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ANIMAL PRODUCTS |
Roman L. Hruska U.S. Meat Animal Research Center, USDA, ARS, Clay Center, NE 68933-0166
Abstract
Experiments were conducted to compare the effects of two cookery methods, two shear force procedures, and sampling location within non-callipyge and callipyge lamb LM on the magnitude, variance, and repeatability of LM shear force data. In Exp. 1, 15 non-callipyge and 15 callipyge carcasses were sampled, and Warner-Bratzler shear force (WBSF) was determined for both sides of each carcass at three locations along the length (anterior to posterior) of the LM, whereas slice shear force (SSF) was determined for both sides of each carcass at only one location. For approximately half the carcasses within each genotype, LM chops were cooked for a constant amount of time using a belt grill, and chops of the remaining carcasses were cooked to a constant endpoint temperature using open-hearth electric broilers. Regardless of cooking method and sampling location, repeatability estimates were at least 0.8 for LM WBSF and SSF. For WBSF, repeatability estimates were slightly higher at the anterior location (0.93 to 0.98) than the posterior location (0.88 to 0.90). The difference in repeatability between locations was probably a function of a greater level of variation in shear force at the anterior location. For callipyge LM, WBSF was higher (P < 0.001) at the anterior location than at the middle or posterior locations. For non-callipyge LM, WBSF was lower (P < 0.001) at the anterior location than at the middle or posterior locations. Consequently, the difference in WBSF between callipyge and non-callipyge LM was largest at the anterior location. Experiment 2 was conducted to obtain an estimate of the repeatability of SSF for lamb LM chops cooked with the belt grill using a larger number of animals (n = 87). In Exp. 2, LM chops were obtained from matching locations of both sides of 44 non-callipyge and 43 callipyge carcasses. Chops were cooked with a belt grill and SSF was measured, and repeatability was estimated to be 0.95. Repeatable estimates of lamb LM tenderness can be achieved either by cooking to a constant endpoint temperature with electric broilers or cooking for a constant amount of time with a belt grill. Likewise, repeatable estimates of lamb LM tenderness can be achieved with WBSF or SSF. However, use of belt grill cookery and the SSF technique could decrease time requirements which would decrease research costs.
Key Words: Cookery • Lamb • Longissimus • Shear Force • Tenderness
Introduction
Warner-Bratzler shear force (WBSF) and trained sensory panel tenderness data are more repeatable when beef longissimus steaks are cooked for a constant amount of time using a belt grill rather than cooking to a constant endpoint temperature using open-hearth electric broilers (Wheeler et al., 1998
). Also, shear force data are more strongly related with sensory panel tenderness rating using the slice shear force (SSF) protocol developed for beef tenderness classification (Shackelford et al., 1999a), rather than the traditional WBSF protocol (Shackelford et al., 1999a). Considering improvements noted in beef, one would think that these technologies could be used to improve the repeatability of lamb shear force data. However, because of differences between species in the cross-sectional area of LM, it is unclear if these technologies would impact the repeatability of shear force measurements in lamb. Moreover, because of differences in the shape and the cross-sectional area of LM across the length of the muscle, it is unclear if the magnitude or repeatability of shear force will differ among sampling locations. Because belt grill cookery is less labor intensive than traditional cooking procedures and SSF is less labor intensive than WBSF, development of these procedures for lamb would reduce the cost of conducting tenderness research in those species. Thus, the present experiments were conducted to compare the effects of two cookery methods (belt grill vs open-hearth electric broiler), two shear force procedures (WBSF vs SSF), and sampling location (anterior, middle, and posterior) within non-callipyge and callipyge lamb longissimus muscle on the magnitude, variance, and repeatability of LM shear force data.
Materials and Methods
Experiment 1
Animals.
The Roman L. Hruska U.S. Meat Animal Research Center (MARC) Animal Care and Use Committee approved the use of animals in this study. Normal (n = 15) and callipyge (n = 15) crossbred (
Dorset, Romonav, 
Finnsheep) lambs were produced by mating homozygous normal (n = 7) and homozygous callipyge (n = 7) Dorset x Romonav rams to Finnsheep ewes. Rams were obtained from a third production year of the F2 generation of the mating scheme described by Freking et al. (1998). Any lamb produced by mating a homozygous normal ram with a Finnsheep ewe (assumed to be homozygous normal at the callipyge locus) would be expected to have the normal lamb phenotype and any lamb produced by mating a homozygous callipyge ram with a Finnsheep ewe would be expected to have the callipyge phenotype (Cockett et al., 1996).
Lambs were reared in an indoor/outdoor production facility. From 1 wk of age (creep fed) to slaughter (222 to 231 d old), lambs were given ad libitum access to long-stem alfalfa hay and a diet that contained 88% DM and 77% total digestible nutrients. Carcasses were dressed conventionally and chilled for 48 h at 1°C. The entire dorsal section (loin and rack) was removed from each carcass, vacuum-packaged, aged (2°C) until 14 d postmortem, and frozen (-30°C). Using a band saw, each frozen dorsal section was sliced to yield 11 double chops (2.54 cm thick). Each double chop was then split down the middle of the vertebral column. Thus, 22 LM chops were obtained from each carcass.
Within each genotype, approximately one-half (n = 8 normal and n = 8 callipyge) of the carcasses were assigned to open-hearth electric broiler cookery and approximately one-half of the carcasses (n = 7 normal and n = 7 callipyge) were assigned to belt grill cookery (Table 1). Within each carcass side, nine of the chops were used to make three independent measurements of WBSF (three chops per measurement) and two of the chops were used to make a single measurement of SSF (Table 1). A single SSF measurement was made using the thickest portion of LM because it is not known whether variation in the muscle fiber angle across the length of LM would permit accurate SSF measurement at other locations.
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Electric broiler cooking was conducted with a model 450N Open Hearth electric broiler (Farberware, Bronx, NY). Chops were turned after reaching 40°C, and then removed from the grill after reaching 71°C internal temperature. Temperature was monitored with iron constantan thermocouple wires inserted into the geometric center of each chop and attached to a Beckman Industrial model 205 data logger (Beckman Industrial, San Diego, CA).
Warner-Bratzler Shear Force.
Cooked chops were cooled for 24 h at 4°C before removal of two 1.27-cm diameter cores from each chop parallel to the longitudinal orientation of the muscle fibers. Each core was sheared once with a WBSF attachment using an electronic testing machine (model 4411; Instron Corp., Canton, MA). The crosshead speed was set at 200 mm/min.
Slice Shear Force.
Immediately after cooking, SSF was determined using a modification of the protocol developed for assessment of beef LM tenderness (Shackelford et al., 1999 a,b). For each of two chops from each carcass side, a 1-cm-thick, 2.5-cm-long slice was removed from each cooked chop parallel to the muscle fibers following procedures similar to those of Shackelford et al. (1999b), except that the slice had to be limited to a length of 2.5 cm because of the small size of some lamb LM chops. Thus, to achieve the same slice length (5 cm) as that used for beef, the 2.5-cm-long slices from each chop from a given carcass side were laid end to end in the shearing apparatus. Each sample was sheared once with a flat, blunt-end blade (Shackelford et al., 1999a) using an electronic testing machine (model 4411, Instron Corp.). As with beef (Shackelford et al., 1999 a,b), the crosshead speed was set at 500 mm/min.
Statistical Analysis.
To help ensure repeatable WBSF data, six cores per sample are typically obtained; however, in the case of lamb LM, three chops are usually needed to obtain six cores (two cores per chop). Thus, the experimental unit was the average WBSF value for the six cores from a set of three consecutive chops within a given carcass side. Specifically, values were averaged for Chops 1, 2, and 3 and denoted posterior; values were averaged for Chops 4, 5, and 6 and denoted middle; and values were averaged for Chops 9, 10, and 11 and denoted anterior (Table 1
).
Analysis of variance was conducted using the GLM procedures of SAS (SAS Inst. Inc., Cary, NC). Warner-Bratzler shear force data were analyzed using a model that included the main effects of genotype (G), cooking method (C), and sampling location (L) and their interactions (G x C, G x L, C x L, and G x C x L). Animals (A) nested within genotype and cooking method served as the error term for G, C, and G x C. Also, A x L was tested. Slice shear force data were analyzed using a model that included the main effects of G and C and their interaction (G x C). Animals nested within G and C served as the error term for G, C, and G x C.
Repeatability of WBSF was calculated for each sampling location, whereas the repeatability of SSF was calculated for the single location examined. Repeatability was calculated as the proportion of the total variance that could be attributed to animal variance: repeatability = s2animal/(
2animal + 2error). Variance components were estimated with the MIVQUEO option of the VARCOMP procedure of SAS.
Experiment 2
Animals used in this experiment were produced using the same matings as in Experiment 1 and were reared in the same contemporary group. There were 44 non-callipyge and 43 callipyge lambs. Lambs were slaughtered and their carcasses were processed as in Exp. 1. Loin sections were aged, frozen, and sliced as in Exp. 1. Chops 7 and 8 of each carcass side were used to measure SSF. All chops were cooked with the belt grill as described previously. Repeatability of SSF was calculated as in Exp. 1.
Results and Discussion
Analysis of variance of cooking loss data is presented in Table 2. Cooking loss was lower (P < 0.001) for lamb LM chops cooked with the belt grill (19.2%) compared with open-hearth electric broilers (22.3%; Figure 1). This finding agrees with our comparison of these cooking methods for beef LM steaks (Wheeler et al., 1998). Cooking loss was lower (P < 0.01) for non-callipyge (19.5%) LM chops as compared to callipyge chops (22.0%). Although several experiments (Rawlings et al., 1994; Koohmaraie et al., 1995; Carpenter et al., 1997) have investigated the effect of callipyge on tenderness, we could only find one other study that reported the effects of callipyge on cooking loss. Shackelford et al. (1997) observed a tendency (P = 0.11) for cooking loss to be higher for callipyge LM chops.
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and 3). Regardless of cooking method, WBSF and SSF values were greater (P < 0.001) for callipyge LM. There was a significant genotype x sampling location interaction on WBSF (P < 0.001; Figure 2). For callipyge LM chops, WBSF was higher (P < 0.001) at the anterior location than at the middle or posterior locations. For non-callipyge LM, WBSF was lower (P < 0.001) at the anterior location than at the middle or posterior locations. Consequently, the difference in WBSF between callipyge and non-callipyge chops was largest at the anterior location. Differences among studies in the magnitude of the effect of the callipyge phenotype on LM shear force may be due in part to the location within the LM that was studied.
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). Among the 15 callipyge carcasses, the range in mean (averaged over sides) shear force among locations ranged from 0.2 to 5.8 kg. A consequence of this interaction was that WBSF values of the anterior location of the left and right sides were more strongly correlated with each other than they were with WBSF values for the other locations (Table 5).
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). For WBSF, repeatability estimates were highest at the anterior location and lowest at the posterior location. The difference in repeatability between locations was largely a function of the greater level of variation in shear force at the anterior location. Repeatability estimates were slightly higher for chops cooked to a constant endpoint temperature with open-hearth electric broilers than for chops cooked for a constant amount of time using a belt grill. Whereas Wheeler et al. (1998) reported that the repeatability of beef LM WBSF was higher if steaks were cooked with a belt grill (0.85) vs. with open-hearth electric broilers (0.64), the present results indicate that the repeatability of lamb LM WBSF is slightly lower for lamb LM chops cooked with a belt grill.
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). This finding is somewhat contradictory with our comparison of SSF and WBSF in beef LM (Shackelford et al., 1999a). Shackelford et al. (1999a) reported that shear force data were more strongly related with sensory panel tenderness rating using the SSF protocol than with the traditional WBSF protocol. Given this contradiction, Exp. 2 was conducted to obtain an estimate of the repeatability of SSF for lamb LM chops cooked with the belt grill using a larger number of animals (n = 87 vs. 14). In Exp. 2, the repeatability of lamb LM SSF was 0.95 (Figure 3), which is comparable to the estimate of beef LM SSF (0.91; Shackelford et al., 1999a).
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Highly repeatable estimates of lamb longissimus muscle tenderness can be achieved either by cooking to a constant endpoint temperature with electric broilers or cooking for a constant amount of time with a belt grill. Likewise, highly repeatable estimates of lamb longissimus muscle tenderness can be achieved with Warner-Bratzler shear force or slice shear force. Use of belt grill cookery and the slice shear force technique could, however, decrease time requirements, which would decrease research costs. Additionally, location effects on shear force of lamb, particularly callipyge, must be considered when evaluating longissimus muscle tenderness.
Footnotes
1 Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of other products that may also be suitable. The authors are grateful to P. Beska, K. Mihm, and P. Tammen for their assistance in the execution of this experiment and to M. Bierman for her secretarial assistance. 
2 Correspondence—phone: 402-762-4223; fax: 402-762-4149; e-mail: shackelford{at}email.marc.usda.gov.
Received for publication February 28, 2003. Accepted for publication November 10, 2003.
Literature Cited
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Cockett, N. E., S. P. Jackson, T. L. Shay, F. Farnir, S. Berghmans, G. D. Snowder, D. M. Nielsen, and M. Georges. 1996. Polar overdominance at the ovine Callipyge locus. Science 273:236–238.[Abstract]
Freking, B. A., J. W. Keele, C. W. Beattie, S. M. Kappes, T. P. L. Smith, T. S. Sonstegard, M. K. Nielsen, and K. A. Leymaster. 1998. Evaluation of the ovine Callipyge locus: I. Relative chromosomal position and gene action. J. Anim. Sci. 76:2062–2071.
Koohmaraie, M., S. D. Shackelford, T. L. Wheeler, S. M. Lonergan, and M. E. Doumit. 1995. A muscle hypertrophy condition in lamb (Callipyge): Characterization of effects on muscle growth and meat quality traits. J. Anim. Sci. 73:3596–3607.[Abstract]
Rawlings, D. M., N. Cockett, V. T. Mendenhall, and G. D. Snowder. 1994. Quality characteristics of cooked lamb from callipyge animals and normal half-siblings. J. Anim. Sci. 72(Suppl. 1):61. (Abstr.)
Shackelford, S. D., T. L. Wheeler, and M. Koohmaraie. 1997. Effect of the Callipyge phenotype and cooking method on tenderness of several major lamb muscles. J. Anim. Sci. 75:2100–2105.
Shackelford, S. D., T. L. Wheeler, and M. Koohmaraie. 1999a. Evaluation of slice shear force as an objective method of assessing beef longissimus tenderness. J. Anim. Sci. 77:2693–2699.
Shackelford, S. D., T. L. Wheeler, and M. Koohmaraie. 1999b. Tenderness classification of beef. II: Design and analysis of a system to measure beef longissimus shear force under commercial processing conditions. J. Anim. Sci. 77:1474–1481.
Wheeler, T. L., S. D. Shackelford, and M. Koohmaraie. 1998. Cooking and palatability traits of beef longissimus steaks cooked with a belt grill or an open hearth electric broiler. J. Anim. Sci. 76:2805–2810.
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