A survey of beef muscle color and ph 1

Transcription

1 A survey of beef muscle color and ph 1 J. K. Page, D. M. Wulf 2, and T. R. Schwotzer Department of Animal Sciences, The Ohio State University, Columbus ABSTRACT: The objectives of this study were to define a beef carcass population in terms of muscle color, ultimate ph, and electrical impedance; to determine the relationships among color, ph, and impedance and with other carcasses characteristics; and to determine the effect of packing plant, breed type, and sex class on these variables. One thousand beef carcasses were selected at three packing plants to match the breed type, sex class, marbling score, dark-cutting discount, overall maturity, carcass weight, and yield grade distributions reported for the U.S. beef carcass population by the 1995 National Beef Quality Audit. Data collected on these carcasses included USDA quality and yield grade data and measurements of muscle color (L*, a*, b*), muscle ph, and electrical impedance of the longissimus muscle. About one-half (53.1%) of the carcasses fell within a muscle ph range of 5.40 to 5.49, and 81.3% of the carcasses fell within a longissimus muscle ph range of 5.40 to A longissimus muscle ph of 5.87 was the approximate cut-off between normal and darkcutting carcasses. Frequency distributions indicated that L* values were normally distributed, whereas a* and b* values were abnormally distributed (skewed because of a longer tail for lower values, a tail corresponding with dark-cutting carcasses). Electrical impedance was highly variable among carcasses but was not highly related to any other variable measured. Color measurements (L*, a*, b*) were correlated (P < 0.05) with lean maturity score (.58,.31, and.43, respectively) and with muscle ph (.40,.58, and.56, respectively). In addition, fat thickness was correlated with muscle ph and color (P < 0.05). There was a threshold at approximately.76 cm fat thickness, below which carcasses had higher muscle ph values and lower colorimeter readings. Steer carcasses (L* = 39.62, a* = 25.20, and b* = 11.03) had slightly higher colorimeter readings (P < 0.05) than heifer carcasses (L* = 39.20, a* = 24.78, and b* = 10.80) even though muscle ph was not different between steer and heifer carcasses. Dairy-type carcasses (ph = 5.59, L* = 37.56, a* = 23.40, and b* = 9.68) had higher muscle ph values and lower colorimeter readings than either native-type (ph = 5.50, L* = 39.55, a* = 25.13, and b* = 11.00) or Brahman-type (ph = 5.46, L* = 39.75, a* = 25.17, and b* = 11.05) carcasses (P < 0.05). Key Words: Beef, Color, Meat Characteristics, Muscles, ph, Impedance 2001 American Society of Animal Science. All rights reserved. J. Anim. Sci : Introduction As beef is merchandized at retail, consumers evaluate several factors when selecting a cut. The visual appraisal of meat products can determine whether a consumer will make a purchase (MacKinney et al., 1966). Hedrick et al. (1994) stated that one of the most important factors in the selection of a meat product is color, and Kropf (1980) suggested that the single 1 This research was funded in part by a grant from the National Cattlemen s Beef Association. Salaries and Research support provided by state and federal funds appropriated to The Ohio State University, Ohio Agriculture Research and Development Center. 2 Correspondence: Current address: Dept. of Animal and Range Sciences, Box 2170, SDSU, Brookings, SD (phone: ; fax: ). Received August 5, Accepted November 13, greatest factor determining the purchase of meat at retail was probably the muscle color. Furthermore, when quality-grading beef carcasses, trained USDA personnel evaluate muscle color as related to carcass maturity and muscle ph when determining quality grades (USDA, 1997). Measuring muscle color is also important because several researchers have shown that meat tenderness is correlated with ultimate muscle ph (Purchas, 1990; Watanabe et al., 1996) and muscle color (Jeremiah et al., 1991; Wulf et al., 1997). However, even though muscle color and ph have many important implications to the U.S. beef industry, the amount of color variation among the U.S. beef carcass population has never been quantified. Measurements of electrical impedance have been shown to be related to muscle ph and water-holding capacity in pork (Oliver et al., 1991; Whitman et al., 1996), but the relationship of electrical impedance measurements to beef muscle ph and color is unknown. The objectives of this 678

2 Beef color and ph survey 679 Table 1. Definition of variables Variable Definition Skeletal maturity 100 = A 00, 200 = B 00, 300 = C 00, 400 = D 00 Lean maturity 100 = A 00, 200 = B 00, 300 = C 00, 400 = D 00 Overall maturity 100 = A 00, 200 = B 00, 300 = C 00, 400 = D 00 Marbling score 100 = Practically devoid 00, 200 = Traces 00, 300 = Slight 00, 400 = Small 00, 500 = Modest 00, 600; = Moderate 00, 700 = Slightly abundant 00, 800 = Moderately abundant 00 USDA quality grade 300 = Utility 00, 400 = Commercial 00, 500 = Standard 00, 600 = Select 00, 700 = Choice 00, 800 = Prime 00 Electrical impedance, Py Lower numbers = lower impedance (greater conductivity), higher numbers = greater impedance (lower conductivity), measurement range = 0to100 L* 0 = black, 100 = white a* Lower numbers = more green (less red), higher numbers = more red (less green); measurement range = ( 60) to 60 b* Lower numbers = more blue (less yellow), higher numbers = more yellow (less blue); measurement range = ( 60) to 60 study were to define a beef carcass population in terms of muscle color, ultimate ph, and electrical impedance; to determine the relationships among color, ph, and electrical impedance and with other carcass characteristics; and to determine the effect of packing plant, breed type, and sex class on these variables. Materials and Methods Data were obtained from 1,062 randomly selected beef carcasses at three packing plants, Illinois (A), Texas (B), and Ohio (C). These carcasses were selected randomly with the exception that sex class and breed type were monitored to reflect the nationwide distribution identified by the 1995 National Beef Quality Audit (68.0% steers, 31.6% heifers, and 0.4% bullocks; 88.7% native, 6.5% Brahman, and 4.8% dairy-type) (Smith et al., 1995). Carcass data were collected by experienced personnel following a 1-d chill in plant A, a 2-d chill in plant B, and a 1- to 4-d chill in plant C. Data collected included breed type, sex class, hot carcass weight, fat thickness, longissimus muscle area, kidney, pelvic, and heart fat (KPH), USDA yield grade, skeletal maturity, lean maturity, overall maturity, marbling score, dark-cutting discount, USDA quality grade (USDA, 1997), electrical impedance (Py value), muscle temperature, muscle ph, and colorimeter readings (L*, a*, and b*) of the longissimus muscle. Definitions of variables measured are presented in Table 1. All carcass data were collected by experienced university personnel, and the same personnel were used throughout the entire study. Breed type was assigned as a subjective evaluation of the carcasses based primarily on hump height for classification of Brahman carcasses and angular carcass conformation for classification as dairy-type carcasses. Breed type was not evaluated on live animals. All female carcasses were classified as heifer carcasses; therefore, a small percentage of the heifer carcasses in this study may actually be from young cows. Electrical impedance, muscle temperature, and muscle ph were obtained using a Meatcheck 160 ph (Sigma Electronic GmbH Erfurt, Erfurt, Germany) meter equipped with a ph probe (LoT406-M6-DXK- S7/25, Mettler Toledo GmbH, Urdorf, Switzerland). Measurements were obtained at the exposed longissimus muscle at the 12th/13th rib interface. Electrical impedance was measured by inserting the two probes of the Meatcheck 160 ph meter parallel to the long axis of the longissimus muscle. Electrical impedance was measured in Py units, a measurement defined by the manufacturer of the Meatcheck 160 ph instrument. According to the manufacturer, Py is a measure of the structural condition of meat, and lower numbers indicate lower electrical impedance, greater muscle cell damage, and greater extracellular water. The ph probe was inserted into the longissimus muscle using one of the holes created by the electrical impedance probes. Colorimeter measurements were taken after ribbing on the exposed longissimus muscle between the 12th and the 13th ribs. Colorimeter readings (L*, a*, and b* values) were measured with a Minolta Chroma Meter CR-310 (Minolta Corp., Ramsey, NJ) with a 50- mm-diameter measurement area using a D65 illuminant. One colorimeter measurement was taken per carcass. Bloom time was not held constant throughout the study because plants differed in bloom time and not all carcasses were measured on the grading chain; rather, bloom time was monitored and colorimeter readings were adjusted to a 90-min bloom time according to the adjustments in Wulf and Wise (1999). Actual bloom times in this study ranged from 18 min to5h. An algorithm was created that selected a subset of 1,000 beef carcasses from the total of 1,062 carcasses

3 680 Page et al. that best matched the national distribution of breed type, sex class, carcass weight, overall maturity, marbling, dark cutting, and yield grade according to the National Beef Quality Audit (Smith et al., 1995). The data from these 1,000 carcasses were used for all statistical analyses. Simple correlations were calculated among all the variables. The main effects of packing plant, sex class, breed type, and chill time (1, 2, 3, or 4 d) were tested for significance with four-way AN- OVA. The effect of external fat thickness was examined by treating fat thickness as a class variable and including it with chill time in a two-way ANOVA analysis. Least squares means were calculated for packing plant, sex class, breed type, and external fat thickness using coefficients that were weighted according to the frequencies found in the data set. This procedure differed from the standard method used to compute least squares means because least squares means computed in the standard fashion use equal beta coefficients among classification effect levels, whereas beta coefficients differed by subclass level here but were necessary because the population was not balanced (68.1% steer, 31.4% heifer, and 0.5% bullock, for example). Least squares means were separated using pair-wise t-tests (SAS Inst. Inc., Cary, NC). Results and Discussion A comparison between the 1995 National Beef Quality Audit s (NBQA-1995) national distribution of beef carcasses (Smith et al., 1995) and the distribution of the carcasses used in this study is shown in Table 2. As stated previously, carcasses were monitored to reflect the NBQA-1995 national distribution of breed type and sex class. Furthermore, as a result of the algorithm designed to select the 1,000 best-matched carcasses, other carcass characteristics, including carcass weight, yield grade, overall maturity, marbling, and dark cutters, also reflected the distributions reported by the NBQA-1995 (Smith et al., 1995). Therefore, the sample of carcasses used in the present study almost exactly matched the distribution of the carcasses in the NBQA Descriptive statistics for carcass and grade data, electrical impedance, muscle temperature, muscle ph, and muscle color are shown in Table 3. The carcasses sampled were highly variable for all carcass traits. The distribution of electrical impedance measurements among beef carcasses in this study is shown in Figure 1. Electrical impedance (Py) did not exhibit a normal bell-shaped distribution; carcasses were approximately evenly distributed between Py values of 30 to 75. Most of the carcasses fell in a very narrow range with respect to muscle ph (Figure 2). Over onehalf of the carcasses evaluated in this study were in the range of 5.40 to 5.49, and over 80% were within the range of 5.40 to 5.59, a range considered as the normal ultimate ph for beef longissimus muscle following normal postmortem metabolism (Lawrie, 1958; Tarrant and Mothersill, 1977). Of the carcasses that had muscle ph values of 5.87 or greater, 22 of 24 (91.7%) were classified as dark cutters according to USDA grading standards (USDA, 1997). Of the carcasses that had muscle ph values of less than 5.87, 6 of 976 (0.6%) were classified as dark cutters. Therefore, it seems that a muscle ph value of approximately Table 2. Comparison of the National Beef Quality Audit 1995 (NBQA 1995) carcasses with the carcasses used in the present study NBQA 1995, % (Smith et al., 1995) The present study,% Item (n = 11,799) (n = 1,000) Breed type Native Brahman Dairy Sex class Steers Heifers Bullocks Marbling score Moderately abundant Slightly abundant Moderate Modest Small Slight Traces Practically devoid Dark-cutting discount Normal / / Full Overall maturity A B C Hot carcass wt < 227 kg kg kg kg kg > 408 kg USDA yield grade Adjusted fat thickness < 0.5 cm cm cm cm > 1.9 cm Plants A 53.3 B 38.7 C 8.0

4 Beef color and ph survey 681 Table 3. Simple statistics for carcass traits, muscle color, muscle ph, muscle temperature, and electrical impedance Variable N Mean Std Dev Minimum Maximum Hot carcass wt, kg 1, Adj. fat thickness, cm 1, Longissimus muscle area, cm 2 1, KPH 1, USDA yield grade 1, Skeletal maturity a 1, Lean maturity a 972 b Overall maturity a 1, Marbling score a 1, USDA quality grade a 1, Electrical impedance, Py a 1, Muscle temperature, C 1, Muscle ph 1, L* a 1, a* a 1, b* a 1, a See Table 1 for definition of variables. b Lean maturity was not evaluated for dark-cutting carcasses (USDA, 1997) was the approximate cut-off between normal and dark-cutting beef carcasses. The distribution of L* values (Figure 3) among the 1,000 carcasses exhibited a normal bell-shaped curve (P of normal distribution = ), and the majority of the carcasses fell within the range of 36 to 43. The distribution of b* values (Figure 4) was not normally distributed (P of normal distribution = ) due to a long tail of carcasses on the low side, which corresponded to the dark-cutting carcasses. The distribution of a* values is not shown in figure form because the distribution of a* values very closely resembled the distribution of b* values (r a*,b* = 0.95). Simple correlations are presented in Table 4. Even weak correlations were statistically significant (P < 0.05) because of the large sample size (n = 1,000), indicating that the correlations reported in this paper are highly accurate estimates (i.e., narrow confidence in- Figure 1. Distribution of longissimus electrical impedance values (Py) among 1,000 beef carcasses. Values represent the number of carcasses within each Py range.

5 682 Page et al. Figure 2. Distribution of longissimus ultimate muscle ph values among 1,000 beef carcasses. Values represent the number of carcasses within each muscle ph range. tervals). The three colorimeter values (L*, a*, and b*) were all intercorrelated; the strongest relationship occurred between a* and b* (r = 0.95). Given this high correlation between a* and b* and looking at the relationships of a* and b* with other variables, it seems that a* offers very little unique information beyond Figure 3. Distribution of longissimus L* values among 1,000 beef carcasses. Values represent the number of carcasses within each L* range.

6 Beef color and ph survey 683 Figure 4. Distribution of longissimus b* values among 1,000 beef carcasses. Values represent the number of carcasses within each b* range. b*, and vice versa, when measuring fresh beef color at the time of carcass grading. However, a* is probably more useful than b* when measuring beef color stability (surface metmyoglobin formation) over time because a* is a value from red to green and metmyoglobin formation changes the color of beef from red to greenish brown. Lean maturity was correlated with L*, a*, and b* values, most highly with L* (Table 4). Other researchers have also reported that L* was more highly correlated to beef carcass lean maturity than was a* or b* (Orcutt et al., 1984; Wulf and Wise, 1999). In the present study, L*, a*, and b* values were negatively correlated to muscle ph, showing that as muscle ph increased, muscle color values decreased. Values for a* and b* were more highly correlated with muscle ph than were values for L*, which agrees with the findings of Wulf and Wise (1999). Our observation and that of previous researchers that lean maturity is most highly associated with L*, whereas muscle ph is most highly associated with a* and b*, indicates that lean maturity is more a function of lightness/darkness, whereas mus- Table 4. Simple correlations a among carcass traits, muscle color, ph, temperature, and electrical impedance (n = 1,000 except for lean maturity, where n = 972) Item Hot carcass wt 2. Adj. fat thickness Longissimus muscle Skeletal maturity b Lean maturity b Overall maturity b Dark-cutting discount, % c Marbling score b Electrical impedance, Py b Muscle temperature Muscle ph L* b a* b b* b a r >0.06 (P < 0.05). b See Table 1 for definition of variables. c Lean maturity was not evaluated on dark-cutting carcasses (USDA, 1997).

7 684 Page et al. cle ph affects muscle color by altering hue (red, yellow, green, blue, or an intermediate) more than lightness/ darkness. According to colorimeter values, higher muscle ph is associated with beef that is more green and more blue, whereas lower muscle ph is associated beef that is more red and more yellow. Based on our subjective observations, higher ph causes beef to appear more purple, whereas lower ph causes beef to appear more orange. These casual observations would agree with the colorimeter in terms of the effect of muscle ph on hue. The negative correlations between colorimeter values and muscle ph can be explained, in that color in muscle tissue is based on the reflectance of light off free water and on oxygenation of the myoglobin (Ledward et al., 1992). At a higher muscle ph, proteins are able to bind more strongly with water, allowing less free water. When the proteins bind more water, the muscle fibers are swollen, leaving less space between muscle fibers. Therefore, meat that has a higher ph will be darker in color because there is less free water to reflect light (Ledward et al., 1992). Furthermore, at a higher muscle ph, enzymes that use oxygen are more active, resulting in less oxygenation of the surface myoglobin and a darker color (Price and Schweigert, 1987; Ledward et al., 1992). In the present study, there was a weak, positive correlation between electrical impedance and muscle ph (Table 4). Electrical impedance is a measure of the resistance of an electrical current through muscle tissue, which is probably related to the amount of free water in the muscle (i.e., more free water would result in a better electrical conductor) (Kauffman, 1997). As previously discussed, there is less free water in muscle tissue at a higher ph. Therefore, the positive correlation between electrical impedance and muscle ph observed in this study supports the hypothesis that less free water equals greater electrical impedance. Weak positive correlations were observed between fat thickness and muscle color (L*, a*, and b*), which is in agreement with the findings of Wulf et al. (1997), who previously reported weak positive correlations of L*, a*, and b* values with the amount of external fat on beef carcasses. Furthermore, both Wulf et al. (1997) and the present study showed a weak negative correlation between fat thickness and muscle ph. Least squares means were calculated for classes of carcasses differing in fat thickness (Table 5). There seemed to be a threshold at approximately 0.76 cm of backfat. For carcasses with less than 0.76 cm of backfat, the meat was darker and muscle ph was higher than for carcasses with more than 0.76 cm of backfat. Tatum et al. (1982) found that leaner carcasses produced less tender beef steaks and that there seemed to be a threshold at approximately 0.76 cm of backfat below which carcasses produced less tender beef. The findings of Tatum et al. (1982), coupled with the results of the present study and the results of previous studies showing relationships between muscle ph/color and beef tenderness (Purchas, 1990; Wulf et al., 1997), seem to indicate that beef carcasses with less than 0.76 cm of backfat have less tender beef than fatter carcasses due, at least in part, to differences in glycolytic metabolism. The higher muscle temperature for fatter carcasses observed in these previous studies and the positive correlation between fat thickness and muscle temperature observed in the present study are probably a result of an insulation effect of fat slowing down the carcass chilling process. The correlations between fat thickness and muscle ph/color could also be an indirect result of the fat insulation effect, or it could be that leaner cattle produce darker meat due to some genetic or environmental correlation between leanness and muscle ph/color. The latter hypothesis is supported by the lack of a significant correlation between muscle temperature and ph in the present study. The relationships between muscle color and fat thickness in this study were similar to the findings of Wulf et al. (1997) in that b* was the most highly correlated with external fat thickness and L* was the most lowly correlated with external fat thickness of the three colorimeter variables. Because there was a relationship between fat thickness and ph/color, there were also muscle ph and color differences observed between USDA quality grades. As quality grade increased, muscle ph declined, color values increased, and variation in ph and color decreased (Standard: ph = 5.57 ± 0.25, L* = ± 3.10; Select: ph = 5.52 ± 0.20, L* = ± 2.64; Choice: ph = 5.48 ± 0.09, L* = ± 2.45; Prime: ph = 5.49 ± 0.07, L* = ± 2.31; data not presented in tabular form). USDA Select carcasses were twice as variable in muscle ph as USDA Choice carcasses. Based on our own retail survey experience (Wulf et al., 1994), those retail meat managers whose stores have switched from selling USDA Choice beef to USDA Select beef have expressed increased dissatisfaction with the increased variability in fresh beef color. The results of the present study would support these concerns of more color variation in USDA Select than in USDA Choice. Furthermore, these observed differences in muscle ph variation between USDA quality grades could, in addition to marbling, explain some of the palatability differences observed between USDA quality grades, because muscle ph has been shown to be related to cooked beef palatability (Purchas, 1990; Wulf et al., 1997). The effects of packing plant on USDA grade data, electrical impedance, muscle temperature, muscle ph, and muscle color are shown in Table 6. Kidney, pelvic, and heart fat (KPH), skeletal maturity, overall maturity, incidence of dark cutters, and muscle ph were not different between packing plants. Plant B had lighterweight carcasses with lower yield grades than plants C and A. Although there were no differences in muscle ph among plants, there were differences among plants in electrical impedance, muscle temperature, and lean color. Plant C had higher electrical impedance readings and lower muscle temperature readings than

8 Beef color and ph survey 685 Table 5. Fat thickness effects on muscle color, ph, temperature, and electrical impedance Fat thickness, cm n L* a* b* ph Temp, C Py < d 23.8 f 10.0 g 5.60 c 2.26 cd 63.7 f d 24.3 ef 10.4 gf 5.54 bc 2.33 cd 57.6 ef cd 24.7 de 10.6 ef 5.53 b 2.33 c 53.7 de bc 25.0 cd 10.9 de 5.49 ab 2.43 bcd 51.6 cd bc 25.1 c 10.9 d 5.50 ab 2.56 ab 49.7 bc ab 25.3 bc 11.2 cd 5.48 a 2.61 a 47.0 ab a 25.6 ab 11.5 abc 5.47 a 2.57 ad 44.9 a bc 25.5 ab 11.3 bd 5.49 ab 2.69 a 48.8 abc ac 25.5 ac 11.3 abd 5.49 ab 2.76 a 47.0 abc > ab 26.3 a 11.8 a 5.47 ab 2.84 a 43.8 a RSD a,b,c,d,e,f,g Means within a column lacking a common superscript letter differ. (P < 0.05). See Table 1 for definition of variables. plants A or B. Plant A showed lower lean maturity scores than the other two plants. Plant C had lower L* values and higher b* values than plant B, and plant C had higher a* values than both plants A and B. These differences among plants in electrical impedance, muscle temperature, and colorimeter readings were probably due to differences in rate of ph decline as a result of differences among plants in carcass handling practices. Plant A used low-voltage electrical stimulation, whereas plants B and C did not use electrical stimulation. Plant A operated on a 24-h chill, plant B on a 48-h chill, and plant C ranged in chill from 24 to 96 h. Plants A and B used spray-chill systems, whereas plant C shrouded carcasses. The effects of sex class (steers, heifers, and bullocks) on USDA grade data, electrical impedance, tempera- ture, ph, and muscle color are shown in Table 7. Heifer carcasses had lighter weights, more external fat, smaller longissimus muscle areas, and more KPH fat than steer or bullock carcasses. Yield grade did not differ between steer and heifer carcasses, but bullock carcasses had lower yield grades than both steer and heifer carcasses. Furthermore, bullock carcasses exhibited greater advanced skeletal and lean maturity than steer and heifer carcasses, in conjunction with lower marbling scores than steer and heifer carcasses, resulting in lower overall quality grades for bullock carcasses. Heifer carcasses had higher skeletal maturity scores, higher overall maturity scores, and higher marbling scores than steer carcasses. There was no difference in muscle ph between steer and heifer carcasses, which is different from the find- Table 6. Plant effects on carcass traits, muscle color, ph, temperature, and electrical impedance Plant A B C Item (n = 533) (n = 387) (n = 80) RSD Hot carcass wt, kg 349 a 326 b 345 a 38 Adj. fat thickness, cm 1.17 ab 1.12 b 1.30 a 0.46 Longissimus muscle area, cm b 84.9 ab 86.2 a 9.6 KPH USDA yield grade 3.0 a 2.5 b 2.8 a 0.8 Skeletal maturity c Lean maturity c 158 b 181 a 179 a 23 Overall maturity c Dark-cutting discount, % Marbling score c 419 ab 397 b 447 a 89 USDA quality grade c 689 ab 668 b 700 a 55 Electrical impedance, Py c 50.7 b 47.5 b 67.1 a 13.7 Muscle temperature, C 2.6 a 2.5 a 1.7 b 0.8 Muscle ph L* c 39.4 ab 39.7 a 38.5 b 2.4 a* c 25.2 b 24.6 b 26.3 a 1.8 b* c 11.1 ab 10.6 a 11.6 b 1.3 a,b Means within a row lacking a common superscript letter differ (P < 0.05). c See Table 1 for definition of variables.

9 686 Page et al. Table 7. Sex class effect on carcass traits, muscle color, ph, temperature, and electrical impedance Sex class Steer Heifer Bullock Item (n = 680) (n = 315) (n = 5) RSD Hot carcass wt, kg 350 a 319 b 359 a 38 Adj. fat thickness, cm 1.14 a 1.24 b 0.53 c 0.46 Longissimus muscle area, cm c 81.3 b 98.7 a 9.6 KPH, % 2.1 b 2.3 a 1.8 b 0.4 USDA yield grade 2.8 a 2.8 a 1.5 b 0.8 Skeletal maturity d 167 c 181 b 205 a 24 Lean maturity d 168 b 169 b 252 a 23 Overall maturity d 168 c 176 b 217 a 19 Dark-cutting discount, % Marbling score d 407 c 426 a 304 b 89 USDA quality grade d 682 a 681 a 579 b 55 Electrical impedance, Py d Muscle temperature, C 2.5 b 2.6 a 2.9 ab 0.8 Muscle ph 5.51 b 5.50 b 5.78 a 0.16 L* d 39.6 a 39.2 b 35.9 c 2.4 a* d 25.2 a 24.8 b 22.4 b 1.8 b* d 11.0 a 10.8 b 8.7 c 1.3 a,b,c Means within a row lacking a common superscript letter differ (P < 0.05). d See Table 1 for definition of variables. ings of Wulf et al. (1997), who reported that steer carcasses had a lower muscle ph than heifer carcasses. In the present study, steer carcasses had higher L*, a*, and b* values than heifer carcasses, despite no difference in muscle ph between steer and heifer carcasses. Wulf et al. (1997) reported higher a* and b* values for steer carcasses than for heifer carcasses; however, unlike the present study, Wulf et al. (1997) did not find a significant difference in L* values when comparing steer to heifer carcasses. It is interesting to note that, in the present study, heifer carcasses had more external fat and darker-colored muscle than steer carcasses (Table 7), whereas fatter carcasses had lighter-colored muscle when all carcasses were analyzed as a group (Tables 4 and 5). This suggests that at the same fat thickness there would be an even greater difference in muscle color between steer and heifer carcasses. It also suggests that the sex class effect on muscle color may result from an underlying mechanism different from the fat thickness effect on muscle Table 8. Breed type effect on carcass traits, muscle color, ph, temperature, and electrical impedance Breed type Native Dairy Brahman Item (n = 887) (n = 48) (n = 65) RSD Hot carcass wt, kg 340 a 323 b 346 a 38 Adj. fat thickness, cm 1.19 a 0.74 b 1.17 a 0.46 Longissimus muscle area, cm a 72.9 b 81.2 a 9.6 KPH, % USDA yield grade Skeletal maturity d Lean maturity d Overall maturity d Dark-cutting discount, % Marbling score d USDA quality grade d Electrical impedance, Py d 50.5 b 62.9 a 45.1 c 13.7 Muscle temperature, C 2.5 a 2.2 b 2.7 a 0.8 Muscle ph 5.50 b 5.59 a 5.46 b 0.16 L* d 39.6 a 37.6 b 39.8 a 2.4 a* d 25.1 a 23.4 b 25.2 a 1.8 b* d 11.0 a 9.7 b 11.1 a 1.3 a,b,c Means within a row lacking a common superscript letter differ (P < 0.05). d See Table 1 for definition of variables.

10 Beef color and ph survey 687 color. Bullock carcasses had higher muscle ph values and lower L* and b* values than steer or heifer carcasses. Table 8 shows the effects of breed type (native, dairy, and Brahman) on USDA grade data, electrical impedance, muscle temperature, muscle ph, and muscle color. Kidney, pelvic, and heart fat, USDA yield grade, skeletal maturity, lean maturity, overall maturity, dark-cutting discount, marbling, and quality grade were not affected by breed type. Those carcasses with dairy-type characteristics possessed lighter hot carcass weights, less external fat, and smaller longissimus muscle areas than native or Brahman-type carcasses. Furthermore, dairy-type carcasses had lower L*, a*, and b* values, higher ph values, and lower muscle temperatures than the native and Brahmantype carcasses. The dairy-type effect on muscle ph and color was substantial; dairy-type carcasses were almost one full standard deviation (Table 3) different from native-type carcasses in muscle ph and color (Table 8). Faustman and Cassens (1991) reported a higher percentage of metmyoglobin in beef from Holstein steers than in beef from beef-type steers, along with several other differences between Holstein and beeftype carcasses in muscle metabolites that could affect muscle color. Although Wulf et al. (1997) previously found Bos taurus carcasses had higher L* values and lower a* values than Bos indicus carcasses, there were no significant color differences found in this study between the native and Brahman-type carcasses. Dairytype carcasses had higher electrical impedance values (indicating higher water-holding capacity) and Brahman-type carcasses had lower electrical impedance values (indicating lower water-holding capacity) than native-type carcasses (Table 7). Implications This study gives industry and research communities a baseline of a beef carcass population in terms of longissimus muscle color, ph, and electrical impedance to be used in decision making and for further research into factors affecting fresh beef muscle quality. There seems to be a threshold fat thickness at approximately 0.76 cm, below which carcasses have higher muscle ph values and darker-colored muscle. Muscle color and muscle ph are all subject to packing plant, sex class, and breed type effects. Literature Cited Faustman, C., and R. G. Cassens The effect of cattle breed and muscle type on discoloration and various biochemical parameters in fresh beef. J. Anim. Sci. 69: Hedrick, H. B., E. D. Aberle, J. C. Forrest, M. D. Judge, and R. A. Merkel Principles of Meat Science. erd ed. Kendall/Hunt Publishing Company, Dubuque, IA. Jeremiah, L. E., A. K. W. Tong, and L. L. Gibson The usefulness of muscle color and ph for segregating beef carcasses into tenderness groups. Meat Sci. 30: Kauffman, R. G National pork quality project. In: Proc. Pork Quality Summit, Des Moines, IA. pp Kropf, D. H Effects of retail display conditions on meat color. In: Proc. 33rd Recip. Meat Conf., West Lafayette, IN. pp Lawrie, R. A Physiological stress in relation to dark-cutting beef. J. Sci. Food Agric. 9: Ledward, D. A., D. E. Johnston, and M. K. Knight The Chemistry of Muscle-Based Foods. pp The Royal Society of Chemistry, Thomas Graham House, Science Park, Cambridge, U.K. MacKinney, G., A. C. Little, and L. Brinner Visual appearance of foods. Food Technol. 20: Oliver, M. A., M. Gispert, J. Tibau, and A. Diestre The measurement of light scattering and electrical conductivity for the prediction of PSE pig meat at various times post mortem. Meat Sci. 29: Orcutt, M. W., T. R. Dutson, D. P. Cornforth, and G. C. Smith Factors affecting the formation of a dark, coarse band ( heatring ) in bovine longissimus muscle. J. Anim. Sci. 58: Price, J. F., and B. S. 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AMS, USDA, Washington, DC. Watanabe, A., C. C. Daly, and C. E. Devine The effects of the ultimate ph of meat on tenderness changes during ageing. Meat Sci. 42: Whitman, T. A., J. C. Forrest, M. T. Morgan, and M. R. Okos Electrical measurement for detecting early postmortem changes in porcine muscle. J. Anim. Sci. 74: Wulf, D. M., S. F. O Connor, J. D. Tatum, and G. C. Smith Using objective measures of muscle color to predict beef longissimus tenderness. J. Anim. Sci. 75: Wulf, D. M., J. R. Romans, and W. J. Costello Current merchandising practices and characteristics of beef wholesale rib usage in three U.S. cities. J. Anim. Sci. 72: Wulf, D. M. and J. W. Wise Measuring muscle color on beef carcasses using the L* a* b* color space. J. Anim. Sci. 77: