1993 Poultry Science 72: Received for publication January 4, Accepted for publication April 26, 1993.

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1 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 C. E. LYON and J. A. DICKENS Poultry Processing and Meat Quality Research Unit, USDA, Russell Research Center, P.O. Box 5677, Athens, Georgia ABSTRACT The study was conducted to determine the effects of electric current and wing restraints on the rate of post-mortem biochemical changes and objective texture of broiler Pectoralis major muscles deboned after chilling. Electric treatments of stun, stun and stimulate, and electrocution were administered to a total of 12 birds in each of six replications of the study. In each replication, wing restraints were applied to two of the four birds subjected to each electric treatment. Birds were subjected to the stunning and electrocution treatments prior to bleeding for 90 s. For the stun and stimulation treatment, the birds were bled during and after the pulsed stimulation. Carcasses were subjected to the wing restraints after feather removal, then eviscerated, prechilled, and chilled. The Pectoralis major muscles were removed 75 min postmortem and evaluated for ph, R value (ratio of adenine to inosine nucleotides), and sarcomere length. Muscles were held at 2 C for 24 h prior to cooking and objective texture evaluation. Stunning and stimulating treatments resulted in significantly higher R values and lower ph values compared with the electrocution treatment. The application of wing restraints significantly increased sarcomere lengths in raw deboned muscle. Stunning followed by pulsed stimulation in conjunction with wing restraints resulted in the lowest shear values (5.95 kg) for cooked meat of muscles deboned 75 min post-mortem. {Key words: electric stimulation, electrocution, wing restraints, sarcomere lengths, meat texture) INTRODUCTION Demand continues to increase for further processed broiler products containing breast meat. Removing the Pectoralis major muscles from the broiler carcass immediately after chilling would benefit the poultry industry. However, researchers have reported that if the intact P. major muscles are removed after chilling, the resulting cooked meat will be tough (Stewart et al, 1984; Lyon et al, 1985). Researchers have reported on a variety of treatments to shorten the post-mortem (PM) aging time and at the same time Received for publication January 4, Accepted for publication April 26, Poultry Science 72: ensure ultimate texture or tenderness in the cooked meat. The use of pulsed electric current applied to the carcass shortly after death has been studied by several researchers (Thompson et al, 1987; Froning and Uijttenboogaart, 1988; Lyon et al, 1989; Sams, 1990). Although there is some disagreement about the impact of pulsed electric current, it does seem to either alter the rate of PM biochemical reactions or disrupt muscle fibers. A physical procedure to stretch or tension the P. major muscles during processing and subsequent aging was evaluated independently (Papa and Fletcher, 1988a; Papa et al, 1989; Lyon et al, 1992) and in conjunction with electrical stimulation (Birkhold et al, 1992). This physical restraining of the muscles, termed "wing

2 1578 LYON AND DICKENS restraint" (WR) (Papa and Fletcher, 1988a) and muscle tensioning (Birkhold et ah, 1992) lengthens the sarcomeres and reduces the force necessary to shear the cooked meat. Heath (1984) recommended that electric current should be used to kill broilers. This recommendation was based on the lack of difference in blood loss between birds that had been electrocuted or stunned prior to bleeding for 3 min, and the lack of difference in muscle ph values measured 2 h PM. Griffiths (1983) evaluated voltage levels ranging from 55 to 200 V and reported no difference in blood loss from broilers. Dickens and Lyon (1991) reported no difference in blood loss for broilers subjected to 50 and 200 V for 10 s in a brine stunner and bled for 90 s. They did note that meat deboned 2 h PM from birds subjected to the 200-V treatment required significantly more force to shear than meat from birds subjected to the 50-V treatment. The objective of this study was to determine the role of electrocution, electrical stimulation, and WR on the rate of PM biochemical reactions and objective texture of cooked meat when the P. major muscles were excised after chilling. MATERIALS AND METHODS Mixed sex, market age broilers ranging in weight from 1.8 to 2.2 kg were purchased from a local processor. Twelve birds were placed in a coop and transported to the research facility. All of the birds were killed within 2 h of their arrival at the facility. Treatments Three electric treatments were evaluated in combination with two WR treatments. The electric treatments were: stun for 10 s at 50 V alternating current (VAC), stun for 10 s at 50 VAC followed by pulsed stimulation (2 s on, 1 s off) at 200 VAC for 1 min, and electrocution for 10 s at 200 VAC. Four birds were subjected to the electric treatment at a time. Voltage was preset and a timer was set!bar-h Livestock Supplies, Chicago, IL for 10 s. Birds were hung in a joined set of shackles, and the set was lowered until the top of the birds' heads contacted a charged brine solution. The circuit was completed by depressing a foot-prompted switch that allowed current to flow from head to feet. For the stimulation treatment, shackles were raised so that the heads of the birds were no longer in contact with the brine solution after initial stunning; the rheostat was set for 200 VAC and the shackles lowered so that the birds' heads contacted the brine solution during stimulation. A foot-prompted off-on switch was used with the sweep-hand timer to control the on-off cycle, and the stimulation treatment lasted for a total of 1 min. For each group of birds, the peak current drawn was recorded in milliamperes. Current drawn was expressed on an individual bird basis by dividing the peak current by four. Wing restraints were applied after feather removal to two of the four carcasses of each treatment. The remaining two carcasses served as a control. A pair of emasculation pliers 1 was used to stretch a rubber band over the wings and secure the band against the back of the carcass. The bands are routinely used for the bloodless castration of bull calves. Processing After the administration of the stun and electrocution treatments, birds were placed in restraining cones, the carotid artery and jugular vein on one side of the neck were severed, and the birds were bled for 90 s. Carcasses subjected to the stimulation treatment were processed last, and were not removed from the shackles during bleeding. The blood entered the brine solution during the 1 min of pulsed stimulation. After bleeding, the carcasses were placed in shackles attached to a variable speed overhead line, scalded by immersion in 56 C agitated water for 2 min, then passed through a five-banked picker. The WR were applied to two of the four carcasses after picking, and all carcasses were manually eviscerated. After evisceration, carcasses were rinsed with water, prechilled in 15 C water for 15 min, and chilled in 1C slush-ice for 30 min. Prechill and chill tanks were both equipped with paddles that rotated at

3 ELECTRIC TREATMENTS AND WING RESTRAINTS rpm to simulate commercial chilling. After chilling, the carcasses were hung on shackles for 10 min to remove excess moisture. This processing procedure resulted in total WR time of 75 min. Muscle and Meat Measurements The P. major muscles were removed from all of the carcasses 75 min PM and the following determinations made. ph. A 2-g sample of each muscle from the anterior region was blended 2 with 25 ml of 5 mm iodoacetate and 150 mm KC1 by pulsing three times (setting 5). The ph of the resulting slurry was measured 3 within 4 h of preparation. For each of six replications, the ph value of each breast muscle was recorded. This resulted in eight ph values for each electric treatment (four carcasses, eight breasts), and four ph values for the WR treatment within each electric treatment. R Values. The R values (ratio of adenosine to inosine nucleotides) were determined according to the procedure of Honikel and Fischer (1977). A 2-g sample was removed from the anterior region of each muscle. The average of duplicate filtrate samples was used for statistical analysis. This resulted in eight R values for each of six replications for each electric treatment and four R values for the WR treatment. Sarcomere Length. The length of the sarcomeres was measured using the laser diffraction method described by Cross et al. (1981) as modified by Papa et al. (1989). A 5-g sample was removed from the posterior region of each muscle. For each of the six replications, two muscles for each electric treatment, one with WR and one without WR, were evaluated for sarcomere length. Ten readings were taken for each muscle sample, and the average of the 10 readings used for statistical analysis. 2 Polytron PT 10/35, Brinkman Instruments, Westbury, NY ^Orion Research ph Meter, Model 611, Cambridge, MA Dazey Corp., Industrial Airport, KS Instron Corp., Canton, MA Storage and Cooking. After sampling for ph, R value, and sarcomere length, the muscles were individually packaged in heat-and-seal bags 4 and held at 2 C for 24 h. Muscles were then cooked in 85 C water for 20 min, cooled in tap water for 15 min, and removed from the bags. Although no direct end-point temperatures were recorded, previous experiments using these cooking conditions resulted in end-point temperatures ranging from 76 to 80 C. Objective Texture. The procedure of Lyon and Lyon (1990) was used to remove two 1.9-cm wide strips from each intact meat sample at room temperature. Each strip was sheared once, and the average shear value of the strips used for statistical analysis. This resulted in 24 shear values for each of the six replications for the electric treatments and 12 for the WR treatment. A Warner-Bratzler attachment to an Instron 5 Model 1122 was used for objective texture evaluation, and the peak load was measured in kilograms. Crosshead speed was 200 mm/min, and downstroke crosshead travel was 45 mm for each test. Statistical Analysis The experiment was replicated six times. The 12 birds evaluated in each replication were distributed so that four birds were subjected to each of the electric treatments, and two of those birds were subjected to WR whereas the other two served as a control (no WR). This resulted in a total of 72 birds or 144 P. major muscles for the study. Forty-eight muscles were evaluated for each electric treatment, and 24 of those muscles were subjected to WR. Data were analyzed by ANOVA using the General Linear Models procedure of base SAS software (SAS Institute, 1987). Main effects were electric treatment, WR, replication, and the interaction of electric treatment, WR, and replication. The interaction of bird within replication by appropriate treatment (electric or WR) was used as the residual error for the main effects of replication, electric treatment, and WR. To test for significant interactions within treatments the three-way interaction of electrical treatment, WR, and replication was used as the error term. When differences among treatments were noted, means were sepa-

4 1580 LYON AND DICKENS TABLE 1. Effects o >f electric treatments on ph, R values, and sarcomere length of broiler Pectoralis major muscle measured 75 min post-mortem Treatment 1 Stun (50 VAC, 10 s, 34 ma) Stun followed by stimulation (200 VAC, 138 ma) Electrocution (200 VAC, 10 s, 132 ma) Sarcomere ph R Value 2 length ±.17«5.88 ±.16b 6.18 ±.19» ±.08>> 1.18 ±.08» 1.02 ±.09' GO ± ± ±.30 a_<: Means ± SD in columns with no common superscripts differ significantly (P <.05). Electric treatment applied by contacting head of birds to a charged brine solution. Current flow from head to feet. Milliamperes of current drawn per bird were determined by dividing the peak current drawn by each group of birds by four. 2 Ratio of adenosine to inosine nucleotides. rated using Tukey's Studentized range test. Significance was accepted at the P <.05 level. RESULTS AND DISCUSSION Heath (1984), summarizing research conducted in Germany, reported that birds electrically stunned with less than 20 ma squawked and flapped and tried to escape immediately after removal from the shackles, but that no birds subjected to 120 ma recovered. In this study, the average current per bird was 34, 138, and 132 ma for the stun, stun and stimulate, and electrocution treatments, respectively. Based on visual observations of wing tucking and body stiffening, all of the birds were affected by the electric treatments. Birds stunned with 50 VAC (34 ma) were not killed, but were immobilized during the short time it took to remove them from the shackles, place them in the restraining cones, and make the neck cut. None of the birds survived the 200 VAC, 10 s electrocution treatment (132 ma). The R values are used as indicators of adenosine triphosphate (ATP) depletion in the PM muscle because they measure the ratio of adenosine nucleotides to inosine nucleotides, which are a product of muscle metabolism. Honikel and Fischer (1977) explained that the R value increases as the content of ATP decreases because of the progressive dephosphorylation and deamination of adenosine nucleotides. Papa and Fletcher (1988b) reported the R values for hot-stripped broiler P. major muscles sampled in the posterior location at 15 min and 24 h PM to be.90 to 1.35, respectively, with the higher value indicative of further development of rigor mortis. Under the conditions of the present study, the electric treatments had a significant effect on R values measured at 75 min PM (Table 1). The stun and stimulation treatment resulted in the highest R value, 1.18, and the electrocution treatment resulted in the lowest R value, Thompson et al. (1987) also reported that stimulation significantly increased R values and decreased ph in broiler P. major muscle deboned after chilling. In that study, the stimulation was applied 2 to 3 min PM for times ranging from 15 to 45 s. Lyon et al. (1989) reported 2 h PM R values of 1.16 for P. major muscles from carcasses that had been stunned with 50 VAC and stimulated with 200 VAC current compared with R values of 1.06 for a control group of birds that had been stunned. The stunned treatment in the present study resulted in an R value of 1.07 for muscles measured 75 min PM. The application of WR did not have a significant effect on the R values. The R value for muscles with and without WR was Papa et al. (1989) reported R values of 1.07 and 1.03 for muscles from carcasses with and without WR, respectively, and also noted that this difference was not significant. The ph values of P. major muscles measured 75 min PM were also significantly affected by the electric treatments

5 ELECTRIC TREATMENTS AND WING RESTRAINTS 1581 (Table 1). The electrocution treatment resulted in the highest muscle ph, 6.18, but this value was not significantly different from the muscle ph for the stun treatment. The stun and stimulation treatment resulted in the lowest muscle ph, Froning and Uijttenboogaart (1988) reported that pulsed electrical stimulation with 100 V for 90 s (1 s on,.5 s off) resulted in a significant decrease in the ph of P. major muscles removed from carcasses 60 min after evisceration compared with the ph of unstimulated control muscles, 5.75 versus 6.10, respectively. The time frame in that study of 60 min after evisceration would be similar to the 75 min PM deboning time in the present study. Birkhold et al. (1992) also reported lower ph values for 1 h PM breast muscle from electrically stimulated broiler carcasses compared with control carcasses, 5.84 versus 6.06, respectively. Froning and Neelakantan (1971) and Lyon et al. (1984) reported that ph values greater than 5.9 could be used to indicate a prerigor condition in broiler breast muscle. Using the ph value of 5.9 as a line between prerigor and the onset of rigor, subjecting the birds to the stun and stimulation treatment caused the P. major muscles to be in the onset phase of rigor within 75 min PM, but the P. major muscles from carcasses subjected to the stun or electrocution treatments were not in the onset phase of rigor at 75 min PM. These results are reinforced by the lower R value for the P. major muscles from the electrocution treatment compared with the muscles subjected to the stun and stimulation treatment. The application of WR did not significantly affect ph values of the P. major muscles. The ph value for the carcasses with WR was 6.05, whereas carcasses without WR exhibited a muscle ph of The length of the sarcomeres was significantly affected by the application of WR. The average sarcomere length for the carcasses with WR applied was 1.99 p compared with a sarcomere length of 1.83 H for the carcasses without WR. Papa et al. (1989) reported that sarcomeres were significantly lengthened when WR were left on the carcasses for 4 h prior to deboning. The authors reported sarcomere lengths of 2.13 n for the muscles from carcasses with WR compared with 1.72 n for muscles from conventionally processed carcasses. The increase in sarcomere length in the present study was not as pronounced, but the time that WR were left on the carcasses was reduced from 4 to 1.25 h. The electric treatments did not significantly affect sarcomere lengths of the P. major muscles (Table 1). These results are in agreement with those reported by Froning and Uijttenboogaart (1988), but are not in agreement with the results reported by Sams (1990) or Thompson et al. (1987). Sams (1990) applied pulsed stimulation (110 V, 1 A, 1 s on, 1 s off) to carcasses for 0, 7, or 14 min after scalding, and deboned the P. major muscles 1 h PM. Sams (1990) reported significantly longer sarcomeres from muscles subjected to the 7 and 14 min stimulation compared to the control group; 1.52, 1.59, and 1.35 ft, respectively. The difference in time of stimulation in the present study (1 min), compared with the 7- and 14-min periods evaluated in the study by Sams (1990), could account for the difference in response of the sarcomeres to the electric treatment. Thompson et al. (1987) reported that stimulation with 820 VAC for 15 s (2 s on, 1 s off), 2 to 3 min PM significantly increased the sarcomere length of P. major muscles deboned after chilling compared with an unstimulated control; 1.68 to 1.50 H, respectively. The difference in voltage level (820 VAC compared with 200 VAC) could account for the difference in the results. Both the electric and WR treatments had significant effects on the shear values of the cooked meat (Table 2). Across electric treatments, the application of WR resulted in significant reductions in shear values for all of the carcasses compared with carcasses not subjected to WR. The difference in shear values between the stun and the stun and stimulation treatment was not significant when WR were applied, 6.67 kg for the stun treatment compared with 5.95 kg for the stun and stimulation treatment. The reduction in shear values due to the application of WR has been reported under commercial and pilot plant condi-

6 1582 LYON AND DICKENS TABLE 2. Effect of electric treatments and wing restraints on shear values of Pectoralis major meat deboned 75 min post-mortem (n = 24) Treatment 1 Stun (50 VAC, 10 s, 34 ma) Stun followed by stimulation (200 VAC, 138 ma) Electrocution (200 VAC, 10 s, 132 ma) With wing restraints 6.67 ± S.OAy 5.95 ± 2.97 b <y ± y Warner-Bratzler shear values (\rr\ Without wing restraints 9.88 ± 4.51 b ' x 9.31 ± 2.76"'" ± 5.27a* a - b Means ± SD in columns with no common superscripts differ significantly (P <.05). x-ymeans ± SD in rows with no common superscripts differ significantly (P <.05). 1 Electric treatment applied by contacting head of birds to a charged brine solution. Current flow from head to feet. Milliamperes of current drawn per bird were determined by dividing the peak current drawn by each group of birds by four. tions. In the commercial study, Lyon et al. (1992) applied WR at the transfer point prior to automatic evisceration. The WR did not disrupt the evisceration procedure, but a significant reduction in Warner-Bratzler shear values was not achieved without a 1-h postchill aging period with the WR on the carcass. In the pilot plant study, Janky et al. (1992) reported a significant reduction in Allo- Kramer shear values for carcasses subjected to WR when the fillets were removed immediately after chilling; however, the authors noted that the meat would not be considered tender based on shear value ranges reported by Simpson and Goodwin (1974). For the present study, the Warner- Bratzler shear value of 6.67 kg for the carcasses stunned with WR would be in the "slightly tender to slightly tough" portion of a sensory scale reported by Lyon and Lyon (1991). Those authors reported that the range of Warner-Bratzler shear values for this portion of the sensory tenderness scale ranged from 6.62 to 9.60 kg. The 5.95-kg value for meat from birds that had been stunned and stimulated with WR applied would be in the "moderately to slightly tender" portion of that scale, with a range from 3.62 to 6.61 kg. Birkhold et al. (1992) reported that the combination of electrical stimulation and muscle tensioning resulted in significantly lower shear values compared with either treatment applied alone and that the combination resulted in an increase in the percentage of fillets harvested 1 h PM that would be considered tender by consumers. The use of electric current to kill the bird via electrocution resulted in elevated shear values for breast muscles deboned after chilling. Electrocution may be a humane way to kill the bird, but the data indicates that it slowed the rate of early PM biochemical reactions. The application of pulsed current applied during bleeding in conjunction with WR applied prior to evisceration resulted in acceptable shear values for muscles deboned after chilling. The results indicate that the electric and WR treatments influence P. major muscle deboned 75 min PM in different ways. The pulsed stimulation during bleeding resulted in an acceleration of biochemical changes noted by elevated R values and lower ph values. The application of WR significantly lengthened the sarcomeres, and the combination of pulsed stimulation and WR resulted in the lowest shear values for cooked meat. REFERENCES Birkhold, S. G., D. M. Janky, and A. R. Sams, Tenderization of early-harvested broiler breast fillets by high-voltage post-mortem electrical stimulation and muscle tensioning. Poultry Sci. 71: Cross, H. R, R. L. West, and T. R. Dutson, Comparison of methods for measuring sarcomere length in beef semitendinosus muscle. Meat Sci. 5: Dickens, J. A., and C. E. Lyon, Blood loss of broilers and some functional properties of the meat as affected by stunning at 50 and 200 VAC. Poultry Sci. 70(Suppl. l):158.(abstr.)

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