PROCESSING AND PRODUCTS

PROCESSING AND PRODUCTS Bleedout Efficiency, Carcass Damage, and Rigor Mortis Development Following Electrical Stunning or Carbon Dioxide Stunning on a Shackle Line 1 I. S. KANG and A. R. SAMS2 Department of Poultry Science, Texas A&M University, College Station, Texas 77843-2472 ABSTRACT In Experiment 1, 400 male broilers were stunned using a gradient of 40 to 60% CO 2 over a period of 25 s or a 1% brine solution that was electrically charged (35 ma) for 7 s. Blood loss during bleeding was measured in 30-s intervals for a total of 120 s. After conventional processing and chilling, carcass damage was subjectively evaluated. Results indicated that the birds stunned with electricity bled faster than the CO 2 - stunned birds until 60 s. However, the cumulative blood loss was not different after 90 s. Carcass damage evaluation indicated that birds stunned with CO 2 had a significantly lower percentage of broken clavicles, and had fewer hemorrhages on the surface of the Pectoralis. However, there was no difference between the two stunning methods in the frequency of damage at the shoulder. In Experiment 2, 256 broilers were stunned using the same conditions as in Experiment 1. Measurements of ph, R-value, sarcomere length (SL), and fragmentation index (FI) were evaluated from the left breast fillets harvested at 0, 1, 2, and 6 h postmortem. Shear values (SV) were determined using the right fillets harvested at the same four postmortem times and aged on ice until 24 h. No significant difference in breast muscle ph value was observed at 0, 2, and 6 h postmortem. However, CO 2 -stunned fillets had significantly higher ph values than the ES fillets at 1 h postmortem. Carbon dioxide produced greater R values than electricity at 2 and 6 h. Sarcomere length, FI, and SV were not significantly different at any time tested. These data suggest that CO 2 stunning reduced carcass damage but did not reduce the need for aging before deboning when compared to the electrical stunning method used. (Key words: stunning, carbon dioxide, blood loss, downgrade, rigor mortis) 1999 Poultry Science 78:139 143 INTRODUCTION Electrical stunning (ES) has been a common method to immobilize poultry prior to slaughter in poultry processing plants (Mountney, 1976). Electricity is convenient, economical, and requires little room (Fletcher, 1993). However, some methods of ES (particularly those required by European regulations) have been reported to increase the incidence of carcass damage such as red wing tips, broken bones, and muscle hemorrhages (Gregory and Wilkens, 1989). There are several alternative methods of ES, such as concussion, cervical dislocation, and gaseous stunning or killing. The anesthetic properties of CO 2 have been known for a century and attempts have been made to use it as a general anesthetic agent (Hickman, 1912; Sieker and Received for publication June 1, 1998. Accepted for publication August 24, 1998. 1This research was supported by Praxair and by grant 999902-147 from the Texas Higher Education Coordinating Board Advanced Technology Program. 2 To whom correspondence should be addressed: asams@poultry.tamu.edu Hickman, 1956). This property of the gas would make it useful in preslaughter stunning by quickly rendering the bird unconscious. The actual stunning of chickens with CO 2 was not studied until the middle of the 1950s (Drewniak et al., 1955; Kotula et al., 1957). Subsequent research on the effect of CO 2 stunning suggested that CO 2 stunning of chickens resulted in improved bleedout (Kotula et al., 1957) and better meat quality (Zeller et al., 1988). Mohan Raj and Gregory (1990) investigated the efficiency and property of stunning with four different CO 2 concentrations (35, 45, 55, and 65% CO 2 ) and found that both 35 and 45% CO 2 resulted in a large number of survivors, whereas 65% CO 2 induced severe convulsions. Therefore, under commercial situations, a final concentration of 55% CO 2 was suggested to be ideal for killing broilers in batches. With continued research, Mohan Raj et al. (1990b) reported that stunning broilers with argon or Co 2 seemed less detrimental to carcass Abbreviation Key: ATP = adenosine triphosphate; ES = electrical stunning; FI = fragmentation index; SL = sarcomere length; SV = shear values. 139

140 and meat quality than ES. Hirschler and Sams (1993) reported that CO 2 stunning reduced the incidence of carcass defects, such as broken clavicles and breast, thigh, and shoulder hemorrhages, compared to ES. The reduced oxygen concentration encountered with gas stunning may have the additional benefit of accelerating rigor mortis development, thereby reducing the need for aging (Mohan Raj, 1994). Processors commonly store intact carcasses for at least 4 h after death to allow rigor mortis development before deboning (Shelton, 1985; Amey, 1988; Sams, 1994). Failing to provide this time results in meat toughening (Stewart et al., 1984, Dawson et al., 1987, Lyon et al., 1989). This aging process is expensive in terms of labor and reduced meat yield (Hirschler and Sams, 1998). The swine industry has been successfully stunning pigs with CO 2 in Denmark (Danish Meat Research Institute, 1985). The successful utilization of CO 2 stunning to avoid the potentially damaging nature of ES in swine and the rising demands for boneless poultry meat has stimulated the poultry industry to evaluate stunning methods to reduce the incidence of visible defects on deboned meat. This experiment was designed to compare the effects of stunning with CO 2 or electricity on bleedout efficiency, the frequency of carcass damage, and the development of rigor mortis-related biochemical and meat quality parameters. Experiment 1 MATERIALS AND METHODS Four hundred male broilers were reared to 7 wk of age with commercial, corn-soybean diets (meeting NRC recommendations) on wood shavings litter. One hundred birds in each of four replicates were divided into two treatment groups (50 birds for CO 2 stunning and 50 birds for ES). To minimize the effect of variation in bird size, extremes in live bird weight were excluded to obtain an average weight of 2.14 kg with a standard deviation of 0.2 kg. Birds were removed from feed and held in coops (eight birds per coop) 12 h prior to slaughter. Birds were hung by their feet in steel shackles and killed in groups of five to facilitate blood collection. Electrical stunning (35 ma, 7 s) was applied by allowing individual bird s head to pass through a 1% charged brine solution. For CO 2 stunning, the shackle line carried the birds into a tunnel containing a pool of CO 2 and air. The concentration of CO 2 at the entrance was 40% (60% air) and increased to 60% (40% air) at the midpoint, where it remained through the remainder of the tunnel. The shackle line speed was constant and set so that the birds were in the stunner for 25 s. The CO 2 concentration inside of the tunnel was monitored at the 3Servomex Ltd., model 1370, Crowborough, Sussex, U.K. 4Model SS-36-SS, Brower, Houghton, IA 52631. 5Model SP-30-SS, Brower, Houghton, IA 52631. KANG AND SAMS entrance and midpoint with CO 2 meters.3 Immediately after exiting the stunning tunnel, both the right carotid artery and jugular vein were cut for bleeding. During bleedout, the actual amount of blood draining from the neck cut was collected into plastic bags at 30, 60, 90, and 120 s. The grams of blood per interval were calculated as grams of blood per kilogram live bird. After completion of bleeding, all five carcasses were scalded4 (60 C, 45 s), and defeathered (rotary drum picker5 for 25 s) together. Following manual evisceration, prechilling in water (18 C, 15 min) and chilling in a water ice slush (1 C, 30 min), all carcasses were subjectively scored for damage to the clavicle and shoulder, and for hemorrhages on the surface of the P. major. Specific defects included a split clavicle apex with hemorrhage stain, shattering of the proximal end of the humerus, and hemorrhages on the surface of the Pectoralis with a cumulative area greater than 1 cm2. Blood loss data were subjected to analysis of variance and means were separated with Duncan s multiple range test procedures at the P < 0.05 level (SAS Institute, 1985). A completely randomized block design was organized with stunning method as a main effect and replicate as a block factor. Because no interactions were detected between replicates and treatments, the data from the replicates were pooled. Chi-square analysis was used to analyze the carcass damage data (SAS Institute, 1985). Experiment 2 Two hundred fifty-six male broilers were randomly divided into two groups of 128 birds for the application of two stunning methods. Sixty-four birds in each of two replications were removed from feed and water and held in coops 12 h prior to slaughter. Electrical stunning, CO 2 stunning, and processing was conducted as described for Experiment 1. The breast fillets were harvested at 0, 1, 2, and 6 h postmortem for measurement of rigor mortis development. The 0-h breast fillets were harvested immediately after picking using the technique described by Hamm (1981), and 1-h samples were obtained after the completion of chilling. The remaining carcasses were packed in ice and stored at 0 to 2 C for an additional 1 or 5 h before harvesting. The anterior halves of the left fillets were frozen immediately after harvesting for ph and R value analysis. The ph was measured using the iodoacetate method of Jeacocke (1977) as modified by Sams and Janky (1986). The R value was measured using the absorbance ratio method of Thompson et al. (1987). The posterior halves of the fillets were packed on ice and allowed to age until 24 h. The aged samples were used to measure sarcomere length (SL) and fragmentation index (FI) by laser and gravimetric methods, respectively (Sams et al., 1990; Thompson et al., 1987). For shear value (SV), whole right fillets from each treatment were aged on ice until 24 h. The aged fillets were baked in an oven at 177 C to an internal temperature of 76 C using raised wire racks in aluminum foil-lined and -covered pans. The cooked fillets were wrapped in aluminum foil and held at 4 C

BLEEDOUT EFFICIENCY, CARCASS DAMAGE, AND RIGOR MORTIS 141 TABLE 1. Cumulative mean (± SD) blood loss 1 from broilers stunned with CO 2 or electrical stunning (ES) Stunning method 2 Bleeding time CO 2 ES (s) (g) 0 to 30 20.4 ± 4.7 b 22.0 ± 4.5 a 0 to 60 25.5 ± 4.8 b 26.9 ± 4.8 a 0 to 90 27.8 ± 5.2 a 28.8 ± 4.9 a 0 to 120 29.0 ± 5.9 a 29.8 ± 4.9 a 1Grams of blood lost per kilogram of live bird weight. 2n = 200 per mean in each row. Same birds used in all four rows. overnight. Duplicate samples (40 20 7 mm) from each cooked fillet were sheared with an Instron Universal Testing Machine6 using a 10-blade Allo-Kramer shear cell as described by Sams (1990). All data were subjected to analysis of variance and means were separated with Duncan s multiple range test procedures at the P < 0.05 level (SAS Institute, 1985). A completely randomized block design was organized with stunning method as a main effect and replicate as a block factor. Because no interactions between replicate and treatment were detected, the data from the replicates were pooled (SAS Institute, 1985). Experiment 1 RESULTS AND DISCUSSION The birds stunned by electricity bled faster than the CO 2 -stunned birds until 60 s. However, the difference in the total amount of blood loss did not exist longer than 90 s (Table 1). This result was consistent with a previous study, which indicated that the initial bleeding rate was faster with ES until 60 s but that the total bleedout was equivalent to CO 2 stunning by 140 s (Mohan Raj and Gregory, 1991). Early in 1966, Kotula and Helbacka (1966) also reported no significant difference at 90 s bleeding time. These results suggest that the ES may initially cause more excitation and stronger muscle contractions than the gaseous stunning. As a result, the electricity leads to better blood flow at the beginning, whereas the excess of CO 2 could have slower bleeding due to less excitation and less muscular contraction. Stunning birds with CO 2 significantly reduced carcass damage in both clavicle and Pectoralis but did not reduce humerus breakage (Table 2). Mohan Raj et al. (1990a) stunned broilers with argon, CO 2, or electricity and observed that the incidence of broken bones was highest with ES, followed by CO 2, whereas argon stunning produced the least damage. The lower incidence of 6Model 1011, Instron Corp., Canton, MA 02021. TABLE 2. Effect of stunning method on broiler carcass damage frequency 1 Stunning method 3 Damage location 2 CO 2 ES (%) Clavicle 28 b 46 a Humerus 11 a 10 a Pectoralis 15 b 36 a 1Percentage of carcasses with the indicated damage. 2Clavicle = split clavicle apex with hemorrhage stain; Humerus = shattering of the proximal end of the humerus; Pectoralis = hemorrhages on the surface with a cumulative area greater than 1 cm 2. 3n = 200 per mean in each row. Same birds used in all four rows. damage to the carcasses stunned by CO 2 is probably due to the calmer nature of a gaseous stun. Gregory and Wotton (1986) reported that stunning with high electrical currents was a humane method when compared to low amperage or no stun because there was less likelihood of the bird s regaining consciousness before it died. However, Gregory and Wilkins (1989) also found that the problems of broken bones and hemorrhages were related to high electrical currents. Bone fragments and splinters caused by high currents contaminated breast muscle during the further portioning process and the blood stains on a muscle surface could result in dark spots on the final products. Along with the rapid and strong muscle contraction, the high electric current may be responsible for the muscle hemorrhages. Katme (1986) reported that electric shock can increase blood pressure up to 3.5 times. These results suggests that CO 2 stunning of broilers can reduce carcass damage associated with ES without inhibiting total blood loss. Reducing this carcass damage would financially benefit processors through reducing trimming and downgrading. However, it should be noted that degree of reduction in carcass damage may be dependent on the ES to which it is compared. Craig and Fletcher (1995) reported that high amperage (125 ma) ES such as those used in Europe cause more carcass damage than the lower amperage (approximately 12 ma) cus- TABLE 3. Breast muscle ph and R value means (± SD) 1 at different postmortem times following stunning with CO 2 or electricity Postmortem time ph R value CO 2 ES CO 2 ES 0 6.43 ± 0.23 a 6.42 ± 0.14 a 1.00 ± 0.16 a 0.92 ± 0.24 a 1 6.38 ± 0.24 a 6.28 ± 0.15 b 1.09 ± 0.25 a 0.97 ± 0.20 a 2 6.18 ± 0.22 a 6.13 ± 0.14 a 1.36 ± 0.29 a 1.05 ± 0.17 b 6 5.95 ± 0.16 a 6.04 ± 0.15 a 1.46 ± 0.19 a 1.31 ± 0.20 b a,bmeans within a row within variable, with no common superscript differ significantly

142 KANG AND SAMS TABLE 4. Breast muscle sarcomere length and fragmentation index (± SD) 1 at different postmortem times following stunning with CO 2 or electricity TABLE 5. Breast muscle cooked meat shear value (± SD) 1 different postmortem times following stunning with CO 2 or electricity at Postmortem time Sarcomere length Fragmentation index CO 2 ES CO 2 ES 0 1.57 ± 0.07 a 1.58 ± 0.05 a 73.4 ± 33.4 a 80.1 ± 37.6 a 1 1.60 ± 0.07 a 1.62 ± 0.10 a 58.5 ± 31.2 a 67.7 ± 36.9 a 2 1.74 ± 0.13 a 1.75 ± 0.13 a 51.0 ± 23.5 a 40.5 ± 11.4 a 6 1.80 ± 0.07 a 1.84 ± 0.06 a 35.5 ± 13.9 a 30.5 ± 8.0 a a,bmeans within a row within variable, with no common superscript differ significantly Stunning method Postmortem time CO 2 ES (kg/g) 0 14.0 ± 3.2 a 13.9 ± 3.0 a 1 9.75 ± 3.6 a 10.2 ± 3.9 a 2 8.18 ± 4.2 a 6.9 ± 3.5 a 6 4.07 ± 1.0 a 4.4 ± 1.3 a tomarily used in the U.S. The 35 ma ES used in the present study is intermediate between these two stunning systems, suggesting that some amperage between 12 and 35 A is the maximum amperage that will stun the bird without damaging the carcass. Experiment 2 There was no consistent difference in ph between the two stunning methods (Table 3). At 1 h postmortem, the ES produced a significantly lower ph but this difference was not sustained. This result suggests that the ES may have caused a temporary acceleration in postmortem metabolism. More severe and stronger muscular contractions induced by ES than CO 2 could be responsible for the lower muscle ph consistent with the bleedout data in Experiment 1. However, the practical importance of the ph difference at 1 h is questionable in view of its transient occurrence and relatively small magnitude. Mohan Raj et al. (1990b) reported that the mean ph was greatest with ES, lowest with argon, and intermediate with CO 2 at 20 min post-mortem. The differences between the two studies could be from different stunning methodology and different sampling times. Mohan Raj et al. (1990b) killed broilers with a 107 ma or in a batch-type gas stunning box and measured ph at 20 min postmortem, whereas the present study stunned the broilers with 35 ma or in a continuous shackle-line gas stunning tunnel and measured ph at 1 h. The R value is the ratio of the concentrations of inosine nucleotides to adenosine nucleotides and indicates the status of adenosine triphosphate (ATP) depletion during rigor mortis development (Calkins et al., 1982). The R values of fillets from CO 2 -stunned birds were significantly higher than those of ES-stunned birds deboned at 2 and 6 h (Table 3) suggesting that CO 2 stunning accelerates the breakdown of ATP and accelerates rigor mortis development. As a result, CO 2 stunning would allow fillets to be harvested at an earlier stage of processing without making them tough (Jones and Grey, 1989; Mohan Raj et al., 1990a). The accelerated depletion of ATP indicated by increased R values with the CO 2 stun may be due to the ES slowing rigor mortis development instead of an acceleration by the CO 2 stun. Craig and Fletcher (1995) reported that high amperage stun (125 ma, 50 Hz) slowed rigor mortis development relative to a lower amperage ES of 10.5 V, 500 Hz. The electrical stun used in the present study was intermediate between these two previous treatments, so it is difficult to determine whether it was a high enough amperage to inhibit rigor mortis development. Sarcomere length is a functional unit indicating the distance between two adjacent Z-lines and the degree of contraction. Sarcomere length is a direct measurement representing the status of muscle contraction, which would increase if deboning were performed before rigor mortis develops because of the presence of ATP to support contraction. The SL for both treatments increased with an extended aging time up to 6 h, but there was no significant difference between the two stunning methods at any postmortem time (Table 4). Fragmentation index decreased without any significant difference at any aging time between stunning treatments (Table 4). In accordance with a lack of stun method effect on ph, SL, and FI, muscle shear values also indicated no difference between stunning methods at any time. Shear value decreased gradually to about 4 kg/g, with the most tender meat obtained at 6 h postmortem, regardless of stunning treatment (Table 5). These experiments suggest that CO 2 stunning may represent some advantages over ES in reduced carcass damage and accelerated rigor mortis development. However, these benefits seem to depend on the gas or ES methods used. REFERENCES Amey, D., 1988. Minimum time process system. Tender meat in 24 minutes. Broiler Ind. 51:2:22 26, 54 56. Calkins, C. R., T. R. Dutson, G. C. Smith, and Z. L. 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