, and each processing operation was timed with the aid of a stopwatch. Harvesting was accomplished by stripping the left breast muscle (pectoralis major only) from each carcass immediately after defeathering, using the method described by Hamm et al. (1984). Thus left breast muscle harvesting was performed without eviscerating. pH of each raw breast was measured within 15 sec of removal from the carcass by the procedure of Stewart et al. (1984a). Feet, head, and viscera were manually removed from the remainder of each carcass, the carcasses prechilled in 16 C water for 10 min and chilled in slush ice (1 part crushed ice to 6 parts water) for 20 min. Carcass cooling and chilling were with pilot plant chillers that simulate commercial continuous chiller agi-
Downloaded from http://ps.oxfordjournals.org/ at Library, University of Guelph on April 2, 2015
but consistent data trends suggested that stunning had beneficial effects. Van Hoof (1979) observed that the shear value of the pectoralis major of unstunned turkeys slaughtered manually at the farm was significantly higher than that of unstunned turkeys slaughtered manually, stunned turkeys slaughtered industrially immediately after transportation, or stunned turkeys slaughtered industrially 24 hr after transportation. In contrast, Boulgakova et al. (1977) observed that electrical stunning created a stress reaction in chickens (hens and broilers), which resulted in a toughening of the meat. The relationship of antemortem and perimortem struggle to meat tenderness has also been studied. Dodge and Stadelman (1960) concluded that struggling did not significantly affect postmortem tenderization of meat aged up to 5 hr. Khan and Nakamura (1970), Froning et al. (1978), and Ngoka et al. (1982) found that minimizing struggle increased tenderness. Grey et al. (1974) determined that the greater the degree of struggle at death, the more rapid the onset of rigor mortis. Because labor, water, and energy are a large proportion of the cost of standard poultry processing, minimizing the input of these resources by process modifications while maintaining quality and wholesomeness of the product can lead to significant economies for the processor and consumer. Hamm (1981, 1982) and Hamm et al. (1984) devised a system of reduced processing, or hot stripping, in which breast and leg meat are removed from poultry carcasses without the conventional eviscerating and chilling stages of standard processing. Both hot deboning and cutting up immediately after slaughter are associated with greater toughness of the breast meat in comparison to standard processing, during which tenderizing occurs in the meat left intact on the carcass as it passes through the extended stages of standard processing and storage (Klose et al., 1971; Treat and Goodwin, 1973; Stewart et al., 1984a; Lyon et al, 1985). Lee et al. (1976) concluded that the toughness of excised breast meat from birds stressed antemortem was attributable primarily to a high initial glycogen level and much less to postmortem glycolysis rate. Stewart et al. (1984b) also reported that toughness of hot deboned breast meat did not appear to be caused by an acceleration of anaerobic glycolysis. Lee et al. (1976) hypothesized that when broiler carcassses are deboned immediately after slaughter, antemortem treatments that lower glycogen in the muscle should enhance meat tenderness. Recommenda-
STUNNING AND HOT DEBONING
dent in both experiments. These data indicate that the effect of stunning is restricted to immediately postmortem, because pH of stunned and nonstunned meat was essentially the same at 24 hr postmortem. Although every effort was made to minimize antemortem stress on the birds, information such as feed and water withdrawal schedules and distance traveled to and time spent at the processing plant was not available. Stewart et al. (1984a) noted that antemortem stress may play an important role in postmortem pH decline, and the large initial pH differences between the two experiments may well be an example of some antemortem factors beyond our control. The ability of electrical stunning to elevate the pH in the early postmortem period could be very important to the functional properties of the breast meat. Froning and Neelakantan (1971) reported that a pH of 5.9 or higher could be used to indicate a prerigor condition in broiler breast meat; meat with a pH of 5.9 was correlated with increased functional properties when compared with postrigor meat with a lower pH. Using this 5.9 pH as a benchmark, and the pH at 20 min postmortem from this study, the breast meat from stunned birds (both experiments) and the unstunned breast meat from Experiment 2 were all prerigor. However, unstunned breast meat from Experiment 1 was already below the 5.9 pH at 20 min postmortem. There was also a stun by age interaction for percent weight loss due to cooking in both exper-
EXPERIMENT1
EXPERIMENT 2
RESULTS AND DISCUSSION
There was a significant stun by age interaction for pH in both experiments (Fig. 1). The most pronounced effect of electrical stunning on pH was in the difference for readings taken within 20 min postmortem. The pH within 20 min for breast meat from stunned birds was higher than meat from nonstunned birds. This trend was evi-
I NO STUN EfffKKXM S£-.tBe
I STUN
2 NO STUN
2 STUN
FIG. 1. The pH of electrically stunned and nonstunned broiler breast muscle at two postmortem times prior to cooking.
Downloaded from http://ps.oxfordjournals.org/ at Library, University of Guelph on April 2, 2015
tation. The chillers contained paddles for agitating the carcasses at a rate of 5 rpm. After chilling, the carcasses were removed from the chiller, drained for approximately 3 min, packed in individual polyethylene bags, and stored on wire racks at 2 C for 24 hr in a controlled temperature room at the end of the storage time. The right breast muscle (pectoralis major only) was removed from each carcass. Each breast was cooked in water at 88 C to an internal temperature of 82 C, which required 35 min for breast meat removed from carcasses before evisceration and 45 min for breast meat removed from carcasses after storage. After cooking, all samples were cooled in ice-slush for 15 min. Elapsed time between killing of the bird (end of the 2 min bleeding time) and start of the cooking procedure for the hot deboned left breast meat averaged 20 min. Objective tenderness of the cooked breast meat was measured as maximum force to shear (kg) with a Warner-Bratzler shear press. A strip of the pectoralis major (2.5 cm wide and 7.6 cm long) was cut by placing a metal template on the breast. The template was placed so that the anterior end of the strip originated at the humeral insertion and posterior end at the area of attachment to the keel. Samples were positioned in the press for shearing to occur from the interior to the exterior surface of the strip, and each strip was sheared twice. All shear measurements were made within 3 hr of cooking and cooling, and all samples were at room temperature. Loss of weight during cooking was determined by weighing each breast to the nearest .1 g before cooking and after cooling, and calculation of percentage of loss based on weight before cooking. The experiment was repeated twice (48 birds per time), but as we had no historical background or control of growing conditions, and the time of year was different for the two runs, data were analyzed as separate experiments. All data were analyzed statistically by analysis of variance; statistical differences were noted at P<.05.
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24h
I STUN
28.
24h
Z NO STUN
20>
24h
2 STUN
FIG. 2. Percent weight loss due to cooking of electrically stunned and nonstunned broiler breast muscle at two postmortem times.
iments (Fig. 2). In Experiment 1, the lower percent weight loss (20.9%) for the birds that were electrically stunned and then immediately water cooked was responsible for the interaction. Birds that were not electrically stunned, and with cooking started within 20 min, exhibited a loss of 23.68%, whereas the percent weight loss for meat aged 24 hr prior to cooking was essentially the same for both treatments: 25.87 (stunned) and 25.45% (nonstunned). Percent weight losses were greater for all treatments in Experiment 2. Average raw weight of the skinless pectoralis major pieces of Experiment 2 were 85 g for the prerigor samples and 92 g for the postrigor, whereas prerigor samples in Experiment 1 aver-
TABLE 1. Effect of electrical stunning and time postmortem before cooking on objective tenderness of cooked broiler breast meat Warner-Bratzler shear value Treatments
Experiment 1
Experiment 2 (kg)
Stunning Yes No Time postmortem 20 min 24 hr
8.07 a 8.77 a
6.96b 8.22 a
11.44 a 5.00°
10.84a 4.35 b
' Means within a column by treatment and experiment followed by different superscripts are significantly different (P<.05) according to analysis of variance; 48 observations per variable.
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28« I NO STUN EVnUEHT 1 SJL-M1 EWOaCNT 2 S£.-.4tt
aged 94 g and postrigor samples 93 g. These weights indicate that meat removal was fairly uniform across the two aging treatments and would rule out weight differences as a major cause of the increased weight loss for Experiment 2. It may be that the lower ultimate pH of the 24 hr aged samples in Experiment 2 compared with Experiment 1 could account for a corresponding decrease in water-holding capacity of the samples and an increase in percent weight loss. The most evident trend in percent weight loss was that samples cooked 20 min postmortem consistently lost less weight than the samples cooked 24 hr postmortem. This trend was evident in both experiments. There appears to be a beneficial effect on percent weight loss due to electrical stunning, but the differences are not as large nor the patterns as consistent as are the differences due to times postmortem in this study. Breast meat introduced to the water for cooking 20 min postmortem exhibited significantly higher shear values; they were less tender than meat cooked 24 hr postmortem (Table 1). This effect on texture was evident for both experiments. The samples in this study progressed from muscle to a cooked intact meat in approximately 1 hr (20 min postmortem into the water plus 35 or 45 min to fully cook). The heat rise associated with the water cooking procedure was not rapid enough to halt early postmortem biochemical reactions in the muscle and thus prevent toughening. The effect of electrical stunning on objective tenderness is not as well defined as is the postmortem time prior to cooking. Cooked breast meat from broilers that had been stunned prior
STUNNING AND HOT DEBONING
ACKNOWLEDGMENTS
Appreciation is expressed to R. E. Vaughn and W. F. Whitehead for technical assistance and to R. L. Wilson for assistance in statistical analysis. REFERENCES Boulgakova, L. W, N. P. Gorbataya, T. V. Ivanova, V. G. Solovyov, and E. G. Shoumkov, 1977. Stress and meat quality. Proc. Eur. Mtg. Meat Res. Workers B7:10-19. Dawson, L. E., J. A. Davidson, M. Frang, and S. Walters, 1958. The effects of time interval between slaughter and freezing on toughness of fryers. Poultry Sci. 37:231-235. Dodge, J. W, and W. J. Stadelman, 1960. Variability in tenderness due to struggling. Poultry Sci. 39:672-677. Froning, G. W , A. S. Babji, and F. B. Mather, 1978. The effect of preslaughter temperature, stress, struggle, and anesthetization on color and textural characteristics of turkey muscle. Poultry Sci. 57:630-633. Froning, G. W, and S. Neelakantan, 1971. Emulsifying characteristics of pre-rigor and post-rigor poultry muscle. Poultry Sci. 50:839-845. Goodwin, T. L., W. C. Mickelberry, and W J. Stadelman, 1961. The influence of humane slaughter on the tenderness of turkey meat. Poultry Sci. 40:921-924. Grey, T. C , J. M. Jones, and D. S. Robinson, 1974. The influence of death stuggle on the rate of glycolysis in chicken breast muscle. J. Sci. FoodAgric. 25:57-66. Hamm, D., 1981. Unconventional meat harvesting. Poultry Sci. 60(Suppl. 1):1666. (Abstr.) Hamm, D., 1982. A new look at broiler meat harvesting. Broiler Ind. 48(7):38-39.
Hamm, D., C. E. Lyon, F. H. Benoff, J. P. Hudspeth, J. L.Ayres, and L. R. Minear, 1984. Meat yields from hot deboned noneviscerated broilers. Poultry Sci. 63:497-501. Harris, C. E., and T. A. Carter, 1977. Broiler blood losses with manual and mechanical killers. Poultry Sci. 56:1827-1831. Heath, G.B.S., 1984. The slaughter of broiler chickens. World's Poult. Sci. J. 40:151-159. Kahn, A. W, and R. Nakamura, 1970. Effects of pre- and postmortem glycolysis on poultry tenderness. J. Food Sci. 35:266-267. Klose, A. A., R. N. Sayre, and M. F. Pool, 1971. Tenderness changes associated with cutting up poultry shortly after warm evisceration. Poultry Sci. 50:585-591. Kotula, A. W, and N. B. Helbacka, 1966. Blood volume of live chickens and influence of slaughter technique on blood loss. Poultry Sci. 45:684-688. Kuenzel, W. J., and A. L. Ingling, 1977. A comparison of plate and brine stunners, A.C. and D.C. circuits for maximizing bleed-out in processed poultry.Poultry Sci. 56:2087-2090. Kuenzel, W. J., A. L. Ingling, D. M. Denbow, J. H. Walther, and M. M. Schaefer, 1978. Variable frequency stunning and a comparison of two bleed-out time intervals for maximizing blood release in processed poultry. Poultry Sci. 57:449^154. Kuenzei, W J., and J. H. Walther, 1978. Heart beat, blood pressure, respiration, and brain waves of broilers as affected by electrical stunning and bleed-out. Poultry Sci. 57:655-659. Lee, Y. B., G. L. Hargus, E. C. Hagburg, and R. H. Forsythe, 1976. Effect of antemortem environmental temperatures on postmortem glycolysis and tenderness in excised broiler breast muscle. J. Food Sci. 41:14661469. Lyon, C. E., D. Hamm, and J. E. Thomson, 1985. pH and tenderness of broiler breast meat deboned various times after chilling. Poultry Sci. 64:307-310. Ma, R. T.-L., and P. B. Addis, 1973. The association of struggle during exsanguination to glycolysis, protein solubility and shear in turkey pectoralis muscle. J. Food Sci. 38:995-997. Ngoka, D. A., G. W. Froning, S. R. Lowry, and A. S. Babji, 1982. Effects of sex, age, preslaughter factors, and holding conditions on the quality characteristics and chemical composition of turkey breast muscles. Poultry Sci. 61:1996-2003. Pollard, W O., J. L. Heath, and C. J. Wabeck, 1973. The effect of electrical stunning of birds on carcass quality. Poultry Sci. 52:2074.(Abstr.) Pool, M. F., D. de Fremery, A. A. Campbell, and A. A. Klose, 1959. Poultry tenderness II. Influence of processing tenderness of chickens. FoodTechnol. 13:25-29. Stewart, M. K., D. L. Fletcher, D. Hamm, and J. E.Thomson, 1984a. The influence of hot boning broiler breast muscle on pH decline and toughening. Poultry Sci. 63:1935-1939. Stewart, M. K., D. L. Fletcher, D. Hamm, and J. E. Thomson, 1984b. The effect of hot boning broiler breast meat muscle on postmortem pH decline. Poultry Sci. 63:2181-2186. Treat, D. W, andT. L. Goodwin, 1973. Effects of sex, size, and time of cutting on processing yields and tenderness of broilers.Poultry Sci. 52:1348-1353. Van Hoof, J., 1979. Influence of ante- and peri-mortem factors on biochemical and physical characteristics of turkey breast muscle. Vet. Q. 1:29-36.
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to killing was significantly more tender than meat from unstunned broilers in Experiment 2; however, the difference in tenderness due to stunning for Experiment 1 was not statistically significant. The beneficial effect of stunning on tenderness in Experiment 2 may well be related to higher initial pH (20 min, no stun: 6.22) versus lower initial pH for Experiment 1 (5.84). Electrical stunning caused an elevation of pH measured 20 min postmortem, and even though the rise in pH was greater for Experiment 1 (.34 pH units) than for Experiment 2 (.18 pH units), any beneficial effect may have been offset by the low inital pH of 5.84. This observation also illustrates the importance of antemortem factors on product quality. Proper electrical stunning had a postiive effect on the quality of broiler breast meat, but the magnitude was not as pronounced as that of postmortem aging. The elevation of muscle pH and its subsequent alteration of postmortem biochemical reactions may have a significant effect on product quality. Effects of electrical stunning on both the biochemical reactions and microstructure of poultry muscle need to be studied further.
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