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ANIMAL PRODUCTS |
Department of Animal and Food Science, Texas Tech University, Lubbock 79409
Abstract
Cattle (n = 303) were visually selected from four feed yards to represent six phenotypes (English [EN; n = 50], 
English-
Brahman [ENB; n = 52], 
English- Exotic [ENEX; n = 56], English- Exotic- Brahman [ENEXB; n = 47], Exotic- Brahman [EXB; n = 49], and Exotic- English- Brahman [EXENB; n = 49]). Carcasses were processed at a commercial beef packing facility, and strip loins were collected after 48-h chilling. Strip loins were aged for 14 d at 2°C and frozen at -20°C for 3 to 5 d before three 2.5-cm-thick steaks were cut for Warner-Bratzler shear force (WBSF) determinations and sensory evaluations. Phenotype EN had the highest (P < 0.05) adjusted fat thickness, and EXB had adjusted fat thickness that was lower (P < 0.05) than all other phenotypes except EXENB. Carcasses of EN and ENB had smaller (P < 0.05) longissimus muscle areas than phenotypes ENEX, EXB, and EXENB. Phenotype EN produced carcasses with the highest (P < 0.05) numerical yield grade, whereas carcasses originating from phenotype EXB had lower (P < 0.05) numerical yield grades than all other phenotypes except ENEX. No differences (P > 0.05) were found among phenotypes for mean WBSF values or sensory panel ratings for initial and sustained tenderness, initial and sustained juiciness, beef flavor characteristics, and overall mouthfeel. More than 90% of steaks from carcasses of all phenotypes had WBSF values less than 3.6 kg when cooked to an internal cooked temperature of 70°C. Results from this study indicated that all phenotypes represented in this study could be managed to produce tender beef.
Key Words: Beef • Cattle • Phenotype • Tenderness
Introduction
Research suggests that 10 to 25% of the beef steaks sold at retail stores are tough (Morgan et al., 1991
; Savell et al., 1991). Miller et al. (2001) reported that tenderness accounts for more than 50% of consumers’ overall acceptability of beef steaks. Additionally, Boleman et al. (1997) noted that consumers are willing to pay a higher price for beef that is more tender. Numerous branded beef programs have been developed to provide consumers with a more satisfactory eating experience; however, many beef producers wish to go further by source verification and identification of guaranteed tender beef products in the retail market.
Numerous studies have shown Bos indicus cattle produce beef that is tougher than the beef of Bos taurus (Ramsey et al., 1963; McKeith et al., 1985; Crouse et al., 1987). As the percentage of Brahman breeding increases, beef tenderness decreases (Crouse et al., 1989; Johnson et al., 1990), and Sherbeck et al. (1996) found that as phenotypic expression of Brahman characteristics increased, tenderness of steaks from those cattle also decreased. Moreover, researchers have shown great variation in tenderness among different Bos taurus breeds (Koch et al., 1976; Gregory et al., 1994; Wulf et al., 1996). Interestingly, more than 20 USDA-certified programs use phenotype as a principal selection criterion (USDA, 2003). Therefore, the objective of this study was to determine whether beef cattle phenotypes selected by an individual packer and their alliance partners can be used to identify carcasses for a guaranteed tender beef program.
Materials and Methods
Cattle Selection
Cattle (n = 303) were selected from four feed yards (Caprock #5, Bovina, TX; Champion Feedyard, Hereford, TX; Swisher, Swisher County, TX; and Tascosa, Bushland, TX) to represent six phenotypes predetermined by the packer (English [EN; n = 50], English- Brahman [ENB; n = 52], English- Exotic [ENEX; n = 56], English- Exotic- Brahman [ENEXB; n = 47], Exotic- Brahman [EXB; n = 49], and Exotic- English- Brahman [EXENB; n = 49]). All feed yards were within 160 km of the beef packing facility. Cattle of each phenotype were selected from numerous pens at each feed yard by two trained evaluators (whose combined experience in beef cattle evaluation amounted to over 50 yr). Before animal selection, each person evaluated over 2,000 feedlot steers and heifers, and discussed phenotype percents and classifications to decrease evaluator variation. If an animal did not fit into one of the phenotype classifications by visual appraisal, the animal was removed from consideration in the study.
Each phenotype possessed certain unique characteristics. Cattle classified as EN appeared to be Angus, Red Angus, Hereford, or Shorthorn, or a cross of these breeds, and were typically smaller framed. Cattle classified as ENB were similar to EN cattle but possessed little to some extension of ear and a small hump along with additional, but not excess, skin in the dewlap and midline sheath areas. Cattle classified as ENEX exhibited characteristics similar to an Angus x Charolais, or other English x exotic-cross cattle. Cattle classified as EXENB were larger framed and heavier muscled than cattle classified as ENB, but smaller framed and less muscular than a full-blood exotic. Cattle classified as ENEXB were slightly smaller framed than ENEX with similar Brahman characteristics as the ENB cattle, showing a little ear extension and extra hide in the brisket and midline sheath areas. Cattle classified as EXB were large-framed, heavy-muscled cattle with little to some extension of ear and a small hump along with additional, but not excess, skin in the dewlap and midline sheath areas. Cattle classified as EXENB contained at least one-half exotic breeding and were slightly larger framed and heavier muscled than ENEXB.
Slaughter and Carcass Grading
Cattle were determined to be market ready based on visual appraisal by the feedlot manager at each of the feedlots. Cattle were transported and slaughtered according to normal, industry-accepted slaughter procedures, except that carcasses were not electrically stimulated. The carcasses were spray-chilled for 48 h at 0°C.
Carcasses were evaluated by two trained Texas Tech University personnel for skeletal maturity, lean maturity, and marbling score to determine quality grade (USDA, 1996b). Carcasses also were evaluated for fat thickness; adjusted fat thickness; LM area; percentage of kidney, pelvic, and heart fat; and yield grade (USDA, 1996b). If the carcass had a marbling score greater than Modest00 or less than Slight00, or was not A-maturity, it was removed from the study because carcasses with higher marbling scores are already used in other programs.
Aging and Further Processing
Carcasses were fabricated according to Institutional Meat Purchase Specifications (IMPS; USDA, 1996a) and strip loins (IMPS #180) were vacuum-packaged, boxed, and transported to the Texas Tech Meat Laboratory to age at 2°C for 14 d. Strip loins were frozen at -20°C for 3 to 5 d. Three 2.5-cm-thick steaks were cut from the anterior end of the strip loin. Two steaks were randomly assigned for Warner-Bratzler shear force (WBSF) determinations, whereas the remaining steak was designated for sensory panel evaluation. Steaks were vacuum-packaged and refrozen at -20°C for 5 to 30 d.
Shear Force Determinations
Steaks were thawed overnight in a cooler to an internal temperature of 3 to 5°C. External fat was completely removed. Steaks were cooked on a belt grill (Model TBG-60 Magigrill; MagiKich’n, Quakertown, PA). Belt grill settings (top heat = 163°C, bottom heat = 163°C, preheat = disconnected, height = 2.16 cm, and cook time = 5.7 min) were chosen based on Wheeler et al. (1998) to achieve a cooked temperature of 70°C. Also, one steak from each strip loin was cooked to 75°C by modifying the belt grill cooking time to 6.4 min. Approximately 60% of today’s consumers cook steaks to medium-well or well-done degrees of doneness (NLSMB, 1995); therefore, researchers also chose to evaluate WBSF at 75°C. Thus, providing consumers with a guaranteed tender product becomes more of a challenge because fewer steaks are tender at medium-well or higher degrees of doneness. Steaks were chilled at 4°C for 24 h, and six 1.3-cm-diameter cores were taken from each steak parallel to the muscle fiber orientation. Cores then were sheared once perpendicular to muscle fiber orientation with a Warner-Bratzler shear machine (Model 235; G-R Electric Manufacturing, Manhattan, KS), and the mean of six cores per steak was used for statistical analyses.
Sensory Evaluations
Steaks were thawed and cooked as described previously for WBSF determinations, and steaks were cooked to an internal cooked temperature of 70°C. Immediately following cooking, steaks were cut into 1-cm3 pieces, and the pieces were placed in prewarmed serving pans. Eight trained panelists (Cross et al., 1978) were served two pieces under red lights. Twelve steaks were served during each panel session, and three panel sessions were conducted each day. The panelists scored (AMSA, 1995) the steaks for initial and sustained juiciness (1 = extremely dry to 8 = extremely juicy), initial and sustained tenderness (1 = extremely tough to 8 = extremely tender), beef flavor intensity (1 = extremely bland to 8 = extremely intense), beef flavor characteristic (1 = extremely uncharacteristic beef flavor to 8 = extremely characteristic beef flavor), and overall mouthfeel (1 = extreme non-beef-like mouthfeel to 8 = extreme beef-like mouthfeel).
Statistical Analyses
Data were analyzed as a completely randomized design using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC), with individual steer/heifer as the experimental unit. Phenotype was the single main effect included in the model. Least squares means were computed for each dependent variable and statistically separated by pairwise t-test (PDIFF option of SAS) when 
0.05.
Frequency tables were constructed using 
2 procedures to determine tender, intermediate, and tough steaks by phenotype. Steaks designated as "Tender" had a WBSF value of less than 3.6 kg and a sensory panel tenderness score 
6.0; steaks of "intermediate" tenderness had WBSF values between 3.6 and 4.5 kg and mean sensory panel tenderness scores between 4.5 and 5.9; and "tough" was considered when the WBSF value was greater than 4.5 kg and the sensory panel tenderness score was less than 4.5.
Results and Discussion
Carcass Traits
Carcass cutability traits by phenotype are presented in Table 1. Hot carcass weights tended to be higher (P = 0.09) for phenotypes showing exotic-breed characteristics (ENEX, ENEXB, EXB, and EXENB). Phenotype EN had the highest (P < 0.05) adjusted fat thickness, and EXB had a lower (P = 0.05) adjusted fat thickness compared with all other phenotypes except EXENB. All phenotypes had similar (P > 0.05) percentages of kidney, pelvic, and heart fat. Phenotypes EN and ENB had smaller LM areas than phenotypes ENEX, EXB, and EXENB. Phenotype EN produced carcasses that were the lowest in cutability, as evidenced by the highest (P < 0.05) numerical yield grade, whereas carcasses originating from phenotype EXB had the lowest (P < 0.05) numerical yield grade, but not (P > 0.05) different from ENEX. Based on the carcass yield grade results, cattle appeared to be classified correctly. Previous research has shown that English cattle have greater fat thickness and smaller LM areas compared with exotic and exotic-cross cattle (Griffin et al., 1985; Crouse et al., 1989). Additionally, Shackelford et al. (1991) and Crouse et al. (1989) found that Brahman-cross cattle produced carcasses with less fat than English cattle, but with similar-sized LM areas.
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). However, other researchers have shown that beef from English and exotic cattle was more tender than that from Brahman-cross cattle (Crouse et al., 1989; Johnson et al., 1990; Sherbeck et al., 1996). Many of the studies reporting that Brahman-cross cattle produce steaks tougher than those from English or exotic cattle were conducted in a controlled setting. Previous research studies also have used a limited genetic base, showing the effects of only a few sires from these breed types. Cattle were randomly selected from four commercial feedlots in the present study to more accurately represent current industry practices. However, our sample of cattle showed no phenotypic differences for tenderness. Steaks cooked to 70°C had lower (P < 0.05) WBSF values than steaks cooked to 75°C. Not surprisingly, palatability characteristics decreased as the degree of doneness increased (Parrish et al., 1973; NLSMB, 1995; Hilton et al., 1998).
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). When cooked to 75°C, over 80% of steaks from phenotypes EN, ENB, ENEX, and EXENB had WBSF values of less than 3.6 kg, whereas phenotypes ENEXB and EXB produced only 67 and 75% steaks that had WBSF values of less than 3.6 kg, respectively. Thus, degree of doneness has an effect on the tenderness classification of steaks, and the effect of internal end-point temperature varies across phenotypes. Less than 4% of steaks from carcasses of all phenotypes, except ENEXB, were rated as slightly tough or lower by sensory panelists. Sensory panelists rated 6.2% of steaks of phenotype ENEXB initially slightly tough and 8.3% slightly tough after chewing.
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Results of this study indicate that beef cattle phenotypes with one-quarter, or less, phenotypic expression of Brahman inheritance can produce beef for a guaranteed tender program. Thus, sorting cattle into biological-type/phenotype groups may allow companies to accurately market a guaranteed tender beef product.
Footnotes
1 Manuscript No. T-5-456 of the College of Agric. Sci. and Natural Resources, Lubbock, TX. This research was supported by Excel Corp., Wichita, KS. 
2 Current address: Angelo State University, San Angelo, TX.
3 Current address: Middle Tennessee State University, Murfreesboro.
5 Correspondence: Box 42162 (phone: 806-742-2804; fax: 806-742-0169; e-mail: mfmrraider{at}aol.com).
Received for publication July 8, 2002. Accepted for publication January 9, 2004.
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