Effect of rapid rigor mortis processes on protein functionality in pectoralis major muscle of domestic turkeys

Effect of selection for growth rate on muscle damage during turkey breast muscle development

Damage to the turkey pectoralis major muscle was studied in a randombred control line (RBC2), a subline (F) from the RBC2 line selected long-term for increased 16-wk BW only, and a commercial sire line (B) at 25 d of incubation and at 1, 4, 8, 16, and 20 wk posthatch. Pectoralis major muscle samples were obtained from three females and three males from each line in a manner to avoid contraction. After being fixed and sectioned, the muscle samples were stained with hematoxylin and eosin to view muscle fiber and muscle fiber bundle morphology. Beginning at 8 wk posthatch, differences in muscle fiber morphology were observed among the different lines. The RBC2 line throughout the duration of the study maintained well-organized muscle fibers and muscle fiber bundles with large capillary networks. In contrast, the growth-selected F line began to show muscle fiber degeneration at 8 wk posthatch, and limited capillary beds were observed as development proceeded. The B line had intermediate muscle morphology between the RBC2 and F lines, but by 20 wk posthatch significant muscle fiber degeneration was present with limited capillary supply. The degenerative muscle fiber changes were predominant in the growth-selected F-line, suggesting that growth selection for just BW may be associated with posthatch muscle damage.

The role of carcass chilling rate in the development of pale, exudative turkey pectoralis

Pale, soft, and exudative meat is a growing problem in the turkey industry that has been associated with processing conditions such as improper chilling. This condition is caused by accelerated postmortem glycolysis while carcass temperatures are still elevated, resulting in protein denaturation and poor meat quality. To evaluate the involvement of chilling rate, 48 toms were conventionally processed at 17.5 wk of age and chilled at 0,10, 20, or 30 C for 45 or 90 min and deboned. Temperature and pH of the breast fillet were recorded at 15 min, deboning time, and at 24 h postmortem (PM). Drip loss, L* value, expressible moisture, gel strength, and cook loss were determined on the fillets at 24 h PM. At 15 min PM, there were no temperature differences among treatments. At deboning, the carcasses chilled at 30 C had the highest fillet temperature and had significantly lower pH values when compared to those chilled at 0 and 10 C. L* value was significantly higher in carcasses chilled at 30 C and deboned at 60 min PM when compared to 0 and 10 C chilled carcasses. There were no significant differences in L* values at 105 min and 24 h PM among any treatment group. Drip loss and cook loss were significantly higher in carcasses chilled at 30 C compared to the remaining treatments. There were no differences in expressible moisture at 60 or 105 min PM or gel strength at 60 min PM in any of the treatments. However, at 105 min PM, carcasses chiled at 0 C had higher gel strength when compared to the remaining treatments. These results indicate that there is a relationship between chilling rates and meat quality with slower chilling producing PSE-like characteristics.

Effect of selection for growth rate on embryonic breast muscle development in turkeys

Muscle development at 20 and 25 d of incubation was studied in a randombred control line (RBC2), a subline (F) of RBC2 selected only for increased 16-wk BW, a commercial sire line (B), and reciprocal crosses of the F and B lines. Muscle samples from three males and three females of each genetic group were collected in such a manner to avoid contraction. After fixing, the muscles were stained with hematoxylin and eosin, measurements of muscle fiber width, muscle fiber bundle length and width, number of fibers within a 15.6 microm2 area, and extracellular matrix perimysial (PW) and endomysial (EW) width were taken with an Olympus XI 70 microscope equipped with an Olympus Magna Fire digital camera linked to Image Pro software. From each slide, 20 measurements were taken for each characteristic analyzed. In most of the muscle traits measured, additive genetic variation, as indicated by line differences, occurred when the RBC2 line was included in the comparison of pure lines. However, when only the B and F lines were compared, line differences were less frequent. In comparisons of the B and F lines and their reciprocal crosses, heterosis, as measured by contrasts of the average of the pure lines and the average of the reciprocal crosses, was an important source of variation for individual fiber measurements (negative) and extracellular space (positive) at 20 d of incubation but was less important at 25 d of incubation. No significant interactions between genetic group and sex were noted at 20 d of incubation, but such interactions were frequent at 25 d of incubation. These results suggest that muscle organizational differences between the two sexes begin to occur between these two ages and are not the same for different genetic groups.

Effect of selection for improved body composition on muscle and meat characteristics of broilers from experimental and commercial lines

Meat quality (pH, color, and drip loss) and muscle characteristics (composition and metabolic pattern) were compared among four broiler lines: an experimental line, a commercial line selected for increased body weight and breast yield, and the respective unselected control lines. By comparison to their controls, the commercially selected birds exhibited higher body weight and breast yield (127 and 61%, respectively), whereas only breast yield was increased (21%) in the experimental selected line. Commercial selection resulted in higher protein content and lower moisture in the breast muscle. Experimental and commercial selection decreased the heme pigment content, which could explain why breast meat of the selected birds was more pale and less red. This change in the color did not correspond to a pale, soft, and exudative (PSE) defect, as the selected birds did not exhibit excessive drip loss. By comparison with their controls, both selected lines showed a lower rate and extent of pH decline postmortem, which was consistent with the lower glycolytic potential they also exhibited. However, no significant changes in the metabolic pathways of breast muscle, as measured by enzyme activities, could be found to explain differences in rates of pH decline among lines. This study did not support the idea that selection had a negative impact on meat quality, despite evidence of modified breast metabolism.

The Effect of Broiler Breast Meat Color on pH, Moisture, Water-Holding Capacity, and Emulsification Capacity

The relationship between broiler breast meat color and pH, moisture content, water-holding capacity (WHC), and emulsification capacity (EC) was investigated. In each of three replicate trials, fillets were collected from three different commercial processing plants according to breast meat lightness (L*) values as follows: lighter than normal (light, L* > 53), normal (48 < L* < 53), and darker than normal (dark, L* < 46). Color values of lightness (L*), redness (a*), and yellowness (b*) were measured at 0 and 24 h after collection. Fillets were then ground and homogenized prior to determining color, pH, moisture, WHC, and EC of the ground meat. There was a significant difference among the three color groups (light, normal, and dark) in L*, a*, pH, WHC, and EC. The L* values of whole raw breast fillets had significant negative correlation coefficients with ground meat EC (-0.9237), pH (-0.9610), and a* (-0.6540). Emulsification capacity had significant positive correlations with pH (0.9572) and water-holding capacity (0.7080). WHC had significant correlations with a* (0.8143), moisture (-0.7647), and pH (0.7963). Lighter-than-normal meat was associated with low pH, high moisture, low EC, and low WHC. These results indicate that wide differences in raw breast meat color exist and that these differences may be used by poultry further processors as an indicator of fillets with altered functional properties.

Effect of stunning current frequency on carcass downgrading and meat quality of turkey

The objective of this study was to determine the effect of frequency of a 150 mA water-bath stunning current on turkey hen carcass and meat qualities. Fifty turkey hens were subjected to water-bath stunning with alternating current of various frequencies: 50 Hz (n = 12), 300 Hz (n = 14), 480 Hz (n = 12), and 600 Hz (n = 12); the duration of stunning was 4 s for each bird. Carcass defects such as engorged wing veins, red wing tips, and hemorrhages were recorded. Turkey meat quality traits (M. Pectoralis major) were assessed based on rigor mortis development, color, drip loss, cooking loss, tenderness, and cooking yield of cured products. The data showed that frequencies of 480 Hz and 600 Hz are associated with an increased rate of postmortem pH decline (during bleeding). This effect is most likely due to the occurrence of vigorous wing flapping during the first 3 min poststunning. Under the experimental conditions of the present work, the increase in rate of pH decline after stunning at 480 and 600 Hz did not induce carcass and meat quality defects. However, before any recommendation is given, the influence of stunning frequency on turkey meat quality needs to be evaluated under industrial conditions.

Characteristics of pale, soft, exudative broiler breast meat

The objective of the study was to characterize pale breast meat, compare it with normal colored breast meat, and determine whether it should be considered pale, soft, and exudative (PSE). Characteristics of 20 normal and 20 pale broiler breasts, obtained at a commercial slaughter plant, were evaluated. Compared with normal meat, the pale breast meat had a significantly (P < 0.05) lower pH (5.7 vs. 5.9), higher color L* value (60.0 vs. 55.1), higher drip loss (1.34 vs. 0.87%), lower marinade uptake (31.2 vs. 44.3%), and lower cooking yields (95.2 vs. 105.8%). Protein solubility in pale samples was slightly (P < 0.05) lower than in normal samples, which suggests increased protein denaturation in the pale breasts. Correlations between pH and L* value (r = -0.76), pH and marinade uptake (r = 0.64), sarcoplasmic protein solubility and L* value (r = -0.71), and sarcoplasmic protein solubility and moisture uptake (r = 0.66) and cooking yield (r = 0.66) were significant (P < 0.05). Correlations between total protein solubility and moisture uptake or cooking yields were not significant. The low ultimate pH of pale breast muscle appears to be the main determinant of its low water-holding capacity (WHC). This lower pH was unrelated to a higher lactate concentration or glycolytic potential of the pale muscle. Further research is needed to determine the causes of the low pH and possible measures to increase the pH (and functionality) of pale broiler breast muscle. Because the pale breast muscle has a low WHC, it can be considered PSE.

Rapid post-mortem glycolysis and delay chilling of turkey carcasses cause alterations to protein extractability and degradation of breast muscle proteins

SDS-PAGE banding patterns of myofibrillar protein samples from turkey breast muscle with pH < or =5.8 at 15 min post-mortem (rapid glycolyzing) contained 133, 142, and 165 kDa bands that were absent in samples from carcasses with pH >6.0 at 15 min post-mortem (normal glycolyzing). These extra protein bands contained fragments of myosin as identified by Western blot analysis. Myosin fragments were also observed in protein samples from breast muscle not allowed to cool until 110 min post-mortem (delay chilled). In addition to myosin degradation, neublin degradation was more extensive in samples from rapid glycolyzing carcasses than for normal controls. Creatine kinase and glycogen phosphorylase were present in myofibrillar protein extracts of rapid glycolyzing carcasses in higher quantities than in normal controls. Results of this study provide insight into the molecular basis for previously reported reductions in meat quality of rapid glycolyzing and delay chilled turkey meat.

Skeletal muscle calcium channel ryanodine binding activity in genetically unimproved and commercial turkey populations

The biochemical basis for the incidence of pale, soft, exudative (PSE) turkey meat was investigated by conducting ryanodine binding experiments on sarcoplasmic reticulum (SR) vesicles prepared from genetically unimproved and commercial turkeys. Ryanodine binding to the Ca2+ channel protein in SR vesicles from both populations of turkeys was activated at a threshold concentration of approximately 0.2 microM Ca2+, reached a plateau over the range of 3 to 30 microM free Ca2+, and was only slightly inhibited at 1 mM Ca2+. The SR fractions, enriched in the Ca(2+)-channel protein, from commercial turkeys exhibited a higher (P < 0.05) mean affinity for ryanodine when compared to that from unimproved turkeys (Kd = 12.2 vs 20.5 nM, respectively). A fourfold difference (P < 0.05) in mean Ca(2+)-channel protein content or Bmax (1.10 pmol/mg vs 4.01 pmol/mg) was observed between commercial and unimproved turkey SR fractions. The apparent difference in channel protein content between the two populations may be partially accounted for by the high abundance of a 75-kDa protein, as yet unidentified, observed in most commercial turkey samples on SDS polyacrylamide gels. The differences in ryanodine binding activity between these two populations of turkeys suggest that altered SR calcium channel protein activity, or altered channel regulation, may be associated with the increased incidence of PSE meat from turkeys selected for growth characteristics.

Rapid postmortem pH decline and delayed chilling reduce quality of turkey breast meat

Effects of rapid postmortem metabolism and delayed chilling on turkey breast meat quality were assessed using color measurements, protein extractability, and gelation characteristics. Based on 15 min postmortem breast muscle pH, tom turkey carcasses were classified as rapid glycolyzing (RG), pH < 5.80, or normal glycolyzing (NG), pH > 6.00. Two carcasses per group with similar ultimate pH values were selected on four occasions for a total of 16 carcasses. One half of each carcass was immersion-chilled at 20 min postmortem, the other half was maintained at body temperature for 110 min and then chilled. Breast meat from RG carcasses had higher carcass temperature (15 min) and lower protein (sarcoplasmic and myofibrillar) extractability than breast meat from NG carcasses. Delayed chilling increased all breast meat color values (L*, a*, b*), and decreased protein extractability and cook yield compared to breast meat from immediately chilled carcass halves. The true strain of cooked gels was reduced for RG carcasses. Delayed chilling reduced both true strain and stress of meat gels. There were no interactions between the rate of postmortem pH decline and initiation of chilling, indicating that reductions in meat quality due to delayed chilling were independent of the carcass classification for rate of postmortem glycolysis. Results indicate that factors that affect both rate of postmortem glycolysis and carcass temperature decline are important to turkey breast meat quality.