Electrical Stimulation Effects on Tenderness of Five

Electrical stimulation effects on tenderness of five muscles from Hampshire x Rambouillet crossbred lambs with the callipyge phenotype. C R Kerth, T L Cain, S P Jackson, C B Ramsey and M F Miller J ANIM SCI 1999, 77:2951-2955.

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Electrical Stimulation Effects on Tenderness of Five Muscles from Hampshire × Rambouillet Crossbred Lambs with the Callipyge Phenotype1 C. R. Kerth, T. L. Cain, S. P. Jackson, C. B. Ramsey, and M. F. Miller2 Department of Animal Science and Food Technology, Texas Tech University, Lubbock 79409-2162

ABSTRACT: The objective of this study was to determine effects of electrical stimulation (ES) on muscle quality and sensory traits of 12 Hampshire × Rambouillet callipyge lambs. One side of each carcass was randomly assigned to an ES treatment of 550 V and 60 Hz of electricity for 2 s on and 2 s off 15 times. The other side was a nonstimulated control (NES). Heated calpastatin, sarcomere length, myofibrillar fragmentation index (MFI), Warner-Bratzler shear (WBS), and trained sensory panel values were measured on the semitendinosus (ST), semimembranosus (SM), longissimus (ML), supraspinatus (SP), and triceps brachii (TB) muscles. Electrically stimulating the carcass sides induced a more rapid (P = .001) pH decline in the longissimus muscle, and ES sides had a brighter (P = .001) red color of loineye than nonstimulated sides. At d 14 of storage (2°C), the TB had the highest (P < .05) MFI value, indicating more protein degradation, and the ST and

ML muscles had the lowest MFI (P = .008). Regardless of ES treatment, SM and ML had the highest (P < .05) WBS values. The ST muscle had higher (P < .05) WBS values than the SP but did not differ (P > .05) from the TB muscle. Electrical stimulation had no effect on WBS or any trained sensory panel values (P > .05). The percentage of loin chops rated slightly tender or better was improved 30 to 34% by electrical stimulation (P < .05). The ML muscle was scored lower (P < .05) in sustained juiciness compared with the SM, SP, and TB but did not differ (P > .05) from the ST muscle. The SM and ML muscles were rated lower (P < .05) in initial and sustained tenderness scores than other muscles. Tenderness scores were higher (P < .05) for the TB than for the SP but did not differ (P > .05) from the ST muscle. Electrically stimulating callipyge carcasses improves the tenderness of loin chops by increasing the percentage of chops rated from slightly tough to slightly tender.

Key Words: Callipyge, Electrical Stimulation, Tenderness, Lamb (Meat) 1999 American Society of Animal Science. All rights reserved.

Introduction Carcasses from lambs expressing the callipyge phenotype are leaner and have more muscle, especially in the loin and hind limb (Jackson et al., 1997). However, tenderness variability of meat from callipyge genotype lambs is a major quality defect. Koohmaraie et al. (1995) and Carpenter et al. (1996) showed that progeny of callipyge Dorset sires have larger muscle fiber areas, and Koohmaraie et al. (1995) reported higher calpastatin activity and less tender muscle from callipyge sheep than from normal sheep. Thus, a means to ensure a more

1 Names are necessary to report factually on available data; however, Texas Tech Univ. neither guarantees nor warrants the standard of the product, and the use of the name by Texas Tech Univ. implies no approval of the product to the exclusion of others that may be suitable. 2 To whom correspondence should be addressed: P. O. Box 42162 (phone: 806/742-2804; fax: 806/742-0169; E-mail: mfmrraider@ aol.com). Received November 27, 1997. Accepted April 24, 1999.

J. Anim. Sci. 1999. 77:2951–2955

consistently tender and acceptable product from callipyge lambs is needed. Electrical stimulation (ES) has been used to increase meat tenderness in beef, lamb, and goat carcasses (Savell et al., 1977) and has produced fractures in muscle fibers (Savell et al., 1978). Electrical stimulation can promote the activity of endogenous proteolytic enzymes, including µ-calpain (Dransfield et al., 1992), that are instrumental in promoting the aging effect (Koohmaraie et al., 1988). The increased calpain activity may be due to a depolarization of the cell membrane (Morton and Newbold, 1982) that causes a release of calcium into the cell, which then activates the calcium-dependent proteases. Ho et al. (1996) reported that ES increased the frequency of myofibrillar I-band fractures and caused wide I-band fractures to appear sooner postmortem due to mechanical disruption. This physical disruption causes an increase in the accumulation of the 30-kDa degradation product of troponin-T (Ho et al., 1994) and accelerates the degradation of titin and nebulin (Ho et al., 1996). In addition, Huff-Lonergan et al. (1995) showed that titin and nebulin were degraded more slowly postmortem in tough than in tender bovine muscle. The objective of this

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study was to improve tenderness of meat aged 14 d from Hampshire × Rambouillet callipyge lambs using ES.

Materials and Methods Slaughter and Dressing Procedures. Twelve Hampshire × Rambouillet lambs that were visually classified as having the callipyge phenotype were fed a standard finishing diet for 90 to 120 d and slaughtered (12 mo, 59 kg live weight) at the Texas Tech Meat Laboratory using USDAapproved humane slaughter procedures. Feed was withheld for 24 h before slaughter, but water intake was not limited. Immediately following evisceration and weighing, each carcass was split and one side of each carcass was randomly assigned to ES with 550 V and 60 Hz of electricity 2 s on and 2 s off for 15 repetitions. Contact with the carcass was made by inserting one 20-cm probe between the first rib and scapula and another 20-cm probe in the shank of the hind limb. The other carcass side received no electrical stimulation (NES). Temperature and pH Determination. Temperature and pH were measured in the semitendinosus (ST), semimembranosus (SM), longissimus (ML), supraspinatus (SP), and triceps brachii (TB) muscles every hour for the first 6 h and then at 24 h postmortem. Muscle pH was measured using an Orion (model 230A, Boston, MA) pH meter with a spear tip probe. Temperature was measured using a Koch digital temperature probe (model 017000, Kansas City, MO) placed in the center of each of the five muscles from each carcass side. The five muscles selected are affected by the callipyge phenotype from the fore limb (TB), loin (ML), and hind limb (SM and ST, Jackson et al, 1997). Even though the ST is larger (Jackson et al., 1997) and has more calpastatin activity (Kerth, 1995; Koohmaraie et al., 1995) in callipyge than in normal lambs, ST tenderness does not differ between callipyge and normal phenotypes (Kerth, 1995). The SP is not affected by the callipyge phenotype in size (Jackson et al., 1997), tenderness (Kerth, 1995), or calpastatin activity (Kerth, 1995; Koohmaraie et al., 1995). Therefore, the objective of selecting these five muscles was to represent the muscles that are either affected or unaffected by the callipyge phenotype. Carcass Fabrication. Carcasses were cooled at 2°C for 24 h and then ribbed between the 12th and 13th ribs. Fat thickness and ML area were measured at the 12th rib. Leg score, marbling score, ML lean color, texture, and firmness, and primary and secondary flank streakings were evaluated. The ML lean color, firmness, and texture were evaluated using an 8-point scale (8 = bright red, firm, or fine, respectively, and 1 = dark, soft, or coarse, respectively; USDA, 1992). The ST, SM, ML, SP, and TB muscles were removed from each carcass side at 24 h postmortem. Samples for sarcomere length, myofibrillar fragmentation index (MFI), and calpastatin assays were removed, and the remaining muscle was vacuum-packaged, boxed, and

stored at 4°C for 14 d. Chops 2.5 cm thick then were cut from each of the muscles, vacuum-packaged, and frozen until WBS force evaluation and sensory panel evaluations were conducted. Calpastatin Activity. A 10-g sample of the ST, SM, ML, SP, and TB muscles was taken and trimmed of visible fat and connective tissue. The heated calpastatin procedure of Shackelford et al. (1994) was used to quantify calpastatin activity (per gram of muscle). Myofibrillar Fragmentation Index. A 4-g sample was taken 24 h and 14 d postmortem from the five muscles. Samples were prepared according to Goll et al. (1977), and MFI was calculated as described by Culler et al. (1978). Sarcomere Length Determination. Samples 1.0 × 1.0 × 3.0 cm were cut from the ST, SM, ML, SP, and TB muscles 24 h postmortem. Samples were frozen in liquid nitrogen and stored at −70°C until sarcomere lengths were determined on fixed samples using helium-neon laser diffraction (Cross et al., 1981). Warner-Bratzler Shear. Chops from the ST, SM, LM, SP, and TB muscles were thawed at 4°C for 24 h and broiled on Farberware Open Hearth electric broilers (Farberware, Bronx, NY) to an internal temperature of 40°C, turned, and removed when they reached 70°C. Internal temperature was measured in the geometric center of the chop using a puncture probe attached to a Cooper Instruments (model SH66A, Middlefield, CT) digital potentiometer. After cooking, chops were chilled for 24 h at 4°C. Two 1.3-cm-diameter cores were removed from each chop parallel to the muscle fiber orientation and sheared once with a WBS machine (AMSA, 1995). Trained Sensory Panel. Chops from each of the five muscles were cooked to 40°C, turned, and removed when they reached 70°C. An eight-member trained sensory panel (Cross et al., 1978) evaluated warm 1-cm3 samples for initial and sustained tenderness, initial and sustained juiciness, characteristic lamb flavor, flavor intensity, and overall mouthfeel using 8-point scales (8 = extremely tender, juicy, characteristic young lamb, intense flavor, and characteristic of young lamb; 1 = extremely tough, dry, mutton flavor, bland flavor, and uncharacteristic of young lamb). Panelists were served in individual booths under red light and provided with water and apple juice for cleansing the palate and a cup for expectoration. Statistical Analyses. Data were evaluated with ANOVA using the GLM procedures of SAS (1988) for a splitplot arrangement of a completely randomized design. Electrical stimulation (ES vs NES) was analyzed in the main plot using the ES × replication mean square as the error term. Muscle (ST, SM, LM, SP, and TB) and ES × muscle interaction effects were analyzed in the split plot. Mean separation for significant (P < .05) main effects and interactions was accomplished with the PDIFF option (a pair-wise t-test) of the least squares procedure for significant differences. Percentage of sensory scores greater than 4 was calculated with the FREQ procedure using the CHISQ option of SAS. Pairwise comparisons


TENDERIZING LAMB WITH ELECTRICAL STIMULATION

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Table 1. Least squares means and SEM for electrical stimulation effects on yield and muscle quality characteristics Trait Fat thickness, mm Yield grade Loineye area, cm2 Leg scorea Marblingb Colorc Textured Firmnesse Primary flank streakingsb Secondary flank streakingsb Quality gradea

Not electrically stimulated

Electrically stimulated

SEM

P .05) pH at 5, 6, or 24 h postmortem. Calpastatin Activity. Electrical stimulation did not affect calpastatin levels (P = .48, Table 2). Calpastatin activities were from 17 to 30% lower (P = .003) for the ST, SM, ML, and TB muscles than for the SP muscle. Sarcomere Length. Sarcomere lengths were not affected by ES (P = .25). The TB muscle had shorter (P = .001) sarcomeres than the ST muscle but longer (P < .05) sarcomeres than the SM, ML, or SP muscles. The SM muscle had shorter (P < .05) sarcomeres than the SP muscle but sarcomere lengths similar (P > .05) to those of the ML muscle. Myofibrillar Fragmentation Index. Electrical stimulation had no effect on MFI (P = .32). The SP and TB muscles had higher (P = .008) MFI values than the SM or ML, indicating more protein degradation. The ST MFI values did not differ (P > .05) from the SM, ML, or SP values. Lower MFI values may partly explain the decrease in tenderness of the ML and SM.

Figure 1. Postmortem pH decline of electrically stimulated (ES) and not electrically stimulated (NES) callipyge longissimus muscle (ML).

Warner-Bratzler Shear Force. No significant ES × muscle interactions or ES main effects were found for WBS force (P > .05). Across ES treatments, SM and ML muscles had higher (P < .05) WBS values than the SP, ST, or TB. The ST muscle had higher (P < .05) WBS values than the SP muscle but did not differ (P > .05) from the TB muscle. Variation in WBS (SEM, .109 kg) was high in this study, indicating a large amount of variation in tenderness. Trained Sensory Panel Evaluation. Electrical stimulation had no effect on any trait evaluated by the sensory panel (P > .05). The five muscles differed in sustained juiciness (P = .01), initial and sustained tenderness, lamb flavor, lamb flavor intensity, and overall mouthfeel (P < .001). Initial juiciness was not different (P = .07) among muscles. The ML muscle scored lower (P < .05) in sustained juiciness than the SM, SP, and TB muscles but did not differ (P > .05) from the ST muscle. The ST, SM, SP and TB muscles all were given similar (P > .05) sustained juiciness scores by the sensory panel. The SM and ML muscles were rated lower (P < .05) in initial and sustained tenderness than other muscles. However, both muscles were rated slightly tender or better by the sensory panel. Tenderness scores were higher (P < .05) for the TB than for all of the other muscles except the ST. Scores for lamb flavor were higher (P < .05) for the SP and TB muscles than for the SM and ML muscles, but the TB and the ST muscles did not differ (P > .05). Flavor intensity and overall mouthfeel scores were lower (P < .05) for the SM and ML than for all other muscles, which did not differ (P > .05). The TB, SP, and ST muscles did not differ in flavor intensity or overall mouthfeel scores. Although the ES × muscle interaction did not affect (P > .05, data not shown) WBS or sensory values, a trend did exist (P = .15) for sustained tenderness scores to be improved by ES in the ML. Due to a large amount of variation in sensory scores, the differences in means


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Table 2. Least squares means and SEM for muscle and electrical stimulation main effects on calpastatin, sarcomere length, myofibrillar fragmentation index (MFI), Warner-Bratzler shear (WBS), and sensory characteristics Treatmenta Trait Calpastatin, units/g Sarcomere, µm MFI WBS, kg Initial juicinessc Sustained juicinessc Initial tendernessd Sustained tendernessd Lamb flavore Flavor intensityf Overall mouthfeelg

NES 4.05 1.97 44.9 3.27 5.7 6.0 5.7 5.9 6.1 6.3 5.8

ES 4.24 1.98 46.2 2.88 5.5 5.9 6.0 6.3 5.9 6.3 6.0

Muscleb SEM .18 .14 3.56 .109 .08 .09 .13 .13 .06 .04 .09

P .05, data not shown) on WBS or any sensory panel scores, trends in WBS and sensory tenderness scores existed. The WBS values were .29 kg less, initial tenderness scores were .92 units greater, and sustained tenderness scores were 1.17 units greater, for ML muscles that were stimulated, compared with the NES treatment. The interaction for sensory tenderness was not significant (P > .1); the high amount of variation in tenderness (SEM = .289 and .300) resulted in a significant interaction. However, high-voltage electrical stimulation increased the percentage of loin chops that were rated as slightly tender or above by 30 to 34% and improved tenderness from slightly tough to slightly tender. Previous research (Shackelford et al., 1997) has shown that comparisons of WBS can be made between treatments within a muscle but comparisons between muscles cannot be made. This is because more variation exists among locations in a muscle than among animals. Muscles other than the longissimus do not vary in WBS values from one animal to the next, and, therefore, are poor predictors of tenderness of other muscles in the carcass. The WBS values for the five muscles reported in the present study did not rank in the same order as sensory panel tenderness scores for the same five muscles. This suggests that WBS is not a good method for determining differences among different muscles in callipyge carcasses.

Implications Because the loin chops in this study were all relatively tender as measured by Warner-Bratzler shear, highvoltage electrical stimulation did not significantly improve the tenderness of any of the five muscles studied from Rambouillet × Hampshire crossbred callipyge sheep. However, electrical stimulation improved sensory tenderness scores by 30 to 34% from slightly tough to slightly tender. Other postmortem treatments should be investigated for their effectiveness in combination with electrical stimulation in improving the tenderness of callipyge chops.

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