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Comparison of Two Shearing Methods for Objective Tenderness Evaluation and Two Sampling Times for Physical-Characteristic Analyses of Early-Harvested Broiler Breast Meat1
Comparison of Two Shearing Methods for Objective Tenderness Evaluation and Two Sampling Times for Physical-Characteristic Analyses of Early-Harvested Broiler Breast Meat1 A. R. SAMS,2 D. M. JANKY, and S. A. WOODWARD3 Institute of Food and Agricultural Sciences, Department of Poultry Science, University of Florida, Gainesville, Florida 32611 (Received for publication December 2, 1988) ABSTRACT Fillets, pectoralis superficialis, were harvested from broiler carcasses immediately after picking (hot-boned), after chilling (chill-boned), or after 24 h of aging post-mortem (age-boned). In Experiment 1, shear-compression shear values were obtained from cooked left-side fillets and compared to Warner-Bratzler shear values obtained from cooked right-side fillets from the same carcasses. In Experiment 2, sarcomere length and pH were determined at the time of boning and were compared to respective values obtained after 24 h of aging. Even though data obtained using the two shear cells were highly correlated (r = .93) over the entire range of values observed, the correlation coefficients derived from data within individual boning times were much smaller and were accompanied by differences in the slopes of the regression lines. Variances associated with boning-time means and shear-method means were significantly different. The conclusion was that comparisons of shear values involving the use of different testing methodologies should only be attempted within narrow ranges of such values. Differences in pH and sarcomere length at the time of boning decreased with fillet aging. Variances associated with pH and sarcomere-length means as a function of the time of boning were quite variable and, in some cases, significantly different. {Key words: tenderness, shear method, pH, sarcomere length, bone time) 1990 Poultry Science 69:348-353 INTRODUCTION
Current commercial interest in incorporating the early harvesting of broiler breast meat into the processing scheme has stimulated research into the effects of this procedure on quality attributes, especially tenderness, of the finished product. Several objective methods for measuring meat tenderness are available to meat scientists; however, researchers working with poultry have generally used the "shearcompression" system (multiple blade) for objectively evaluating the tenderness of broiler breast meat. However, researchers working with red meats have generally used the "Warner-Bratzler" method (single blade). Because the Warner-Bratzler system provides a much faster system of sample-by-sample anal-
1 Number 9471, Florida Agricultural Experiment Stations Journal Series, University of Florida, Gainesville, FL 32611. Present address: Department of Poultry Science, Texas A&M University, College Station, TX 77843-2472. 3 Present address: Sunny Fresh Foods, P.O. Box 428, Monticello, MN 55362.
ysis for evaluation, poultry-meat researchers have shown an interest in using this system. Burrill et al. (1962) reported that, using four beef muscles of varying tenderness, the two shearing systems were highly correlated when values from all four muscles were combined; but, within an individual muscle, the correlations were lower and of less significance. Many researchers have reported that the early harvesting of broiler breast tissue produces a wide range of shear-compression shear values in broiler breast tissue (Stewart et al, 1984; Sams and Janky, 1986; Thompson et al, 1987; Dawson et al, 1987). Sams and Janky (1986) also reported that variances associated with shear-value means obtained from fillets boned at different times postmortem were significantly different. This would indicate mat a comparative study is needed of the two shear systems in evaluating broiler Pectoralis superficialis muscles over a wide range of tenderness, such as that produced over post-mortem time. Researchers have often associated chemical and physical characteristics, such as pH and sarcomere length, with differences in meat
348
SHEAR AND SAMPLING METHOD COMPARISON
tenderness induced by boning at various times post-mortem (Hamm, 1982; Janky et al., 1983; Stewart et al, 1984; Sams and Janky, 1986; Dawson et al, 1987; Thompson et al., 1987). Differing variances that might be associated with higher pH and shorter sarcomere lengths commonly observed with early-harvested broiler breast meat would be expected if these physical characteristics and tenderness are causally related. The ultimate (after fillet aging) pH and sarcomere length of earlyharvested broiler breast fillets should also reflect differences similar to those reported at the time of boning if these factors are causally related to ultimate differences in tenderness associated with early harvesting. The purposes of the present studies were to determine the correlation and comparability between the shear-compression and the Warner-Bratzler shearing systems for objectively determining the tenderness of broiler breast meat; and to evaluate the changes in pH and sarcomere length associated with early harvested breast meat both at the time of boning and after fillet aging. MATERIALS AND METHODS
Experiment 1 Feather-sexed, male broilers (Cobb) were reared on wood-shaving litter in floor pens and were fed commercial-type starter, finisher, and withdrawal corn-soybean meal diets. Twelve broilers within a weight range of 1,900 to 2,400 g were selected from the general population of 56-day-old birds. The 12 broilers were cooped and were held without feed and water for 12 h prior to slaughter. The broilers were electrically stunned (Cervin Model FS stunner, Cervin Electrical Systems, Minneapolis, MN, setting Number 4, 10 s), killed by exsanguination, subscalded (60 C, 45 s), and rotary-drum picked (25 s). Immediately after picking (15 min postmortem), the Pectoralis superficialis muscles from four carcasses were harvested (hot-boned fillets) using the stripping method described by Hamm (1981) and were individually identified. The remaining carcasses were manually eviscerated and were chilled along with hot-boned fillets for 15 min in tap water (20 C), followed by an additional 30 min in ice slush (1 C). The chill temperatures were monitored with copper, constantan thermocouples and a recording po-
349
tentiometer and were maintained by adding small amounts of crushed ice. The ratio of ice to water in the ice slush was not allowed to exceed 1:9. The chill tanks were manually shaken to mimic commercial agitation of the chill solution. The ratio of the chill solution to the carcasses and fillets was maintained at 3:1. Immediately after chilling (1 h post-mortem), the fillets were harvested (chill-boned fillets) as previously described and were identified from four additional carcasses. All of the fillets and the remaining carcasses were packed in crushed ice and held at 2 C. At 24 h post-mortem, the fillets were harvested (age-boned fillets) and were identified from the remaining four carcasses. The fillets were cooked together to an internal temperature of 80 C on raised wire racks in pans lined and covered with aluminum foil in a conventional electric oven maintained at 177 C. The internal temperature was monitored with copper, constantan thermocouples inserted into one representative fillet in each pan and a recording potentiometer. The cooked fillets were cooled at room temperature (30 min), wrapped in aluminum foil, and held at 2 C overnight prior to the shear-value analyses. Two samples (35 by 20 by 7 mm) from the anterior portion of the right-side fillet of each carcass were each weighed and then sheared, using a Food Technology Corporation Texture Test System® (Food Technology Corporation, Rockville, MD) equipped with a 10-blade, shear-compression cell attached to a 136-kg force transducer. The samples were oriented in the shear cell so the direction of the muscle fiber was perpendicular to the blades. The descent speed was maintained at 8 mm per s. The two values for each fillet were averaged in order to determine a mean shear value for the fillet Two samples each (50 by 10 by 7 mm) from the anterior portion of the left-side fillet of each carcass were each sheared twice using a Food Technology Corporation Texture Test System® (Food Technology Corporation) equipped with a one-blade, Warner-Bratzler shear cell attached to a 13.6-kg force transducer. In the shear cell, the samples were oriented so the direction of the muscle fiber was perpendicular to the blade. The descent speed was maintained at 8 mm per s. The four values for each fillet were averaged in order to determine a mean shear value for the fillet. All blades of the shear-compression cell and the single-bladed, Warner-Bratzler cell were of
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the same width (3 mm) and configuration (rightangle edged). All of the blade edges from both cells contacting the samples appeared to be similar and in good condition. Deformation curves were also obtained on selected, representative samples sheared with each of the two shear cells by connecting the transducer to a recorder. The experiment was repeated with four additional groups of 12 broilers. Because there was no significant interaction for replication by boning-time treatment, the data from the five replicates were pooled. Linear regressions of the Wamer-Bratzler shear value as a function of shear-compression shear value were calculated for the data, when all data were pooled as well as with the data separated into the three boning treatments (Steel and Torrie, 1980). The significance of each correlation was tested with the independent /-test (Steel and Torrie, 1980). Variances were calculated for each boning time and shearing method and were tested for inequality using the folded F statistic (Steel and Torrie, 1980). The differences between means were tested for significance with the approximate /-test for unequal variances found in the Statistical Analysis System (SAS Institute, 1985).
The pH of the anterior half of each 5-cm section of each fillet was determined by using the iodoacetate procedure described by Marsh (1954). Sarcomere length was determined on the posterior half of each 5-cm section of each fillet, using the laser diffraction method described by Cross et al. (1980) as modified by adding .05 mM sodium iodoacetate and 2 mAf potassium chloride to the homogenization medium and by decreasing the homogenization time to 5 s. This procedure produced a 3 by 2 factorial design with three boning times and two sampling times (time of boning versus 24-h postmortem). The experiment was repeated with four additional groups of 12 broilers. Because there was no significant interaction for replication by boning-time treatment, the data from the five replications were pooled. Variances around treatment means were calculated and were tested for inequality with the folded F statistic (Steel and Torrie, 1980). Differences between means were tested for significance with the approximate /-test for comparison of the means with unequal variances found in the Statistical Analysis System (SAS Institute, 1985). RESULTS AND DISCUSSION
Experiment 2 All procedures associated with broiler rearing, selection, slaughter, and carcass boning in this experiment were identical with those described for Experiment 1. The breast fillets were harvested from each of four carcasses from a group of 12 broilers immediately after carcasspicking (hot-boned fillets), immediately after chilling (chill-boned fillets), and after a 24-h period of carcass aging (age-boned fillets). Right-side fillets from hot-boned and chillboned carcasses, were packed in crushed ice and were aged to 24 h post-mortem with the remaining, intact carcasses. The anterior 2.5-cm portion of each left-side fillet was removed at the time of boning and was discarded. A 5-cm portion of the anterior end of each partial fillet was then removed and halved by cutting parallel to the direction of the muscle fiber. The resulting two samples from each leftside fillet were immediately frozen and held in liquid nitrogen. At 24-h post-mortem, the remaining carcasses were boned and all unsampled fillets were sectioned, frozen, and held in liquid nitrogen until analyzed, as previously described.
Experiment 1 A comparison of the curves for shear compression and Wamer-Bratzler shear deformation indicated that with samples from the same carcass, the peak load for the shearcompression cell was from 20 to 25 times greater than that observed for the Wamer-Bratzler cell (Figure 1). Differences in sample size associated with the two shearing systems accounted for a portion of this difference. However, using a sample strip of 35 by 20 mm for shearcompression involved six of the ten available blades and twice the sample width as that of the Wamer-Bratzler, 10-mm-wide sample sheared with only one blade. Therefore, one would have expected a shear-compression value at least 12 times greater than the Wamer-Bratzler shear value. As the name implies, however, the shearcompression cell produced a marked compression of the meat since several blades simultaneously came into contact with the sample prior to the shearing action. This compression factor magnified the peak load required to shear the sample compared to the peak load values obtained with the one blade of the Warner-
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TABLE 1. Shear values and variances for cooked broiler breast fillets boned at various times post-mortem and sheared with either a shearcompression or a Warner-Bratzler shear cell, Experiment 1 Treatment Shear method
Hot-boned Chill-bonedAge-boned
Shear compression, kg/g of sample Warner-Bratzler, kg/sample
13.0" (6.0W) 6.1C (1.8")
10.4b (11.7V) 4.5 d (2.4")
4.5 a (.7") 2.0e (.2Z)
i_e
— Relative downstroke distance - » -
FIGURE 1. Representative deformation curves from cooked broiler breast meat samples sheared with either a shear-compression (35 by 20 by 7 mm) or Warner-Bratzler (50 by 10 by 7 mm) shear cell at 8 mm/s, Experiment 1.
Bratzler cell. Because the entire sample is involved in the shearing operation with the multiple-bladed, shear-compression cell, the peak load ofeach sample reflected the maximum (rather than the average) load required for the shear. With the Warner-Bratzler cell, multiple shears were done individually and, when averaged, reflected an average (rather than a maximum) value for the peak load required to shear the sample. Both of the sample, weight-corrected, mean shear values (shear-compression, kilograms per gram of sample; and Warner-Bratzler, kilograms per sample) significantly decreased as the postmortem boning time was increased (Table 1). However, at all boning times, the mean shearcompression values and respective variance components were significantly larger than the mean Warner-Bratzler shear values and respective variances. Compression effects, coupled with the maximum shear measurement observed with the shear-compression cell, would be expected to produce higher, mean, peak-shearvalue values and increased variability compared to the mean values and variability observed with the Warner-Bratzler shear cell. Within each shearing method, the mean shear values associated with the fillets harvested after 24 h of aging had significantly smaller variances than those associated with the mean shear values obtained from fillets boned immediately after carcass-picking (hot-boned) (Table 1). The variances associated with the mean shear value for hot-boned fillets were smaller than those
Means with no common superscripts are significantly different (P<.05), n = 20. v-z Variances (in parentheses) with no common superscripts are significantly different (P<05), n = 20.
associated with the mean shear value for chillboned fillets. These differences most probably resulted from individual variations among birds in the rate of rigor mortis development, interacting with post-mortem time interval prior to boning. Similar variance differences between boning-time treatments have been reported previously (Sams and Janky, 1986). Although the correlation was quite high (r = .93) between shear values obtained with the shear-compression cell and the values obtained with the Warner-Bratzler cell from fillets harvested at all boning times combined, the correlations between the shear methods within individual boning times were decreased (Figure
Hot boned y=.487x-.257 r=.89 range of x = 9.3 -17.5 Overall y=.487x-.257 r=.93 range of x = 3.1-17.5 s^^--*' -^
^^^
^ ^ ^
^Chill boned y=.326x + 1.147 r=.72 range of x = 4.9-17.1
" fcAge boned y=.283x + .614 range ot x = 3.1 -6.1 Shear-compression shear value (kg/g sample)
FIGURE 2. Overall and individual boning-time treatment comparison (linear regression) of shear-compression shear values (x) and Warner-Bratzler shear values (y) from cooked breast fillet samples harvested after carcass-picking (hot-boned), after carcass-chilling (chill-boned), or after carcass-aging (24 h, age-boned), Experiment 1.
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SAMS ET AL. TABLE 2. Means for pH and sarcomere length with respective variances for raw broiler breast fillets boned at various times post-mortem and sampled either immediately after boning or following a 24-h aging period, Experiment 2 Treatment
Parameters pH After boning After aging Sarcomere length, urn After boning After aging a x_z
Hot-boned
ChiU-boned
Age-boned
6.44" (.03?) 5.84c (.03?)
6.26b (.08") 5.86c (.03?)
5.82c (.02yz) 5.80c (•01z)
1.39d (.04?) 1.51c (•01z)
1.61b (.05?) LSI** (•01z)
1.85a (•01r) 1.79a (•01z)
Means within a parameter with no common superscripts are significantly different (P<.05), n = 20. Variances (in parentheses) within a parameter with no common superscripts are significantly different (P<.05), n = 20.
2). Only the values from fillets that were hotboned produced a similar regression line and correlation coefficient (r = .89) to the overall correlation. The regression lines associated with the shear values obtained with the two methodologies from chill-boned and age-boned samples were quite different in slope and y intercept from each other and from the overall regression line. The correlation coefficients associated with those lines were also markedly lower than the overall correlation. These results indicated that either shear system was effective in terms of differentiating between samples across a wide range of shear values. Because of differences in correlation and in variances between the two shear systems across boning times and differences in the magnitude of response, however, any comparison of Warner-Bratzler shear values with shear compression-values should be conducted within the appropriate statistics and limitations. Subjective sensory data would be required in order to definitively relate objective tenderness data to consumer acceptance.
hot-boned and chiU-boned fillets, was not significantly affected by the time of boning. These results confirmed earlier findings reported by Stewart et al. (1984) indicating that the ultimate pH was not affected by the postmortem, boning-time interval. The variance associated with the mean pH for the chUl-boned fiUet at the time of boning was significandy greater than the variances associated with all other pH means (Table 2). At 1 h post-mortem, there would be a greater variation in pH because of the normal variation in the rate of lactic-acid production among the carcasses. Hot-boned fillets would have had too little time to manifest this variation, and age-boned fillets would have had enough time for equilibration to occur. Aging chiU-boned fillets significandy reduced the variation associated with the mean pH to the same level as mat observed for hotboned fillets. Hot-boned and chill-boned fillets exhibited significantly greater variance components man age-boned fillets when the sampling was accomplished after 24 h of aging, even though equilibration of the means had occurred by that time. The sampling time (before or after fillet Experiment 2 aging) had no significant effect on the mean Fillet pH at the time of boning was decreased value for sarcomere length of the chilled-boned as the post-mortem boning-time interval was or age-boned fillets, although the chiU-boned increased. The hot-boned fillets had a signifi- fillets had significandy shorter sarcomeres than cantly higher pH than the chiU-boned fillets; and the age-boned fiUets at both sampling times the chiU-boned fillets had a significantly higher (Table 2). The mean of the sarcomere length for pH than age-boned fillets (Table 2). However, hot-boned fiUets, measured after boning, was the ultimate fillet pH, following 24 h of aging for significandy shorter than all of the other means
SHEAR AND SAMPLING METHOD COMPARISON
for sarcomere lengths measured; however, aging hot-boned fillets 24 h prior to analysis appeared to allow the mean sarcomere length to significantly increase to a length similar to the one observed for aged, chill-boned fillets. Exposing the muscle to the chilled water, in combination with an unimpeded contraction of the excised muscle, caused a large sarcomere-shortening effect in the hot-boned fillets. Similar effects were described by Thompson et al. (1987). However, the results of the present study indicated that a portion of the sarcomereshortening effect was alleviated during the filletaging period. In the present studies and others comparing the tenderness of hot-boned broiler breast fillets with mat of chill-boned fillets (Experiment 1) (Sams and Janky, 1986; Thompson etal., 1987), hot-boned fillets were significantly tougher (increased shear value) than chill-boned fillets. If increased and sustained sarcomere-shortening were the only reason for this apparent difference in tenderness, the ultimate sarcomere lengths of hot-boned and chill-boned fillets should remain significantly different. In the present experiments, the variances associated with the sarcomere-length means for hot-boned and chill-boned fillets sampled at time of boning were significantly greater than the variances associated with all other sarcomere-length means (Table 2). After 24 h of aging (prior to sampling), the variance components for the mean sarcomere lengths associated with hot-boned and chill-boned fillets had decreased to a level compatible with the variance component for the mean sarcomere length associated with the age-boned fillets. The data indicated that pH and sarcomere length could be used to predict the tenderness of broiler breast meat only when the samples
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analyzed were obtained at the time of boning. Due to differences in variance components around the means, however, appropriate statistical analysis methods should be used to determine the differences in means. REFERENCES Bunill, L. M., D. Deethardt, and R. L. Saffle, 1962. Two mechanical devices compared with taste panel evaluation for measuring tenderness. Food Technol. 16(10): 145-146. Cross, H. R., R. L. West, and T. R. Dutson, 1980. Comparison of methods for measuring sarcomere length in beef Semitendinosus muscle. Meat Sci. 5:261-266. Dawson, P. L., M. G. Dukes, L. D. Thompson, S. A. Woodward, and D. M. Janky, 1987. Effect of postmortem boning time during simulated commercial processing on the tenderness of broiler breast meat. Poultry Sci. 66:1331-1333. Hamm, D., 1981. Unconventional meat harvesting. Poultry Sci. 60:1666. (Abstr.) Hamm, R., 1982. Postmortem changes in muscle with regard to processing of hot-boned beef. Food Technol. 36: 105-115. Janky, D. M., M. D. Carpenter, D. L. Fletcher, A. S. Arafa, J. A. Koburger, and R. L. West, 1983. Physical characteristics of Pectoratis superficialis from brine-chilled broiler carcasses. Poultry Sci. 62:433-436. Marsh, B. B„ 1954. Rigor mortis in beef. J. Sci. Food Agric. 5:70-75. 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, 1985. SAS User's Guide: Statistics. SAS Inst. Inc., Cary, NC. 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 meat muscle on pH decline and toughening. Poultry Sci. 63: 1935-1939. Thompson, L. D., S. A. Woodward, and D. M. Janky, 1987. Effect of postmortem electrical stimulation on the tenderness of hot-boned, chill-boned, and aged-boned broiler breast fillets. Poultry Sci. 66:1158-1167.
Current commercial interest in incorporating the early harvesting of broiler breast meat into the processing scheme has stimulated research into the effects of this procedure on quality attributes, especially tenderness, of the finished product. Several objective methods for measuring meat tenderness are available to meat scientists; however, researchers working with poultry have generally used the "shearcompression" system (multiple blade) for objectively evaluating the tenderness of broiler breast meat. However, researchers working with red meats have generally used the "Warner-Bratzler" method (single blade). Because the Warner-Bratzler system provides a much faster system of sample-by-sample anal-
1 Number 9471, Florida Agricultural Experiment Stations Journal Series, University of Florida, Gainesville, FL 32611. Present address: Department of Poultry Science, Texas A&M University, College Station, TX 77843-2472. 3 Present address: Sunny Fresh Foods, P.O. Box 428, Monticello, MN 55362.
ysis for evaluation, poultry-meat researchers have shown an interest in using this system. Burrill et al. (1962) reported that, using four beef muscles of varying tenderness, the two shearing systems were highly correlated when values from all four muscles were combined; but, within an individual muscle, the correlations were lower and of less significance. Many researchers have reported that the early harvesting of broiler breast tissue produces a wide range of shear-compression shear values in broiler breast tissue (Stewart et al, 1984; Sams and Janky, 1986; Thompson et al, 1987; Dawson et al, 1987). Sams and Janky (1986) also reported that variances associated with shear-value means obtained from fillets boned at different times postmortem were significantly different. This would indicate mat a comparative study is needed of the two shear systems in evaluating broiler Pectoralis superficialis muscles over a wide range of tenderness, such as that produced over post-mortem time. Researchers have often associated chemical and physical characteristics, such as pH and sarcomere length, with differences in meat
348
SHEAR AND SAMPLING METHOD COMPARISON
tenderness induced by boning at various times post-mortem (Hamm, 1982; Janky et al., 1983; Stewart et al, 1984; Sams and Janky, 1986; Dawson et al, 1987; Thompson et al., 1987). Differing variances that might be associated with higher pH and shorter sarcomere lengths commonly observed with early-harvested broiler breast meat would be expected if these physical characteristics and tenderness are causally related. The ultimate (after fillet aging) pH and sarcomere length of earlyharvested broiler breast fillets should also reflect differences similar to those reported at the time of boning if these factors are causally related to ultimate differences in tenderness associated with early harvesting. The purposes of the present studies were to determine the correlation and comparability between the shear-compression and the Warner-Bratzler shearing systems for objectively determining the tenderness of broiler breast meat; and to evaluate the changes in pH and sarcomere length associated with early harvested breast meat both at the time of boning and after fillet aging. MATERIALS AND METHODS
Experiment 1 Feather-sexed, male broilers (Cobb) were reared on wood-shaving litter in floor pens and were fed commercial-type starter, finisher, and withdrawal corn-soybean meal diets. Twelve broilers within a weight range of 1,900 to 2,400 g were selected from the general population of 56-day-old birds. The 12 broilers were cooped and were held without feed and water for 12 h prior to slaughter. The broilers were electrically stunned (Cervin Model FS stunner, Cervin Electrical Systems, Minneapolis, MN, setting Number 4, 10 s), killed by exsanguination, subscalded (60 C, 45 s), and rotary-drum picked (25 s). Immediately after picking (15 min postmortem), the Pectoralis superficialis muscles from four carcasses were harvested (hot-boned fillets) using the stripping method described by Hamm (1981) and were individually identified. The remaining carcasses were manually eviscerated and were chilled along with hot-boned fillets for 15 min in tap water (20 C), followed by an additional 30 min in ice slush (1 C). The chill temperatures were monitored with copper, constantan thermocouples and a recording po-
349
tentiometer and were maintained by adding small amounts of crushed ice. The ratio of ice to water in the ice slush was not allowed to exceed 1:9. The chill tanks were manually shaken to mimic commercial agitation of the chill solution. The ratio of the chill solution to the carcasses and fillets was maintained at 3:1. Immediately after chilling (1 h post-mortem), the fillets were harvested (chill-boned fillets) as previously described and were identified from four additional carcasses. All of the fillets and the remaining carcasses were packed in crushed ice and held at 2 C. At 24 h post-mortem, the fillets were harvested (age-boned fillets) and were identified from the remaining four carcasses. The fillets were cooked together to an internal temperature of 80 C on raised wire racks in pans lined and covered with aluminum foil in a conventional electric oven maintained at 177 C. The internal temperature was monitored with copper, constantan thermocouples inserted into one representative fillet in each pan and a recording potentiometer. The cooked fillets were cooled at room temperature (30 min), wrapped in aluminum foil, and held at 2 C overnight prior to the shear-value analyses. Two samples (35 by 20 by 7 mm) from the anterior portion of the right-side fillet of each carcass were each weighed and then sheared, using a Food Technology Corporation Texture Test System® (Food Technology Corporation, Rockville, MD) equipped with a 10-blade, shear-compression cell attached to a 136-kg force transducer. The samples were oriented in the shear cell so the direction of the muscle fiber was perpendicular to the blades. The descent speed was maintained at 8 mm per s. The two values for each fillet were averaged in order to determine a mean shear value for the fillet Two samples each (50 by 10 by 7 mm) from the anterior portion of the left-side fillet of each carcass were each sheared twice using a Food Technology Corporation Texture Test System® (Food Technology Corporation) equipped with a one-blade, Warner-Bratzler shear cell attached to a 13.6-kg force transducer. In the shear cell, the samples were oriented so the direction of the muscle fiber was perpendicular to the blade. The descent speed was maintained at 8 mm per s. The four values for each fillet were averaged in order to determine a mean shear value for the fillet. All blades of the shear-compression cell and the single-bladed, Warner-Bratzler cell were of
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the same width (3 mm) and configuration (rightangle edged). All of the blade edges from both cells contacting the samples appeared to be similar and in good condition. Deformation curves were also obtained on selected, representative samples sheared with each of the two shear cells by connecting the transducer to a recorder. The experiment was repeated with four additional groups of 12 broilers. Because there was no significant interaction for replication by boning-time treatment, the data from the five replicates were pooled. Linear regressions of the Wamer-Bratzler shear value as a function of shear-compression shear value were calculated for the data, when all data were pooled as well as with the data separated into the three boning treatments (Steel and Torrie, 1980). The significance of each correlation was tested with the independent /-test (Steel and Torrie, 1980). Variances were calculated for each boning time and shearing method and were tested for inequality using the folded F statistic (Steel and Torrie, 1980). The differences between means were tested for significance with the approximate /-test for unequal variances found in the Statistical Analysis System (SAS Institute, 1985).
The pH of the anterior half of each 5-cm section of each fillet was determined by using the iodoacetate procedure described by Marsh (1954). Sarcomere length was determined on the posterior half of each 5-cm section of each fillet, using the laser diffraction method described by Cross et al. (1980) as modified by adding .05 mM sodium iodoacetate and 2 mAf potassium chloride to the homogenization medium and by decreasing the homogenization time to 5 s. This procedure produced a 3 by 2 factorial design with three boning times and two sampling times (time of boning versus 24-h postmortem). The experiment was repeated with four additional groups of 12 broilers. Because there was no significant interaction for replication by boning-time treatment, the data from the five replications were pooled. Variances around treatment means were calculated and were tested for inequality with the folded F statistic (Steel and Torrie, 1980). Differences between means were tested for significance with the approximate /-test for comparison of the means with unequal variances found in the Statistical Analysis System (SAS Institute, 1985). RESULTS AND DISCUSSION
Experiment 2 All procedures associated with broiler rearing, selection, slaughter, and carcass boning in this experiment were identical with those described for Experiment 1. The breast fillets were harvested from each of four carcasses from a group of 12 broilers immediately after carcasspicking (hot-boned fillets), immediately after chilling (chill-boned fillets), and after a 24-h period of carcass aging (age-boned fillets). Right-side fillets from hot-boned and chillboned carcasses, were packed in crushed ice and were aged to 24 h post-mortem with the remaining, intact carcasses. The anterior 2.5-cm portion of each left-side fillet was removed at the time of boning and was discarded. A 5-cm portion of the anterior end of each partial fillet was then removed and halved by cutting parallel to the direction of the muscle fiber. The resulting two samples from each leftside fillet were immediately frozen and held in liquid nitrogen. At 24-h post-mortem, the remaining carcasses were boned and all unsampled fillets were sectioned, frozen, and held in liquid nitrogen until analyzed, as previously described.
Experiment 1 A comparison of the curves for shear compression and Wamer-Bratzler shear deformation indicated that with samples from the same carcass, the peak load for the shearcompression cell was from 20 to 25 times greater than that observed for the Wamer-Bratzler cell (Figure 1). Differences in sample size associated with the two shearing systems accounted for a portion of this difference. However, using a sample strip of 35 by 20 mm for shearcompression involved six of the ten available blades and twice the sample width as that of the Wamer-Bratzler, 10-mm-wide sample sheared with only one blade. Therefore, one would have expected a shear-compression value at least 12 times greater than the Wamer-Bratzler shear value. As the name implies, however, the shearcompression cell produced a marked compression of the meat since several blades simultaneously came into contact with the sample prior to the shearing action. This compression factor magnified the peak load required to shear the sample compared to the peak load values obtained with the one blade of the Warner-
351
SHEAR AND SAMPLING METHOD COMPARISON
TABLE 1. Shear values and variances for cooked broiler breast fillets boned at various times post-mortem and sheared with either a shearcompression or a Warner-Bratzler shear cell, Experiment 1 Treatment Shear method
Hot-boned Chill-bonedAge-boned
Shear compression, kg/g of sample Warner-Bratzler, kg/sample
13.0" (6.0W) 6.1C (1.8")
10.4b (11.7V) 4.5 d (2.4")
4.5 a (.7") 2.0e (.2Z)
i_e
— Relative downstroke distance - » -
FIGURE 1. Representative deformation curves from cooked broiler breast meat samples sheared with either a shear-compression (35 by 20 by 7 mm) or Warner-Bratzler (50 by 10 by 7 mm) shear cell at 8 mm/s, Experiment 1.
Bratzler cell. Because the entire sample is involved in the shearing operation with the multiple-bladed, shear-compression cell, the peak load ofeach sample reflected the maximum (rather than the average) load required for the shear. With the Warner-Bratzler cell, multiple shears were done individually and, when averaged, reflected an average (rather than a maximum) value for the peak load required to shear the sample. Both of the sample, weight-corrected, mean shear values (shear-compression, kilograms per gram of sample; and Warner-Bratzler, kilograms per sample) significantly decreased as the postmortem boning time was increased (Table 1). However, at all boning times, the mean shearcompression values and respective variance components were significantly larger than the mean Warner-Bratzler shear values and respective variances. Compression effects, coupled with the maximum shear measurement observed with the shear-compression cell, would be expected to produce higher, mean, peak-shearvalue values and increased variability compared to the mean values and variability observed with the Warner-Bratzler shear cell. Within each shearing method, the mean shear values associated with the fillets harvested after 24 h of aging had significantly smaller variances than those associated with the mean shear values obtained from fillets boned immediately after carcass-picking (hot-boned) (Table 1). The variances associated with the mean shear value for hot-boned fillets were smaller than those
Means with no common superscripts are significantly different (P<.05), n = 20. v-z Variances (in parentheses) with no common superscripts are significantly different (P<05), n = 20.
associated with the mean shear value for chillboned fillets. These differences most probably resulted from individual variations among birds in the rate of rigor mortis development, interacting with post-mortem time interval prior to boning. Similar variance differences between boning-time treatments have been reported previously (Sams and Janky, 1986). Although the correlation was quite high (r = .93) between shear values obtained with the shear-compression cell and the values obtained with the Warner-Bratzler cell from fillets harvested at all boning times combined, the correlations between the shear methods within individual boning times were decreased (Figure
Hot boned y=.487x-.257 r=.89 range of x = 9.3 -17.5 Overall y=.487x-.257 r=.93 range of x = 3.1-17.5 s^^--*' -^
^^^
^ ^ ^
^Chill boned y=.326x + 1.147 r=.72 range of x = 4.9-17.1
" fcAge boned y=.283x + .614 range ot x = 3.1 -6.1 Shear-compression shear value (kg/g sample)
FIGURE 2. Overall and individual boning-time treatment comparison (linear regression) of shear-compression shear values (x) and Warner-Bratzler shear values (y) from cooked breast fillet samples harvested after carcass-picking (hot-boned), after carcass-chilling (chill-boned), or after carcass-aging (24 h, age-boned), Experiment 1.
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SAMS ET AL. TABLE 2. Means for pH and sarcomere length with respective variances for raw broiler breast fillets boned at various times post-mortem and sampled either immediately after boning or following a 24-h aging period, Experiment 2 Treatment
Parameters pH After boning After aging Sarcomere length, urn After boning After aging a x_z
Hot-boned
ChiU-boned
Age-boned
6.44" (.03?) 5.84c (.03?)
6.26b (.08") 5.86c (.03?)
5.82c (.02yz) 5.80c (•01z)
1.39d (.04?) 1.51c (•01z)
1.61b (.05?) LSI** (•01z)
1.85a (•01r) 1.79a (•01z)
Means within a parameter with no common superscripts are significantly different (P<.05), n = 20. Variances (in parentheses) within a parameter with no common superscripts are significantly different (P<.05), n = 20.
2). Only the values from fillets that were hotboned produced a similar regression line and correlation coefficient (r = .89) to the overall correlation. The regression lines associated with the shear values obtained with the two methodologies from chill-boned and age-boned samples were quite different in slope and y intercept from each other and from the overall regression line. The correlation coefficients associated with those lines were also markedly lower than the overall correlation. These results indicated that either shear system was effective in terms of differentiating between samples across a wide range of shear values. Because of differences in correlation and in variances between the two shear systems across boning times and differences in the magnitude of response, however, any comparison of Warner-Bratzler shear values with shear compression-values should be conducted within the appropriate statistics and limitations. Subjective sensory data would be required in order to definitively relate objective tenderness data to consumer acceptance.
hot-boned and chiU-boned fillets, was not significantly affected by the time of boning. These results confirmed earlier findings reported by Stewart et al. (1984) indicating that the ultimate pH was not affected by the postmortem, boning-time interval. The variance associated with the mean pH for the chUl-boned fiUet at the time of boning was significandy greater than the variances associated with all other pH means (Table 2). At 1 h post-mortem, there would be a greater variation in pH because of the normal variation in the rate of lactic-acid production among the carcasses. Hot-boned fillets would have had too little time to manifest this variation, and age-boned fillets would have had enough time for equilibration to occur. Aging chiU-boned fillets significandy reduced the variation associated with the mean pH to the same level as mat observed for hotboned fillets. Hot-boned and chill-boned fillets exhibited significantly greater variance components man age-boned fillets when the sampling was accomplished after 24 h of aging, even though equilibration of the means had occurred by that time. The sampling time (before or after fillet Experiment 2 aging) had no significant effect on the mean Fillet pH at the time of boning was decreased value for sarcomere length of the chilled-boned as the post-mortem boning-time interval was or age-boned fillets, although the chiU-boned increased. The hot-boned fillets had a signifi- fillets had significandy shorter sarcomeres than cantly higher pH than the chiU-boned fillets; and the age-boned fiUets at both sampling times the chiU-boned fillets had a significantly higher (Table 2). The mean of the sarcomere length for pH than age-boned fillets (Table 2). However, hot-boned fiUets, measured after boning, was the ultimate fillet pH, following 24 h of aging for significandy shorter than all of the other means
SHEAR AND SAMPLING METHOD COMPARISON
for sarcomere lengths measured; however, aging hot-boned fillets 24 h prior to analysis appeared to allow the mean sarcomere length to significantly increase to a length similar to the one observed for aged, chill-boned fillets. Exposing the muscle to the chilled water, in combination with an unimpeded contraction of the excised muscle, caused a large sarcomere-shortening effect in the hot-boned fillets. Similar effects were described by Thompson et al. (1987). However, the results of the present study indicated that a portion of the sarcomereshortening effect was alleviated during the filletaging period. In the present studies and others comparing the tenderness of hot-boned broiler breast fillets with mat of chill-boned fillets (Experiment 1) (Sams and Janky, 1986; Thompson etal., 1987), hot-boned fillets were significantly tougher (increased shear value) than chill-boned fillets. If increased and sustained sarcomere-shortening were the only reason for this apparent difference in tenderness, the ultimate sarcomere lengths of hot-boned and chill-boned fillets should remain significantly different. In the present experiments, the variances associated with the sarcomere-length means for hot-boned and chill-boned fillets sampled at time of boning were significantly greater than the variances associated with all other sarcomere-length means (Table 2). After 24 h of aging (prior to sampling), the variance components for the mean sarcomere lengths associated with hot-boned and chill-boned fillets had decreased to a level compatible with the variance component for the mean sarcomere length associated with the age-boned fillets. The data indicated that pH and sarcomere length could be used to predict the tenderness of broiler breast meat only when the samples
353
analyzed were obtained at the time of boning. Due to differences in variance components around the means, however, appropriate statistical analysis methods should be used to determine the differences in means. REFERENCES Bunill, L. M., D. Deethardt, and R. L. Saffle, 1962. Two mechanical devices compared with taste panel evaluation for measuring tenderness. Food Technol. 16(10): 145-146. Cross, H. R., R. L. West, and T. R. Dutson, 1980. Comparison of methods for measuring sarcomere length in beef Semitendinosus muscle. Meat Sci. 5:261-266. Dawson, P. L., M. G. Dukes, L. D. Thompson, S. A. Woodward, and D. M. Janky, 1987. Effect of postmortem boning time during simulated commercial processing on the tenderness of broiler breast meat. Poultry Sci. 66:1331-1333. Hamm, D., 1981. Unconventional meat harvesting. Poultry Sci. 60:1666. (Abstr.) Hamm, R., 1982. Postmortem changes in muscle with regard to processing of hot-boned beef. Food Technol. 36: 105-115. Janky, D. M., M. D. Carpenter, D. L. Fletcher, A. S. Arafa, J. A. Koburger, and R. L. West, 1983. Physical characteristics of Pectoratis superficialis from brine-chilled broiler carcasses. Poultry Sci. 62:433-436. Marsh, B. B„ 1954. Rigor mortis in beef. J. Sci. Food Agric. 5:70-75. 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, 1985. SAS User's Guide: Statistics. SAS Inst. Inc., Cary, NC. 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 meat muscle on pH decline and toughening. Poultry Sci. 63: 1935-1939. Thompson, L. D., S. A. Woodward, and D. M. Janky, 1987. Effect of postmortem electrical stimulation on the tenderness of hot-boned, chill-boned, and aged-boned broiler breast fillets. Poultry Sci. 66:1158-1167.