Postmortem aging to improve palatability of cooked beef is a common practice. Many studies have evaluated the tenderness of various subprimal cuts, the longissimus dorsi muscle, or other individual beef muscles after various postmortem aging times (Smith et al., 1978; Lorenzen et al., 1998; Meis et al., 1998; Johnson, 2003). George et al. (1999) reported a range of 89 days in post fabrication age of striploin and top sirloin steaks sold at retail stores in eight differing U.S. cities. As the industry moves towards merchandising individual beef muscles, standardized postmortem aging times for muscles must be determined. Unfortunately, the majority of studies have been unable to discern differences in the amount of postmortem aging time required for individual beef muscles varying by USDA quality grade. Furthermore, most previous studies have relied on WarnerBratzler shear force (WBSF) measurements obtained following freezing and thawing of beef steaks. This study was designed to develop standardized wetaging time recommendations for individual beef muscles. Thus, allowing packers, retailers, and food service operations to manage the palatability of a wide range of beef muscles differing in USDA quality grade.
Product selection. USDA Select (n = 40) and upper twothirds USDA Choice (n = 40) beef carcasses were selected over a sevenmonth period from Swift and Company Greeley, CO (Table 1). Two days postmortem the following subprimals were removed from the right side of each carcass by inplant fabrication: shoulder clod (IMPS 114), chuck roll (IMPS 116 C), chuck tender (IMPS 116 B), top round (IMPS 168), bottom round (IMPS 171 B), eye of round (IMPS 171 C), knuckle (IMPS 167), sirloin (IMPS 181), tenderloin (IMPS 189), and striploin (IMPS 180); the shoulder clod (IMPS 114), chuck roll (IMPS 116 C), chuck tender (IMPS 116 B), knuckle (IMPS 167), and bottom sirloin (IMPS 185) were removed from the left side of each carcass (NAMP, 1997). Subprimals were then transported to the Colorado State University Meat Laboratory for further processing.
Muscle fabrication and steak allocation. The following individual muscles were removed from subprimal cuts: (a) complexus, (b) semimembranosus, (c) semitendinosus, (d) serratus ventralis, (e) spinalis dorsi/multifidus dorsi, (f) supraspinatus, (g) vastus lateralis, and (h) vastus medialis (Table 2). Due to size, the complexus and spinalis dorsi/multifidus dorsi muscles were not separated; individual muscle identification was maintained throughout sampling, but muscles were fabricated and cooked as a complex. Following fabrication, individual muscles within a carcass were cut into oneinchthick steaks and the seven most suitable steaks within a muscletype were each randomly assigned to one of the following aging periods: 2, 4, 6, 10, 14, 21, and 28 days. Steaks assigned to the 2day aging period were immediately evaluated by WarnerBratzler shear force, and the remaining six steaks per muscletype were vacuum packaged and stored (2°C) until the assigned agingperiod was complete.
WarnerBratzler shear force determination. Upon completion of designated agingtime, steaks were removed from storage (2°C, never frozen) for shear force analysis. Steaks most similar in thickness were cooked in groups of three on electric grills (model GGR64, Salton,Inc., Mt. Prospect, IL) that heated steaks from both sides simultaneously to a final internal temperature of 70°C. A Type K thermocouple (Omega Engineering Inc., Stamford, CT) was placed in the geometric center of each steak, and the internal temperature of each steak was monitored during cooking using a microprocessor thermometer (model HH21, Omega Engineering Inc.,Stamford, CT). After cooking each steak was allowed to equilibrate to room temperature (22°C) and up to 10 cores (1.27 cm in diameter) were removed from each steak parallel to the muscle fiber orientation. Each core was sheared once, perpendicular to the muscle fiber orientation, with an Instron testing machine fitted with a WarnerBratzler shear head; peak shear force measurements of each core were recorded and averaged to obtain a single shear force value for each steak.
Statistical methods. Analysis of WarnerBratzler shear force (WBSF) was conducted using the least squares, mixed models procedure of SAS (SAS Inst. Inc., Cary, NC). The ANOVA model included the threeway interaction between the fixed independent effects of quality grade (grade), postmortem aging period (age), and muscle type (muscle). Random effects included carcass nested within grade, and the twoway interactions of carcass within grade × muscle, and carcass within grade × age. Because this preliminary analysis resulted in a significant interaction between grade, muscle, and age, WBSF data was subsequently analyzed within each of the two quality grades (upper 2/3 Choice and Select). The final statistical model included the two way interaction of muscle × age as a fixed effect. Random effects included carcass, carcass × muscle, and carcass × age. Peak internal steak temperature served as a covariate for all analyses of WBSF.
Within each quality grade, least squares means were generated for each muscle by aging period subclass, and aging curves were fit for each muscle using the least squares, nonlinear models procedure of SAS (SAS Inst. Inc., Cary, NC.). Aging time was used as the independent variable in each regression equation.
Aging response
Least squares means of WBSF for each aging period by muscle subclass within a quality grade are presented in Tables 3 and 4. The nonlinear equations fit to each muscle within a quality grade are illustrated in Figures 1 – 18.
To estimate an optimal aging time for each muscle within a grade the following must be examined: a) WBSF at two days postmortem, b) the maximum decrease in WBSF that can be expected (“aging response”)(Table 5), and c) the time that it takes for this reduction to occur. Based on the nonlinear models fit to each muscle, within a quality grade, a predicted shear force value at two days postmortem, the change in shear force from day 2 to day 28, and the proportion of that change that has occurred at each of 6 aging periods is displayed in Tables 6 and 7. Estimates of decrease in shear force past twentyeight days are not warranted in this data set and should not be extrapolated; however, the predicted instantaneous rate of change in WBSF for each muscle was ≤0.05 kg on day 28. The combination of these data determines the extent to which aging can improve tenderness (as determined by WBSF), and the time required for each muscle to obtain this improvement.
Although postmortem aging will decrease WBSF values, if consumers cannot detect a change in beef palatability, postmortem aging has not added value to a muscle. Several studies have attempted to examine the impact of changes in WBSF on consumer acceptance of steaks (Miller et al., 2001; Lorenzen et al., 2003); Platter et al. (2003) reported predicted probabilities of consumer steak acceptance of 50 and 68% at approximate WBSF values of 4.4 and 3.7 kg, respectively. Although these probabilities of consumer acceptance are based on WBSF values of longissimus dorsi steaks, the WBSF values associated with them could be used as conservative thresholds. These thresholds could prove valuable in determining the length of time in days a beef muscle should be aged.
Upper 2/3 Choice complexus muscles decreased 1.5 kg after 28 days of postmortem aging, and approximately 92% of this change was complete after 21 days; however, according to Platter et al. (2003) the complexus was only capable of obtaining shear force values that would correspond to 50% of consumer steak acceptance. WBSF values corresponding to this acceptance (4.4 kg) were reached 12 days postmortem. Complexus muscles from USDA Select carcasses had an aging response of 1.7 kg, and reached approximately 78% of this reduction 21 days postmortem. WBSF values of approximately 4.4 kg were reached at 26 days postmortem.
The aging response of the longissimus dorsi muscle varied greatly by quality grade. Top choice longissimus dorsi muscles decreased 2.0 kg in 28 days, and approximately 99% of this change was complete by day 21. Top choice longissimus dorsi muscles reached a 68% consumer acceptance (3.7 kg) by day 16. Conversely, longissimus dorsi steaks from a Select carcass reached WBSF levels of 4.2 kg after 28 days postmortem, and only 87% of this 2.5 kg reduction in shear force was complete by day 21.
Regardless of grade, neither semimembranosus nor semitendinosus muscles reached WBSF values corresponding to 50% consumer acceptance. Premium choice semimembranosus and semitendinosus muscles exhibited a 1.4 kg aging response, of which approximately 98% was complete day 21. Although higher grade semimembranosus and semitendinosus muscles exhibited similar aging responses, Select semimembranosus and semitendinosus muscles responded differently to aging. Semimembranosus muscles exhibited a large (2.3 kg) response to aging, but semitendinosus muscles exhibited an aging response similar to that of semitendinosus muscles from upper 2/3 Choice carcasses.
Serratus ventralis muscles removed from carcasses of both grades reached WBSF values corresponding to 68% consumer acceptance of steaks. Upper 2/3 Choice carcasses yielded serratus ventralis muscles that began with WBSF values below those corresponding to 50% consumer steak acceptance (Platter et al., 2003), and reached shear values of 3.7 kg (68% consumer acceptance) by 12 days postmortem. Notably, top choice serratus ventralis muscles exhibited the slowest rate in total postmortem WBSF decrease, reaching only 78% of its change in shear force by day 21. Serratus ventralis muscles removed from USDA Select carcasses also reached a 3.7 kg threshold, but not until day 26.
Premium choice spinalis dorsi/multifidus dorsi muscles decreased 1.0 kg after 28 days of postmortem aging, and greater than 90% of this change was complete day 14. Select spinalis dorsi/multifidus dorsi muscles had a 28 day aging response of 1.3 kg , 91% of which was complete by 21 days postmortem. Upper 2/3 choice and Select spinalis dorsi/multifidus dorsi muscles reached WBSF values corresponding to 68% consumer acceptance (3.7 kg) at 10 and 19 days postmortem, respectively.
Upper 2/3 Choice and Select supraspinatus muscles reached WBSF value corresponding to 50% consumer acceptance (4.4 kg), at 17 and 25 days postmortem, respectively. Supraspinatus muscles of both grades had similar reductions in postmortem WBSF values; however, top choice “mock tenders” reached 99% of this reduction day 21, and only 92% of this reduction had occurred in Select muscles by 21 days postmortem. Regardless of quality grade, neither muscle removed from the knuckle (IMPS 167) reached WBSF values corresponding to 68% consumer acceptance (3.7 kg), and all but the Select vastus lateralis muscles obtained 4.4 kg or lower shear values (50 % consumer acceptance ) before 21 days postmortem. Vastus medialis muscles of both grades displayed similar aging responses, but USDA Select vastus medialis muscles had only reached 88% of their total decrease in WBSF day 21, whereas premium choice vastus medialis muscles had completed 95% of their total decrease day 21. Vastus lateralis muscles of both grades also exhibited similar aging responses, and 94% or greater of the response was complete day 21.
In general, muscles from USDA Select carcasses had higher initial (two days postmortem) WBSF values, exhibited greater decreases in shear force values through 28 days of postmortem aging, and required more days of postmortem aging to complete the majority of this decrease in WBSF than did muscles from upper 2/3 USDA Choice beef carcasses.
Muscle tenderness
A rank of beef muscles by WarnerBratzler shear force (WBSF) within a quality grade at each of seven postmortem aging periods is located in Tables 8  21. Although numerous studies have characterized the tenderness of individual beef muscles (Ramsbottom et al., 1945, McKeith et al., 1985, Johnson et al., 1988; NCBA, 2000), properties of the longissimus dorsi muscle are still the most widely recognized. Therefore, an index value was created in this study for each muscle to facilitate comparisons in tenderness (as determined by WBSF). Within a quality grade, at each postmortem aging period, this index (Tables 821) identifies muscles that can be expected to perform similarly to the longissimus dorsi, in terms of tenderness, as well as those muscles that can be expected to outperform the longissimus dorsi (Gruber et al., 2003). Also, an index has been created that compares the tenderness of individual muscles at each aging period to the tenderness of the longissimus dorsi aged 14 days (Tables 22 and 23). Caution, however, should be used when comparing muscles by index value alone. Because the index value is a proportion ((WBSF of the longissimus dorsi /WBSF of the individual muscle) * 100), small differences are magnified, and index values that may appear different are not significantly different (P < 0.05). Mean WBSF values are labeled with superscript letters identifying significant differences, and should always be used to test for tenderness differences between muscles.
Postmortem aging can be used to maximize tenderness potential of individual beef muscles. Combining initial WBSF measurements, aging responses within a 28day period, and the rate at which this response occurs can estimate optimal aging time of individual beef muscles varying by quality grade. The conservative use of WBSF thresholds in consumer acceptability may also prove useful in identifying muscles that can be marketed as steaks, and distinguish palatability improvements throughout postmortem aging.
Table 1. Simple means for carcass traits of sample population stratified by quality grade
Upper ⅔ Choice 
Select 

Trait 
n 
Mean 
SEM 
n 
Mean 
SEM 

Carcass weight, kg 
40 
375 
5.2 
40 
356 
2.4 

Adjusted fat thickness, cm 
35 
1.32 
0.05 
40 
1.06 
0.05 

Ribeye area, cm2 
35 
91.1 
1.5 
40 
93.8 
1.6 

Kidney, pelvic, and heart fat % 
35 
2.2 
0.06 
40 
2.1 
0.06 

Calculated yield grade 
35 
2.8 
0.1 
40 
2.3 
0.1 

Marbling^{a} 
40 
575.3 
7.7 
40 
351.3 
3.0 
^{a}300 = slight, 400 = small, 500 = modest.
Table 2. Individual beef muscles removed from a carcass, the number of each muscle excised from each carcass, and the subprimal from which each muscle was removed
Muscle 
N 
Subprimal 
IMPS^{a} 
Complexus 
2 
Chuck roll 
116 C 
Longissimus dorsi 
1 
Striploin 
180 
Semimembranosus 
1 
Top round 
168 
Semitendinosus 
1 
Eye of round 
171C 
Serratus ventralis 
2 
Chuck roll 
116 C 
Spinalis dorsi/Multifidus dorsi 
2 
Chuck roll 
116 C 
Supraspinatus 
2 
Chuck tender 
116 B 
Vastus lateralis 
2 
Knuckle 
167 
Vastus medialis 
2 
Knuckle 
167 
^{a}IMPS = Institutional Meat Product Specification (NAMP, 1997).
Table 3.. Least squares means ± standard error of the mean of WarnerBratzler shear force (kg) for upper 2/3 USDA Choice beef muscles at seven postmortem aging periods
Days postmortem 

Muscle 
2 
4 
6 
10 
14 
21 
28 
Complexus 
5.48 ± 0.14v 
4.88 ± 0.14w 
4.90 ± 0.14w 
4.64 ± 0.13w 
4.16 ± 0.14x 
4.03 ± 0.13x 
3.91 ± 0.13x 
Longissimus dorsi 
5.64 ± 0.14v 
4.90 ± 0.13w 
4.31 ± 0.13x 
3.94 ± 0.13y 
3.97 ± 0.14y 
3.67 ± 0.13yz 
3.55 ± 0.13z 
Semimembranosus 
5.92 ± 0.14v 
5.63 ± 0.14v 
5.08 ± 0.13w 
4.82 ± 0.13wx 
4.67 ± 0.14xy 
4.69 ± 0.13xy 
4.45 ± 0.13y 
Semitendinosus 
6.17 ± 0.14v 
5.63 ± 0.13w 
5.21 ± 0.13x 
5.13 ± 0.13x 
4.94 ± 0.14xy 
4.81 ± 0.14y 
4.51 ± 0.13z 
Serratus ventralis 
4.10 ± 0.14v 
4.06 ± 0.13v 
3.98 ± 0.13vw 
3.69 ± 0.13wx 
3.68 ± 0.14wx 
3.48 ± 0.14xy 
3.20 ± 0.13y 
Spinalis dorsi/Multifidus dorsi 
4.59 ± 0.14v 
4.05 ± 0.14w 
4.09 ± 0.14w 
3.68 ± 0.13x 
3.63 ± 0.15x 
3.48 ± 0.14x 
3.55 ± 0.14x 
Supraspinatus 
5.94 ± 0.14v 
5.05 ± 0.13w 
5.06 ± 0.13w 
4.71 ± 0.13x 
4.60 ± 0.14xy 
4.36 ± 0.14y 
4.32 ± 0.13y 
Vastus lateralis 
5.76 ± 0.14v 
5.29 ± 0.13w 
5.09 ± 0.13w 
4.73 ± 0.13x 
4.57 ± 0.14xy 
4.36 ± 0.13yz 
4.17 ± 0.13z 
Vastus medialis 
5.48 ± 0.14v 
5.39 ± 0.13v 
4.70 ± 0.13w 
4.26 ± 0.14x 
4.05 ± 0.15xy 
3.91 ± 0.13y 
3.74 ± 0.13y 
^{v,w,x,y,z}Means in the same row lacking common superscript letters differ (P < 0.05).
Table 4. Least squares means ± standard error of the mean of WarnerBratzler shear force (kg) for USDA Select beef muscles at seven postmortem aging periods
Days postmortem 

Muscle 
2 
4 
6 
10 
14 
21 
28 
Complexus 
6.13 ± 0.16u 
5.87 ± 0.15uv 
5.58 ± 0.15vw 
5.28 ± 0.15wx 
5.19 ± 0.16xy 
4.87 ± 0.15y 
4.23 ± 0.15z 
Longissimus dorsi 
6.64 ± 0.16u 
6.36 ± 0.15uv 
5.91 ± 0.15v 
5.50 ± 0.15w 
5.01 ± 0.16x 
4.52 ± 0.15y 
4.21 ± 0.15y 
Semimembranosus 
7.41 ± 0.16u 
6.81 ± 0.15v 
6.21 ± 0.15w 
5.81 ± 0.15x 
5.67 ± 0.16x 
5.05 ± 0.15y 
4.96 ± 0.15y 
Semitendinosus 
6.41 ± 0.16u 
5.88 ± 0.15v 
5.72 ± 0.15vw 
5.43 ± 0.15wx 
5.21 ± 0.16x 
4.82 ± 0.15y 
4.74 ± 0.15y 
Serratus ventralis 
4.67 ± 0.16u 
4.60 ± 0.15u 
4.42 ± 0.15uv 
4.24 ± 0.15v 
4.03 ± 0.16w 
3.92 ± 0.15wx 
3.63 ± 0.15x 
Spinalis dorsi/Multifidus dorsi 
4.99 ± 0.16u 
4.45 ± 0.15v 
4.23 ± 0.15vw 
4.26 ± 0.15vw 
4.01 ± 0.16wx 
3.70 ± 0.15xy 
3.52 ± 0.15y 
Supraspinatus 
6.00 ± 0.16u 
5.68 ± 0.15u 
5.29 ± 0.15v 
5.08 ± 0.15vw 
4.85 ± 0.16wx 
4.52 ± 0.15xy 
4.37 ± 0.15y 
Vastus lateralis 
6.23 ± 0.16u 
5.70 ± 0.15v 
5.48 ± 0.15v 
4.93 ± 0.15w 
5.00 ± 0.16w 
4.80 ± 0.15w 
4.43 ± 0.15x 
Vastus medialis 
5.74 ± 0.16u 
5.31 ± 0.15v 
5.27 ± 0.15v 
4.63 ± 0.15w 
4.56 ± 0.16w 
4.01 ± 0.15x 
3.87 ± 0.16x 
^{u,v,w,x,y,z}Means in the same row lacking common superscript letters differ (P < 0.05).
Table 5. Categorization of muscles by responsiveness to postmortem aging
Muscle 
Upper 2/3 USDA Choice Aging response^{a} 
USDA Select Aging response^{a} 
Complexus 
Moderate 
Moderate 
Longissimus dorsi 
Moderately high 
High 
Semimembranosus 
Moderate 
High 
Semitendinosus 
Moderate 
Moderate 
Serratus ventralis 
Moderately low 
Moderately low 
Spinalis dorsi/Multifidus dorsi 
Moderately low 
Moderate 
Supraspinatus 
Moderate 
Moderate 
Vastus lateralis 
Moderate 
Moderate 
Vastus medialis 
Moderately high 
Moderately high 
^{a}Change in WBSF from 2 to 28 days postmortem. High = ≥ 2.3 kg; Moderately high = 2.2 to 1.8 kg; Moderate = 1.7 to 1.1 kg; Moderately low = 1.0 to 0.7 kg; Low = ≤ 0.6 kg.
Table 6. WarnerBratzler shear force (WBSF) for upper 2/3 Choice muscles at 2 days postmortem (kg), the change in shear force through 28 days postmortem, and the percentage (%) of that change completed at each of 6 postmortem aging periods.
Days postmortem 

Muscle 
2Day WBSF^{a} 
Aging response (kg)^{b} 
4 
6 
10 
14 
21 
28 
Complexus 
5.39 
1.5 
20.2 
36.7 
60.8 
76.6 
92.4 
100.0 
Longissimus dorsi 
5.63 
2.0 
38.5 
62.2 
85.7 
94.7 
99.2 
100.0 
Semimembranosus 
5.96 
1.4 
32.4 
54.4 
79.4 
90.9 
98.1 
100.0 
Semitendinosus 
6.10 
1.4 
30.1 
51.2 
76.4 
88.9 
97.5 
100.0 
Serratus ventralis 
4.11 
0.9 
9.5 
18.6 
35.9 
52.0 
77.5 
100.0 
Spinalis dorsi/Multifidus dorsi 
4.54 
1.0 
34.3 
56.9 
81.6 
92.3 
98.5 
100.0 
Supraspinatus 
5.83 
1.4 
37.2 
60.5 
84.5 
94.0 
99.0 
100.0 
Vastus lateralis 
5.70 
1.5 
22.9 
40.8 
65.6 
80.7 
94.0 
100.0 
Vastus medialis 
5.60 
1.8 
24.7 
43.5 
68.7 
83.1 
95.3 
100.0 
^{a}WBSF at two days postmortem predicted by nonlinear regression model.
^{b}Aging response = Predicted WBSF day 2 – Predicted WBSF day 28.
Table 7. WarnerBratzler shear force (WBSF) for Select muscles at 2 days postmortem (kg), the change in shear force through 28 days postmortem, and the percentage (%) of that change completed at each of 6 postmortem aging periods.
Days postmortem 

Muscle 
2Day WBSF^{a} 
Aging response (kg)^{b} 
4 
6 
10 
14 
21 
28 
Complexus 
6.06 
1.7 
9.6 
18.9 
36.4 
52.5 
77.9 
100.0 
Longissimus dorsi 
5.63 
2.5 
14.7 
27.6 
49.1 
65.8 
86.6 
100.0 
Semimembranosus 
7.34 
2.3 
22.9 
40.7 
65.5 
80.6 
94.3 
100.0 
Semitendinosus 
6.32 
1.6 
19.6 
35.6 
59.5 
75.5 
91.9 
100.0 
Serratus ventralis 
4.68 
1.0 
12.0 
23.1 
42.6 
59.2 
82.5 
100.0 
Spinalis dorsi/Multifidus dorsi 
4.83 
1.3 
18.7 
34.2 
57.7 
73.9 
91.1 
100.0 
Supraspinatus 
5.96 
1.6 
19.2 
35.0 
58.7 
74.8 
91.5 
100.0 
Vastus lateralis 
6.18 
1.6 
25.5 
44.7 
69.9 
84.1 
95.7 
100.0 
Vastus medialis 
5.71 
1.9 
15.8 
29.6 
51.7 
68.4 
88.1 
100.0 
^{a}WBSF at two days postmortem predicted by nonlinear regression model.
^{b}Aging response = Predicted WBSF day 2 – Predicted WBSF day 28.
Table 8. Rank of USDA Select beef muscles by WarnerBratzler shear force (WBSF) at two days of postmortem aging, and an index value of individual muscle tenderness at two days postmortem (Longissimus dorsi = 100)
Rank 
Muscle 
WBSF (kg) 
SEM 
Tenderness index^{a } 
1 
Serratus ventralis 
4.67z 
0.16 
142 
2 
Spinalis dorsi/Multifidus dorsi 
4.99z 
0.16 
133 
3 
Vastus medialis 
5.74y 
0.16 
116 
4 
Supraspinatus 
6.00xy 
0.16 
111 
5 
Complexus 
6.13wx 
0.16 
108 
6 
Vastus lateralis 
6.23wx 
0.16 
107 
7 
Semitendinosus 
6.41vw 
0.16 
104 
8 
Longissimus dorsi 
6.64uv 
0.16 
100 
9 
Semimembranosus 
7.41u 
0.16 
89 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi / Mean WBSF (kg) of the individual muscle} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle.
^{u,v,w,x,y,z}Means in the same column lacking common superscript letters differ (P < 0.05).
Table 9. Rank of USDA Select beef muscles by WarnerBratzler shear force (WBSF) at four days of postmortem aging, and an index value of individual muscle tenderness at four days postmortem (Longissimus dorsi = 100)
Rank 
Muscle 
WBSF (kg) 
SEM 
Tenderness index^{a } 
1 
Spinalis dorsi/Multifidus dorsi 
4.45z 
0.15 
143 
2 
Serratus ventralis 
4.60z 
0.15 
138 
3 
Vastus medialis 
5.31y 
0.15 
120 
4 
Supraspinatus 
5.68xy 
0.15 
112 
5 
Vastus lateralis 
5.70x 
0.15 
111 
6 
Complexus 
5.87x 
0.15 
108 
7 
Semitendinosus 
5.88x 
0.15 
108 
8 
Longissimus dorsi 
6.36w 
0.15 
100 
9 
Semimembranosus 
6.81v 
0.15 
93 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi / Mean WBSF (kg) of the individual muscle} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle.
^{v,w,x,y,z}Means in the same column lacking common superscript letters differ (P < 0.05).
Table 10. Rank of USDA Select beef muscles by WarnerBratzler shear force (WBSF) at six days of postmortem aging, and an index value of individual muscle tenderness at six days postmortem (Longissimus dorsi = 100)
Rank 
Muscle 
WBSF (kg) 
SEM 
Tenderness index^{a } 
1 
Spinalis dorsi/Multifidus dorsi 
4.23z 
0.15 
140 
2 
Serratus ventralis 
4.42z 
0.15 
134 
3 
Vastus medialis 
5.27y 
0.15 
112 
4 
Supraspinatus 
5.29y 
0.15 
112 
5 
Vastus lateralis 
5.48xy 
0.15 
108 
6 
Complexus 
5.58wxy 
0.15 
106 
7 
Semitendinosus 
5.72wx 
0.15 
103 
8 
Longissimus dorsi 
5.91vw 
0.15 
100 
9 
Semimembranosus 
6.21v 
0.15 
95 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi / Mean WBSF (kg) of the individual muscle} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle.
^{v,w,x,y,z}Means in the same column lacking common superscript letters differ (P < 0.05).
Table 11. Rank of USDA Select beef muscles by WarnerBratzler shear force (WBSF) at 10 days of postmortem aging, and an index value of individual muscle tenderness at 10 days postmortem (Longissimus dorsi = 100)
Rank 
Muscle 
WBSF (kg) 
SEM 
Tenderness index^{a} 
1 
Spinalis dorsi/Multifidus dorsi 
4.22z 
0.15 
130 
2 
Serratus ventralis 
4.24yz 
0.15 
130 
3 
Vastus medialis 
4.62xy 
0.15 
119 
4 
Vastus lateralis 
4.93wx 
0.15 
111 
5 
Supraspinatus 
5.08vw 
0.15 
108 
6 
Complexus 
5.28uvw 
0.15 
104 
7 
Semitendinosus 
5.43tuv 
0.15 
101 
8 
Longissimus dorsi 
5.50tu 
0.15 
100 
9 
Semimembranosus 
5.81t 
0.15 
95 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi / Mean WBSF (kg) of the individual muscle} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle.
^{t,u,v,w,x,y,z}Means in the same column lacking common superscript letters differ (P < 0.05).
Table 12. Rank of USDA Select beef muscles by WarnerBratzler shear force (WBSF) at 14 days of postmortem aging, and an index value of individual muscle tenderness at 14 days postmortem (Longissimus dorsi = 100)
Rank 
Muscle 
WBSF (kg) 
SEM 
Tenderness index^{a } 
1 
Spinalis dorsi/Multifidus dorsi 
4.01z 
0.16 
125 
2 
Serratus ventralis 
4.03z 
0.16 
125 
3 
Vastus medialis 
4.56y 
0.16 
110 
4 
Supraspinatus 
4.85xy 
0.16 
103 
5 
Vastus lateralis 
5.00x 
0.16 
100 
6 
Longissimus dorsi 
5.01x 
0.16 
100 
7 
Complexus 
5.19x 
0.16 
96 
8 
Semitendinosus 
5.20x 
0.16 
96 
9 
Semimembranosus 
5.69w 
0.16 
88 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi / Mean WBSF (kg) of the individual muscle} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle.
^{w,x,y,z}Means in the same column lacking common superscript letters differ (P < 0.05).
Table 13. Rank of USDA Select beef muscles by WarnerBratzler shear force (WBSF) at 21 days of postmortem aging, and an index value of individual muscle tenderness at 21 days postmortem (Longissimus dorsi = 100)
Rank 
Muscle 
WBSF (kg) 
SEM 
Tenderness index^{a } 
1 
Spinalis dorsi/Multifidus dorsi 
3.70z 
0.15 
122 
2 
Serratus ventralis 
3.91z 
0.15 
115 
3 
Vastus medialis 
4.01z 
0.15 
113 
4 
Longissimus dorsi 
4.52y 
0.15 
100 
5 
Supraspinatus 
4.52y 
0.15 
100 
6 
Vastus lateralis 
4.80xy 
0.15 
94 
7 
Semitendinosus 
4.82xy 
0.15 
94 
8 
Complexus 
4.87xy 
0.15 
93 
9 
Semimembranosus 
5.08x 
0.15 
89 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi / Mean WBSF (kg) of the individual muscle} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle.
^{x,y,z}Means in the same column lacking common superscript letters differ (P < 0.05).
Table 14. Rank of USDA Select beef muscles by WarnerBratzler shear force (WBSF) at 28 days of postmortem aging, and an index value of individual muscle tenderness at 28 days postmortem (Longissimus dorsi = 100).
Rank 
Muscle 
WBSF (kg) 
SEM 
Tenderness index^{a } 
1 
Spinalis dorsi/Multifidus dorsi 
3.52z 
0.15 
120 
2 
Serratus ventralis 
3.63z 
0.15 
116 
3 
Vastus medialis 
3.87yz 
0.16 
109 
4 
Longissimus dorsi 
4.21xy 
0.15 
100 
5 
Complexus 
4.23xy 
0.15 
100 
6 
Supraspinatus 
4.37wx 
0.15 
96 
7 
Vastus lateralis 
4.43wx 
0.15 
95 
8 
Semitendinosus 
4.74vw 
0.15 
89 
9 
Semimembranosus 
4.96v 
0.15 
85 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi / Mean WBSF (kg) of the individual muscle} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle.
^{v,w,x,y,z}Means in the same column lacking common superscript letters differ (P < 0.05).
Table 15. Rank of upper 2/3 USDA Choice beef muscles by WarnerBratzler shear force (WBSF) at two days of postmortem aging, and an index value of individual muscle tenderness at two days postmortem (Longissimus dorsi = 100).
Rank 
Muscle 
WBSF (kg) 
SEM 
Tenderness index^{a } 
1 
Serratus ventralis 
4.10z 
0.14 
138 
2 
Spinalis dorsi/Multifidus dorsi 
4.59y 
0.14 
123 
3 
Complexus 
5.48x 
0.14 
103 
4 
Vastus medialis 
5.48x 
0.14 
103 
5 
Longissimus dorsi 
5.64wx 
0.14 
100 
6 
Vastus lateralis 
5.76wx 
0.14 
98 
7 
Semimembranosus 
5.92vw 
0.14 
95 
8 
Supraspinatus 
5.94vw 
0.14 
95 
9 
Semitendinosus 
6.17v 
0.14 
91 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi / Mean WBSF (kg) of the individual muscle} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle.
^{v,w,x,y,z}Means in the same column lacking common superscript letters differ (P < 0.05).
Table 16. Rank of upper 2/3 USDA Choice beef muscles by WarnerBratzler shear force (WBSF) at four days of postmortem aging, and an index value of individual muscle tenderness at four days postmortem (Longissimus dorsi = 100)
Rank 
Muscle 
WBSF (kg) 
SEM 
Tenderness index^{a} 
1 
Spinalis dorsi/Multifidus dorsi 
4.05z 
0.14 
121 
2 
Serratus ventralis 
4.06z 
0.13 
121 
3 
Complexus 
4.88y 
0.13 
100 
4 
Longissimus dorsi 
4.90y 
0.13 
100 
5 
Supraspinatus 
5.05xy 
0.13 
97 
6 
Vastus lateralis 
5.29wx 
0.13 
93 
7 
Vastus medialis 
5.39vw 
0.13 
91 
8 
Semimembranosus 
5.63v 
0.14 
87 
9 
Semitendinosus 
5.63v 
0.13 
87 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi / Mean WBSF (kg) of the individual muscle} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle.
^{v,w,x,y,z}Means in the same column lacking common superscript letters differ (P < 0.05).
Table 17. Rank of upper 2/3 USDA Choice beef muscles by WarnerBratzler shear force (WBSF) at six days of postmortem aging, and an index value of individual muscle tenderness at six days postmortem (Longissimus dorsi = 100).
Rank 
Muscle 
WBSF (kg) 
SEM 
Tenderness index^{a } 
1 
Serratus ventralis 
3.96z 
0.13 
108 
2 
Spinalis dorsi/Multifidus dorsi 
4.09yz 
0.14 
105 
3 
Longissimus dorsi 
4.31y 
0.13 
100 
4 
Vastus medialis 
4.70x 
0.13 
91 
5 
Complexus 
4.90wx 
0.14 
88 
6 
Supraspinatus 
5.06w 
0.13 
85 
7 
Semimembranosus 
5.08w 
0.13 
85 
8 
Vastus lateralis 
5.09w 
0.13 
84 
9 
Semitendinosus 
5.21w 
0.13 
83 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi / Mean WBSF (kg) of the individual muscle} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle.
^{w,x,y,z}Means in the same column lacking common superscript letters differ (P < 0.05).
Table 18. Rank of upper 2/3 USDA Choice beef muscles by WarnerBratzler shear force (WBSF) at ten days of postmortem aging, and an index value of individual muscle tenderness at ten days postmortem (Longissimus dorsi = 100).
Rank 
Muscle 
WBSF (kg) 
SEM 
Tenderness index^{a} 
1 
Spinalis dorsi/Multifidus dorsi 
3.68z 
0.13 
107 
2 
Serratus ventralis 
3.69yz 
0.13 
107 
3 
Longissimus dorsi 
3.94xy 
0.13 
100 
4 
Vastus medialis 
4.26x 
0.14 
92 
5 
Complexus 
4.64w 
0.13 
85 
6 
Supraspinatus 
4.71w 
0.13 
84 
7 
Vastus lateralis 
4.73w 
0.13 
83 
8 
Semimembranosus 
4.82vw 
0.13 
82 
9 
Semitendinosus 
5.13v 
0.13 
77 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi / Mean WBSF (kg) of the individual muscle} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle.
^{v,w,x,y,z}Means in the same column lacking common superscript letters differ (P < 0.05).
Table 19. Rank of upper 2/3 USDA Choice beef muscles by WarnerBratzler shear force (WBSF) at 14 days of postmortem aging, and an index value of individual muscle tenderness at 14 days postmortem (Longissimus dorsi = 100).
Rank 
Muscle 
WBSF (kg) 
SEM 
Tenderness index^{a} 
1 
Spinalis dorsi/Multifidus dorsi 
3.63z 
0.15 
109 
2 
Serratus ventralis 
3.68yz 
0.14 
108 
3 
Longissimus dorsi 
3.97xy 
0.14 
100 
4 
Vastus medialis 
4.05x 
0.15 
98 
5 
Complexus 
4.16x 
0.14 
96 
6 
Vastus lateralis 
4.57w 
0.14 
87 
7 
Supraspinatus 
4.60w 
0.14 
86 
8 
Semimembranosus 
4.67vw 
0.14 
85 
9 
Semitendinosus 
4.94v 
0.14 
80 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi / Mean WBSF (kg) of the individual muscle} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle.
^{v,w,x,y,z}Means in the same column lacking common superscript letters differ (P < 0.05).
Table 20. Rank of upper 2/3 USDA Choice beef muscles by WarnerBratzler shear force (WBSF) at 21 days of postmortem aging, and an index value of individual muscle tenderness at 21 days postmortem (Longissimus dorsi = 100).
Rank 
Muscle 
WBSF (kg) 
SEM 
Tenderness index^{a} 
1 
Serratus ventralis 
3.48z 
0.13 
105 
2 
Spinalis dorsi/Multifidus dorsi 
3.48z 
0.14 
105 
3 
Longissimus dorsi 
3.67yz 
0.13 
100 
4 
Vastus medialis 
3.91xy 
0.13 
94 
5 
Complexus 
4.03x 
0.13 
91 
6 
Vastus lateralis 
4.36w 
0.13 
84 
7 
Supraspinatus 
4.36w 
0.14 
84 
8 
Semimembranosus 
4.69v 
0.13 
78 
9 
Semitendinosus 
4.81v 
0.14 
76 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi / Mean WBSF (kg) of the individual muscle} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle.
^{v,w,x,y,z}Means in the same column lacking common superscript letters differ (P < 0.05).
Table 21. Rank of upper 2/3 USDA Choice beef muscles by WarnerBratzler shear force (WBSF) at 28 days of postmortem aging, and an index value of individual muscle tenderness at 28 days postmortem (Longissimus dorsi = 100).
Rank 
Muscle 
WBSF (kg) 
SEM 
Tenderness index^{a } 
1 
Serratus ventralis 
3.20z 
0.13 
111 
2 
Spinalis dorsi/Multifidus dorsi 
3.55y 
0.14 
100 
3 
Longissimus dorsi 
3.55y 
0.13 
100 
4 
Vastus medialis 
3.74xy 
0.13 
95 
5 
Complexus 
3.92wx 
0.13 
91 
6 
Vastus lateralis 
4.17vw 
0.13 
85 
7 
Supraspinatus 
4.32uv 
0.13 
82 
8 
Semimembranosus 
4.45uv 
0.13 
80 
9 
Semitendinosus 
4.51u 
0.13 
79 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi / Mean WBSF (kg) of the individual muscle} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle.
^{u,v,w,x,y,z}Means in the same column lacking common superscript letters differ (P < 0.05).
Table 22. Index value^{a} of individual muscle tenderness for upper 2/3 Choice muscles at 7 postmortem aging periods ( 14 day upper 2/3 Choice Longissimus dorsi = 100).
Days postmortem 

Muscle 
2 
4 
6 
10 
14 
21 
28 
Complexus 
72 
81 
81 
86 
95 
99 
102 
Longissimus dorsi 
70 
81 
92 
101 
100 
108 
112 
Semimembranosus 
67 
71 
78 
82 
85 
85 
89 
Semitendinosus 
64 
71 
76 
77 
80 
83 
88 
Serratus ventralis 
97 
98 
100 
108 
108 
114 
124 
Spinalis dorsi/Multifidus dorsi 
86 
98 
97 
108 
109 
114 
112 
Supraspinatus 
67 
79 
78 
84 
86 
91 
92 
Vastus lateralis 
69 
75 
78 
84 
87 
91 
95 
Vastus medialis 
72 
74 
84 
93 
98 
102 
106 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi at 14 days postmortem/ Mean WBSF (kg) of the individual muscle at each respective aging period} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle at 14 days postmortem.
Table 23. Index value^{a} of individual muscle tenderness for Select muscles at 7 postmortem aging periods ( 14 day Select Longissimus dorsi = 100)
Days postmortem 

Muscle 
2 
4 
6 
10 
14 
21 
28 
Complexus 
82 
85 
90 
95 
97 
103 
118 
Longissimus dorsi 
75 
79 
85 
91 
100 
111 
119 
Semimembranosus 
68 
74 
81 
86 
88 
99 
101 
Semitendinosus 
78 
85 
88 
92 
96 
104 
106 
Serratus ventralis 
107 
109 
113 
118 
124 
128 
138 
Spinalis dorsi/Multifidus dorsi 
100 
113 
118 
118 
125 
135 
142 
Supraspinatus 
84 
88 
95 
99 
103 
111 
115 
Vastus lateralis 
80 
88 
91 
102 
100 
104 
113 
Vastus medialis 
87 
94 
95 
108 
110 
125 
129 
^{a}Tenderness Index = {Mean WBSF (kg) of the longissimus dorsi at 14 days postmortem/ Mean WBSF (kg) of the individual muscle at each respective aging period} * 100. Tenderness index values greater than 100 indicate more desirable values for tenderness than the longissimus dorsi muscle at 14 days postmortem.
Figure 1. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for upper 2/3 Choice complexus at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 2. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for Select complexus at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 3. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for upper 2/3 Choice longissimus dorsi at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 4. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for Select longissimus dorsi at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 5. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for upper 2/3 Choice semimembranosus at 7 postmortem aging periods. and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 6. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for Select semimembranosus at 7 postmortem aging periods. and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 7. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for upper 2/3 Choice semitendinosus at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 8. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for Select semitendinosus at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 9. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for upper 2/3 Choice serratus ventralis at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 10. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for Select serratus ventralis at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 11. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for upper 2/3 Choice spinalis dorsi at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 12. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for Select spinalis dorsi at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 13. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for upper 2/3 Choice supraspinatus at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 14. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for Select supraspinatus at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 15. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for upper 2/3 Choice vastus lateralis at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 16. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for Select vastus lateralis at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 17. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for upper 2/3 Choice vastus medialis at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).
Figure 18. Least squares means ± standard error of the mean of WarnerBratzler shear force (WBSF) for Select vastus medialis at 7 postmortem aging periods, and the nonlinear regression model fit to these points. The variable “age” is the days of postmortem aging. The R^{2} is the maximum proportion of total variability explained by the model. The constant "e" equals the base of the natural logarithm (2.718282).