The effects of antemortem electrical stunning and postmortem electrical stimulation on biochemical and textural properties of broiler breast meat

The Effects of Antemortem Electrical Stunning and Postmortem Electrical Stimulation on Biochemical and Textural Properties of Broiler Breast Meat E. W. CRAIG, D. L. FLETCHER,1 and P. A. PAPINAHO Department of Poultry Science, The University of Georgia, Athens, Georgia 30602-2772 nucleotides), and sarcomere length. Raw breast meat color (CIELAB), cook loss, and shear values were determined on samples held at 2 C for 24 h. Results showed both STUN and STIM significantly affected blood loss, pH, R-value, sarcomere length, color, and shear, and there were significant STUN by STIM interactions. Blood loss was significantly lower for the HC STUN and all the STIM treatments. STIM at 440 V resulted in accelerated rigor development as measured by pH, R-value, and sarcomere length, similar to the unstunned or LV STUN samples, but different from the HC STUN birds. These results indicate that electrical stimulation may accelerate rigor most effectively following high current stunning, which tends to delay early rigor development.

(Key words: electrical stunning, electrical stimulation, rigor development, meat quality) 1999 Poultry Science 78:490–494

the adverse effects associated with early deboning can be avoided only if the carcass remains intact until the rigor process is complete. A number of “rigor accelerating” treatments have been evaluated, including electrical stimulation (Thompson et al., 1987), electrical stimulation in combination with high temperature conditioning (Clatfelter and Webb, 1987), wing restraints or muscle tensioning (Papa et al., 1989), and electrical stimulation with muscle tensioning (Birkhold and Janky, 1989). Although the use of electrical stimulation as a tenderizing treatment is well established for red meat animals (Pearson and Dutson, 1985), it has not been widely used in the poultry industry. This difference is primarily due to the fact that, although a few treatments have reduced cooked muscle shear force of early deboned breast meat (Thompson et al., 1987; Papa et al., 1989; Birkhold and Janky, 1989), these reductions have either not been great enough to consistently eliminate toughness or have not decreased aging times enough to eliminate the need for large holding capacities.

INTRODUCTION The poultry industry in the U.S. has changed dramatically over the last 30 yr. Poultry consumption has risen substantially and at the same time, poultry marketing has changed. In 1970, the most common market form for broilers was a whole, ready-to-cook carcass, with less than 20% of the carcasses marketed as cut-up, deboned, or further processed. Estimates in 1991 indicated that less than 15% of broilers were marketed in whole, ready-to-cook form, whereas 55% were marketed as cut-up and 30% as deboned or further processed (Amey, 1991). These changes in marketing and an increased demand for deboned meat have pressured poultry processors to debone meat as soon as possible after chilling. Earlier deboning times and shorter aging times have resulted in a marked increase in tough breast meat. For example, Stewart et al. (1984) found a positive correlation between early deboning times and breast meat toughness and concluded that, without the application of an effective accessory tenderizing treatment,

Received for publication December 18, 1997. Accepted for publication October 20, 1998. 1To whom correspondence should be addressed: fletcher@arches. uga.edu

Abbreviation Key: HC = high current; LV = low voltage; R-value = ratio of inosine to adenosine; STIM = postmortem electrical stimulation; STUN = antemortem electrical stunning.

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ABSTRACT Experiments were conducted to determine the combined effects of antemortem electrical stunning (STUN) and postmortem electrical stimulation (STIM) on breast muscle rigor development and meat quality attributes. Birds were either unstunned, stunned with low voltage (LV), or stunned with high current (HC) prior to conventional killing. Immediately after exsanguination, birds were either unstimulated, or were subjected to electrical stimulation with 12 1s on/1s off pulses of 440 V AC and allowed to bleed for 90 s to determine the effect of treatment on blood loss. Breast fillets (Pectoralis major) were removed from carcasses immediately after evisceration (0.25 h) or after aging in a static ice-water slush for 1 or 2 h, and analyzed for muscle pH, R-value (ratio of inosine to adenosine

STUNNING AND STIMULATION EFFECTS ON MEAT QUALITY

MATERIALS AND METHODS In each of three replicate trials, 72 live broilers obtained from the holding area of a commercial processing plant were subjected to one of three antemortem electrical stunning (STUN) treatments and one of two postmortem electrical stimulation (STIM) treatments. The stunning treatments consisted of a no stun control, a low voltage (LV) STUN with a constant voltage of 11 V pulsating DC at 500 Hz for 10 s (average of 7 to 8 mA per bird), and a high current (HC) STUN with a constant current of 125 mA at 60 Hz for 5 s. The HC system was built specifically to simulate European recommended stunning conditions. The LV system was a commercially available stunner (Simmons SF-70002) similar to those used in approximately 66% of the poultry plants in the U.S. (Heath et al., 1994). The STIM treatments consisted of a no STIM control or a 440 V AC STIM applied for 12 pulses of 1 s on and 1 s off using incircuit electrical timers. Both STUN and STIM treatments were applied to individual birds by hanging the bird on a shackle and lowering the shackle until the bird’s head came into contact with an electrical grid submerged 0.5 in below the surface of a 1% saline solution, allowing the electrical current to pass through the bird from head to foot.

2Simmons Engineering Co., Dallas, GA 30132. 3Minolta Corp., Ramsey, NJ 07446. 4Instron Model 1122, Instron Corp., Canton, MA

02021.

To reduce uncontrolled weight loss during killing that might affect blood loss data, a tampon was inserted into the cloaca of each bird to prevent fecal discharge during stunning and slaughter. Birds were then individually weighed, stunned, and killed using a unilateral neck cut that severed both the carotid artery and jugular vein. The STIM treatment was applied immediately after cutting the neck during the first 24 s of the 90 s total bleed time. At the end of the 90 s bleed time, carcasses were reweighed and blood loss was calculated by weight difference as a percentage of live body weight. Carcasses were then placed in a batch scalder at 54 C for 2 min, picked in a rotary drum batch picker for 25 s, and hand eviscerated. Following evisceration, carcasses were deboned at either 0.25, 1 or 2 h postmortem. Carcasses to be deboned at 1 or 2 h postmortem were placed in a static ice-water slush until time of deboning. Both breast halves (Pectoralis major) were removed, and one breast half was sampled at the cranial end for immediate pH, R-value (the ratio of inosine to adenosine) and sarcomere length determinations. The other breast half was placed in a plastic bag and held at 2 C for 24 h for subsequent color, cook loss, and tenderness evaluation. Breast muscle pH was determined according to the iodoacetate method as described by Jeacocke (1977). Rvalue was determined as described by Honikel and Fischer (1977). Sarcomere length was determined by laser diffraction using the method of Cross et al. (1981) with the following modification: Crude homogenates of the breast samples were prepared by blending 2.5 g of muscle with a solution containing 150 mM KCl and 5 mM sodium iodoacetate. Color was measured using a Minolta Chromameter II,3 using illuminant C, and color values were expressed using the CIELAB system (L* = lightness, a* = redness, and b* = yellowness). Color readings were taken at the cranial end of the raw breast muscle sample. Cook loss was expressed as a percentage weight loss and determined by the formula [Raw breast weight – Cooked breast weight/Raw breast weight] × 100, using the cooking procedure described by Papinaho and Fletcher (1996). Tenderness was evaluated by measuring Allo-Kramer shear force of cooked breast meat samples using an Instron Universal Testing Machine4 according to the procedure described by Papinaho and Fletcher (1996).

Statistical Analysis Blood loss, pH, R-value, sarcomere length, color, cook loss, and shear value were determined for each bird within a particular treatment and deboning time. The experimental design was a 3 × 3 × 2 × 3 factorial arrangement of treatments for trial, STUN, STIM, and deboning time (total of 216 birds with 4 birds per treatment cell). Data were analyzed using the GLM procedure of SAS/STAT (SAS Institute, 1988) to test the main effects of STUN, STIM, deboning time, and STUN by

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A thorough review of electrical sitmulation by Li et al. (1993) gives a detailed summary of the major findings concerning its use in poultry up until 1991. The authors reported that electrical stimulation varied considerably between studies with regard to its effect upon muscle tenderness. Li et al. (1993) concluded that electrical stimulation accelerates rigor mortis development as indicated by pH, R-value, and sarcomere length. More recent work by Sams (1995) suggests that electrical stimulation may have some practical commercial application. Recent work has demonstrated that high current electrical stunning delays rigor development (Papinaho and Fletcher, 1995; Papinaho et al., 1995; Papinaho and Fletcher, 1996). It is interesting that antemortem electrical stunning delays early rigor development whereas postmortem electrical stimulation accelerates rigor development. The purpose of this study was to determine the combined effects of antemortem electrical stunning and postmortem electrical stimulation on early rigor development and broiler meat quality. A major emphasis was to determine whether the reported delay in rigor mortis due to electrical stunning affects the apparent rigor accelerating phenomena often associated with electrical stimulation.

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STIM interaction. As there were no treatment by trial interactions, main effects and treatment interactions were tested using residual error. Where the treatment interactions were significant, the data are presented across treatments. Means were separated using Tukey’s studentized range test option of the GLM procedure of SAS/ STAT (SAS Institute, 1988) at a significance level of P < 0.05.

TABLE 2. The effects of no stunning (0), low voltage (LV) or high current (HC) electrical stunning, and no stimulation (0) or 440 V electrical stimulation on pH and R-value (ratio of inosine to adenosine nucleotides) Electrical stimulation Measurement pH

R-Value

RESULTS AND DISCUSSION

TABLE 1. The effect of no stunning (0), low voltage (LV), or high current (HC) electrical stunning, and no stimulation (0) or 440 V electrical stimulation on 90 s bleed time percentage blood loss

0 LV HC 0 LV HC

Stunning treatment

0

0 LV HC

3.7 ± 0.1a 3.7 ± 0.1a 3.1 ± 0.1b

440 V (%) 2.8 ± 0.1b 3.1 ± 0.1b 3.0 ± 0.1b

a,bMeans ± SEM with no common superscript differ significantly (P < 0.05).

6.10 6.17 6.41 1.10 1.07 0.93

440 V ± ± ± ± 0.02bc ± 0.02bc ± 0.01d 0.03b 0.03b 0.03a

6.16 6.05 6.08 1.03 1.19 1.13

± ± ± ± ± ±

0.03b 0.03b 0.03b 0.02c 0.02a 0.02ab

a-dMeans ± SEM within measurement with no common superscript differ significantly (P < 0.05).

values from 6.41 (unstimulated) to 6.08, which was not statistically different from the other stunning treatments whether stimulation was applied or not. R-value results were similar to pH effects observed for the STIM treatments and the unstunned and LC STUN birds. The HC birds had the lowest R-values. Electrical stimulation had no significant effect on the unstunned treatment but did result in significantly higher R-values for both the LV and HC STUN treatments. The results of the color analyses are summarized in Table 3. There were no significant interactions between trial, stunning, stimulation, or deboning time; therefore only the main effects of STUN and STIM are presented. Both STUN treatments resulted in lower lightness (L*) values than the no stun controls. The LV STUN resulted in higher redness (a*) values than the no stun controls. Stunning had no effect on yellowness (b*). In contrast to these results, Craig and Fletcher (1997) reported finding no differences in color between HC and LV STUN birds. Stimulation with 440 V resulted in significantly lower L*, increased a*, and decreased b* values in the raw breast muscle samples. Neither STUN nor STIM significantly effected cook loss (data not shown). However, breast fillets deboned at

TABLE 3. The effects of no stunning (0), low voltage (LV) or high current (HV) electrical stunning, and no stimulation (0) or 440 V electrical stimulation on CIELAB color values of lightness (L*), redness (a*), and yellowness (b*) Color Treatment

Electrical stimulation

0

Stunning treatment 0 LV HC Stimulation voltage, V 0 440

L*

a*

b*

47.0 ± 0.4a 45.7 ± 0.3b 46.3a ± 0.4b

2.5 ± 0.2b 3.1 ± 0.2a 2.7 ± 0.2ab

–0.1 ± 0.2 –0.5 ± 0.2 –0.3 ± 0.2

47.4 ± 0.3a 45.3 ± 0.3b

2.2 ± 0.1b 3.3 ± 0.1a

0.0 ± 0.1a –0.7 ± 0.1b

a,bMeans ± SEM within a treatment and column with no common superscript differ significantly (P < 0.05).

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A significant stunning by stimulation interaction existed between STUN and STIM for 90 s blood loss as shown in Table 1. The no stun controls and the LV stun blood loss values were the same (3.7%) and both were significantly greater than HC stun values (3.1%) for birds receiving no STIM. These results are similar to those reported by Craig and Fletcher (1997), who observed slightly greater blood losses following LV STUN after 150 s as compared to HC STUN. Blood loss values for birds stimulated at 440 V were significantly lower than unstimulated, unstunned control birds, and LV STUN birds. For HC STUN birds, there were no significant differences in blood loss for STIM birds. The HC STUN and STIM treatments probably decreased cardiac activity during early bleeding, decreasing total blood loss measured at 90 s postkill. The effects of STUN and STIM on breast muscle pH and R-value are presented in Table 2. There was a significant STUN by STIM interaction for both pH and R-value, but no significant deboning time interaction. Therefore, the data were combined across deboning times. The unstimulated, HC STUN had a significantly higher pH value (6.41) than both the unstimulated, unstunned controls (6.10) and the unstimulated, LV STUN birds (6.17), which were not significantly different from each other. These results are similar to those reported by Craig and Fletcher (1997), in which HC STUN produced breast fillets with a higher pH than LV stunned birds when removed at 0.25 h postmortem. However, the authors reported no differences in pH at 24 h postmortem. Upon stimulation, the differences in pH between stunning treatments disappeared. Electrical stimulation applied to the HC STUN birds decreased pH

Stun

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TABLE 4. The effects of no stunning (0), low voltage (LV) or high current (HC) electrical stunning, and no stimulation (0) or 440 V electrical stimulation on sarcomere length and Allo-Kramer shear values (AK) of breast meat deboned at 0.25, 1, or 2 h postmortem Deboning time 0.25 h Measurement Sarcomere length, mm

AK, kg/g

a,bMeans

Stun 0 LV HC 0 LV HC

0 1.57 1.58 1.49 8.1 7.5 5.7

1 h

440 V ± ± ± ± ± ±

0.09 0.07 0.06 0.8 0.7 0.4

1.55 1.65 1.59 7.3 8.7 7.5

± ± ± ± ± ±

0 0.06 0.09 0.07 0.7 0.8 0.6

1.72 1.66 1.42 9.1 8.6 9.9

2 h

440 V ± ± ± ± 1.5 ± 1.4 ± 1.3

0.08a 0.07ab 0.04b

1.62 1.82 1.64 11.3 7.9 11.4

0

± ± ± ± 1.3 ± 1.0 ± 1.5

0.07ab 0.08a 0.07ab

1.84 1.73 1.45 8.9 6.5 15.2

440 V ± ± ± ± 1.9b ± 0.8b ± 1.4a

0.07ab 0.07b 0.04c

1.76 1.97 1.93 6.5 4.2 4.3

± ± ± ± ± ±

0.07ab 0.03a 0.04ab 1.1b 0.5b 0.4b

± SEM within measurement and deboning time with no common superscript differ significantly (P < 0.05).

STUN. Electrical stimulation significantly accelerated rigor development, primarily when compared to HC STUN, but had little or no effect when compared to no stunning. The effect of STIM following LV STUN was not consistent. This phenomenon may explain much of the variability in results for previous STIM studies as reported by Li et al. (1993).

ACKNOWLEDGMENTS This research was supported by state and Hatch funds allocated to the Georgia Agricultural Experiment Station. Appreciation is extended to Simmons Engineering Company for supplying equipment and technical support. The authors are grateful for the technical assistance provided by Christine Allen, Patrik Holm, Gavin Poole, and Reg Smith.

REFERENCES Amey, D., 1991. Broiler industry continues meteoric growth. Page 34 in: Watt Poultry Yearbook. USA Edition. Watt Publishing Co., Morris, IL. Birkhold, S. G., and D. M. Janky, 1989. The effects of high voltage post-mortem electrical stimulation and muscle tensioning on tenderness and post-mortem metabolism of early-harvested broiler fillets. Poultry Sci. 68(Suppl. 1):13. (Abstr.) Clatfelter, K. A., and J. E. Webb, inventors; Campbell Soup Co., assignee, 1987. Method of eliminating aging step in poultry processing. U.S. patent 4,675,947. July 9. 12 p. Int. Cl.4 A22C 21/00. Craig, E. W., and D. L. Fletcher, 1997. A comparison of high current and low voltage electrical stunning systems on broiler breast rigor development and meat quality. Poultry Sci. 76:1178–1181. Cross, H. R., R. L. West, and T. R. Dutson, 1981. Comparison of methods for measuring sarcomere length in beef Semitendinosus muscle. Meat Sci. 5:261–266. Heath, G. E., A. M. Thaler, and W. O. James, 1994. A survey of stunning methods currently used during slaughter of poultry in commercial poultry plants. J. Appl. Poult. Res. 3(3):297–302. Honikel, K. O., and C. Fischer, 1977. A rapid method for the detection of PSE and DFD porcine muscles. J. Food Sci. 42: 1633–1636.

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0.25 h postmortem had significantly lower cook loss values (23.0%) than fillets deboned at 1 or 2 h postmortem (24.4 and 24.8%, respectively). Sarcomere length and Allo-Kramer shear results are summarized in Table 4. Stunning, stimulation, and deboning time all significantly affected sarcomere length and Allo-Kramer shear. Due to STUN by STIM by deboning time interactions, the data are presented by deboning time. There were no differences between treatments in sarcomere length at 0.25 h deboning time. At 1 h deboning time, the unstimulated, HC STUN birds had significantly shorter sarcomere lengths than the STIM, LV STUN group. At 2 h deboning time, the nonstimulated, HC STUN samples were shorter than all the other treatments. At the 0.25 and 1 h postmortem deboning times, there were no differences in shear value for either STUN or STIM. At 2 h deboning, the unstimulated, HC STUN fillets had the highest shear values. Shear values above approximately 6.0 kg are generally considered to be in the “moderately tough” to “tough” range based on comparisons to previous studies by Lyon and Lyon (1990) and Papinaho and Fletcher (1996). Therefore, the only samples that would have been described as “tender” at 2 h postmortem were those from the STUN and STIM treatments (4.2 and 4.3, kg, respectively, for the LV STUN and HC STUN STIM treatments). These results are consistent with previous findings in which the effects of higher amperage stunning caused delayed rigor development in broiler breast meat (Papinaho et al., 1995; Papinaho and Fletcher, 1995). These authors reported higher pH values and lower Rvalues for birds stunned at higher amperages at early deboning times, but these differences disappeared after 24 h of aging. In this study, STIM eliminated differences between LV STUN or HC STUN birds, but the unstunned controls remained significantly different. Stimulation caused a significant increase in R-value for both the LV STUN and HC STUN birds. Hence, stimulation may increase adenosine triphosphate depletion when compared with unstimulated birds. These results indicate that the effect of STIM may be due, in part, to a function of the muscle state following

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Jeacocke, R. E., 1977. Continuous measurement of the pH of beef muscle in intact beef carcasses. J. Food Technol. 12: 375–386. Li, Y., T. J. Siebenmorgen, and C. L. Griffis, 1993. Electrical stimulation in poultry: A review and evaluation. Poultry Sci. 72:7–22. Lyon, C. E., and B. G. Lyon, 1990. The relationship of objective shear values and sensory tests to changes in tenderness of broiler breast meat. Poultry Sci. 69:1420–1427. Papa, C. M., C. E. Lyon, and D. L. Fletcher, 1989. Effects of post-mortem wing restraint on the development of rigor and tenderness of broiler breast meat. Poultry Sci. 68: 238–243. Papinaho, P. A., and D. L. Fletcher, 1995. Effect of stunning amperage on broiler breast muscle rigor development and meat quality. Poultry Sci. 74:1527–1532. Papinaho, P. A., and D. L. Fletcher, 1996. The effects of stunning amperage and deboning time on early rigor development and breast meat quality of broilers. Poultry Sci. 75:672–676.

Papinaho, P. A., D. L. Fletcher, and R. J. Buhr, 1995. Effect of electrical stunning amperage and peri-mortem struggle on broiler breast rigor development and meat quality. Poultry Sci. 74:1533–1539. Pearson, A. M., and T. R. Dutson, ed., 1985. Advances in Meat Research. Vol. 1: Electrical Stimulation. AVI Publishing Co., Inc., Westport, CT. Sams, A., 1995. Electrical stimulation at commercial line speeds-An update. Broiler Industry 58(11):20–23. SAS Institute, 1988. SAS Users Guide for Personal Computers, Release 6.03. SAS Institute Inc., Cary, NC. Stewart, M. K., D. L. Fletcher, D. Hamm, and J. E. Thompson, 1984. The influence of hot boning broiler breast muscle on pH decline and toughening. Poultry Sci. 63:1935– 1939. Thompson, L. D., D. M. Janky, and S. A. Woodward, 1987. Tenderness and physical characteristics of broiler breast fillets harvested at various times from post-mortem electrically stimulated carcasses. Poultry Sci. 66:1158–1167. Downloaded from http://ps.oxfordjournals.org/ by guest on April 1, 2015