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Introduction
Slaughter processing is important for animal well-being, meat quality, safety, and public health in the 21st century (Sabow et al., 2016). In recent years, increased concern about animal welfare demands the researchers to elucidate the implications of animal handling, transportation, stunning and slaughtering on live animal stress and meat quality. Slaughter of food animals is normally a two-stage process i.e. stunning and bleeding (exsanguination). Stunning is deliberately induced process which lead to loss of consciousness and sensibility without pain and also reduces struggling through a more precise and immediate slaughtering process. Species specific slaughter legislation codes are available for slaughtering procedure. However, the appropriateness of generally used methods does not only depend on species but also the accessibility of services, consumer demands and/or acuities and economic reflections (Anil, 2012).
Slaughter of animals without stunning is the biggest animal welfare issue for the meat industry around the world (Grandin, 2017). Alterations in the slaughter techniques may not only effect animal welfare but also affects postmortem muscle metabolism (Bourguet et al., 2011). The traditional slaughter of animals without stunning is still a relevant method in this century. However, firm guidelines are followed throughout slaughtering sequences, i.e animal welfare, working environment, food cleanliness, and protection (Bergeaud-Blackler et al., 2007). Stunning animals before slaughter was not a legal requirement until 1902 in Finland, 1929 in Norway, 1937 in Sweden, 1947 in the UK, 1953 in Denmark (Metcalf, 1989), 1985 in the USA (USC, 1958), and 1974 in the EU (Council Directive, 1974). Studies have reported the impact of stunning and slaughtering methods on the meat quality. Majority of the studies were conducted on sheep and cattle (Anil et al., 2004, Onenc and Kaya, 2004; Sazili et al., 2013; Vergara et al., 2005). There are very little information existing on slaughter techniques and meat quality traits of goat meat. Therefore, the objective of the current study was to compare the physicochemical characteristics of longissimus lumborum (LL) muscle from goats exposed to stunning and without stunning.
Materials and Methods
A total of ten Korean black goats (KBGs) (yielding 20 muscle left and right side) with age of 18 months were attained from a commercial farm. Goats were raised under same environments and nourished with same diets. Goats were transferred from the commercial farm to slaughter house one day before the experiment, and were rested for 18 h with free watering but no food before slaughtering.
The goats were separated into two groups and slaughtered by two different methods. For the non-stunned method (NS, n=10), slaughtering was carried out by license slaughter man for halal slaughtering with following method. The head of each animal was dragged dorsally and stretch toward the neck for the purpose of exsanguinations. Transverse section was accomplished using a piercing knife. Without removing the head a sharp and swift cut was carried on neck served the major veins, arties, and nerves.
The head-only electrical stunning method (HOES, n=10) was carried out before slaughtering and similar procedure as earlier described in NS slaughtering. Animals were stunned electrically using the head only technique at a constant of 1 A, 50 Hz for 3 s, the head electrodes were positioned between the eyes and the ears on both edges. The procedure was carried out using electrical stunning transformer type CS-1 system (Karl Schermer, Ettlingen, Germany) linked to double-electrode scissor type dry stunning tongs (Z3, Karl Schermer, Ettlingen, Germany). Instantly after stunning, the goats were bled to eliminate extra blood from the carcass. The regular stun-to-stick interval was 8.61±0.11 s, and the interval of 2–3 min was adopted between slaughter and dressing.
After slaughter, all carcasses were stored in cold room at 4℃ for 24 h. The muscle pH was measured with 3 g meat sampled at 1, 2, 3, 6, 12, and 24 h postmortem from carcass. The LL muscle was excised at 24 h postmortem to investigate meat quality traits.
Blood loss % was determined as the difference of goat weight between pre-slaughter weight (pre-SW) and post-slaughter weight (post-SW) as followed:
The pH of the LL muscle was measured using a portable pH meter (Mettler Toledo, MP 230, Switzerland). A total of 3 g of meat from each group was chopped and homogenized (IKA T25 ULTRA-TURRAX Germany) in 27 mL of distilled water for 30 s. The pH meter was first calibrated on 7, 4.01, and 9.21 before evaluation of pH.
Minolta Chromameter (Minolta CR-300, Japan) was used for determination of meat color. Before measuring the color values, the Minolta Chromameter was calibrated with white plate (Y=93.5, X=0.3132, y=0.3198) the different color values was evaluated by measuring L* (lightness), a*(redness/greenness) and b* (yellowness/blueness) hue (h°) and Chroma (C). For statistical analysis, an average value from different positions from each sample surface was carried out.
Water-holding capacity (WHC) of meat was determined by drip loss percentage and cooking loss percentage. Drip loss percentage was measured based on the method as described by Honikel (1998). A sample weight of approximately 25–30 g was weighed and suspended on a supporting wire and then placed within the container. Samples were stored at 4℃ chilling room for 24 h and again weighed after dry. Drip loss % was calculated as a percentage of the initial weight.
For cooking loss %, the LL muscle was cut into 4×3×3 cm (L×H×W) dimension with weight 25–30 g and packed in a low-density polyethylene bag. Samples were cooked at 75℃ for 30 min and chilled immediately in the ice flake for 10 min. Cooking loss % was determined by weight difference before and after cooking.
Warner-Bratzler shear force (WBSF) was carried out on the cooked sample based on AMSA (1995) guideline. Samples core (1.0 cm-diameter) were inserted parallel to the myofiber direction of the cooked sample. The cores were sheared perpendicular to the myofibers position using an Instron tensile testing machine (Model 4443, Instron Corp., USA) with a V-shaped shear blade. Peak force was obtained using 100 N load cell tension applied at a crosshead speed of 250 mm/min and the full-scale load was 50 kg. Shear force was reported as maximum peak force recorded during the test. For each sample group average of five measurements were recorded.
Sarcomere length was determined by the method of Cross et al. (1981). Samples (3.0×3.0×2.0 cm) were run longitudinally and put in vials comprising solution A (0.1 M KCl, 0.39 M boric acid, and 5 mM ethylene-diaminetetra acetic acid in 2.5% glutaraldehyde) for 2 h. Samples were then relocated to fresh vials comprising solution B (0.25 M KCl, 0.29 M boric acid, and 5 mM ethylene-diaminetetra acetic acid in 2.5% glutaraldehyde) for 17–19 h. On the next day, individual fibers were torn into fragments and placed onto microscope slides with a droplet of solution B. The slide was placed straight in the path of a vertically oriented laser beam to give a display of diffraction bands on a screen. Sarcomere length (µm) was calculated using the following equation.
Where D is a distance from specimen to diffraction pattern screen (D=98 mm) and T is the separation (mm) between zero and the first maximum band.
The data obtained were analyzed using analysis of variance (ANOVA) using SPSS (SPSS 16.0, Chicago, IL, USA) and variances between mean values were obtained by Student t-test. Significance was defined at a level of p<0.05. The results were stated as the least square mean values of three independent replications, except for WBSF has recorded the average for five measurements.
Results and Discussion
The blood loss (BL) results are shown in the Table 1 in which goats were assigned to slaughtering technique, i.e. NS and HOES slaughter. There was no significant difference (p>0.05) in BL % between NS and HOES. However this was not statistical difference but the BL of NS was somewhat higher than that of HOES. The probable reason could be the outcome of Tachycardia of the heart instantly after slaughter in NS group than HOES group. Contrasting result have been observed on different studies which is carried out on slaughter method and BL. Results of our experiment are similar with Anil et al. (2004, 2006) who reported no effect of slaughter methods including stunning and no stunning on BL in sheep and cattle. Anil et al. (2004) reported approximately 3.98% and 3.78% of BL for sheep slaughtered with or without stunning, respectively. On the other hand, Velarde et al. (2003) also assessed the effect of two slaughtering methods (NS and HOES) on lambs. They found that the amount of BL was much lower as relative to the body weight in non-stunned as compared to head stunned animal in which the BL was significantly higher.
The postmortem pH decline pattern of LL muscle from goats slaughtered with NS or HOES are shown in Fig. 1. The pH values for both groups were almost identical throughout the monitoring period (p>0.05). Our results agree with Velarde et al. (2015) and Wong et al. (2003) but contradict to findings obtained by (Kadim et al., 2010; King et al., 2004). According to Devine et al. (1984) and Velarde et al. (2003), electrical stunning is one of the main reason for the increased rate of postmortem glycolysis. However, our results showed that the changes in pH during postmortem muscle glycolysis was not different from that observed in non-stunned goats. This might be due to the conditions in pre-stunning that resulted in these outcomes. Since the very minor and short stun-stick interval can reduce the rate of postmortem glycolysis (Velarde et al., 2003), in the present study, the postmortem pH decline pattern was not much affected by slaughtering methods.
Meat color properties of the LL muscles subjected to NS and HOES are presented in Table 2. As expected, no significant differences in lightness (L*), redness (a*), yellowness (b*), color saturation (C), and hue angle (h°) values were observed between NS and HOES sample groups. The similar color properties of stunned (HOES) and non-stunned (NS) sample groups can be associated with the pH values with having no difference after 24 h postmortem. These findings were agreed with Velarde et al. (2003) and Vergara et al. (2005) who reported that stunned sheep showed no significant difference in L*, a* and b* values as associated to non-stunned sheep meat. However, the meat of NS seemed to be brighter (higher L* values), redder (higher a* values), and lower discoloration (lower h° values) than those of the HOES sample, although the difference was not significant.
In the present study, WHC was measured as drip loss and cooking loss (Fig. 2). Different slaughtering condition had no effect on cooking loss and drip loss (p>0.05). Although the numerical difference was marginal, however, slightly high drip loss % and cooking loss % were observed in NS goat meat compared to HOES goat meat. This might be due to the small changes in pH after cooking loss and drip loss procedure, even though the pH values were not significantly different between NS and HOES groups after 24 h postmortem. Corroborating the present observation, this result agrees with Lokman et al. (2017), and Onenc and Kaya (2004) in WHC with no difference recorded among method of slaughter in goat and cattle, respectively. However, in contrast to Wong (2015) who described that non-stunned animals shows a lower cooking loss than stunned animals. This author defined the effect of protein denaturation caused by heat from cooking in the stunning samples were higher and thus resulting in a higher loss than non-stunned samples.
The results obtained for shear force and sarcomere length are shown in Fig. 3. The values obtained for both NS and HOES samples were not significantly different, but NS samples showed slightly lower WBSF values than HOES samples. Interestingly, data in sarcomere length shown that pre-stunning induced HOES samples were slightly lower than NS samples. It is well recognized that when sarcomere length is increased, the overlap of actin and myosin filament is also decreased, which in turn results in the tenderness of cooked meat (Kannan et al., 2006). However, sarcomere length could not be concluded to be the main factor for meat tenderness, because some previous studies had found that sarcomere length did not influence meat tenderness (Tschirhart-Hoelscher et al., 2006; Wheeler et al., 2000). Also, Lokman et al. (2017) found that different methods of slaughtering either with or without stunning had no effect on sarcomere length, rather it had affected by the postmortem storage or duration of aging (Pen et al., 2012).
Conclusion
The current study suggests that meat quality traits of LL muscle from KBGs subjected to NS or HOES slaughtering are not significantly different. The slaughtering methods has no effects on BL %, muscle pH decline pattern, meat color measurements, and WHC, but a little effect on shear force and sarcomere length. Consequently, results in this study imply that NS slaughtering does not result in poor quality of goat meat.
