Broiler performance and the effects of carcass weight, broiler sex, and postchill carcass aging duration on breast fillet quality characteristics

Transcription

1 2010 Poultry Science Association, Inc. Broiler performance and the effects of carcass weight, broiler sex, and postchill carcass aging duration on breast fillet quality characteristics A. Y. Abdullah 1 and S. K. Matarneh Department of Animal Production, Faculty of Agriculture, Jordan University of Science and Technology, Irbid 22110, Jordan Primary Audience: Consumers, Plant Managers, Researchers, Scientists SUMMARY The influence of carcass weight, bird sex, and carcass aging time on meat quality traits of pectoralis major muscles was studied in broiler birds. A total of 800 birds were used. After processing, carcasses were graded into 3 categories: 1,500 to 1,600 g, 1,600 to 1,700 g, and greater than 1,700 g. Forty-two carcasses from broilers of each sex were randomly selected from each carcass weight category. Seven carcasses of broilers from each sex within the same carcass weight category were aged for 0, 2, 4, 6, 8, and 24 h postchilling. The ADG and FCR increased (P < 0.001) with increasing age. Breast muscle temperature was higher (P < 0.001) for heavier carcasses, whereas bird sex affected (P < 0.05) the carcass temperature at 8 and 24 h postchilling. Water-holding capacity, color, and chemical composition were not affected (P > 0.05) by any of the factors. Cooking loss was affected only by bird sex. Lighter carcasses had a higher (P < 0.001) thawing loss percentage, with breast muscle from males having a higher (P < 0.01) thawing loss percentage than that from females. Thawing loss percentage decreased significantly (P < 0.001) with an increase in aging time. Higher (P < 0.001) shear force values were recorded in breast muscle from heavier carcasses, with breast muscle from females having higher (P < 0.05) shear force values than that from males. Shear force values were higher (P < 0.001) for breast fillets aged for 0 and 2 h. However, a major improvement in tenderness resulted after 4 h of aging, with tenderness being comparable among carcasses of all weights. Carcass weight, bird sex, and postchilling carcass aging duration are critical to breast meat quality characteristics. Key words: broiler breast fillet, carcass weight, bird sex, aging time, meat quality 2010 J. Appl. Poult. Res. 19 :46 58 doi: /japr DESCRIPTION OF PROBLEM The self-sufficiency of local red meat (beef and mutton) production in Jordan is approximately 28%, whereas the self-sufficiency of the local broiler meat (white meat) production is approximately 96% [1]. However, because of price differences when purchasing broiler chicken meat (white meat), compared with red meat, and differences in their nutritive value and carcass 1 Corresponding author: abdullah@just.edu.jo

2 Abdullah and Matarneh: CARCASS WEIGHT, SEX, AGING 47 composition, the demand for white meat has increased dramatically over the past 2 decades. This increase has also been associated with a continuous shift in the market from whole birds to further processed products. Therefore, the demand for high-quality parts and further processed convenience foods has driven the poultry industry to change its marketing practices. Today, with the vast majority of poultry being marketed in this manner (accompanied by an increase in meat quality problems associated with toughness, color, and water-holding properties [2]), yield of high-value items such as breasts and boneless fillets and the carcass composition and processing quality of poultry meat have become critical for both the processor and the consumer. Several authors [2 4] have indicated that factors such as bird strain, BW or carcass weight, nutrition, sex, age, and environmental conditions influence the yield of broiler parts, the carcass composition, and the processing quality of poultry meat. Poultry meat tenderness and other meat quality characteristics can be improved by aging (maturation), a procedure in which intact carcasses are stored for several hours at a refrigerated temperature (<4 C) before deboning to allow the depletion of adenosine triphosphate and the development of rigor mortis [5]. A 4-h duration between chilling and boning has been reported as a critical period after which deboning does not cause toughening [6 10]. Dawson et al. [11] found that broiler breast fillets processed earlier than 3.33 h postmortem had shear values that would be judged by most consumers as tough, whereas Lyon et al. [6] found that as postchill carcass aging time increased from 4 to 6 h before carcasses were cut up and deboned, the percentage of breast fillets (pectoralis major muscle) rated as having acceptable tenderness increased because meat tenderness is greatly affected by the enzymatic processes during aging. The objectives of the present study were to evaluate broiler performance and the effect of carcass weight on male and female broiler breast fillet tenderness and other meat quality characteristics. Another objective was to study the effect of controlled postchilling aging before deboning on the tenderness of cooked broiler breast meat and other meat quality characteristics of raw fillets during the aging process. MATERIALS AND METHODS Birds and Plane of Nutrition A total of 800 one-day-old mixed-sex Hubbard broiler birds were obtained from commercially hatched eggs [12] and were used to examine their growth performance and the effects of changes in carcass weight, bird sex, and postchilling carcass aging time on meat quality. The birds were reared and grown to market age under standard commercial conditions. All procedures and methods were approved by the Institutional Animal Care and Use Committee at the Jordan University of Science and Technology. At d 1 of age, birds were randomly allocated to 32 floor pens ( m) with wood shavings (25 birds per pen). The floor pens were located in an open-sided house, and each pen was equipped with an automatic bell drinker and 1 tube feeder. The pen was considered the experimental unit for performance measurements. The diets offered to all birds were formulated to meet bird requirements as recommended by the NRC [13]. Rations were corn- and soybean meal-based diets consisting of a starter (1 to 21 d; 22.8% CP and 3,150 kcal of ME) and a finisher (21 to 41 d; 20.7% CP and 3,220 kcal of ME) diet. The diet ingredients were 58% yellow corn, 28% soybean meal, 10% broiler concentrate (46% CP and 2,350 kcal of ME/kg of diet), 3% vegetable oil, 0.3% dicalcium phosphate, 0.5% limestone, 0.1% methionine, and 0.1 lysine for the starter diet; and 62.5% yellow corn, 23% soybean meal, 10% broiler concentrate, 3.5% vegetable oil, 0.3% dicalcium phosphate, 0.5% limestone, 0.1% methionine, and 0.1 lysine for the finisher diet. Birds were provided free access to feed and water, with constant illumination of 23 h of light and 1 h of dark per day during the entire growing period. Feed consumption and mortality were recorded daily and BW was recorded at 0, 7, 14, 21, 28, 35, and 41 d of age, by pen (average BW of all birds), to determine the FCR and ADG. Experiment and Procedures All birds were slaughtered and processed at 42 d of age. On the day of processing, all birds were transported 60 km to the processing plant. Birds were electrically stunned head to shank by

3 48 using a brine (1% sodium chloride) stunner with a fixed voltage (50 V, alternating current) for 5 s, with a variable current of approximately 33 ma. After stunning, birds were immediately exsanguinated by manually severing both the carotid arteries and at least 1 jugular vein with a knife, and were allowed to bleed for 120 s. After bleeding, birds were scalded at 59 C for 180 s in a rotary scalder followed by carcass defeathering, and the process was completed by removing the heads. In the evisceration room, the vent was cut with a plunging cylindrical knife and an eviscerator pulled the viscera from the cavity. The slaughter process was completed with several internal and external washings of the carcasses. The whole process was completed within 20 min from the hanging of live birds. The eviscerated carcasses were tumblechilled at 4 C for 20 min in chlorine water. After the tumble-chilling process, all carcasses entered the air-chilling room at 4 C for 20 min, and the carcasses were then graded into 3 categories: group 1 was 1,500 to 1,600 g, group 2 was 1,600 to 1,700 g, and group 3 was greater than 1,700 g. Forty-two carcasses from birds of each sex were randomly selected from each carcass weight category. The sex of each bird was determined by a visual examination of gonads during evisceration. Seven carcasses from birds of each sex within the same carcass weight category were aged for 0, 2, 4, 6, 8, and 24 h postchilling in a 4 to 7 C chiller before cutting them into forequarters and leg quarters as described by Hudspeth et al. [14]. Forequarters were cut into wings and breasts with a knife by severing the wings from the forequarter at the proximal ends of the humeri. Immediately after cutting the carcasses, the internal muscle ph and temperature were measured directly at 0, 2, 4, 6, 8, and 24 h postchilling through an incision made by a knife in the right pectoralis major muscle by means of a portable ph meter [15] and a digital thermometer [16]. The whole breast from each carcass was individually weighed and placed on a labeled, sealed polyethylene plate, wrapped in wax paper, and placed in a 32 C freezer. All samples were transported to the meat quality laboratory at the Animal Production Department, where meat quality measurements were performed. Meat Quality Measurements JAPR: Research Report Of each group of 7 breasts, 5 breasts were used for measurements of meat quality characteristics and 2 breasts were used for chemical analysis. While the frozen muscles were still on their plates, they were thawed overnight in a refrigerator at 4 C. The muscles were then removed from the plates and manually deboned (left and right pectoralis major muscles without skin). Breast thawing loss was recorded by the weight of the breast before and after thawing. Both muscles were removed by severing the humeral-scapular joint and pulling it downward to strip the meat from the breast. The deboning process was performed by the same person, and care was taken to ensure that all fillets were removed in the same manner so that the meat quality variables would not be affected by the deboning procedure. For meat quality analysis, 1 pectoralis muscle was chosen randomly and used for measurements of cooking loss and shear force, whereas the other was used for color, ph, and water-holding capacity measurements. After breasts were deboned, 1 of the pectoralis muscles was weighed (initial weight) and then placed in a labeled polythene bag. The bags were placed in a thermostatically controlled water bath and cooked for 25 min at 85 C to achieve a maximum internal temperature of 80 C. After cooking, the bags were cooled at room temperature (25 C) before opening to drain the liquid, and the cooked samples were then dried with a paper towel to remove excess surface moisture and reweighed. Cooking loss was reported as the weight lost during cooking divided by the fresh sample weight and was expressed as a percentage. Within 3 h of cooking, the dried samples from each pectoralis major muscle were cut to obtain 6 cores ( mm) of similar sizes, parallel to a line beginning at the humoral insertion and ending at the point adjacent to the keel, including the complete depth of each cooked muscle sample. Each core was sheared perpendicularly to the longitudinal orientation of the muscle fiber, using a Warner-Bratzler shear blade with the triangular slot-cutting edge mounted on a Salter model 235 instrument [17] to determine the peak force (in newtons) when shearing the

4 Abdullah and Matarneh: CARCASS WEIGHT, SEX, AGING 49 samples. Shear force was determined as the average of the maximum force of the 6 replicates from each pectoralis major muscle sample. Thawed tissue samples collected from the second aged pectoralis major muscles at 0, 2, 4, 6, 8 or 24 h were used for ph determination. The ph values were determined in duplicate samples using the iodoacetate method as described by Jeacocke [18] and Sams and Janky [19]. Raw muscles samples of 1 to 1.5 g were added to plastic test tubes containing 10 ml of neutralized 5 mm iodoacetate reagent and 150 mm potassium chloride and were homogenized with a homogenizer [20]. Before recording the ph values of the solutions on a ph meter [15], the electrode was rinsed with distilled water and dried with soft tissue paper. Instrumental color measurements of raw pectoralis muscles were taken at 24 h postthawing with a colorimeter [21], which was calibrated throughout the study by using a standard white ceramic reference (Commission Internationale de l Éclairage L* = 97.91, a* = 0.68, b* = 2.45). Samples were placed on a tray, covered with wax paper (to avoid surface drying), and left in the refrigerator for approximately 2 h to allow enough contact with atmospheric oxygen to turn them to a normal color. Random readings were taken at 3 different locations on the muscle surface that had been adjacent to the skin and in an area of each sample free of any noticeable color defects, such as bruises or broken blood vessels. The readings from the 3 locations were averaged and the color for each sample was expressed in terms of Commission Internationale de l Éclairage brightness (L*), redness (a*), and yellowness (b*). The water-binding properties of the pectoralis major muscles were estimated by measuring the amount of water released from the muscle protein by the application of force (expressible juice) and by measuring the ability of muscle protein to retain water present in excess and under the influence of an external force (waterholding capacity). The water-holding capacity was measured using the method described by Grau and Hamm [22] and modified by Sañudo et al. [23], by using samples of approximately 5 g of raw meat (initial weight). Each sample was cut into small pieces and covered with 2 filter papers [24] and 2 thin plates of quartz material, and then pressed with a weight of 2,500 g for 5 min. The meat samples were then removed from the filter paper and their weights were recorded (final weight). Water-holding capacity was reported as the weight lost during sample pressing divided by the initial sample weight and was expressed as a percentage. Proximate analysis was performed on the raw breast meat according to AOAC [25] for DM (100 C for 24 h; method ), ash (550 C for 8 h; method 942), CP (Kjeldahl procedure; method ), and total lipid (ether extraction procedure; Soxhlet procedure, method ). Statistical Analysis The data were analyzed as a factorial design using the statistical analysis and GLM procedure of SAS [26]. Data were analyzed by ANOVA, with broiler carcass weight, bird sex, and postchilling carcass aging duration as the main effects. The least squares means were calculated for all variables in the study, and the related LSD were calculated to determine significant differences. Differences were considered significant at P The data were analyzed according to the following statistical model: Y ijk1 = µ + W i + S j + A k + (WS) ij + (WA) ik + (SA) jk + (WSA) ijk + E ijk1, where µ is the population mean; W i is the effect of carcass weight (i = 1 to 3); S j is the effect of sex (j = 1 to 2); A k is the effect of postchilling aging time (k = 1 to 6); (WS) ij, (WA) ik, (SA) jk, and (WSA) ijk are the interactions of the main effects; and E ijk1 is the overall error term. RESULTS AND DISCUSSION Growth Performance The results related to BW gain, feed intake, ADG, and FCR during the rearing period (1 to 41 d of age) are shown in Table 1. Body weight increased rapidly until 35 d of age, at which time the maximum growth rate (81 g/d) was attained, but beyond this age, growth rate declined. Rjoup [27] also found that the growth rate of Hubbard classic broiler birds declined during the sixth week of age. However, Goliomytis et al. [28]

5 50 and Scheuermann et al. [29] both reported that the growth rate increased progressively up to 6 wk of age and then decreased. This result was expected because it was associated with the reduction in feed intake from 35 to 41 d of age. Feed intake increased (P < 0.001) progressively from 1 to 35 d of age, but after 35 d of age, feed intake declined. This reduction was not expected, but feed intake may have been inhibited by the high environmental temperature during the last few days of the experiment. The FCR increased (P < 0.001) with age; the best FCR was obtained during the first 2 wk of age. After this period, FCR increased significantly (P < 0.001) up to 35 d of age. Similar results have been found by many researchers [30 33], in which growth performance decreased with increasing BW and age. The demand of birds for maintenance increased with increasing BW, which decreased the energy available for growth. Postchilling Carcass ph and Temperature JAPR: Research Report The mean ph and temperature measurements of broiler pectoralis major muscles at 0, 2, 4, 6, 8, and 24 h, as affected by carcass weight and bird sex, are shown in Table 2. There were no significant differences among carcass weight categories in pectoralis major ph at 0, 4, 8, and 24 h. However, at 2 h postchilling, ph was low (P < 0.05) for carcass weights between 1,600 and 1,700 g. At 6 h postchilling, ph of carcass weights greater than 1,700 g was the lowest (P < 0.01). This variation might be associated with individual differences in the glycogen stores in the muscle, which reflect the rate of completion of rigor mortis and the range muscle ph extends, or may have resulted from differences in the glycolytic potential among these carcasses. Ngoka et al. [34] and Mehaffey et al. [35] both reported that BW did not affect the initial ph measured immediately after slaughter or the final ph measured after chilling carcasses overnight. However, other researchers have reported that BW can affect meat ph [36, 37]. This could be due to differences in bird strain, bird age, and holding time before slaughter, which can influence the ph of meat. No statistically significant differences in pectoralis major ph were due to bird sex at any postchilling time period (0, 2, 4, 6, 8, and 24 h). Similar results were reported by Ngoka et al. [34] and Wheeler et al. [38], who reported that bird sex did not significantly affect initial or final ph. On the other hand, Yates et al. [39] reported that breast muscle from male birds had a higher ph value than that from female birds. The temperature of pectoralis major muscles was significantly different (P < 0.001) among the different carcass weights within different postchilling times. The heavier carcasses (1,600 to 1,700 g and >1,700 g) had significantly (P < 0.001) higher breast temperatures than the lighter carcasses at 0, 2, 6, 8, and 24 h postchilling, but not at 4 h of aging. These differences in carcass temperatures were expected because the heavier carcasses always had thicker muscles, which led to an increase in the time needed to reduce the internal musculature temperature. Rathgeber et al. [40] reported that large-sized breast muscles could impede the chilling process. Berri et al. [37] found that breast muscle temperatures at 0.25 and 1 h postmortem were significantly higher in the line selected for high breast meat yield than in the corresponding control line. Bird sex did not significantly affect postchilling carcass temperatures at 0, 2, 4, and 6 Table 1. Least squares means for BW gain, feed intake, ADG, and FCR measured weekly as affected by age of broiler chickens Age (d) Item P-value BW gain (g/bird) 116 ± 1 e 293 ± 4 d 420 ± 5 c 513 ± 10 b 568 ± 17 a 422 ± 11 c *** Feed intake (g/bird) 144 ± 1.2 e 376 ± 1.2 d 685 ± 1.2 c 951 ± 1.2 b 1264 ± 1.2 a 955 ± 1.2 b *** ADG (g/bird per day) 17 ± 1.3 e 42 ± 1.3 d 60 ± 1.3 c 73 ± 1.3 b 81 ± 1.3 a 70 ± 1.3 b *** FCR (intake/gain) 1.2 ± 0.03 d 1.3 ± 0.03 d 1.6 ± 0.03 c 1.9 ± 0.03 b 2.2 ± 0.03 a 2.3 ± 0.03 a *** a e Means within the same row with different superscripts differ. ***P <

6 Abdullah and Matarneh: CARCASS WEIGHT, SEX, AGING 51 Table 2. Least squares means for broiler breast postchill ph and temperature as affected by carcass weight and bird sex Time postchilling (h) Item n ph Carcass weight (g) 1,500 to 1, a b ,600 to 1, b a >1, ab b SE P-value NS * NS ** NS NS Sex Male Female SE P-value NS NS NS NS NS NS Temperature ( C) Carcass weight (g) 1,500 to 1, b 10.9 b 10.2 c 9.6 b 10.2 b 7.0 b 1,600 to 1, a 11.9 a 10.8 b 10.6 a 11.7 a 7.7 a >1, a 11.7 a 11.2 a 10.8 a 11.6 a 8.0 a SE P-value *** *** *** *** *** *** Sex Male a 7.3 b Female b 7.8 a SE P-value NS NS NS NS * *** Interaction (carcass weight bird sex) ph NS NS NS NS *** NS Temperature NS NS NS NS NS NS a c Means within the same column within the same variable with different superscripts differ according to the indicated level of significance. *P < 0.05; **P < 0.01; ***P < h. This result was expected because the weights of male and female carcasses were comparable for all weight categories. At 8 h postchilling, carcasses from male birds exhibited higher temperatures than those from female birds, whereas at 24 h postchilling, carcasses from male birds had lower temperatures than those from female birds. We can offer no explanation for these differences. No carcass weight bird sex interaction was observed for internal breast muscle temperature in any of the postchilling aging periods. A significant carcass weight bird sex interaction was recorded at 8 h postchilling (Figure 1A), at which time lighter carcasses from female birds had higher breast muscle ph and heavier carcasses from male birds had higher ph. However, at 0, 2, 4, 6, and 24 h, there was no carcass weight bird sex interaction for breast muscle ph. Postthawing Breast Weights and Loss Percentage Initial and postthawing broiler breast weights and thawing loss percentages of broilers are presented in Table 3. Breast initial and thawing weights increased (P < 0.001) as carcass weight increased. However, neither characteristic was affected (P > 0.05) by bird sex or aging time. There were no significant differences between male and female birds. This could have been due to the absence of large differences in carcass weights. Thawing loss percentage was significantly affected by carcass weight (P < 0.001), bird sex (P < 0.01), and postchilling aging time (P < 0.001). The lighter carcasses (1,500 to 1,600 g) had greater thawing loss percentages than the heavier carcasses (1,600 to 1,700 g and >1,700 g). This could have been due to a greater denaturation of muscle protein in the lighter carcasses

7 52 compared with heavier ones. Ngoka and Froning [41] reported that thawing loss percentage was significantly higher in carcasses from lighter birds than in carcasses from heavier birds. The carcasses of male birds exhibited higher thawing loss values than those from female birds. This may have resulted from the excess amount of moisture picked up by carcasses from male birds because of differences in breast thickness or the space between muscle fibers, or for some other reason that was not investigated in this study. Aging time significantly (P < 0.001) affected thawing loss percentage. We observed that the carcasses aged for 0 h had the greatest thawing loss and those with a 6-h aging time had the least JAPR: Research Report thawing loss. The 6-, 8-, and 24-h aging periods showed no significant differences (P > 0.05) in thawing loss. This increase of thawing loss percentage from the carcasses aged up to 4 h was probably because the least amount of water was lost during aging. A significant (P < 0.05) carcass weight bird sex interaction was observed for breast thawing weight. Breast fillets from female birds had higher thawing weights, at less than 1,700 g, after which the thawing weights of breasts from male birds became greater than those from female birds (Figure 1B). Thawing loss percentage was significantly (P < 0.05) affected by the interaction between carcass weight and bird sex (Figure 1C), with breast fillets from Figure 1. Effect of breast muscle ph at 8 h postchilling (A), breast thawing weight (B) and thawing loss percentage (C) for male and female broilers in relation to different carcass weights. Also shown are the interactions of Warner- Bratzler shear force for breast fillets from carcasses of 3 different weights in relation to changes in aging time (D) and for breast fillets from male and female broilers in relation to changes in aging time.

8 Abdullah and Matarneh: CARCASS WEIGHT, SEX, AGING 53 male birds having greater thawing loss percentages than those from females for the lighter weight carcasses. A significant carcass weight aging time interaction was observed for thawing loss percentage (Table 3). Postthawing ph, Cooking Loss Percentage, Water-Holding Capacity, and Warner-Bratzler Shear Force Values Tenderness, cooking loss, water-holding capacity, and ph (after thawing) as affected by carcass weight, bird sex, and aging time are presented in Table 4. Warner-Bratzler shear force values were significantly affected (P < 0.001) by carcass weight. The means of shear force values for the carcass weight categories of 1,600 to 1,700 g and greater than 1,700 g were not statistically different from each other, but they both had significantly (P < 0.001) higher values than those for lighter carcasses (1,500 to 1,600 g). This increase in shear force values could be associated with an increasing amount of connective tissues in the meat of the heavier birds. Meat tenderness is affected by the amount and quality of connective tissue and by the contractile state of muscle fibers and bundles [42, 43]. The results of this study are in full agreement with the results reported by Cooper and Fletcher [44] and Poole et al. [45]. However, the shear force values obtained in the present study were lower than those reported by Lyon et al. [6], Northcutt et al. [7], Liu et al. [8], Lyon et al. [46], and Smith et al. [47]. This could have been due to the rapid growth of birds used in the present study. Dransfield and Sosnicki [48] suggested that selecting birds for a rapid growth rate results in more tender meat than that obtained from birds with a slow growth rate. In addition, this difference could be related to differences in bird age, bird size, bird strain, and fat content in the breast muscle. Male broilers produced meat with significantly (P < 0.05) lower shear forces than that Table 3. Least squares means for initial and postthawing broiler breast weights and thawing loss percentage as affected by carcass weight, bird sex, and aging time Item n Initial breast weight (g) Postthawing breast weight (g) Thawing loss (%) Carcass weight (g) 1,500 to 1, c c 4.72 a 1,600 to 1, b b 2.82 b >1, a a 2.96 b SE P-value *** *** *** Sex Male a Female b SE P-value NS NS ** Aging time (h) a b b c bc c SE P-value NS NS *** Interaction Carcass weight bird sex NS * * Carcass weight aging time NS NS * Bird sex aging time NS NS NS Carcass weight bird sex aging time NS NS NS a c Means within the same column within the same variable with different superscripts differ according to the indicated level of significance. *P < 0.05; **P < 0.01; ***P <

9 54 JAPR: Research Report Table 4. Least squares means for broiler breast ph (postthawing), cooking loss, water-holding capacity, and Warner-Bratzler shear force (WBSF) values as affected by carcass weight, bird sex, and aging time Item n ph Cooking loss (%) Water-holding capacity (%) WBSF (newtons) Carcass weight (g) 1,500 to 1, b 1,600 to 1, a >1, a SE P-value NS NS NS *** Sex Male a 26.7 b b Female b 27.8 a a SE P-value ** ** NS * Aging time (h) c a b b bc c ab d ab cd a cd SE P-value *** NS NS *** Interaction Carcass weight bird sex NS NS NS NS Carcass weight aging time NS NS NS * Bird sex aging time NS NS NS ** Carcass weight bird sex aging time NS ** NS NS a d Means within the same column within the same parameter with different superscripts differ according to the indicated level of significance. *P < 0.05; **P < 0.01; ***P < from female broilers, with Warner-Bratzler shear value means of 29.5 and 31.7 newtons for males and females, respectively (Table 4). Simpson and Goodwin [49] reported that shear values for male broilers were significantly lower than those for females when the meat was cooked in an autoclave for 20 min and held for 2 to 4 h at 2 C postchilling. Our results disagree with those of Lyon et al. [46] and Musa et al. [50], who reported that breast fillets from females had more tender meat than those from males. However, Northcutt et al. [7], Ngoka et al. [34], Poole et al. [45], and Lyon and Wilson [51] all reported that bird sex did not significantly affect breast fillet tenderness. The difference between our results and those reported in previous studies may have resulted from differences in the bird age, the muscle region, or the commercial strain used. The tenderness of breast fillets increased significantly (P < 0.001) with an increase in aging time (Table 4). There were gradual decreases in Warner-Bratzler values during the first 6 h. Moreover, aging up to 24 h did not bring about any significant change in tenderness. Breast fillets that were removed immediately after slaughter at 0 h postchill had the highest shear force values, whereas breast fillets aged for 6 h had the lowest shear force values (Table 4). Similar results were reported by Lyon et al. [6], Northcutt et al. [7], Liu et al. [8], Souza et al. [9], Lyon et al. [46], Smith et al. [47], and Huezo et al. [52]. Koohmaraie et al. [43] reported that meat tenderness is greatly affected by the enzymatic processes during aging; thus, the postmortem proteolysis process is responsible for most of the tenderization during aging. A significant (P < 0.05) carcass weight aging time interaction was observed for shear force values (Figure 1D). Shear force values were higher for heavier carcasses than for lighter carcasses at 0 and 2 h postchilling. However, after 4 h, shear force values became comparable between all carcass

10 Abdullah and Matarneh: CARCASS WEIGHT, SEX, AGING 55 weight categories. Figure 1E shows the shear force values as affected by the interaction of bird sex and aging time (P < 0.01). Breast fillets from female birds had greater shear force values at 0 and 2 h postchilling; however, shear force values became comparable for breast fillets from birds of both sexes from 4 to 24 h. Water-holding capacity percentage was not significantly affected (P > 0.05) by differences in carcass weight, bird sex, aging time, or their interactions (Table 4). Ngoka et al. [34] reported that the water-holding capacity of turkey breast muscles was not significantly affected by a change in BW from 5.42 and 9.87 kg. This lack of differences in water-holding capacity in the present study could be explained by there being no difference in muscle ph values among carcass weights or between sexes. Similar results were reported by Ngoka et al. [34] and Musa et al. [50], especially within the effect of sex. Aging time did not significantly affect (P > 0.05) water-holding capacity (Table 4). This result was probably due to the slow rate of ph decline and the high ultimate ph. The small change in ph might not have brought about any significant alteration in protein denaturation, which greatly affects the water-holding capacity of meat. Cooking loss percentage was not significantly affected (P > 0.05) by differences in carcass weight (Table 4). The normal trend reported is that heavier carcasses have less loss, mainly because the percentage of water in heavier carcasses decreases with increasing BW, whereas the percentage of fat increases with increasing BW. This leads to a decrease in the amount of water in carcasses, thus decreasing the percentage of cooking loss and increasing the ability to hold more water. Therefore, the increase in BW in our study was not large enough to alter breast muscle cooking loss because fat content in the breast was not significantly affected by the carcass weight. Aging time did not significantly affect the cooking loss percentage (Table 4). This result agrees with those reported by previous authors [8, 9, 35]. In contrast, other authors reported that the cooking loss percentage measured in pectoralis major muscle increased with an increase in aging time [7, 53]. Statistically significant differences (P < 0.001) in cooking loss percentage were attributable to bird sex (Table 4). Male broilers had less cooking loss than female broilers. Lyon et al. [54] reported that pectoralis major muscles from females exhibited higher cooking losses than those from males. This could have resulted from the excess amount of water loss during thawing of muscles from males compared with those from females (Table 3). A significant (P < 0.01) interaction was observed between carcass weight, bird sex, and aging time on breast fillet cooking loss percentage. The ph after thawing was not significantly affected by carcass weight, but it was affected by bird sex (P < 0.01) and aging time (P < 0.001), with male broilers having breast fillets with a higher ph than those from females and with ph values increasing as aging time increased. The effects of aging time on Warner-Bratzler shear force values of breast fillets from male and female broilers at 3 different carcass weights are presented in Table 5. Warner-Bratzler shear force values were significantly affected by aging time for both male and female broilers in the 3 different carcass weight categories. Breast fillet tenderness improved with aging time. The first 2 aging periods (0 and 2 h postchilling) had the highest shear force values. These values decreased significantly (P < 0.001) when the carcasses were aged from 4 to 24 h, but without a significant difference in shear force values from 4 to 24 h postchilling. Similar results were reported by Lyon et al. [6], Northcutt et al. [7], Liu et al. [8], and Souza et al. [9]. All these authors reported that the 4-h time between chilling and deboning is a critical period after which deboning does not cause toughening. Female broilers produced breast fillets with greater shear force values than those aged for 0 h from male broilers with carcass weights between 1,500 and 1,600 g and those aged 0 and 2 h from male broilers with carcasses weights between 1,600 and 1,700 g. Breast Color Measurements Pectoralis major muscle lightness (L*), redness (a*), yellowness (b*), chroma, and hue angle values were not significantly (P > 0.05) affected by carcass weight, bird sex, or postchilling aging time. Overall means of L*, a*, b*, chroma, and hue values were 53.6 ± 0.7, 2.0 ± 0.1, 14.3 ± 0.5, 14.9 ± 0.5, and 82.2 ± 0.4, respectively. These results are in agreement with those reported in previous studies [34, 35, 38, 55, 56].

11 56 JAPR: Research Report Table 5. Least squares means for broiler breast Warner-Bratzler shear force values (newtons) of males and females of 3 different carcass weights (1,500 to 1,600 g, 1,600 to 1,700 g, and >1,700 g) as affected by aging time 1,500 to 1,600 (n = 60) 1,600 to 1,700 (n = 60) >1,700 (n = 60) Aging time (h) Male Female Male Female Male Female a,x 51.0 a,y 41.0 a,x 60.0 a,y 55.0 a 56.0 a b 41.0 b 44.0 a,x 51.0 b,y 52.0 a 55.0 a c 20.0 c 26.0 b 26.0 c 25.0 b 22.0 b c 17.0 c 23.0 b 23.0 c 19.0 b 23.0 b c 23.0 c 24.0 b 24.0 c 22.0 b 21.0 b c 19.0 c 23.0 b 20.0 c 23.0 b 21.0 b SE a c Means within the same column with different superscripts differ significantly (P < 0.05). x,y Means within the same row and carcass weight with different superscripts differ significantly (P < 0.05). Meat color varies according to the concentration of pigments, the chemical state of pigments, and the way light is reflected off the meat. Nishida and Nishida [57] reported that, as a general rule, animal age plays a key role because myoglobin increases with age, shifting the meat color toward a darker and redder color. These results contrast with other results reported by Bianchi et al. [58] showing that heavier birds produced darker breast meat (lower L* value) than lighter birds. Mehaffey et al. [35], Huezo et al. [52], Qiao et al. [59], and Petracci and Fletcher [60] all reported that aging time had a significant effect on broiler breast meat color. The difference between our results and those from previous studies may be due to differences in bird age, the muscle region used, or the commercial strain or genetic background of the birds. A significant (P < 0.05) carcass weight aging time interaction was observed for breast muscle lightness, yellowness, and chroma and a significant (P < 0.05) 3-way interaction was observed for redness and hue. Chemical Composition of Broiler Breast Muscle Breast fillet chemical composition was not significantly affected (P > 0.05) by either carcass weight, bird sex, or their interaction. Overall means for moisture, CP, EE, and ash percentages were 75.0 ± 0.2, 22.5 ± 0.2, 0.87 ± 0.08, and 1.3 ± 0.1%, respectively. The normal trend reported is that heavier carcasses have more fat and lower percentages of CP and water. Therefore, the increase in BW in our study was not large enough to alter the chemical composition of breast muscle. Our chemical analysis values were comparable with results reported by Abeni and Bergoglio [55] and Qiao et al. [61]. CONCLUSIONS AND APPLICATIONS 1. Thawing loss and toughness decreased with increasing carcass weights, with males having breast muscle with greater thawing loss and lower toughness values compared with that from females. Aging reduced the thawing loss percentage without affecting the cooking loss. 2. Breast meat from lighter carcasses was more tender than that from heavier carcasses, with males having more tender meat than that from females. Aging improved the tenderness of breast meat from birds of both sexes at all carcass weights. However, a major improvement in tenderness resulted after 4 h of aging, with tenderness being comparable among all carcass weight groups. 3. As a result, carcass weight, bird sex, and postchilling carcass aging duration are critical to breast meat quality characteristics. 4. Four hours of aging is required before deboning to obtain more tender breast fillets. This is particularly important when carcasses are of different weights and are from birds of different sexes (as in the case of all commercial poultry production in Jordan). Such information is of importance to all poultry processing plants.

12 Abdullah and Matarneh: CARCASS WEIGHT, SEX, AGING 57 REFERENCES AND NOTES 1. Ministry of Agriculture The Annual Report of the Animal Production Department. Ministry of Agriculture, Amman, Jordan. self_2002_2007/self_2007.pdf Accessed April 21, Young, L. L., J. K. Northcutt, R. J. Buhr, C. E. Lyon, and G. O. Ware Effects of age, sex, and duration of post-mortem aging on percentage yield of parts from broiler chicken carcasses. Poult. Sci. 80: Peebles, E. D., S. M. Doyle, T. Pansky, P. D. Gerard, M. A. Latour, C. R. Boyle, and T. W. Smith Effects of breeder age and dietary fat on subsequent broiler performance. 2. Slaughter yield. Poult. Sci. 78: Le Bihan-Duval, E., C. Berri, E. Baeza, N. Millet, and C. Beaumont Estimation of the genetic parameters of meat characteristics and of their genetic correlations with growth and body composition in an experimental broiler line. Poult. Sci. 80: Sams, A. R Meat quality during processing. Poult. Sci. 78: Lyon, C. E., D. Hamm, and J. E. Thompson ph and tenderness of broiler breast meat deboned various time after chilling. Poult. Sci. 64: Northcutt, J. K., R. J. Buhr, L. L. Young, C. E. Lyon, and G. O. Ware Influence of age and postchill carcass aging duration on chicken breast fillet quality. Poult. Sci. 80: Liu, Y., B. G. Lyon, W. R. Windham, C. E. Lyon, and E. M. Savage Principal component analysis of physical, color, and sensory characteristics of chicken breasts deboned at two, four, six, and twenty-four hours post-mortem. Poult. Sci. 83: Souza, P. A., L. M. Kodawara, E. R. L. Pelicano, H. B. A. Souza, A. Oba, F. R. Leonal, E. A. Norkus, and T. M. A. Lima Effect of deboning time on the quality of broiler breast meat (pectoralis major). Braz. J. Poult. Sci. 7: Battula, V., M. W. Schilling, Y. Vizzier-Thaxton, J. M. Behrends, J. B. Williams, and T. B. Schmidt The effects of low-atmosphere stunning and deboning time on broiler breast meat quality. Poult. Sci. 87: Dawson, P. L., D. M. Janky, M. G. Dukes, L. D. Thompson, and S. A. Woodward Effect of postmortem boning time during stimulated commercial processing on the tenderness of broiler breast meat. Poult. Sci. 66: Aljazeera, Dhlail, Jordan. 13. NRC Nutrient Requirements of Poultry. 9th rev. ed. Natl. Acad. Press, Washington, DC. 14. Hudspeth, J. P., C. E. Lyon, B. G. Lyon, and A. J. Mercuri Weights of broiler parts as related to carcass weights and type of cut. J. Food Sci. 38: ph spear, large-screen, waterproof ph/temperature tester, double-injection model , Eurotech Instruments, Selangor Darul Ehsan, Malaysia. 16. Electro-term, model TM99A, Cooper Instrument Corporation, Middlefield, CT. 17. Warner-Bratzler meat shear, G-R Manufacturing Co., Manhattan, KS. 18. Jeacocke, R. E Continuous measurement of the ph of beef muscle in intact beef carcasses. J. Food Technol. 12: Sams, A. R., and D. M. Janky The influence of brine chilling on tenderness of hot boned, chill-boned, and age-boned broiler fillets. Poult. Sci. 65: UltraTurrax T8, IKA Labortechnik, Janke and Kunkal GmbH and Co., Staufen, Germany mm aperture U instrument, Cole-Parmer International, Accuracy Microsensors Inc., Pittsford, NY. 22. Grau, R., and R. Hamm A simple method for the determination of water binding in muscles. Naturwissennshaften 40: Sañudo, C., I. Sierra, M. Lopez, and F. Forcada La qualité de la viande ovion. Etude des differents facteurs qui la conditionnent. Commision C. E. Rapport EUR 11479: Filter papers, qualitative, 185 circles, fine crystalline retention, Whatman International Ltd., Maidstone, UK. 25. AOAC Official Methods of Analysis. 15th ed. Assoc. Offic. Anal. Chem., Gaithersburg, MD. 26. SAS Institute SAS/STAT Guide for Personal Computers. Version 8.2 Edition. SAS Inst. Inc., Cary, NC. 27. Rjoup, M Growth performance, carcass and meat quality characteristics of different commercial crosses of broiler chicken strains. MSc Thesis. Jordan University of Science and Technology, Irbid. 28. Goliomytis, M., E. Panopoulou, and E. Rogdakis Growth curves for body weight and major component parts, feed consumption, and mortality of male broiler chickens raised to maturity. Poult. Sci. 82: Scheuermann, G. N., S. F. Bilgili, J. B. Hess, and D. R. Mulvaney Breast muscle development in commercial broiler chickens. Poult. Sci. 82: May, J. D., B. D. Lott, and J. D. Simmons The effect of environmental temperature and body weight on growth rate and feed:gain of male broilers. Poult. Sci. 77: Smith, E. R., G. M. Pesti, R. I. Bakalli, G. O. Ware, and J. F. M. Menten Further studies on the influence of genotype and dietary protein on the performance of broilers. Poult. Sci. 77: Smith, E. R., and G. M. Pesti Influence of broiler strain cross and dietary protein on the performance of broilers. Poult. Sci. 77: Coetzee, G. J. M., and L. C. Hoffman Effect of dietary vitamin E on the performance of broilers and quality of broiler meat during refrigerated and frozen storage. S. Afr. J. Anim. Sci. 31: Ngoka, D. A., G. W. Froning, S. R. Lowry, and A. S. Babji Effects of sex, age, preslaughter factors, and holding conditions on the quality characteristics and chemical composition of turkey breast muscles. Poult. Sci. 61: Mehaffey, J. M., S. P. Pradhan, J. F. Meullenet, J. L. Emmert, S. R. Mckee, and C. M. Owens Meat quality evaluation of minimally aged broiler breast fillets from five commercial genetic strains. Poult. Sci. 85: Le Bihan-Duval, E., N. Millet, and H. Remignon Broiler meat quality: Effect of selection for increased carcass quality and estimates of genetic parameters. Poult. Sci. 78: Berri, C., N. Wacrenier, N. Millet, and E. Le Bihan- Duval Effect of selection for improved body composition on muscle and meat characteristics of broilers from experimental and commercial lines. Poult. Sci. 80:

13 58 JAPR: Research Report 38. Wheeler, B. R., S. R. Mckee, N. S. Mathews, R. K. Miller, and A. R. Sams A halothane test to detect turkeys prone to developing pale, soft, and exudative meat. Poult. Sci. 78: Yates, J. D., C. C. Brunson, and J. E. Webb Relationships of certain biochemical, Physical, and quality characteristics of broiler muscles. Poult. Sci. 55: Rathgeber, B. M., J. A. Boles, and P. J. Shand Rapid postmortem ph decline and delayed chilling reduce quality of turkey breast meat. Poult. Sci. 78: Ngoka, D. A., and G. W. Froning Effect of free struggle and preslaughter excitement on color of turkey breast muscles. Poult. Sci. 63: Forrest, J. C., E. D. Aberle, H. B. Hedrick, M. D. Judge, and R. K. Merkel Structure and composition of muscles and associated tissues. Pages in Principles of Meat Science. W. H. Freeman and Company, San Francisco, CA. 43. Koohmaraie, M., M. P. Kent, S. D. Shackelford, E. Veiseth, and T. L. Wheeler Meat tenderness and muscle growth: Is there any relationship? Meat Sci. 62: Cooper, M. A., and D. L. Fletcher A comparison of broilers from heavy and light flocks on breast muscle rigor development, ph, and shear. Poult. Sci. 76(Suppl. 1):48. (Abstr.) 45. Poole, G. H., C. E. Lyon, R. J. Buhr, L. L. Young, A. Alley, J. B. Hess, S. F. Biligli, and J. K. Northcutt Evaluation of age, gender, strain, and diet on the cooked yield and shear values of broiler breast fillets. J. Appl. Poult. Res. 8: Lyon, C. E., B. G. Lyon, C. M. Papa, and M. C. Robach Broiler tenderness: Effects of postchill deboning time and fillet holding time. J. Appl. Poult. Res. 1: Smith, D. P., D. L. Fletcher, and C. M. Papa Duckling and chicken processing yields and breast meat tenderness. Poult. Sci. 71: Dransfield, E., and A. A. Sosnicki Relationship between muscle growth and poultry meat quality. Poult. Sci. 78: Simpson, M. D., and T. L. Goodwin Tenderness of broilers as affected by processing plants and seasons of the year. Poult. Sci. 54: Musa, H. H., G. H. Chen, J. H. Cheng, E. S. Shuiep, and W. B. Bao Breed and sex effect on meat quality of chicken. Int. J. Poult. Sci. 5: Lyon, C. E., and R. L. Wilson Effects of sex, rigor condition, and heating method on yield and objective texture of broiler breast meat. Poult. Sci. 65: Huezo, R., J. K. Northcutt, D. P. Smith, and D. L. Fletcher Effect of chilling method and deboning time on broiler breast fillet quality. J. Appl. Poult. Res. 16: McNeal, W. D., and D. L. Fletcher Effects of high frequency electrical stunning and decapitation on early rigor development and meat quality of broiler breast meat. Poult. Sci. 82: Lyon, C. E., D. Hamm, J. P. Hudspeth, and F. H. Benoff Effects of age and sex of the bird on thaw and cooking losses and texture of broiler breast meat. Poult. Sci. 62:1459. (Abstr.) 55. Abeni, F., and G. Bergoglio Characterization of different strains of broiler chicken by carcass measurements, chemical and physical parameters and NIRS on breast muscle. Meat Sci. 57: Smith, D. P., C. E. Lyon, and B. G. Lyon The effect of age, dietary carbohydrate source, and feed withdrawal on broiler breast fillets color. Poult. Sci. 81: Nishida, J., and T. Nishida Relationship between the concentration of myoglobin and parvalbumin in various types of muscle tissues from chickens. Br. Poult. Sci. 26: Bianchi, M., M. Petracci, and C. Cavani The influence of genotype, market live weight, transportation, and holding conditions prior to slaughter on broiler breast meat color. Poult. Sci. 85: Qiao, M., D. L. Fletcher, D. P. Smith, and J. K. Northcutt The effect of broiler breast meat color on ph, moisture, water-holding capacity, and emulsification capacity. Poult. Sci. 80: Petracci, M., and D. L. Fletcher Broiler skin and meat color changes during storage. Poult. Sci. 81: Qiao, M., D. L. Fletcher, J. K. Northcutt, and D. P. Smith The relationship between raw broiler breast meat color and composition. Poult. Sci. 81: Acknowledgments The authors thank the Deanship of Scientific Research at the Jordan University of Science and Technology for financial support for this project. Thanks are expressed to personnel of the Jordan University of Science and Technology for their technical assistance: M. Abu Ishmais, R. I. Qudsieh, and I. Al-sukhni.