A total of six mature Western Crossbred (Black x White Face) ewes (average four years old), were slaughtered and the carcasses were eviscerated and split within 30 to 45 minutes post-exsanguination. Then, electrical stimulation (350 V, for 45 sec using a total of 15 impulses, 1.5 second on and off) was applied to the right sides of each carcass within 30 to 45 minutes postmortem. At 24 hours postmortem, the LD and SM muscles were excised from both sides of the carcasses. After the application of the ES, pH and temperature values of the carcasses were recorded at hour intervals.
The mutton chops for sensory evaluation were cooked using a water bath as described by Bouton et al. (1975) for homogeneous cooking. The meat samples were weighed and enclosed in water impermeable polyethylene, then completely immersed in constant temperature water of 90oC to an internal temperature of 70oC. The meat was then cooled with running tap water and removed from the bags. From the sample weights, before and after cooking, percent-cooking losses were calculated. A total of six trained panelists independently evaluated each LD and SM samples for degree of tenderness, juiciness, amount of residue remaining after chewing, and the number of chews before breaking up of the meat tissue. Scores, (except number of chews) were obtained using a 1 to 9 point scale as described by Ockerman (1985). The number of chews was determined by counting the chews prior to swallow.
Fragmentation index values were determined by the procedure described by Davis et al. (1980). Mechanical assessment of muscle tenderness was carried out employing two different tests by using the Warner Bratzler Shear (WBS) head and the Compression Tests on the Instron. The cooked meat samples prepared for the sensory panel evaluation were also used for Instron WBS measurements in which four 1.3 cm cores were removed, parallel to the longitudinal orientation of the muscle fibers, and sheared twice for the WBS force value. A WBS head attached to the Instron was used with a crosshead speed of 100 mm/min and with a chart speed of 100 mm/min with 50 kg being a full-scale load. The following parameters were measured from the force deformation curves; initial yield force (kg); peak force (kg); initial yield distance (cm); final yield distance (cm); peak force minus initial yield force value, and work done (total amount of work needed to shear the core) which was determined by using the total area under the curve expressed in mm2 as described by Rao and Gault (1990).
The instron compression test was performed with the Instron Universal Testing Machine Model 1000 (Instron Co. Canton, Maine) by compressing a 1 cm thick muscle sample, 80% of its original height with a 0.07 cm diameter flat plunger descending at a rate of 50 mm/min as described by Hayward et al. (1980). The cooked samples were presented to the instrument with the fibers parallel to the main surface and perpendicular to the direction of plunger travel. The plunger was driven into the meat twice at the same location, and work and force penetration curves were recorded. The parameters obtained from the compression measurements were; peak force 1 (hardness) (kg), peak force 2 (kg), peak force distance 1 (cm), peak force distance 2 (cm), work done 1 (area of the first peak, A1 in mm2), work done 2 (area of the second peak, A2 in mm2), cohesiveness (The ratio of the area A2/A1), and chewiness (peak force 1 (kg) x cohesiveness) as stated by Stolarz et al. (1984).
Sarcomere length was measured by the procedure described by Smith et al. (1989). The data obtained in this study was analyzed using the GLM with SAS (1986).