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Duckling and Chicken Processing Yields and Breast Meat Tenderness
Duckling and Chicken Processing Yields and Breast Meat Tenderness D. P. SMITH and D. L. FLETCHER1 Department of Poultry Science, University of Georgia, Athens, Georgia 30602 C. M. PAPA 2 USDA, Agricultural Research Service, Richard B. Russell Agricultural Research Center, Athens, Georgia 30613
ABSTRACT Twenty-eight live Pekin ducklings and 28 broiler chickens were obtained at 49 days of age from commercial processing facilities for each of two trials to determine processing yields and breast meat tenderness. Birds were withdrawn from feed for 8 h and then processed. Breast halves, without skin, were removed from four birds of each species at .25, .5,1,2,4,6, and 24 h postmortem. One side of each breast was cooked immediately after deboning (0-h aging) and the other half held 24 h at 4 C before cooking (24-h aging). Tenderness of the cooked breast meat was evaluated by Allo-Kramer shear. Duckling live, dry shell without giblets (WOG), and breast weights were significantly greater (P<.01) than chicken weights (3,410,2,143, and 319 g versus 2,780,1,915, and 295 g, respectively). Dry shell WOG, breast, and cooked breast yields were significantly lower for duckling than chicken (62.9,14.8, and 60.4% versus 68.8, 15.4, and 67.8%, respectively). Allo-Kramer shear values for duckling decreased (P<.01) from .25 to 24 h post-mortem for both the 0-h aged samples (from 13.2 to 9.1 kg shear/g sample) and the 24-h aged samples (from 14.0 to 7.2 kg shear/g sample), and chicken shear values decreased from 19.6 to 4.2 and 19.1 to 4.1 kg shear/g sample, respectively, for the 0-h and 24-h aged samples. There was a significant difference in duckling and chicken processing yields and breast meat tenderness as affected by deboning and aging times. (Key words: duckling, chicken, processing yields, breast meat tenderness, aging) 1992 Poultry Science 71:197-202
INTRODUCTION Pekin duckling is a commercially important poultry species, ranking third in per capita consumption in the United States after chicken and turkey (Heffernan, 1977). Both ducklings and broiler chickens are grown commercially under similar conditions to approximately the same age and weight; however, little information is
To whom correspondence should be addressed. Present address: OK Foods, Inc., P.O. Box 1787, Fort Smith, AR 72902. 2
available on either processing yields or the effect of aging and deboning time on meat tenderness for duckling. Snyder and Orr (1964), Stadelman and Meinert (1977), and Sheldon and Tarver (1987) have reported processing weights and yields for Pekin ducklings, as have Brahma et al. (1985) for Indian Runner ducks. No information on the effect of aging or deboning on tenderness was found. Information on chicken processing yields is readily available (e.g., Moran and Orr, 1970; Chen et al, 1983, 1987; Orr et al, 1984), as is the effect of aging and of deboning time on tenderness (Dodge and Stadelman, 1959; Goodwin,
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(Received for publication April 5, 1991)
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1984; Stewart et al.r 1984; Dawson et at, 1987). The purpose of the present study was to compare duckling and chicken for both 1) processing weights and yields; and 2) the effect of deboning and aging times on breast tenderness.
MATERIALS AND METHODS
^ s t r o n Corporation, Canton, MA 02021.
RESULTS AND DISCUSSION Processing Yields Average processing weights and the calculated yields for both duckling and chicken are presented in Table 1. Live, dry shell WOG, and raw breast weights were significantly greater (P<.01) for duckling than for chicken. Cooked breast weight of
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 30, 2015
Twenty-eight commercially reared Pekin ducklings and 28 broiler chickens were obtained at 49 days of age, for each of two trials. Birds were housed for approximately 1 additional wk in pens with free access to feed and water to allow recovery from commercial harvesting and transport variations. Ducks were processed at an average age of 56 days and chickens at an average of 55 days. Feed was removed from the birds 8 h prior to cooping and transport of the animals to a nearby pilot processing facility. Birds were stunned at 100 V alternating current (AC) for 5 s, killed by conventional neck cut, bled for 2 min, scalded at 60 C for 2 min, and picked in a rotary-drum picker for 30 s. Carcasses were eviscerated, and inedible and edible viscera, shanks, neck, head, and fat pads were removed and discarded. Carcasses were chilled using paddle-agitated chillers in a two-step process; first, for 15 min in water maintained at 13 C with ice, then for 30 min at 1 C in an ice and water mixture. Carcasses were then held covered in a cold room at 4 C prior to deboning and cooking. Weights were recorded prior to slaughter (live weight) and after evisceration but prior to chilling [dry shell without giblets (WOG)]. Dry shell WOG weight as a percentage of live weight was used to calculate dry shell WOG yield. Breast halves (Pectoralis major muscles only) were removed from each carcass at the following times post-mortem: .25 (after evisceration), .5 (after first chilling step), 1 (after complete chilling), 2, 4, 6, and 24 h. One side of each breast was cooked immediately after deboning (0-h aging); the other side was placed in a plastic bag and held at 4 C until 24 h post-mortem
before cooking (24-h aging). Breast halves were cooked in covered pans in a rotary oven for 45 min at 177 C, cooled at room temperature for 30 min, and drained. Breast weights were recorded after removal from the carcass (raw weight) and after cooking and draining (cooked weight). Raw breast weight as a percentage of dry shell WOG weight was used to calculate breast yield, and cooked breast weight as a percentage of raw breast weight was used to calculate cooked yield. A 2.54-cm diameter core was removed from the cranial area of each breast half, weighed, and evaluated for tenderness at room temperature using the Allo-Kramer shear cell mounted on an Instron Universal Testing Machine, 3 according to procedures described by Smith et al. (1988). Cores were placed with surface fibers perpendicular to the descending blades and peak load values were recorded. Processing data were analyzed using ANOVA (SAS Institute, 1985). Species were compared using residual error as the test statistic because the species by trial interaction was not significant. For the meat tenderness trials, the experimental model tested sources of variation due to trial, species, aging time, and post-mortem deboning time, i n a 2 x 2 x 2 x 7 arrangement of treatments with four breast halves per treatment cell (n = 224). Data were subjected to ANOVA. Means were separated using Duncan's multiple range test. Data are presented b y species for weights and yields, as no significant trial by species interaction was noted. Shear values were analyzed by species and aging time due to a significant aging time by post-mortem deboning time interaction, with the residual mean square error used as the test statistic.
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TABLE 1. Comparison of processing weights and yields obtained from Fekin ducklings and broiler chickens (for each mean, n = 56)1
Weight parameters
Processing weights Duckling Chicken
Live Dry shell WOG Raw breast Cooked breast
3,410^ 2,143A 319A 193A
(g) 2,780B 1,915B 295B 200^
Processing yields Duckling Chicken
(%) 62.9B 14.8B 60.4B
68.8* 15.4^ 67.8^
duckling was not significantly different from chicken. Dry shell WOG, raw breast, and cooked breast yields were significantly lower for duckling than for chicken. Sheldon and Tarver (1987) reported that, for the heaviest group of ducklings evaluated, ready-to-cook (RTC) WOG-carcass weights ranged from 2,072 to 2,236 g, raw breast weights from 245 to 343 g, and cooked breast weights from 141 to 168 g, depending on the brand of duckling tested. Duckling breast meat yield (as a percentage of RTC WOG) was 11.8 to 15.4% and cooked yield was 51.4 to 53.7%, depending on the brand tested in the heaviest group of carcasses as reported by Sheldon and Tarver (1987). Breast meat yield, as a percentage of carcass WOG, was 12.6% for 49-day-old duckling (Stadelman a n d Meinert, 1977). Many researchers have reported on broiler chicken processing weights and yields (Moran and Orr, 1970; Treat and Goodwin, 1973; Orr et ah, 1984; Chen et at., 1987). Results presented in Table 1 for the broiler chicken do not differ greatly from the results presented in these previous reports. The results indicate that at similar commercial processing ages, the duckling has larger absolute body weight, dry shell WOG, and raw breast weight, but lower dry shell WOG, breast, and cooked breast yields than the chicken. The lower dry shell yield for the duckling is apparently d u e to this animal having a greater percentage of blood, feathers, neck, head, shanks, viscera, and fat pad in comparison with the broiler chicken. Snyder and Orr (1964) found
average head and giblet weight, as a percentage of live weight, was lower for broiler chickens (2.7 and 4.6%, respectively) than for ducklings (4.2 and 5.6%, respectively). Winter and Clements (1957) observed lower neck weight (as a percentage of RTC weight) for broiler chickens (3.8%) than for ducklings (5.1%). Brahma et al. (1985) reported Indian Runner ducks had a higher percentage of blood, feather, and head in comparison with White Leghorn hens of similar live weight. The lower breast meat yield for the duckling when compared with the broiler chicken may be due to less selection pressure for body weight and breast conformation for the commercial duckling. Lower cooked breast yield for the duckling may be due to a difference in muscle composition (higher fat content) as compared with the chicken, allowing for greater loss during cooking.
Breast Meat Tenderness Duckling breast meat tenderness as determined at the post-mortem deboning times of .25, .5,1,2,4,6, and 24 h after aging either 0 or 24 h is reported in Table 2. Shear values for the 0-h aged meat did not differ significantly (P<.01) from the .25 through the 6 h times (12.8 k g / g average), but the shear value at 24 h (9.1 kg/g) was significantly lower than the earlier shear values. Shear values for the meat aged 24 h before cooking decreased at a faster rate than the 0-h aged samples. Shear values decreased by approximately 50% between .25 and 24 h for the 24-h aged treatment.
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• ^ ^ e a n s in the same row within either processing weights or yields with no common superscripts are significantly different (P<.01). ^Yield of dry shell without giblets (WOG) calculated on the basis of live weight; yield of raw breast meat calculated on the basis of dry shell WOG weight; yield of cooked breast meat calculated on the basis of raw breast meat weight.
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TABLE 2. Allo-Kramer shear values (kilograms shear per gram of meat) of Fekin duckling and broiler chicken breast meat deboned at .25, .5, 1, 2, 4, 6, and 24 h post-mortem and then cooked either immediately after deboning (0-h aging) or 24 h after deboning (for each mean, n = 8) Duckling aging period (h)
Post-mortem deboning time
A E
24
24 (kg shear/g meat) 13.2 A 14.0 A 132A 13.0* 11.6 A 11.8 A 9.1 B
14.0^ 13.2"AB 105 1;BC 9.4"CD 9 5 '|CD 9.6 C D 7.2 D
19.6^ 20.9* 17.1AB 14.1BC 8.4'DE 10.4'CD 4.2 H
19.1' 17.5",AB 1 3 5BC 10.1 C 8.9C 9.4C 4.1 E
Means in the same column with no common superscripts are significantly different (P<.01).
Shear values are also presented in Table 2 for broiler chicken breast meat deboned at .25, . 5 , 1 , 2, 4, 6, or 24 h post-mortem then aged either 0 or 24 h. Breast meat shear values for the 0-h aged samples decreased significantly (P<.01), almost 80% from .25 h (19.6 k g / g ) to 24 h (4.2 k g / g ) . The 24-h aged breast meat shear values decreased in a similar manner, from 19.1 k g / g (.25 h) to 4.1 k g / g (24 h). Previous researchers have described the effect of post-mortem aging on the tenderization of chicken meat. Goodwin (1984) stated factors that could affect broiler meat tenderness included chilling, aging, and prerigor cutting of the muscle, and recommended aging the carcass 8 to 16 h before cutting into parts to avoid toughness. Broiler meat aged 0, 2, 4, 6, and 8 h postmortem showed an increase in tenderness as aging time increased (Dodge and Stadelman, 1959). Dawson et al. (1987) deboned broiler breast meat over several postmortem times, from .08 to 24 h, and shear values decreased from 14.1 to 4.1 kg shear/ g sample. Stewart et al. (1984) found broiler breast meat aged from 0 to 4 h prior to deboning had a significant decrease in shear values, from 10.3 to 5.0 kg shear/g sample. Allo-Kramer shear values reported to be the upper limit of acceptable tenderness for chicken meat (when correlated with sensory evaluation) are 8.0 (Simpson and Goodwin, 1974) or 8.8 (Lyon and Lyon, 1990) kg shear/g sample. Chicken breast
meat evaluated in the present study would require 4 h of aging to fall within these limits. An upper limit on the objective measure of acceptable tenderness for duckling breast meat has not been established. Meat tenderness as affected by deboning time is illustrated by plotting duckling and chicken shear values against the natural log function of deboning time (Figure 1). The 0-h and 24-h aging time lines were averaged together to represent the overall effect of post-mortem aging on both species for comparative purposes. The log e function lines represent the highest coefficient of regression when compared with linear or quadratic functions. Duckling shear values decreased slightly as deboning time increased, from approximately 12 to 9 k g / g (a slowly decreasing slope), for an overall difference of approximately 3 k g / g . Chicken shear values decreased at an accelerated rate, from approximately 18 to 4 k g / g , for an overall difference of 14 k g / g . The different patterns of breast meat tenderness for deboning at selected postmortem times during aging between duckling and chicken must be due to the differing fiber types of the breast muscles from each species, as other possible variables such as age, weight, and muscle function were constant. Duckling breast muscle is darker than the predominately white-fibered chicken breast muscle d u e to a higher content of red fibers. Beecher et al. (1965a,b) found that porcine muscles differing with respect to fiber-type composition
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(h) .25 .5 1 2 4 6 24
Chicken aging period (h)
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due to the different post-mortem metabolism associated with differences in muscle fiber composition; and secondly, the residual toughness for duckling (after 24 h) when compared with chicken is d u e to the presence of greater amounts of connective tissue associated with the presence of smaller, more numerous red fibers per unit of muscle volume or cross-sectional area. ACKNOWLEDGMENT
REFERENCES
Postmortem deboning time (h) FIGURE 1. Plot of the loge of duckling and chicken shear values (kilograms shear per gram of meat) with the post-mortem deboning time (hours). Chicken shear value = -3.73 (logg post-mortem deboning time) + 15.50, r 2 = .75; Duckling shear value = -.79 (loge postmortem deboning time) + 11.86, r 2 = .19.
(red versus white) responded differently in terms of glycolytic rate and contraction state during post-mortem aging. Kiessling (1977) reported metabolic differences between red (goose Pectoralis) and white (chicken Pectoralis) post-mortem muscle. The differences between duckling and chicken final (24-h) shear values (9 k g / g versus 4 k g / g , respectively) could be due to differences in the contents of stromal protein. Duckling breast muscle may contain a greater total number of fibers in a given volume of muscle, because red fibers are smaller in diameter than white fibers. The greater number of total fibers would provide a higher content of endomysial collagen. The difference in the pattern of meat tenderness during aging between duckling and chicken could thus be explained as a two-step process: first, the early tenderness but slower tenderization rate for the duckling, when compared with the chicken, is
Beecher, G. R., E. J. Briskey, and W. G. Hoekstra, 1965a. A comparison of glycolysis and associated changes in light and dark portions of the porcine emitendinosus. J. Food Sci. 30:477-485. Beecher, G. R., R. G. Cassens, W. G. Hoekstra, and E. J. Briskey, 1965b. Red and white fiber content and associated post-mortem properties of seven porcine muscles. J. Food Sci. 30569-976. Brahma, M. L., D. R. Nath, and P. L. Narayana Rao, 1985. Comparative studies on carcass yields in duck and hen. Haryana Vet. 24:52-57. Chen, T. C , S. Omar, D. Schultz, B. C. Dilworth, and E. J. Day, 1987. Processing, parts, and deboning yields of four ages of broilers. Poultry Sci. 66: 1334-1340. Chen, T. C, C. D. Schultz, F. N. Reece, B. D. Lott, and J. L. McNaughton, 1983. The effect of extended holding time, temperature, and dietary energy on yields of broilers. Poultry Sci. 62:1566-1571. Dawson, P. L., D. M. Janky, M. G. Dukes, L. D. Thompson, and S. A. Woodward, 1987. Effect of post-mortem boning time during simulated commercial processing on the tenderness of broiler breast meat. Poultry Sci. 66:1331-1333. Dodge, J. W., and W. J. Stadelman, 1959. Post mortem aging of poultry meat and its effect on the tenderness of the breast muscles. Food Technol. 13:81-«4. Goodwin, T. L., 1984. It takes tough discipline to make tender chicken! Broiler bid. 47(9):43-44. Heffernan, B. E., 1977. C & D Foods wants you to try duckling. Poultry Processing Marketing 28(12): 1Z Kiessling, K. H., 1977. Muscle structure and function in the goose, quail, pheasant, guinea hen, and chicken. Comp. Biochem. Physiol. 57287-292. 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. Moran, E. T., Jr., and H. L. Orr, 1970. Influence of strain on the yield of commercial parts from the chicken broiler carcass. Poultry Sci. 49:725-729. Orr, H. L., E. C. Hunt, and C. J. Randall, 1984. Yield of carcass, parts, meat, skin, and bone of eight strains of broilers. Poultry Sci. 632197-2200.
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 30, 2015
This study was supported in part by state and Hatch funds allocated to the Georgia Agricultural Experiment Station.
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SAS Institute, 1985. SAS/STAT® Guide for Personal Computers, Version 6 Edition. SAS Institute Inc., Cary, NC. Sheldon, B. W., and F. R. Tarver, 1987. Comparison of carcass and cooking yields across five weight classes for seven commercially available readyto-cook duckling brands. Poultry Sci. 66: 995-1000. Simpson, M. D., and T. L. Goodwin, 1974. Comparison between shear values and taste panel scores for predicting tenderness of broilers. Poultry Sci. 53:2042-2046. Smith, D. P., C. E. Lyon, and D. L. Fletcher, 1988. Comparison of the Allo-Kramer shear and Texture Profile methods of broiler breast meat texture analysis. Poultry Sci. 67:1549-1556. Snyder, E. S., and H. L. Orr, 1964. Poultry m e a t -
processing, quality factors, yields. Ontario Department of Agriculture, Publication 9, Ottawa, ON, Canada. Stadelman, W. J., and C. F. Meinert, 1977. Some factors affecting meat yield from young ducks. Poultry Sci. 56:1145-1147. 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. Treat, D. W., and T. L. Goodwin, 1973. Effects of sex, size and time of cutting on processing yields and tenderness of broilers. Poultry Sci. 52: 1338-1353. Winter, A. R., and P. Clements, 1957. Cooked edible meat in ready-to-cook poultry. J. Am. Dietet. Assoc. 33:800-802. Downloaded from http://ps.oxfordjournals.org/ at New York University on May 30, 2015
ABSTRACT Twenty-eight live Pekin ducklings and 28 broiler chickens were obtained at 49 days of age from commercial processing facilities for each of two trials to determine processing yields and breast meat tenderness. Birds were withdrawn from feed for 8 h and then processed. Breast halves, without skin, were removed from four birds of each species at .25, .5,1,2,4,6, and 24 h postmortem. One side of each breast was cooked immediately after deboning (0-h aging) and the other half held 24 h at 4 C before cooking (24-h aging). Tenderness of the cooked breast meat was evaluated by Allo-Kramer shear. Duckling live, dry shell without giblets (WOG), and breast weights were significantly greater (P<.01) than chicken weights (3,410,2,143, and 319 g versus 2,780,1,915, and 295 g, respectively). Dry shell WOG, breast, and cooked breast yields were significantly lower for duckling than chicken (62.9,14.8, and 60.4% versus 68.8, 15.4, and 67.8%, respectively). Allo-Kramer shear values for duckling decreased (P<.01) from .25 to 24 h post-mortem for both the 0-h aged samples (from 13.2 to 9.1 kg shear/g sample) and the 24-h aged samples (from 14.0 to 7.2 kg shear/g sample), and chicken shear values decreased from 19.6 to 4.2 and 19.1 to 4.1 kg shear/g sample, respectively, for the 0-h and 24-h aged samples. There was a significant difference in duckling and chicken processing yields and breast meat tenderness as affected by deboning and aging times. (Key words: duckling, chicken, processing yields, breast meat tenderness, aging) 1992 Poultry Science 71:197-202
INTRODUCTION Pekin duckling is a commercially important poultry species, ranking third in per capita consumption in the United States after chicken and turkey (Heffernan, 1977). Both ducklings and broiler chickens are grown commercially under similar conditions to approximately the same age and weight; however, little information is
To whom correspondence should be addressed. Present address: OK Foods, Inc., P.O. Box 1787, Fort Smith, AR 72902. 2
available on either processing yields or the effect of aging and deboning time on meat tenderness for duckling. Snyder and Orr (1964), Stadelman and Meinert (1977), and Sheldon and Tarver (1987) have reported processing weights and yields for Pekin ducklings, as have Brahma et al. (1985) for Indian Runner ducks. No information on the effect of aging or deboning on tenderness was found. Information on chicken processing yields is readily available (e.g., Moran and Orr, 1970; Chen et al, 1983, 1987; Orr et al, 1984), as is the effect of aging and of deboning time on tenderness (Dodge and Stadelman, 1959; Goodwin,
197
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 30, 2015
(Received for publication April 5, 1991)
198
SMITH ET AL.
1984; Stewart et al.r 1984; Dawson et at, 1987). The purpose of the present study was to compare duckling and chicken for both 1) processing weights and yields; and 2) the effect of deboning and aging times on breast tenderness.
MATERIALS AND METHODS
^ s t r o n Corporation, Canton, MA 02021.
RESULTS AND DISCUSSION Processing Yields Average processing weights and the calculated yields for both duckling and chicken are presented in Table 1. Live, dry shell WOG, and raw breast weights were significantly greater (P<.01) for duckling than for chicken. Cooked breast weight of
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 30, 2015
Twenty-eight commercially reared Pekin ducklings and 28 broiler chickens were obtained at 49 days of age, for each of two trials. Birds were housed for approximately 1 additional wk in pens with free access to feed and water to allow recovery from commercial harvesting and transport variations. Ducks were processed at an average age of 56 days and chickens at an average of 55 days. Feed was removed from the birds 8 h prior to cooping and transport of the animals to a nearby pilot processing facility. Birds were stunned at 100 V alternating current (AC) for 5 s, killed by conventional neck cut, bled for 2 min, scalded at 60 C for 2 min, and picked in a rotary-drum picker for 30 s. Carcasses were eviscerated, and inedible and edible viscera, shanks, neck, head, and fat pads were removed and discarded. Carcasses were chilled using paddle-agitated chillers in a two-step process; first, for 15 min in water maintained at 13 C with ice, then for 30 min at 1 C in an ice and water mixture. Carcasses were then held covered in a cold room at 4 C prior to deboning and cooking. Weights were recorded prior to slaughter (live weight) and after evisceration but prior to chilling [dry shell without giblets (WOG)]. Dry shell WOG weight as a percentage of live weight was used to calculate dry shell WOG yield. Breast halves (Pectoralis major muscles only) were removed from each carcass at the following times post-mortem: .25 (after evisceration), .5 (after first chilling step), 1 (after complete chilling), 2, 4, 6, and 24 h. One side of each breast was cooked immediately after deboning (0-h aging); the other side was placed in a plastic bag and held at 4 C until 24 h post-mortem
before cooking (24-h aging). Breast halves were cooked in covered pans in a rotary oven for 45 min at 177 C, cooled at room temperature for 30 min, and drained. Breast weights were recorded after removal from the carcass (raw weight) and after cooking and draining (cooked weight). Raw breast weight as a percentage of dry shell WOG weight was used to calculate breast yield, and cooked breast weight as a percentage of raw breast weight was used to calculate cooked yield. A 2.54-cm diameter core was removed from the cranial area of each breast half, weighed, and evaluated for tenderness at room temperature using the Allo-Kramer shear cell mounted on an Instron Universal Testing Machine, 3 according to procedures described by Smith et al. (1988). Cores were placed with surface fibers perpendicular to the descending blades and peak load values were recorded. Processing data were analyzed using ANOVA (SAS Institute, 1985). Species were compared using residual error as the test statistic because the species by trial interaction was not significant. For the meat tenderness trials, the experimental model tested sources of variation due to trial, species, aging time, and post-mortem deboning time, i n a 2 x 2 x 2 x 7 arrangement of treatments with four breast halves per treatment cell (n = 224). Data were subjected to ANOVA. Means were separated using Duncan's multiple range test. Data are presented b y species for weights and yields, as no significant trial by species interaction was noted. Shear values were analyzed by species and aging time due to a significant aging time by post-mortem deboning time interaction, with the residual mean square error used as the test statistic.
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TABLE 1. Comparison of processing weights and yields obtained from Fekin ducklings and broiler chickens (for each mean, n = 56)1
Weight parameters
Processing weights Duckling Chicken
Live Dry shell WOG Raw breast Cooked breast
3,410^ 2,143A 319A 193A
(g) 2,780B 1,915B 295B 200^
Processing yields Duckling Chicken
(%) 62.9B 14.8B 60.4B
68.8* 15.4^ 67.8^
duckling was not significantly different from chicken. Dry shell WOG, raw breast, and cooked breast yields were significantly lower for duckling than for chicken. Sheldon and Tarver (1987) reported that, for the heaviest group of ducklings evaluated, ready-to-cook (RTC) WOG-carcass weights ranged from 2,072 to 2,236 g, raw breast weights from 245 to 343 g, and cooked breast weights from 141 to 168 g, depending on the brand of duckling tested. Duckling breast meat yield (as a percentage of RTC WOG) was 11.8 to 15.4% and cooked yield was 51.4 to 53.7%, depending on the brand tested in the heaviest group of carcasses as reported by Sheldon and Tarver (1987). Breast meat yield, as a percentage of carcass WOG, was 12.6% for 49-day-old duckling (Stadelman a n d Meinert, 1977). Many researchers have reported on broiler chicken processing weights and yields (Moran and Orr, 1970; Treat and Goodwin, 1973; Orr et ah, 1984; Chen et at., 1987). Results presented in Table 1 for the broiler chicken do not differ greatly from the results presented in these previous reports. The results indicate that at similar commercial processing ages, the duckling has larger absolute body weight, dry shell WOG, and raw breast weight, but lower dry shell WOG, breast, and cooked breast yields than the chicken. The lower dry shell yield for the duckling is apparently d u e to this animal having a greater percentage of blood, feathers, neck, head, shanks, viscera, and fat pad in comparison with the broiler chicken. Snyder and Orr (1964) found
average head and giblet weight, as a percentage of live weight, was lower for broiler chickens (2.7 and 4.6%, respectively) than for ducklings (4.2 and 5.6%, respectively). Winter and Clements (1957) observed lower neck weight (as a percentage of RTC weight) for broiler chickens (3.8%) than for ducklings (5.1%). Brahma et al. (1985) reported Indian Runner ducks had a higher percentage of blood, feather, and head in comparison with White Leghorn hens of similar live weight. The lower breast meat yield for the duckling when compared with the broiler chicken may be due to less selection pressure for body weight and breast conformation for the commercial duckling. Lower cooked breast yield for the duckling may be due to a difference in muscle composition (higher fat content) as compared with the chicken, allowing for greater loss during cooking.
Breast Meat Tenderness Duckling breast meat tenderness as determined at the post-mortem deboning times of .25, .5,1,2,4,6, and 24 h after aging either 0 or 24 h is reported in Table 2. Shear values for the 0-h aged meat did not differ significantly (P<.01) from the .25 through the 6 h times (12.8 k g / g average), but the shear value at 24 h (9.1 kg/g) was significantly lower than the earlier shear values. Shear values for the meat aged 24 h before cooking decreased at a faster rate than the 0-h aged samples. Shear values decreased by approximately 50% between .25 and 24 h for the 24-h aged treatment.
Downloaded from http://ps.oxfordjournals.org/ at New York University on May 30, 2015
• ^ ^ e a n s in the same row within either processing weights or yields with no common superscripts are significantly different (P<.01). ^Yield of dry shell without giblets (WOG) calculated on the basis of live weight; yield of raw breast meat calculated on the basis of dry shell WOG weight; yield of cooked breast meat calculated on the basis of raw breast meat weight.
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TABLE 2. Allo-Kramer shear values (kilograms shear per gram of meat) of Fekin duckling and broiler chicken breast meat deboned at .25, .5, 1, 2, 4, 6, and 24 h post-mortem and then cooked either immediately after deboning (0-h aging) or 24 h after deboning (for each mean, n = 8) Duckling aging period (h)
Post-mortem deboning time
A E
24
24 (kg shear/g meat) 13.2 A 14.0 A 132A 13.0* 11.6 A 11.8 A 9.1 B
14.0^ 13.2"AB 105 1;BC 9.4"CD 9 5 '|CD 9.6 C D 7.2 D
19.6^ 20.9* 17.1AB 14.1BC 8.4'DE 10.4'CD 4.2 H
19.1' 17.5",AB 1 3 5BC 10.1 C 8.9C 9.4C 4.1 E
Means in the same column with no common superscripts are significantly different (P<.01).
Shear values are also presented in Table 2 for broiler chicken breast meat deboned at .25, . 5 , 1 , 2, 4, 6, or 24 h post-mortem then aged either 0 or 24 h. Breast meat shear values for the 0-h aged samples decreased significantly (P<.01), almost 80% from .25 h (19.6 k g / g ) to 24 h (4.2 k g / g ) . The 24-h aged breast meat shear values decreased in a similar manner, from 19.1 k g / g (.25 h) to 4.1 k g / g (24 h). Previous researchers have described the effect of post-mortem aging on the tenderization of chicken meat. Goodwin (1984) stated factors that could affect broiler meat tenderness included chilling, aging, and prerigor cutting of the muscle, and recommended aging the carcass 8 to 16 h before cutting into parts to avoid toughness. Broiler meat aged 0, 2, 4, 6, and 8 h postmortem showed an increase in tenderness as aging time increased (Dodge and Stadelman, 1959). Dawson et al. (1987) deboned broiler breast meat over several postmortem times, from .08 to 24 h, and shear values decreased from 14.1 to 4.1 kg shear/ g sample. Stewart et al. (1984) found broiler breast meat aged from 0 to 4 h prior to deboning had a significant decrease in shear values, from 10.3 to 5.0 kg shear/g sample. Allo-Kramer shear values reported to be the upper limit of acceptable tenderness for chicken meat (when correlated with sensory evaluation) are 8.0 (Simpson and Goodwin, 1974) or 8.8 (Lyon and Lyon, 1990) kg shear/g sample. Chicken breast
meat evaluated in the present study would require 4 h of aging to fall within these limits. An upper limit on the objective measure of acceptable tenderness for duckling breast meat has not been established. Meat tenderness as affected by deboning time is illustrated by plotting duckling and chicken shear values against the natural log function of deboning time (Figure 1). The 0-h and 24-h aging time lines were averaged together to represent the overall effect of post-mortem aging on both species for comparative purposes. The log e function lines represent the highest coefficient of regression when compared with linear or quadratic functions. Duckling shear values decreased slightly as deboning time increased, from approximately 12 to 9 k g / g (a slowly decreasing slope), for an overall difference of approximately 3 k g / g . Chicken shear values decreased at an accelerated rate, from approximately 18 to 4 k g / g , for an overall difference of 14 k g / g . The different patterns of breast meat tenderness for deboning at selected postmortem times during aging between duckling and chicken must be due to the differing fiber types of the breast muscles from each species, as other possible variables such as age, weight, and muscle function were constant. Duckling breast muscle is darker than the predominately white-fibered chicken breast muscle d u e to a higher content of red fibers. Beecher et al. (1965a,b) found that porcine muscles differing with respect to fiber-type composition
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(h) .25 .5 1 2 4 6 24
Chicken aging period (h)
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due to the different post-mortem metabolism associated with differences in muscle fiber composition; and secondly, the residual toughness for duckling (after 24 h) when compared with chicken is d u e to the presence of greater amounts of connective tissue associated with the presence of smaller, more numerous red fibers per unit of muscle volume or cross-sectional area. ACKNOWLEDGMENT
REFERENCES
Postmortem deboning time (h) FIGURE 1. Plot of the loge of duckling and chicken shear values (kilograms shear per gram of meat) with the post-mortem deboning time (hours). Chicken shear value = -3.73 (logg post-mortem deboning time) + 15.50, r 2 = .75; Duckling shear value = -.79 (loge postmortem deboning time) + 11.86, r 2 = .19.
(red versus white) responded differently in terms of glycolytic rate and contraction state during post-mortem aging. Kiessling (1977) reported metabolic differences between red (goose Pectoralis) and white (chicken Pectoralis) post-mortem muscle. The differences between duckling and chicken final (24-h) shear values (9 k g / g versus 4 k g / g , respectively) could be due to differences in the contents of stromal protein. Duckling breast muscle may contain a greater total number of fibers in a given volume of muscle, because red fibers are smaller in diameter than white fibers. The greater number of total fibers would provide a higher content of endomysial collagen. The difference in the pattern of meat tenderness during aging between duckling and chicken could thus be explained as a two-step process: first, the early tenderness but slower tenderization rate for the duckling, when compared with the chicken, is
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This study was supported in part by state and Hatch funds allocated to the Georgia Agricultural Experiment Station.
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