Effect of different stunning systems on meat quality of light lamb

MEAT SCIENCE Meat Science 76 (2007) 675–681 www.elsevier.com/locate/meatsci

Effect of different stunning systems on meat quality of light lamb M.B. Linares a

a,b

, R. Bo´rnez

a,b

, H. Vergara

a,b,*

Departamento de Ciencia y Tecnologı´a Agroforestal, Escuela Te´cnica Superior de Ingenieros Agro´nomos, Campus Universitario, 02071 Albacete, Spain b Seccio´n de Calidad Alimentaria, Instituto de Desarrollo Regional, Universidad de Castilla-La Mancha, 02071 Albacete, Spain Received 7 April 2006; received in revised form 30 January 2007; accepted 12 February 2007

Abstract The present study was proposed to compare the effect that different types of stunning (TS) had on the quality of refrigerated meat from light lambs of the Spanish Manchega breed at 24 h and 7 days post-mortem. Lambs were electrically stunned (ESL; n = 10), using CO2 (GSL; n = 10) or slaughtered without previous stunning (USL; n = 10). Measurements on meat quality were carried out by evaluating pH, colour coordinates (L*, a*, b*), water holding capacity (WHC), cooking loss (CL), shear force (SF) and drip loss (DL). At 24 h post-mortem, no significant differences were found in any of the variables studied. However, at 7 days post-mortem, meat quality was affected by the different TS: pH, CL and DL were lower (P < 0.001) in the USL group and GSL obtained the lowest a* (redness) and b* (yellowness) values (P < 0.01) than in the other groups. Ageing of meat affected SF in the ESL group (P < 0.01), although there were no significant differences due to treatments at any of the ageing times. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Slaughter; Stunning; Carbon dioxide (CO2); Electrical; Meat quality; Light lamb

1. Introduction In the UE setting, more than half the census of sheep (>55 * 106 of livestock heads) and meat production of this specie (>500.000 Mtm) (FAOSTAT, 2005) are concentrated in Mediterranean countries (Alfonso et al., 2001). In Spain, lamb meat is highly valued by consumers due to its nutritional and organoleptic qualities, although both the relative high price and the consumer habit of buying lamb mainly for special events have led this product to be considered as a ‘‘luxury food’’ (Vergara & Gallego, 2001). However, a previous study (Bernabe´u & Tendero, 2005) shows that the price factor is a secondary element at the moment of purchase, while other factors such as the image

*

Corresponding author. Address: Departamento de Ciencia y Tecnologı´a Agroforestal, Escuela Te´cnica Superior de Ingenieros Agro´nomos, Campus Universitario, 02071 Albacete, Spain. Tel.: +34 967 599200 2831; fax: +34 967 599238. E-mail address: [email protected] (H. Vergara). 0309-1740/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2007.02.007

of the product, food safety or final quality have greater influence on consumer choices. In addition, animal welfare has become an important aspect that concerns habitual consumers of meat, (Blokhuis, Jones, Geers, Miele, & Veissier, 2003). Among the numerous factors that can alter meat quality, stress previous to slaughter is probably of greatest interest due to its influence on product image as well as its effect on meat quality (San˜udo, Sa´nchez, & Alfonso, 1998). With respect to this, the current bibliography indicates that the type of stunning is a factor which affects final meat quality in lamb (Paulick, Stolle, & von Mickwitz, 1989; Vergara, Linares, Berruga, & Gallego, 2005). Thus, many authors (Paulick et al., 1989; Vergara & Gallego, 2000) conclude that meat from electrically stunned lambs aged earlier than meat from the un-stunned groups. According to European law (EU Council Directive 93/119/EC) electrical stunning in sheep is a compulsory procedure to ensure an adequate state of unconsciousness in animals previous to slaughter. However, some disadvantages have been described (Petersen, Carr, Davies, & Pick-

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ett, 1986; Vergara & Gallego, 2000) in relation to this stunning system, e.g., haemorrhage, blood splash, bone fractures, lowered safety for slaughter-men etc. Other methods, such as those using gas (mainly CO2), could contribute to the preservation of meat quality (Gregory, 2005) improving bleeding of carcasses as a consequence of the increase in the heart rate frequency and ´ lvarez, 2002). However this last author blood pressure (A indicated that a variable response in animals subjected to different concentrations of CO2 can produce contradictory results, since Martoft et al. (2002) pointed out that the CO2 inhalation reduces heart rate. In a previous paper (Vergara et al., 2005) we examined the effect of pre-slaughter handling on meat quality from suckling Manchego lambs (un-weaned and at a slaughter weight of 12.8 kg). However, effects on the meat quality of light lambs, which is the type of meat preferred by habitual consumers of lamb (Bernabe´u & Tendero, 2005), are still unknown. In addition, Napolitano, Marino, De Rosa, Capparelli, and Bordi (1995) argued that younger lambs (suckling lambs) showed higher cortisol levels than the older animals (light lambs). These differences in the levels of hormones in lambs at different slaughter weights are the reason for this study, since these hormones can have an effect on meat quality parameters. Okeudo and Moss (2005) showed that cortisol concentration was negatively correlated with cooking losses and initial pH; Yoshioka, Imaeda, Ohtani, and Hayashi (2005) indicated that an increase of cortisol reduced meat quality in piglets. Hence, the aim of this study was to evaluate the effects of different types of stunning (TS) on the meat quality of light lamb at 24 h (initial meat quality) and at 7 days post-mortem (maximum time permitted for sale according to the requirements on its official label). 2. Materials and methods The research protocol used in this work was previously approved by the Animal Ethics Committee of the University of Castilla-La Mancha, in agreement with Executive Committee 86/609/CEE of 2 November 1986 concerning the protection of animals used in research and for scientific purposes. 3. Animals and experimental design Light lambs (25.1 ± 0.1 kg live weight at slaughter and 70 days old) were transported from the farm to the abattoir (20 km of distance during approximately 30 min). After transportation, lambs were held in pens for 15 h without feed but with ad libitum access to water. After lairage, lambs were always moved to the stunning point by the same slaughter-man. Animals were distributed into three different pre-slaughter groups depending on the type of stunning: ESL, (n = 10): lambs stunned electrically at 110 V, 50 Hz for

5 s (electrodes applied on both sides of the head, behind the ears); GSL, (n = 10): lambs stunned using CO2 gas in groups of five in the box, 90% CO2 for 90 s at the bottom of the well. Afterwards, lambs were slaughtered using standard commercial procedures. In both groups the stun-stick interval was approximately of 8–10 s. The third group was called USL, (n = 10): lambs slaughtered without previous stunning. In all treatments the interval between slaughter and dressing was 2–3 min approximately. All carcasses were chilled at 4 °C for 24 h in a conventional chiller. 4. Instrumental measurement All quality measurements were assessed in the Longissimus dorsi muscle, which was removed at 24 h post-mortem from the carcass and divided into two pieces from the T7 to T11 in both sides of carcasses: one of them was used to evaluate the initial meat quality (at 24 h post-mortem) and the other was packed in a clear tray (LINPAC Plastic) with a film (having an oxygen permeability of 500 cm3 m 2 day 1 at 1 atm and 25 °C) and was then analysed after 7 days of storage at 2 °C. The following parameters were measured:  Before removal of the Longissimus dorsi muscle, pH was measured in the carcass using Crison 507 equipment with a penetrating electrode at 0 and 45 min after dressing and at 24 h post-mortem (pH0, pH45 and pH24, respectively).  Water Holding Capacity (WHC) as a percentage of free water (Grau & Hamm, 1953), and colour coordinates (L*, lightness, a*, redness, b*, yellowness values) using a Minolta CR400 colorimeter according to the proposal by Vergara, Molina, and Gallego (1999). These were measured at 24 h post-mortem.  At 72 h post-mortem we analysed: cooking loss (CL), expressed as the percentage of loss related to the initial weight (Vergara, Gallego, Garcı´a, & Landete-Castillejos, 2003) followed by shear force (SF), which was analysed using a TA.XT2 texture analyser equipped with a Warner–Bratzler device. For this analysis, each meat sample was individually placed in polyethylene bags in a water bath at 70 °C for 15 min. After drying the cooked samples with filter paper, they were cut into three replicates with a 1 cm2 cross-section and 2–3 cm in length. SF was then recorded. Finally, after 7 days post-mortem, all the above-mentioned parameters (pH7, colour, WHC, CL and SF) and also drip loss (DL) expressed as a percentage of the initial portion weight (Vergara et al., 2003), were analysed. 5. Statistics analysis The effect of different TS on initial meat quality and after 7 days post-mortem was analysed using an ANOVA

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test. When the differences among groups of TS were significant (P < 0.05), Tukey’s test at a significance level of P < 0.05 was carried out to check the differences between pairs of groups. The differences in meat parameters due to time of storage (initial and after 7 days) were analysed using an analysis of variance. Data were analysed using the SPSS 11.0 version statistical package. 6. Results and discussion 6.1. Values and decline of pH Table 1 shows that the GSL group presented the lowest values (P < 0.001) of pH after dressing (pH0) and at 45 min post-mortem (pH45). In a previous paper, Vergara et al. (2005) also reported a pH0 in gas-stunned lambs lower than in electrically and un-stunned groups, although these differences disappeared at 45 min post-mortem. Perhaps residual CO2 in muscle could be responsible of this lower value in GSL group in agreement with Fleming, Froning, Beck, and Sosnicki (1991). At 24 h post-mortem significant differences were not found among the three groups (GSL, ESL and USL) which is similar to findings in turkey meat by Northcutt, Buhr, and Young (1998). However, Hambrecht et al. (2004) found lower values of pH24 in electrically stunned pigs than in gas-stunned ones, a fact which was attributed to the faster muscular glycolysis due to the effect of current flow and convulsive movements during the clonic phase (Channon, Payne, & Warner, 2003). At 7 days post-mortem, a higher pH (P < 0.001) value was observed in the stunned-lambs groups (5.57 ± 0.01, 5.65 ± 0.02 for ESL and GSL, respectively) than in unstunned lambs (5.46). It is possible that the high value of pH in stunned group could be related with a high level of catecholamines as showed Foury et al. (2005) who explained that catecholamines increase the glycogenolysis and therefore reduce the lactic acid production post-mortem. Also, high levels of these hormones have been more related with the stunning technique itself more than the amount of stress (Hambrecht et al., 2004; Nowak, Muef-

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fling, & Hartung, 2007). Troeger (1989) reported an important increase of adrenaline and noradrenaline levels in pigs subjected to electrical and gas stunning that he attributed to pre-slaughter handling including the use of single path runways, electric prods and conveyor restrainers. Also, Pearson, Kilgour, de Langen, and Payne (1977) in lambs, noted that the levels of catecholamines were higher in the electrically stunned animals than in non-stunned lambs. On the other hand, the rate of pH decline (Table 1; pH 45–24 and pH0–24) was always less (P < 0.05) in GSL than in the other two groups (ESL and USL), which agrees with Vergara et al. (2005) in suckling lambs. Channon, Payne, and Warner (2002) found similar pH decline between electrically and gas stunned pigs. Electrical stunning methods cause a faster fall in the pH due to the passing of the current flow through carcasses and the increase of muscular activity, which results in an acceleration of post-mortem glycolysis (Troeger & Woltersdorf, 1990). Therefore, pH decline seems to be affected by the type of stunning (Vergara et al., 2005) although other work did not find differences between various stunning systems (Channon et al., 2003). As shown by Henckel, Karlsson, Jensen, Oksjerg, and Petersen (2002) CO2 stunning is responsible of a decrease in the glycogen level, causing a reduction in lactic acid production which promotes a slower decline of pH in the GSL group (Rosenvold et al., 2001). 6.2. Colour coordinates Effects of TS of light lambs on colorimetric coordinates (L*, a* and b* values) are shown in Table 2. At 24 h postmortem, no significant differences were found in L*, a*, b* coordinates, although significant differences (P < 0.01) were observed at 7 days post-mortem due to the type of stunning. Meat from GSL reached the lowest values of a* (redness), as shown by Fleming et al. (1991) in turkeys, and also of b* (yellowness) according to Hambrecht et al. (2004) in pigs, and Velarde, Gispert, Faucitano, Manteca, and Diestre (2000) in lambs. Other authors, in broilers, (Craig, Fletcher, & Papinaho, 1999) showed that the value of the b* coordinate was not affected by the type of stun-

Table 1 Effect of type of stunning (TS) on the pH (mean ± SE) of meat and its evolution with time in Manchego light lambs Parameter

pH

pH decline

Time post-mortem

TS

Analysis of variance

ESL (n = 10)

GSL (n = 10)

USL (n = 10)

After dressing (pH0) 45 min (pH45) 24 h (pH24) 7 days (pH7)

6.64 ± 0.05b,z 6.36 ± 0.04b,y 5.49 ± 0.01x 5.57 ± 0.01b,x

6.38 ± 0.07a,z 6.08 ± 0.03a,y 5.56 ± 0.04x 5.65 ± 0.02c,x

6.77 ± 0.04b,z 6.36 ± 0.04b,y 5.46 ± 0.01x 5.46 ± 0.00a,x

pH0–pH45 pH45–pH24 pH0–pH24

0.28 ± 0.06 0.87 ± 0.05b 1.15 ± 0.05b

0.29 ± 0.04 0.52 ± 0.07a 0.81 ± 0.11a

0.41 ± 0.05 0.89 ± 0.05b 1.30 ± 0.04b

ESL: electrically stunned lambs; GSL: gas stunned lambs; USL: un-stunned lambs. NS, not significant. a,b,c Values in the same row with different superscripts are significantly different (P < 0.05). x,y,z Values in the same column with different superscripts are significantly different (P < 0.05). *** Indicates significance levels at 0.001.

*** ***

NS ***

NS *** ***

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Table 2 Effect of type of stunning (TS) on meat colour (coordinates L*, a*, b*) of Manchego light lambs (mean ± SE) Coordinate

Time post-mortem

L*

24 h 7 days

a*

b*

24 h 7 days 24 h 7 days

TS

Analysis of variance

ESL (n = 10)

GSL(n = 10)

USL (n = 10)

41.3 ± 0.58 44.7 ± 0.71b

40.08 ± 0.69 43.09 ± 0.5a,b

39.9 ± 0.49 41.6 ± 0.58a

**

**

*

17.95 ± 0.45 17.11 ± 0.59a NS

16.62 ± 0.68 14.55 ± 0.36b *

17.39 ± 0.29 16.99 ± 0.53a NS

5.66 ± 0.36 12.15 ± 0.41a

4.56 ± 0.52 10.39 ± 0.28b

5.15 ± 0.12 11.55 ± 0.12a

***

***

***

NS **

NS **

NS **

ESL: electrically stunned lambs; GSL: gas stunned lambs; USL: un-stunned lambs. NS, not significant. a,b Values in the same row with different superscripts are significantly different (P < 0.05). *,**,*** Indicates significance levels at 0.05, 0.01 and 0.001, respectively.

ning. It is possible that this lower b* value in the GSL group could be attributed to the relation between the use of CO2 to stun with a lower level of haemoglobin in the muscle and therefore a lower total heme-pigment in meat as shown by Fleming et al. (1991). However in a previous paper, (Vergara et al., 2005), in suckling lambs, contradictory results were described and b* was higher in the gasstunned group than in electrically stunned lambs. Perhaps an interaction could exist between factors, the age of animals and the type of stunning on b* coordinate. Moreover it is well known that many intrinsic and extrinsic factors affect colour of ruminant meat (San˜udo et al., 1998) including nutrition (Beriain et al., 2000). Even light lambs (weaned at 30 days old) could be subjected to an intense emotional experience related to the weaning/separation from their mothers and lack of ewe milk (Napolitano et al., 1995) that could be responsible of depletion in glycogen stores (Jacob, Pethick, & Chapman, 2005) and therefore a lower b* (Hambrecht et al., 2005) than animals fed exclusively with milk (suckling lambs). Our data showed that meat from un-stunned lambs was darker (lower L* value) than ESL (P < 0.01). This result disagrees with findings by Onenc and Kaya (2004); and Vergara and Gallego (2000), which found similar results among these treatments (ESL, USL). The L* coordinate value has been related with the levels of cortisol and catecholamines in various papers but the results have been contradictory. So, while Apple et al. (1995) found a negative correlation between L* and these hormones, others such as Yoshioka et al. (2005) observed that, in piglets, a higher cortisol level implied a lighter meat (higher L* value). In our study we have found a paler meat in ESL than in USL group, which could be attributed to the possible higher level of catecholamines in ESL than non-stunned lambs. This last group (USL) also showed lower pH7 possibly related positively with these hormones according to Foury et al. (2005). In general we have found a darker and redder meat in this study on light lambs than in a previous paper (Vergara et al., 2005) on suckling lambs. The main reason could be

that the ewe milk contains a low iron content and thus produce a paler meat than that of older lambs fed with concentrated and cereal straw (rich in iron atoms), as described by Beriain et al. (2000). 6.3. Water holding capacity (WHC), cooking loss (CL), drip loss (DL) and shear force (SF) At 24 h post-mortem there were no significant differences in WHC among groups (Table 3), but after 7 days of ageing this parameter decreased significantly (P < 0.001) (more water expelled) in the GSL group, and therefore differences with the others groups were found (P < 0.05) at this time. A positive correlation between the tendency to release water and the juiciness of the meat has been suggested by Vergara and Gallego (2000). Similar results were found by Vergara et al. (2005) in suckling lambs subjected to different TS, although without significant differences between groups. As reported by van der Wal, Engel, and Reimert (1999) a stressful experience for 1 min immediately before slaughter can alter meat quality, which is reflected by a reduced WHC, as occurs in the GSL group. In this sense, Bond, Can, and Warner (2004) also pointed out that an increase in adrenaline in the bloodstream of animals due to stress or by external injection has an important effect on muscular proteolysis since it decreases myofibrillar space and therefore increases water loss (minor WHC). Our findings showed that GSL, which obtained the lowest pH decline and a high pH24, had the lowest value of WHC (more water expelled) (P < 0.05) at 7 days postmortem. However Huff-Lonergan and Lonergan (2005) in pigs, indicated that a faster pH decline and a low ultimate pH imply higher water loss. In lamb a previous study (Vergara et al., 2005) showed that a lower pH decline was associated with a higher tendency to release water (minor WHC) in agreement with our results. On the other hand, cooking loss (CL) for the gas-stunned lambs was intermediate between electrical and un-stunned animals. The ESL group caused the highest CL, showing

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Table 3 Effect of type of stunning (TS) on water holding capacity (WHC), cooking loss (CL), drip loss (DP) and shear force (SF) of meat from Manchego light lambs (mean ± SE) Parameter

WHC (% water expelled)

CL (%)

Time post-mortem

2

SF (N/cm )

Analysis of variance

ESL (n = 10)

GSL (n = 10)

USL (n = 10)

15.02 ± 1.55 17.74 ± 0.81a NS

15.61 ± 1.30 26.14 ± 0.82b

NS

***

16.63 ± 1.59 17.29 ± 0.81a NS

11.35 ± 1.30a 15.09 ± 0.92a

7.32 ± 0.37b 11.70 ± 1.18b

9.44 ± 0.58ab 6.04 ± 0.36c

**

*

**

***

7 days

1.53 ± 0.18a

1.84 ± 0.30a

0.52 ± 0.03b

***

72 h 7 days

75.65 ± 0.68 44.29 ± 0.62

71.93 ± 0.62 54.48 ± 0.94 NS

82.51 ± 0.75 72.52 ± 1.00 NS

NS NS

24 h 7 days 72 h 7 days

DL (%)

TS

**

***

***

ESL: electrically stunned lambs; GSL: gas stunned lambs; USL: un-stunned lambs. NS, not significant. a,b,c Values in the same row with different superscripts are significantly different (P < 0.05). *,**,*** Indicates significance levels at 0.05, 0.01 and 0.001, respectively.

significant differences (P < 0.05) with regard to the GSL (at 24 h and 7 days post-mortem) and USL (at 7 days postmortem). As shown by Allen, Fletcher, Northcutt, and Russell (1998) in broilers and Mckee, Hargis, and Sams (1998) in turkeys, paler meat (higher L*) was associated with an increase of CL, which agrees with our results. Drip loss (DL) was higher in stunned animals than in the un-stunned group (P < 0.001). Perhaps, in stunned animals, ageing of meat starts earlier (Vergara & Gallego, 2000) and also proteolysis of muscle implies shorter sarcomeres associated with an increase in DL as a consequence of the stunning system (Melody et al., 2004; Rosenvold et al., 2002). On the other hand a decrease in the glycogen level (and therefore a high pH) just before slaughter supposes a higher value of drip loss (Stoier, Aaslyng, Olsen, & Henckel, 2001) like in the stunned lamb groups (ESL and GSL), which showed a high pH (5.57, 5.65, respectively) than the USL group (5.46). As regards shear force (SF), Bond et al. (2004) pointed out that stress previous to slaughter has no effect on tenderness values. According to our results, no significant differences were found among the three groups of TS (ESL, GSL and USL). However, Vergara et al. (2005) observed that meat from gas-stunned suckling lambs was more tender than the electrically or un-stunned lambs, a fact attributed to differences in pH24 (minor in stunned groups). In this study with older lambs (light lambs), pH24 did not vary (no significant differences) among different TS groups, which could explain why our results for SF did not show any differences. In addition, the ESL group showed significant differences throughout time (P < 0.01) probably as a consequence of an acceleration in ageing due to the flow of current (Vergara & Gallego, 2000). 7. Conclusions The effect of TS on meat quality of light lambs has been determined in this study. In general, TS did not affect pH

ultimate value (pH0) or tenderness of meat at 24 h or 7 days post-mortem. Colorimetric coordinates (L* a* b*) showed significant differences at 7 days post-mortem, and meat from gas-stunned lambs had the lowest values of a* and b* parameters. At this time of ageing, the stunning (electrical or gas system) of light lambs produced higher CL and DL than those slaughtered without previous stunning (USL group). This fact implies that the stunning system could accelerate the ageing of meat and favours changes in some quality parameters, such as colour and water losses. Acknowledgements The authors would like to thank the slaughter-men at the Municipal Abattoir in Albacete (Spain) for their valuable help and Prof. K. Walsh for assistance with the preparation of this manuscript in English. This work has been made possible by financial help from the Consejerı´a of Ciencia and Tecnologı´a of the Junta de Comunidades of Castilla-La Mancha (Project-02-034). References Alfonso, M., San˜udo, C., Berge, P., Fisher, A.V., Stamataris, C., Thorkelsson, G., et al., (2001). Influential factors in lamb meat quality. Acceptability of specific designations. In R. Rubino, P. Morand-Fehr (Eds.), Production systems and product quality in sheep and goats (19–28). Zaragoza (Spain), CIHEAM-IAMZ. Allen, C. D., Fletcher, D. L., Northcutt, J. K., & Russell, S. M. (1998). The relationship of broiler breast color to meat quality and shelf-life. Poultry Science, 77, 361–366. ´ lvarez, D., (2002). Influencia de las condiciones ante-mortem y la A tecnologı´a del sacrificio sobre la calidad de la carne porcina. Doctoral Thesis, Spain, pp. 334. Apple, J. K., Dikeman, M. E., Minton, J. E., McMurphy, R. M., Fedde, M. R., Leith, D. E., et al. (1995). Effects of restraint and isolation stress and epidural blockade on endocrine and blood metabolite status, muscle glycogen metabolism and incidence of dark-cutting Longissimus muscle of sheep. Journal of Animal Science, 73, 2295–2307.

680

M.B. Linares et al. / Meat Science 76 (2007) 675–681

Beriain, M. J., Horcada, A., Purroy, A., Lisazo, G., Chasco, J., & Mendiza´bal, J. A. (2000). Characteristics of Lacha and Rasa Aragonesa lambs slaughtered at three live weights. Journal of Animal Science, 78, 3070–3077. Bernabe´u, R., & Tendero, A. (2005). Preference structure for lamb meat consumers. A Spanish case study. Meat Science, 71, 464–470. Blokhuis, H. J., Jones, R. B., Geers, R., Miele, M., & Veissier, I. (2003). Measuring and monitoring animal welfare: transparency in the food product quality chain. Animal Welfare, 12(4), 445–455. Bond, J. J., Can, L. A., & Warner, R. D. (2004). The effect of exercise stress, adrenaline injection and electrical stimulation on changes in quality attributes and proteins in semimembranous muscle of lamb. Meat Science, 68, 469–477. Channon, H. A., Payne, A. M., & Warner, R. D. (2002). Comparison of CO2 stunning with manual electrical stunning (50 Hz) of pigs on carcass and meat quality. Meat Science, 60, 63–68. Channon, H. A., Payne, A. M., & Warner, R. D. (2003). Effect of stun duration and current level applied during head to back and head only electrical stunning of pigs on pork quality compared with pigs stunned with CO2. Meat Science, 65, 1325–1333. Craig, E. W., Fletcher, D. L., & Papinaho, A. (1999). The effects of antemortem electrical stunning and post-mortem electrical stimulation on biochemical and textural properties of broiler breast meat. Poultry Science, 78, 490–494. Directive 86/609/CEE. (1986). on protection of animals designated for experimentation and scientific experiments. EU Council Directive 93/119/93. (1993). On the protection of animals at time of slaughter or killing, Official J. Eur. Commun. No. L340/21. FAOSTAT (2005). In http://faostat.fao.org/?language=ES. In database, Animal Production. Fleming, B. K., Froning, G. W., Beck, M. M., & Sosnicki, A. A. (1991). The effect of carbon dioxide as a preslaughter stunning method for turkeys. Poultry Science, 70, 2201–2206. Foury, A., Devillers, N., Sanchez, M. P., Griffon, H., Le Roy, P., & Mormede, P. (2005). Stress hormones carcass composition and meat quality in Large White*Duroc pigs. Meat Science, 69, 703–707. Grau, R., & Hamm, R., 1953. Muscle as food. In Food Science and Technology. A series of monographs, (1985) New York: Academic Press. Gregory, N. G. (2005). Recent concerns about stunning and slaughter. Meat Science, 70, 481–491. Hambrecht, E., Eissen, J. J., Newman, D. J., Smits, C. H. M., den Hartog, L. A., & Verstegen, M. W. A. (2005). Negative effects of stress immediately before slaughter on pork quality are aggravated by suboptimal transport and lairage conditions. Journal of Animal Science, 83, 440–448. Hambrecht, E., Eissen, J. J., Nooijen, R. I. J., Ducro, B. J., Smits, C. H. M., den Hartog, L. A., et al. (2004). Pre-slaughter stress and muscle energy largely determine pork quality at two commercial processing plants. Journal of Animal Science, 82, 1401–1409. Henckel, P., Karlsson, A., Jensen, M. T., Oksjerg, N., & Petersen, J. S. (2002). Metabolic conditions in porcine longissimus muscle immediately pre-slaughter and its influence on peri and post mortem energy metabolism. Meat Science, 62, 145–155. Huff-Lonergan, E., & Lonergan, S. M. (2005). Mechanisms of waterholding capacity of meat: The role of post-mortem biochemical and structural changes. Meat Science, 71, 194–204. Jacob, R. H., Pethick, D. W., & Chapman, H. M. (2005). Muscle glycogen concentrations in commercial consignments of Australia lamb measured on farm and post-slaughter after three different lairage periods. Australian Journal of Experimental Agriculture, 45, 522–543. Martoft, L., Lomholt, L., Kolthoff, C., Rodriguez, B. E., Jensen, E. W., Jorgensen, P. F., et al. (2002). Effects of CO2 anaesthesia on central nervous system activity in swine. Laboratory Animals, 36(2), 115–126. Mckee, S. R., Hargis, B. M., & Sams, A. R. (1998). Pale, soft and exudative meat in turkeys treated with succinylcholine. Poultry Science, 77, 356–360.

Melody, J. L., Lonergan, S. M., Rowe, L. J., Huiatt, T. W., Mayes, M. S., & Huff-Lonergan, E. (2004). Early post-mortem biochemical factors influence tenderness and water-holding capacity of three porcine muscles. Journal Animal Science, 82, 1195–1205. Napolitano, F., Marino, V., De Rosa, G., Capparelli, R., & Bordi, A. (1995). Influence of artificial rearing on behavioral and immune response of lambs. Applied Animal Behaviour Science, 45, 245–253. Northcutt, J. K., Buhr, R. J., & Young, L. L. (1998). Influence of preslaughter stunning on turkey breast muscle quality. Poultry Science, 77, 487–492. Nowak, B., Mueffling, T. V., & Hartung, J. (2007). Effect of different carbon dioxide concentrations and exposure times in stunning of slaughter pigs: Impact on animal welfare and meat quality. Meat Science, 75, 300–308. Okeudo, N. J., & Moss, B. W. (2005). Serum cortisol concentration in different sex-types and slaughter weights and its relationship with meat quality and intramuscular fatty acid profile. Pakistan Journal of Nutrition, 4(2), 64–68. Onenc, A., & Kaya, A. (2004). The effects of electrical stunning and percussive captive bolt stunning on meat quality of cattle processed by Turkish slaughter procedures. Meat Science, 66, 809–815. Paulick, C., Stolle, F. A., & von Mickwitz, G. (1989). The influence of different stunning methods on meat quality of sheep meat. Fleischwirtschaft, 69(2), 227–230. Pearson, A.J., Kilgour, R., de Langen, H., & Payne, E., (1977). Hormonal responses of lamb to trucking, handling and electric stunning. In Proceeding of New Zealand Society. Animal Production, 37, 243–248. Petersen, G. V., Carr, D. H., Davies, A. S., & Pickett, B. T. (1986). The effect of different methods of electrical stunning of lambs on blood pressure and muscular activity. Meat Science, 16, 1–15. Rosenvold, K., Laerke, H. N., Jensen, S. K., Karlsson, A. H., Lundstrom, K., & Andersen, H. J. (2002). Manipulation of critical quality indicators and attributes in pork through vitamin E supplementation, muscle glycogen reducing finishing feeding and pre-slaughter stress. Meat Science, 62, 485–496. Rosenvold, K., Petersen, J. S., Laerke, H. N., Jensen, S. K., Therkildsen, M., Karlsson, A. H., et al. (2001). Muscle glycogen stores and meat quality as affected by strategic finishing feeding of slaughter pigs. Journal of Animal Science, 79, 382–391. San˜udo, C., Sa´nchez, A., & Alfonso, M. (1998). Small ruminant production systems and factors affecting lamb meat quality. Forty fourth International Congress of Meat Science and TechnologyBarcelona, Spain, Meat Science, 49(Suppl. 1), S29–S64. Stoier, S., Aaslyng, M. D., Olsen, E. V., & Henckel, P. (2001). The effect of stress during lairage and stunning on muscle metabolism and drip loss in Danish pork. Meat Science, 59, 127–131. Troeger, K. (1989). Plasma adrenaline levels of pigs after different preslaughter handling and stunning methods. In Proceedings of 35th International Congress of Meat Science and Technology, Copenhagen, Denmark, pp. 81. Troeger, K., & Woltersdorf, W. (1990). Electrical stunning and meat quality in the pig. Fleischwirtschaft, 70(8), 901–904. van der Wal, P. G., Engel, B., & Reimert, H. G. M. (1999). The effect of stress, applied immediately before stunning on pork quality. Meat Science, 53, 101–106. Velarde, A., Gispert, M., Faucitano, L., Manteca, X., & Diestre, A. (2000). The effect of stunning method on the incidence of PSE meat and haemorrhages in pork carcasses. Meat Science, 55, 309–314. Vergara, H., & Gallego, L. (2000). Effect of electrical stunning on meat quality of lamb. Meat Science, 56, 345–349. Vergara, H., & Gallego, L. (2001). Effects of gas composition in modified atmosphere packaging on the meat quality of Spanish Manchega lamb. Journal of Science and Food Agriculture, 81, 1353–1357. Vergara, H., Gallego, L., Garcı´a, A., & Landete-Castillejos, T. (2003). Conservation of cervus elaphus meat in modified atmospheres. Meat Science, 65, 779–783.

M.B. Linares et al. / Meat Science 76 (2007) 675–681 Vergara, H., Linares, M. B., Berruga, M. I., & Gallego, L. (2005). Meat quality in suckling lambs: effect of pre-slaughter handling. Meat Science, 69, 473–478. Vergara, H., Molina, A., & Gallego, L. (1999). Influence of sex and slaughter weight on carcass and meat quality in light and medium

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weight lambs produced in intensive systems. Meat Science, 52, 221–226. Yoshioka, G., Imaeda, N., Ohtani, T., & Hayashi, K. (2005). Effects of cortisol on muscle proteolysis and meat quality in piglets. Meat Science, 71, 590–593.