Tenderness and Physical Characteristics of Broiler Breast Fillets Harvested at Various Times from Post-Mortem Electrically Stimulated Carcasses1

Tenderness and Physical Characteristics of Broiler Breast Fillets Harvested at Various Times from Post-Mortem Electrically Stimulated Carcasses 1 L. D. THOMPSON,2 D. M. JANKY,3 and S. A. WOODWARD Department of Poultry Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, Florida 32611 (Received for publication August 1, 1986) ABSTRACT In three experiments, tenderness and various physical characteristics were determined for broiler breast fillets harvested after picking (hot boning), after chilling (chill boning), or after a 48-h aging period (aged boning) from high (240, 530, 820 V) or low (45 V) voltage electrically stimulated carcasses. Electrical stimulation was applied within 2 to 3 min post-mortem. Low voltage post-mortem electrical stimulation, regardless of tested duration, significantly decreased toughness of hot-boned breast meat. High voltage electrical stimulation, regardless of voltage or duration, had no significant effect on the tenderness or moisture content of hot-boned or aged-boned fillets. Stimulation significantly increased absorbance values and decreased pH at time of hot boning and chill boning but had no effect on these characteristics in aged-boned fillets. High voltage stimulation (820 V) significantly decreased shear values and increased sarcomere lengths of chill-boned breast fillets producing an acceptable level of tenderness. The data from the three experiments indicated that low voltage (45 V) electrical stimulation improved tenderness of hot-boned fillets; however, high voltage electrical stimulation (820 V) was required to produce a tenderizing response in chill-boned fillets. Tenderness response was more highly related to myofibrillar disruption and increased sarcomere length than to pH or ATP disappearance (absorbance ratio) and was of sufficient magnitude to alleviate toughness associated with chill-bone fillet products. (Key words: electrical stimulation, tenderness, boning-time, pH, broiler fillets, sarcomere, hot boning, chill boning) 1987 Poultry Science 66:1158-1167

INTRODUCTION

Until recently, there has been little reason for the broiler industry to be overly concerned with meat tenderness. In the past decade, however, the production of boned broiler breast meat has increased dramatically due to the high demand for whole fillet and restructured boneless products by the fast food industry and the retail consumer. To meet this demand under the constraints of efficient plant operation including requirements for reduced labor, handling, and storage, many processors harvest meat from carcasses immediately after chilling. Consumer response and research have indicated that this harvesting technique produces meat with a wide variation in tenderness and causes unacceptably increased toughness in a large proportion of the product (Lyon et al., 1985; Sams and Janky, 1986). Lyon et al. (1985) observed increased

Florida Agricultural Experiment Stations Journal Series Number 7454. 2 Present address: Department of Animal Science/Food Technology, Texas Tech University, Lubbock, TX 79409. 3 To whom correspondence should be addressed.

toughness of breast meat due to boning as long as 4 to 6 h postchill. Dawson et al. (1986) observed a significant decrease in toughness associated with time of boning when breast meat was harvested 3.5 h or more post-mortem. Shelton (1985) has suggested that unless tenderness problems associated with boning immediately postchill are solved, processors will be forced to adopt a minimum 4-h postchill aging period prior to carcass boning, regardless of the cost of increased labor and storage requirements. Other researchers have suggested that hot boning of the broiler carcass, involving removal of the breast meat, wings, and leg quarters from the picked but uneviscerated carcass, could result in substantial processing savings compared to more conventional meat harvesting techniques (Hamm, 1981; Hamm, 1982; Hamm and Thomson, 1983). However, this technique, like chill boning, causes increased toughness levels in poultry meat (de Fremery and Pool, 1960; Klose etal., 1972; Lyon et al., 1973; Peterson, 1977; Stewart et al., 1984; Sams and Janky, 1986). Solutions to tenderness problems associated with boning time include the injection of phos-

1158

ELECTRICAL STIMULATION AND FILLET TEXTURE

phates (Peterson, 1977) or use of salt in a tenderizing marinade either during the chilling process (Sams and Janky, 1986) or postchill (Hamm, 1983). Tumbling of the product in salt solutions has also been shown to reduce toughness (Hamm, 1983; Kotula and Heath, 1986). Several problems associated with these procedures are evident including increased sodium levels in a traditionally low sodium food, special equipment and waste water treatment requirements, and product labeling requirements. Post-mortem electrical stimulation has been used in the beef and lamb industry to hasten the development of rigor mortis, reducing toughness associated with cold shortening and hot boning (Carse, 1973; Pearson and Dutson, 1985). This procedure is readily adaptable to current broiler processing systems, adds nothing to the composition of the product, and is relatively inexpensive in equipment and operational costs. Although the process has been extensively investigated in red meats, there are little published data concerning the effects of post-mortem electrical stimulation on the texture of poultry meat (Maki and Froning, 1984; Dransfield et al., 1984). The purpose of this research was to determine if post-mortem electrical stimulation could be used to improve the tenderness of chill-boned or hot-boned broiler breast meat and to examine some physical and biochemical parameters that might be affected by this processing technique. Data were obtained for fillets harvested from intact aged carcasses to provide base line information on various physical characteristics and to determine the effect of electrical stimulation on an already tender product. MATERIALS AND METHODS

Experiment 1. Thirty-six male broilers were selected and cooped (8 to 9/coop) at random from a population of 49-day-old, Cobb X Cobb, feather-sexed birds reared on wood shaving litter and fed commercial-type, corn-soy diets (starter, finisher, and withdrawal). Six birds (12 h fasted) per replication were selected and hung on shackles by the shanks, individually identified with duplicate wing bands, stunned with a Cervin Model FS stunner (Cervin Electrical Systems, Inc., Minneapolis, MN) (setting No. 4), and killed by exsanguination. After a 90 s bleeding period, two carcasses from each replication were subjected to either 0, 9, or 18 s pulsed electrical stimulation (2 s on, 1 s off) at 45 V using a Koch low voltage electrical stimulator (Kansas City, MO). The positive electrode of

1159

the stimulator was attached to the neck of the carcass at the first cervical vertebrae while the rail/shackle line functioned as the ground. After subscalding (60 C, 45 s) and picking in a rotary drum picker (25 s), carcasses were suspended from a shackle by the neck, the breast was skinned, and the fillets (pectoralis superficialis) removed by severing the humeralscapular joints and stripping the meat from the carcass by pulling downward on the wings. Fillets with wings attached were chilled in unagitated ice slush (1 C) for one h. Chill solution to fillet ratio was maintained at 3:1 (w/w) and ice to chill water ratio was 1:9 (w/w). Chilled fillets were paired, drained (10 min), and packed in crushed ice (2 C) for 24 h prior to packaging in Cryovac® bags (W. R. Grace & Co., Apex, NC), freezing (-23 C), and storage. Thawed fillets (24 h, 7 C) with wings attached were placed on roasting racks in aluminum foillined and covered stainless steel pans and cooked to an internal temperature of 82 C in a rotary hearth oven at 177 C. Internal temperature was monitored with a recording potentiometer and copper constantan thermocouples inserted into the thickest portion of one breast fillet per replication. Cooked fillets were cooled to room temperature, wrapped in aluminum foil, and held overnight at 7 C for shear force evaluation. Duplicate samples (1 x 1 x 2-3 cm) were cut from the anterior third of each cooked fillet (7 C) with the longest dimension parallel to muscle fiber direction. Natural depth of the muscle sample was not altered (approximately 1 cm). Weighed samples were sheared in a direction perpendicular to muscle fiber in a standard 10blade shear compression cell using a Food Technology Corporation Texture Test System® (Rockville, MD) equipped with a 136 kg force transducer and a TG-4A Texturegage (Food Technology Corp., Rockville, MD) at a descent speed of .7 cm/s. The four values from each pair of fillets per carcass were averaged to obtain a shear force value (kilogram force per gram sample) for each carcass. Means and standard error of the means were calculated and analyzed with analysis of variance and Duncan's Multiple Range Test procedures (Steel and Torrie, 1980) using computer programs available in the Statistical Analysis Systems (SAS Institute Inc., 1982). Experiment 2. In each of two trials, 60 male birds were selected within a uniform weight range from a population of 59-day-old (Trial 1) or 60-day-old (Trial 2) Cobb, feather-sexed

1160

THOMPSON ET AL.

broilers. Birds were reared and fed under similar conditions to those previously described for Experiment 1. Broilers were cooped (10/coop) and fasted 9 h prior to processing. Twelve broilers per replication (five replications per trial) were hung, stunned, and bled as previously described. After a 90-s bleeding period, carcasses were subjected to 15 s of pulsed electrical stimulation (2 s on, 1 s off) at either 0, 240, 530, or 820 volts (three carcasses per treatment per replication). To provide these high voltages, the Cervin Model FS stunner was adjusted to the highest setting producing 340 mA of current, equipped with a rheostat to vary the voltage (between the wall outlet and the stunner), and used as an electrical stimulator. The positive electrode (kill knife) was placed on the skin at the back of the neck (last cervical vertibrae) with the rail/ shackle line used as the ground. After feather removal as previously described, fillets were harvested using the technique outlined above (hot boning) from four carcasses per replication (one carcass per stimulation treatment). Left side fillets (pectoralis superficialis) were weighed and chilled. Anterior sections of right side fillets were sectioned, frozen, and stored in liquid nitrogen for subsequent pH and absorbance ratio analyses; however, due to a shortage of liquid nitrogen freezing and storage facilities, posterior sections of right side fillets for fragmentation index and sarcomere length analyses were frozen and stored at -23 C. Concurrently, the remaining eight carcasses per replication were eviscerated by standard methods, rinsed, weighed, and chilled. Carcasses and hot-boned fillets with wings attached were chilled separately in wire baskets immersed in chilling solutions using a two stage process to simulate commercial time-temperature conditions: 15 min in tap water (21 C), followed by 30 min in ice slush (1 C). A 3:1 (w/w) chill solution to carcass or fillet ratio and a 1:9 (w/w) ice to water ratio (ice slush solution only) were maintained. To improve the cooling rate, wire baskets containing either carcasses or fillets were raised and lowered in the chilling solutions continuously during the chilling process. After chilling, carcasses and fillets were suspended from shackles by the wings, rinsed, drained (5 min), and weighed to determine chill water uptake. Fillets were harvested from four chilled carcasses (chill boned) per replication (one carcass per stimulation treatment) immediately after carcass weights were obtained. Right side fillets

were sectioned, frozen, and stored as described for right side hot-boned fillets, while left side fillets, chilled hot-boned fillets, and the remaining four chilled carcasses per replication were packed in ice and aged (2 C) for 48 hours. After fillets and carcasses were weighed to determine percent drip loss, fillets were harvested (aged boned) from the remaining four intact carcasses (one carcass per stimulation treatment per replication) with right side fillets sectioned and frozen as previously described. Wings were removed from all left side fillets and fillets were reidentified prior to cooking as described in Experiment 1. Fillets were weighed before cooking and after cooling at room temperature to determine percent of cooking loss. Duplicate cooked meat samples were obtained and sheared as described in Experiment 1 and averaged to produce a shear force value per carcass. Percent cooked meat moisture was also determined in duplicate for each fillet using standard procedures (Association of Official Analytical Chemists, 1984). Samples obtained from right side fillets at time of boning were removed from the liquid nitrogen and pulverized. A 1:10 (w/v) mixture of meat powder and .005 M sodium iodoacetate (7 C, pH 7) was blended at 14,600 rpm for 30 s prior to pH determination. Absorbance or R value at the time of boning, an indicator of the ratio of the concentration of adenosine triphosphate (ATP) to that of one of its breakdown products, inosine monophosphate (IMP), was determined using procedures described by Khan and Frey (1971) and Honikel and Fischer (1977) on liquid nitrogen-frozen samples from each right side fillet. Approximately 3 g of pulverized meat powder were homogenized in 20 mL of 1 M perchloric acid for 1 min at 14,600 rpm. After gravity filtration through Fisher P8 filter paper (Fisher Scientific, Plainfield, NJ), .1 mL of the acid filtrate was added to 4 mL of .1 M phosphate buffer (pH 7). Absorbances of this solution were determined at 250 nm (IMP) and 260 nm (ATP) using a spectrophotometer with a .5 mm slit width. Absorbance or R value was calculated as the ratio of absorbance at 250 nm divided by the absorbance at 260 nm. A frozen (-23 C) 10 to 15 g sample from each right side fillet was cubed (1 to 1.5 cm) and homogenized in 25 mL of cold (7 C) .25 M sucrose at 11,500 rpm until fiber separation was noted (10 to 15 s). Two drops of homogenate were placed on a microscope slide, covered with a cover slip, and placed into the light path

ELECTRICAL STIMULATION AND FILLET TEXTURE

of a helium-neon laser (632.8 nm). Sarcomere length was determined by measuring the distance from origin (central diffraction band) to first order diffraction band according to the procedure outlined by Cross et al. (1980) and calculated using the equation supplied by these same authors. Fragmentation index was determined by adapting procedures used for beef muscle as outlined by Calkins and Davis (1978) and Davis et al. (1980). Frozen (-23 C) 5 to 6 g samples, obtained at the time of boning from each right side fillet, were diced into 5 mm cubes, weighed to the nearest .0001 g, and homogenized for 30 s with 50 mL of .25 M sucrose, .02 M KC1 solution (7 C) at high speed in a Waring blender. The homogenate was vacuum aspirated through a tared 250-m nylon screen to visible dryness. After air drying for 10 min on filter paper, the weight of residue was determined and fragmentation index calculated using the formula: Fragmentation index = 1000 x (residue weight/ original sample weight). Data within each boning treatment were analyzed separately using analysis of variance, Duncan's Multiple Range Test, and, where appropriate, orthogonal comparisons (Steel and Torrie, 1980) with computer programs available in the Statistical Analysis Systems (SAS Institute Inc., 1982). No attempt was made to statistically compare means from different boning times because unequal variance components due to differences in boning time have been reported (Sams and Janky, 1986). Correlations between physical characteristics within boning times and standard errors of the means were also calculated (SAS Institute Inc., 1982). Because no significant interactions between stimulation treatments and trials were noted, data from the two trials were pooled. Experiment 3. In this experiment, an electrical stimulation voltage of 240 V was used with pulsed stimulation duration treatments of 0, 15, 30, and 45 s. Experimental design, procedures,

1161

physical characteristic analyses, and data evaluation were identical in all respects to those outlined for Experiment 2. RESULTS AND DISCUSSION

Experiment 1. Low voltage post-mortem electrical stimulation (45 V), regardless of tested duration, significantly decreased toughness of hot-boned breast meat (Table 1). However, shear values for electrically stimulated muscles were still higher than the 8.0 kg force/g sample defined by Simpson and Goodwin (1974) as the upper level of shear force indicative of tender product. In contrast, Dransfield et al. (1984) using relatively low voltage (94 V) observed no tenderizing effect of post-mortem electrical stimulation on turkey breast. Low voltage electrical stimulation tenderizes muscle tissue by increasing the rate of glycolysis within the muscle, shortening the time interval for rigor development (Carse, 1973), and is dependent for its tenderizing effect on muscle activation by the nervous system (Morton and Newbold, 1982). In the present study, data from one replication were discarded due to equipment failure that resulted in a post-mortem time lag of 9 min prior to stimulation. When electrically stimulated, these carcasses did not respond with the usual movement of the wings to the forward position indicating that the nervous system was completely inoperative within 9 min post-mortem. Considering the relatively high metabolic rate of avian species in comparison to most mammals and the high oxygen demand of nervous tissue in general, it is possible that a degree of nervous impairment could occur in extremely short periods of time post-mortem. Nerve impairment could decrease the tenderizing effect of low voltage stimulation by reducing action potential conduction. It is possible that stimulation with higher voltages or longer durations might cause greater improvements in tenderness. Maki and Froning

TABLE 1. Mean sb ear values and standard errors of the means of hot-boned broiler breast meat harvested from carcasses electrically stimulated post-mortem with 45 volts for 0, 9, or 18 s (Experiment 1) i

Stimulation duration (s) Shear force

0

9

18

kg/Force/g sample

11.9 b ± .7

9.2 a ± .6

9.0 a ± .7

a,b Means with different superscripts are significantly different (P<.05), n = 10.

1162

THOMPSON ET AL.

(1984) reported a significant tenderizing response of turkey breast meat to post-mortem electrical stimulation at high voltage (800 V). Morton and Newbold (1982) observed that high voltage electrical stimulation was not dependent on an operative nervous system, because it was capable of direct depolarization of the muscle sarcolemma. High voltage stimulation has been shown to be even more effective than low voltage stimulation in increasing the rate of glycolysis (Bouton et al., 1980) and might also tenderize the tissue through physical myofibrillar damage and the release of lysozomal catheptic enzymes (Savell et al., 1978). Experiment 2. High voltage post-mortem electrical stimulation for 15 s did not produce a tenderizing response (reduced shear force) in hot-boned broiler breast meat, regardless of the stimulation voltage tested (Table 2). However, high voltage (530 and 820 V) post-mortem electrical stimulation significantly increased the rate of rigor mortis development in hot-boned fillets as evidenced by lower pH values and higher absorbance ratios for these fillets compared with values for fillets from nonstimulated and low voltage (240 V)-stimulated carcasses. Khan and Frey (1971) reported that monitoring the postmortem change in the ratio of IMP:ATP (absorbance ratio) was useful in determining the state of rigor mortis. They found that changes in the absorbance value (R value) over time corresponded to the development of rigor mortis with these values increasing as rigor developed and plateauing once maximum rigor contraction occurred. In the present study, fillets were removed from the carcass prior to full rigor development, releasing physical anatomical restraints and allowing for unimpeded contraction as the muscle progressed into rigor mortis. In addition, hot boning provided an extra stimulus, inducing increased muscle contraction. The conclusion drawn from these data was that the time interval between death of the animal and boning was too short (less than 15 min) to produce a significant tenderness response due to the increased rate of rigor mortis development produced by electrical stimulation. Although all hot-boned tissue had very short sarcomeres, those of fillets from nonstimulated carcasses were significantly shorter than sarcomeres of fillets from stimulated carcasses (Table 2). Because fillets from nonstimulated carcasses had a slower rate of rigor development, more ATP would have been available to produce a more severe shortening during the fillet chilling

process. Locker and Hagyard (1963) have associated shortened sarcomeres with increased toughness of the meat; however, Marsh and Leet (1966) and Marsh et al. (1974) reported that extremely severe shortening (greater than 40% in beef muscle) produced a tenderness response due to physical disruption of the fibers. Sarcomere length was the only measured variable that was significantly correlated with shear value (r = -.33) indicating that variations in sample tenderness were more closely linked to changes in sarcomere lengths than to other measured variables. A nonsignificantly lower shear force and significantly increased fragmentation (lower fragmentation index = more fragmentation) of hot-boned fillets from nonstimulated carcasses in comparison to hot-boned fillets from stimulated carcasses (Table 2) might be used as evidence to support the hypothesis that fillets from nonstimulated carcasses were slightly more tender due to extreme sarcomere shortening. Electrical stimulation reduced the sarcomere shortening and might have negated the slight tenderizing effect of extreme shortening. Fillets harvested from chilled carcasses (chill boned) that had been electrically stimulated post-mortem at 820 V had significantly lower shear values than fillets from either nonstimulated chilled carcasses or fillets from chilled carcasses that had been electrically stimulated postmortem at lower voltages (Table 2). Further, post-mortem electrical stimulation with 820 V reduced shear values of chill-boned fillets to a level below the level of 8 kg force/g tissue suggested by Simpson and Goodwin (1974) as the upper limit of tenderness acceptability. Increasing stimulation voltage to 530 V from 240 V resulted in a nonsignificant reduction in shear force. These data indicated that problems associated with toughness induced by boning breast meat from carcasses immediately postchill could be alleviated by electrical stimulation at high voltage. Some processors are currently "poststunning" carcasses during or after bleeding to minimize toughness problems associated with struggling due to inadequately stunned birds preslaughter. Because this procedure is normally accomplished with high voltage, only slight modifications to provide a pulsed duration of 15 s would be required to benefit from the tenderizing effect of electrical stimulation. Electrical stimulation, regardless of voltage, increased the rate of rigor mortis development in fillets boned from chilled carcasses as evidenced by significantly decreased pH and signif-

2 3 4 2

5.69 a 5.67 a 5.70 a 5.80 a

.04 .06 .06 .06

± .05 + .08

+ .04 + .06

6.12 b + 5.91 a + 5.96 a + 5.83 a ±

6.28 D ± .04 6.15 a b + .05 6.05 a ± .05 6.06 a + .03

PH

1.33* 1.44* 1.42* 1.41*

.90* 1.07 ab 1.17 b 1.12 b ± ± ± ±

± ± ± ± .07 .01 .01 .01

.04 .07 .06 .06

.93* + .04 .92* + .02 1.00 ab ± .04 1.04 b ± .03

Absorbance ratio 1

2

1

Fragmentation index = 1,000 X (residue weight/sample weight).

Absorbance ratio = absorbance 250 nm/absorbance 260 nm of an acid extract of muscle tissue.

a ' b Means within a column and boning time group with different superscripts are significantly different (P<.05), n = 1

3.7* ± 3.9* ± 4.0* ± 3.6* ±

0 240 530 820

Aged

±12 ±10 ± 9 ± 8

9.4 b 9.2 b 8.2 b 6.5*

+12 ±16 ±14 ±16

15.0* 16.3* 16.2* 16.2*

(kg force/g sample)

Shear force

0 240 530 820

(V) 0 240 5 30 820

Stimulation voltage

Chill

Hot

Boning time

TABLE 2. Means with standard errors for shear values, pH, absorbance ratios, sarcomere lengths, and fragmentation in breast meat from broiler carcasses electrically stimulated post-mortem for 15 s with either 0, 240, 53

1164

THOMPSON ET AL.

icantly (530 and 820 V treatments) and nonsignificantly (240 V treatment) increased absorbance ratios (Table 2). These data, however, do not fully explain the tenderizing effect observed at 820 V because values were not significantly affected by stimulation voltage and were not significantly correlated to shear force values. Sarcomeres of fillets from electrically stimulated carcasses were significantly (530 and 820 V treatments) and nonsignificantly (240 V treatment) longer than sarcomeres of fillets from nonstimulated carcasses (Table 2). Sarcomere length appeared to increase as stimulation voltage was increased and was significantly correlated with shear value (r = -.32), pH (r = -.38), and absorbance ratio (r = .39). These data indicated that increased sarcomere length was a result of increased rate of rigor mortis development and that decreased shear force was related to increased sarcomere length. The relationship of increased sarcomere length to increased tenderness has been well documented in the red meat industry (Herring et al., 1967) where electrical stimulation is used to deter coldinduced sarcomere shortening (Pearson and Dutson, 1985). Although increases were not statistically significant, myofibril fragmentation of fillets from chill-boned carcasses was increased (decreased fragmentation index) with electrical stimulation (Table 2) and was correlated with shear force (r = .56) within stimulation treatments but not correlated with shear force (r = .09) within nonstimulated controls. Sayre (1970) and Culler et al. (1978) demonstrated that myofibril fragmentability was related to the tenderness of poultry and beef, respectively, with tougher meat having a greater resistance to fragmentation. Sonaiya et al. (1982) observed that the improvement in tenderness of electrically stimulated beef carcasses over nonstimulated carcasses was related to myofibril disruption as indicated by increased fragmentation. Savell et al. (1978) and Sorinmade et al. (1982) observed ill defined I bands, Z lines, contracture bands, and stretched sarcomeres in electrically stimulated meat that were not evident in nonstimulated meat. Savell et al. (1978) concluded that these types of myofibril disruptions were related to increased tenderness and increased stimulation voltage. In the present study, data indicated that the tenderness response associated with high voltage electrical stimulation was more directly related to myofibril structural changes (sarcomere length and fragmentation) than to increased rate of rigor

development (pH and absorbance ratio). Post-mortem electrical stimulation had no significant effect on shear, ultimate pH and absorbance ratios, or myofibril structure (sarcomere length and fragmentation index) of fillets harvested from chilled, 48-h aged carcasses (Table 2). Khan and Frey (1971) reported that the ultimate pH and absorbance ratio of poultry muscle was achieved within 24 and 48 h, respectively. Because aged boning occurred 48 h postmortem, pH and absorbance ratios reflected the ultimate levels achieved in typically processed meat and were similar to pH values reported by Stewart et al. (1984) in poultry and absorbance ratios (R values) reported by Honikel and Fischer (1977) in beef. Complete rigor mortis development and aging took place with the muscle attached to the carcass; therefore, no toughening effect due to premature removal of the fillets was observed. These data indicated that electrical stimulation produced no adverse toughness effects on already tender muscle. Within boning times, electrical stimulation had no significant effect on water uptake, drip loss, cooking loss, or moisture content of hotboned, chill-boned, or aged-boned fillets (data not shown). Experiment 3. Although not observed in Experiment 2, it is possible that electrical stimulation with high voltage could cause structural damage to bone and ligaments due to the extreme degree of contraction elicited. It was hypothesized that the use of a lower voltage but with longer duration of stimulation might produce a similar effect to high voltage treatment but eliminate problems with hard tissue damage. Results of Experiment 3 showed that variation in durations of electrical stimulation at 240 V (0, 15, 30, and 45 s) produced no significantly different effects on shear values of either hotboned, chill-boned, or aged-boned meat (Table 3). There was a slight increase in the rate of rigor mortis development (absorbance ratio) in hot-boned fillets at stimulation durations of 30 or 45 s; however, this phenomenon was not reflected in pH, sarcomere lengths, or fragmentation indices. Electrical stimulation at durations of 30 and 45 s significantly increased the rate of rigor development in chill-boned fillets over that observed for fillets from nonstimulated carcasses as evidenced by significantly lower pH and significantly higher absorbance ratios. Sarcomere length was nonsignificantly increased as stimulation duration was increased, as was fragmentation index. As in Experiment 2, electrical

0 15 30 45

Aged

•

0 15 30 45

Chill

1

2

+ .02 + .04

.03 .02

1.37* 1.39* 1.40* 1.40*

± ± ± ±

.01 .01 .02 .02

1.02* .05 1.12*b .03 1.18 b ± .04 1.22 b + .02

.92* .98* b 1.03 b 1.02 b

Fragmentation index = 1,000 X (residue weight/sample weight).

Absorbance ratio = absorbance 250 nm/absorbance 260 nm of an acid extract of muscle tissue.

' Means within a column and boning time group with different superscripts are significantly different (P<.05), n =

± .06 ± .06 ± .05 ± .05

+ .04 ± .04 ± .05 ± .05 ± .07 ± .05 ± .05 + .07 +i

5.71* 5.72* 5.67* 5.68*

6.08" 6.11* 6.07* 6.06* 6.00 b 5.94 a b 5.83* 5.89*

(kg force/ g sample) 15.7*: 1.4 15.2*: 1.6 15.7*. 1.7 15.2*: 1.4 aa . 9.9" 8.2*: 9.0*: 8.3*:

Absorbance ratio 1

+i

4.2* : 3.8*: 4.0*: 3.7*:

PH

Shear force

+i

a b

0 15 30 45

(s)

Stimulation voltage

Hot

Boning time

TABLE 3. Means with standard errors for shear values, pH, absorbance ratios, sarcomere lengths, and fragmentation i breast meat from broiler carcasses electrically stimulated post-mortem with 240 volts for either 0,

+i

THOMPSON ET AL.

1166

stimulation had no significant effect on physiobiochemical parameters of fillets harvested from chilled, 48-h-aged carcasses. There was no significant effect of variations in duration of electrical stimulation on water uptake, drip loss, thaw loss, cook loss, or moisture content (data not shown). Data from this experiment supported the hypothesis that the tenderization effect observed in chill-boned fillets with high voltage (820 V) electrical stimulation was due to increased myofibril disruption that resulted from the more severe contraction elicited at this voltage. Rate of rigor mortis development was affected in a similar manner in both experiments; however, fragmentation indices in Experiment 3 were not affected to the same degree by electrical stimulation as in Experiment 2. In conclusion, the data from the three experiments indicated that low voltage (45 V) electrical stimulation improved tenderness of hotboned fillets. However, high voltage electrical stimulation (820 V) was required to produce a tenderizing response in chill-boned fillets. This response in tenderness was more related to myofibrillar disruption and increased sarcomere length than to pH or ATP disappearance (absorbance ratio) and was of sufficient magnitude to alleviate toughness problems associated with chill-boned fillet products. REFERENCES Association of Official Analytical Chemists, 1984. Official Methods of Analysis. 14th ed. Assoc. Offic. Anal. Chem., Washington, DC. Bouton, P. E., A. L. Ford, P. V. Harris, and F. D. Shaw, 1980. Electrical stimulation of beef sides. Meat Sci. 4:145-155. Calkins, C. R., and G. W. Davis, 1978. Refinement of a muscle fragmentation procedure for predicting meat tenderness. Tenn. Farm Home Sci. 108:14—15. Carse, W. A., 1973. Meat quality and the acceleration of postmortem glycolysis by electrical stimulation. J. FoodTechnol. 8:163-166. Cross, H. R., R. L. West, and T. R. Dutson, 1980. Comparison of methods for measuring sarcomere length in beef semitendinosis muscle. Meat Sci. 5:261-266. Culler, R. D., F. C. Parrish, Jr., G. C. Smith, and H. R. Cross, 1978. Relationship of myofibril fragmentation index to certain chemical, physical, and sensory characteristics of bovine longissimus muscle. J. Food Sci. 43:1177-1180. Davis, G. W., T. R. Dutson, G. C. Smith, and Z. L. Carpenter, 1980. Fragmentation procedure for bovine longissimus muscle as an index of cooked steak tenderness. J. Food Sci. 45:881-884. Dawson, P. L., M. G. Dukes, L. D. Thompson, S. A. Woodward, and D. M. Janky, 1986. Effect of postmortem boning time during simulated commercial process-

ing on the tenderness of broiler breast meat. Poultry Sci. 65(Suppl. 1):32. (Abstr.) de Fremery, D., and M. F. Pool, 1960. Biochemistry of chicken muscle as related to rigor mortis and tenderization. Food Res. 25:73-87. Dransfield, E., A. A. Down, A. A. Taylor, and P. K. Locker, 1984. Influence of electrical stimulation and slow chilling on the texture of turkey breast muscle. Proc. European Meeting of Meat Res. Workers No. 30, 4:10,180 in: Food Sci. Technol. Abstr., 17(8):8S138. Hamm, D., 1981. Unconventional meat harvesting. Poultry Sci. 60:1666. (Abstr.) Hamm, D., 1982. A new look at meat harvesting. Broiler Industry 48(7):38-39. Hamm, D., 1983. Techniques for reducing toughness in hot-stripped broiler breast meat. Poultry Sci. 62:1430. (Abstr.) Hamm, D., and J. E. Thomson, 1983. Adapting hot stripping techniques to existing processing facilities. Poultry Sci. 62:1349. (Abstr.) Herring, H. K., R. G. Cassens, G. G. Suess, V. H. Brungardt, and E. J. Briskey, 1967. Tenderness and associated characteristics of stretched and contracted bovine muscles. J. Food Sci. 32:317-323. 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. Khan, A. W., and A. R. Frey, 1971. A simple method for following rigor mortis development in beef and poultry meat. Can. Inst. Food Technol. J. 4:139-142. Klose, A. A., R. N. Sayer, D. de Fremery, and M. F. Pool, 1972. Effects of hot-cutting and related factors in commercial broiler processing on tenderness. Poultry Sci. 51:634-638. Kotula, K. L., and J. L. Heath, 1986. Effect of tumbling chill-boned and hot-boned broiler breasts in either acetic acid or sodium chloride solutions on cooked yield, density, and shear values. Poultry Sci. 65:717-725. Locker, R. H., and C. J. Hagyard, 1963. A cold shortening effect in beef muscles. J. Sci. Food Agric. 14:787793. 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. Lyon, C. E., B. G. Lyon, and J. P. Hudspeth, 1973. The effect of different cutting procedures on the cooked yield and tenderness of cut up broiler parts. Poultry Sci. 52:1103-1111. Maki, A., andG. W. Froning, 1984. Effect of post-mortem electrical stimulation on quality of turkey meat. Poultry Sci. 63(Suppl. 1):142. (Abstr.) Marsh, B. B., and N. G. Leet, 1966. Studies in meat tenderness. III. The effects of cold shortening on tenderness. J. Food Sci. 31:450-459. Marsh, B. B., N. G. Leet, and M. R. Dickson, 1974. The ultrastructure and tenderness of highly cold shortened muscle. Food Technol. 9:141-147. Morton, H. C , and R. P. Newbold, 1982. Pathways of high and low voltage electrical stimulation in sheep carcasses. Meat Sci. 7:285-289. Pearson, A. M., and T. R. Dutson, 1985. Scientific basis for electrical stimulation. In: Advances in Meat Research. Vol. 1. Electrical Stimulation. Ch. 6. AVI Publishing Co., Westport, CT. Peterson, D. W., 1977. Effects of polyphosphates on the

ELECTRICAL STIMULATION AND FILLET TEXTURE tenderness of hot-cut chicken breast meat. J. Food Sci. 42:100-101. Sams, A. R., and D. M. Janky, 1986. The influence of brine chilling on tenderness of hot-boned, chill-boned, and age-boned broiler breast fillets. Poultry Sci. 65:1316-1321. SAS Institute Inc., 1982. SAS User's Guide: Statistics. SAS Institute Inc., Cary, NC. Savell, J. W., T. R. Dutson, G. C. Smith, and Z. L. Carpenter, 1978. Structural changes in electrically stimulated beef muscle. J. Food Sci. 43:1606-1607,1609. Sayre, R. N., 1970. Chicken myofibril fragmentation in relation to factors influencing tenderness. J. Food Sci. 35:7-10. Shelton, T. ,1985. Broiler industry in the year 2,000. Broiler Industry 48(11):36, 38, 40-42, 44. Simpson, M. D., and T. L. Goodwin, 1974. Comparison

1167

between shear values and taste panel scores for predicting tenderness of broilers. Poultry Sci. 53:2042-2046. Sonaiya, E. B., J. R. Stouffer, and D. H. Beerman, 1982. Electrical stimulation of mature cow carcasses and its effect on tenderness, myofibril protein degradation and fragmentation. J. Food Sci. 47:889-891. Sorinmade, S. O., H. R. Cross, K. Ono, and W. P. Wergen, 1982. Mechanisms of ultrastructure changes in electrically stimulated beef Longissimus muscle. Meat Sci. 6:71-77. Steel, R.G.D., and J. H. Torrie, 1980. Principles and Procedures of Statistics. 2nd ed. McGraw-Hill Book Co., New York, NY. Stewart, M. K., D. L. Fletcher, D. Hamm, and J. E. Thomson, 1984. The influence of hot boning broiler breast muscle on pH decline and toughening. Poultry Sci. 63:1935-1939.