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Effect of gas stunning and modified-atmosphere packaging on the quality of meat from Spanish Manchego light lamb
Small Ruminant Research 108 (2012) 87–94
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Effect of gas stunning and modified-atmosphere packaging on the quality of meat from Spanish Manchego light lamb María Belén Linares a , Herminia Vergara b,c,∗ a
Department of Food Science and Technology, Faculty of Veterinary, University of Murcia, 30100 Espinardo, Spain Department of Agroforestal Science, Technology and Genetics, Escuela Técnica Superior de Ingenieros Agrónomos, University of Castilla-La Mancha, Campus Universitario, 02071 Albacete, Spain c Food Quality Division, Instituto de Desarrollo Regional, University of Castilla-La Mancha, Campus Universitario, 02071 Albacete, Spain b
a r t i c l e
i n f o
Article history: Received 20 December 2011 Received in revised form 22 June 2012 Accepted 29 June 2012 Available online 21 July 2012 Keywords: Gas stunning Meat quality Light lamb Modified atmosphere Carbon monoxide Shelf life
a b s t r a c t The aim of the present study was to evaluate the effect of different stunning methods (using two different CO2 concentrations and exposure times) and modified atmosphere packaging systems (MA-O2 : 70 O2 + 30 CO2 vs MA-CO: 69.3% N2 + 30% CO2 + 0.7% CO) on the meat quality of Manchego Spanish male light lambs (n = 50). One electrically stunned control group was used. The type of stunning affected pH value, meat tenderness and water losses (P < 0.05) but did not modify most of the colour coordinates or the lipid oxidation level. Furthermore the modified atmosphere with a low CO level (MA-CO) promoted more tender meat with higher oxidative stability than the high-oxygen packed meat (MA-O2 ). Most likely both the CO2 gas concentration and the exposure time are relevant in the evolution of meat quality from light lambs stunned with different gas stunning systems. In addition, the use of a low CO level to pack lamb meat permits to remove the oxygen from the pack, which improves meat tenderness and the oxidative stability. © 2012 Elsevier B.V. All rights reserved.
1. Introduction The current European law to protect animals at slaughter (EU Council Directive 1009, 2009) requires electrical stunning of sheep in order to guarantee that these animals are unconscious and insensitive. Although the gas method is not considered under the present law for sheep slaughter, this system should be seen as an alternative in ovine specie since important advantages have been reported (Linares and Vergara, 2009). In previous works (Linares et al., 2007a; Bórnez et al., 2009a) authors found the gas system to be more effective since it enables to reduce the stun–stick
∗ Corresponding author at: Departamento de Ciencia y Tecnología Agroforestal y Genética, ETSIA, University of Castilla-La Mancha, Campus Universitario s/n, 02071, Albacete, Spain. Tel.: +34 967599200. E-mail address: [email protected] (H. Vergara). 0921-4488/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.smallrumres.2012.06.015
interval with almost not any handling of animals, thus improving welfare. Furthermore, since less kicking is described during the exsanguinations, the gas method is much safer for the slaughterer (Bórnez et al., 2009b), while fewer haemorrhages and blood spots were observed in carcasses, hence improving meat quality. In other species such as pig (Channon et al., 2003) or poultry (Gregory, 2005) the electrical method has been replaced by the gas system due to the numerous favourable effects observed. On the other hand, meat preservation under modified atmosphere systems and the effect of gases commonly used in the gas mixture have been extensively studied in lamb (Vergara and Gallego, 2001; Kennedy et al., 2004; Lauzarica et al., 2005; Linares et al., 2008) as in many other species (Jakobsen and Bertelsen, 2000; Livingston et al., 2004; Vergara et al., 2003, 2005; Sekar et al., 2006). In fact, the high oxygen concentration in packs can help to preserve colour while also promoting the development of important
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M.B. Linares, H. Vergara / Small Ruminant Research 108 (2012) 87–94
oxidative processes (Livingston et al., 2004). The use of a low carbon monoxide concentration (less than 1%) in the gas blends could be an option to pack red meat due to the increase in the oxidative stability and colour in lamb meat (Linares et al., 2007b). Similar conclusions regarding the use of this gas have been observed in pork (Wilkinson et al., 2006), beef (Jayansingh et al., 2001) or turkey (Pexara et al., 2002). In addition, the use of this gas at low levels, similar to those proposed in the present study (0.7%), is completely safe for consumers (Sorhein et al., 2006). The packing of fresh meat under modified atmosphere systems by adding carbon monoxide (<1%) has been allowed in countries such as the United States, New Zealand and Australia since 2004. By other side, previous papers, which evaluated the effect of the gas stunning systems on initial meat quality (24 h and 7 days post-mortem, packed under aerobic conditions) from Manchego Spanish breed lamb, showed that results depend on the lamb age. Thus, in light lamb (Vergara et al., 2009) the main finding was that the application of a low CO2 concentration (80%) for an extended time (90 s) could cause lower values of lipid oxidation, pH, cooking loss, and tenderness. In suckling lamb (Bórnez et al., 2009b), however, the same gas concentration at stunning was related to more drip loss and greater tenderness. In addition, studies (Bórnez et al., 2009c, 2010) concerning the effect of these same gas stunning methods on the quality of suckling-lamb meat packed under different modified atmospheres showed that the use of low CO in packing could increase oxidative stability and tenderness in all the stunning groups, even though it does not improve microbial quality. However, the effect of both factors, gas stunning typemodified atmosphere, is unknown for light lamb meat and, as authors has pointed out in previous studies (Linares et al., 2008), the evolution of meat quality could vary in accordance with the slaughter weight/age of lambs in this breed. Therefore the aims of this study were (1) to examine the effect of gas stunning systems using different concentrations/time of exposure on physic-chemical characteristics and lipid oxidation of light lamb meat and (2) to determine optimal gas stunning system-modified atmosphere combinations for light-lamb meat quality. 2. Materials and methods The research protocol used in this study was previously approved by the Animal Ethics Committee of the University of Castilla-La Mancha, according to guidelines regarding the protection of animals used in research and for scientific purposes (Directive 65/2003 EC). 2.1. Animals In this trial 50 male Spanish Manchego light lambs were used. Animals were fed with milk up to 12 kg of weight (30 days old) and after that a commercial concentrate (16% crude protein; 12.443 kJ/kg dry matter) and cereal straw ad libitum were provided until slaughter time at 25 kg live weight (70 days old). According to the type of stunning, lambs were distributed into five groups (n = 10): - Four groups were stunned with gas using different CO2 concentrations and exposure times [G1: 80% – 90 s; G2: 90% – 90 s; G3: 90% – 60 s;
G4: 80% – 60 s] using a gondola dip-lift system (G van Wijnsberghe & Co. NV, Veurne, Belgium) generally used to stun pigs (3 m long × 1.5 m wide × 1 m high). This system indicates the concentration of CO2 in the pit, a factor which was tested every day during the experiment by authorised personnel. Groups of three or four lambs were placed in the box. The motor of the gondola transporter was set to reach the bottom of the pit in 10 s and to return to the ejection level 16 s after restarting. The lambs were shackled by the leg and hoisted onto the overhead rail where they were bled by cutting the blood vessels in the neck between 25 and 35 s after removal from the gondola. - One control group (G5) was electrically stunned at 110 V, 50 Hz for 5 s (plate electrodes applied on both sides of the head, behind the ears; Electronarcosis Panel, MAC-01, Bernard, S.L. Albacete, Spain). Immediately after stunning, lambs were slaughtered and dressed using standard commercial procedures. All carcasses were chilled at 4 ◦ C for 24 h in a conventional chiller. 2.2. Sampling After this period, the Longissimus dorsi from both sides of the carcasses was removed and cut into similarly sized portions (8 per lamb). Two samples were used to determine initial meat quality (at 24 h and 7 days) and results were shown by Vergara et al. (2009). The remaining samples were placed in clear trays (LINPAC Packaging West Yorkshire, UK) with an oxygen permeability rate of 3.2 cm3 m−2 day−1 atm−1 at 23 ◦ C, and covered by a film with transmission rates of 1 cm3 m−2 day−1 atm−1 for oxygen (23 ◦ C; 50% RH); 5.5 cm3 m−2 day−1 for CO2 (23 ◦ C; 0% RH) and 2.2 g m−2 day−1 for H2 O (25 ◦ C; 90% RH) and packed under modified atmosphere using a packaging machine (Efabind L-650, Efabind, Murcia, Spain). All samples remained in a conventional chiller at 2 ◦ C in the dark. The following modified atmospheres (MA) were compared: MA-O2 : 70% O2 + 30% CO2 MA-CO: 69.3% N2 + 30% CO2 + 0.7% CO Gas composition was tested in the packs by using a ChecMate machine (PBI Dansensor, Ringsted, Denmark). Samples from each lamb were packed under both types of modified atmosphere (MA-O2 , MA-CO) and analysed at 7, 14, 21 days post-packing. 2.3. Analysis The following characteristics were assessed: A. Physical and chemical characteristics - pH was measured using a Crison 507 (Barcelona, Spain, Crison Instruments, S.A.) equipment with a penetrating electrode. - Cooking losses (CL), expressed as the percentage of weight after cooking relative to the initial weight (before cooking). Each meat sample (approximately 40 g) was weighed and individually placed in polyethylene bags in a water bath at 70 ◦ C for 15 min. After surfacedrying of the cooked samples with filter paper samples were again weighed. - Water holding capacity (WHC), calculated as the percentage of free water in accordance with the procedure established by Grau and Ham (1953). - Drip losses (DL), expressed as a percentage of the initial portion weight (Vergara et al., 2005). - Shear force (SF) was analysed with a TA.XT2 texture analyser equipped with a Warner-Bratzler device with 50 mm/min test speed. For the analysis, each meat sample (40 g) was individually placed in polyethylene bags in a water bath at 70 ◦ C for 15 min. The cooked samples were cooled for 30 min at 20 ◦ C room temperature and maintained at 4 ± 1 ◦ C until the texture analysis. At this time the samples were cut into three (1 cm cross-section and 2–3 cm length) and the SF was by triplicate recorded. The pieces were cut in a perpendicular position as respect to the orientation fibres. - Colour coordinates (L, a*, b* values) were measured on the surface of the Longissimus dorsi muscle (80 mm diameter), immediately after the packs were opened, with a colorimeter Minolta CR-400 (Osaka, Japan) using illuminant D65 and 10◦ standard
M.B. Linares, H. Vergara / Small Ruminant Research 108 (2012) 87–94 observer after standardisation with respect to the white calibration plate. Chroma [C* = (a* + b*)1/2 ] and Hue angle [h* = arctan (b*/a*)] were also calculated. All measurements were carried out by triplicate. B. Lipid oxidation 2-Thiobarbituric acid reactive substances were determined (Tarladgis et al., 1964) and results were expressed as mg of malonaldehyde (MDA) per kg of meat. The absorbance at 532 nm was read with a 140 Helios alfa spectrophotometer (Thermo, Electron Corporation, Leicester, England). 2.4. Statistical analysis Statistical analyses were performed using the Statistical Package SPSS 15.0 version (SPSS Inc., Chicago, USA, 2005). A General Lineal Model procedure was used to examine the effect of the stunning method and the type of modified atmosphere at 7, 14 and 21 days post-packaging on meat quality parameters. An ANOVA was carried out to check the effect of time (7, 14, 21) in each stunning method-modified atmosphere group and when the differences were statistically significant a Tukey’s test was carried out.
3. Results and discussion 3.1. Physical and chemical parameters Table 1 shows the effect of the modified atmosphere and the stunning method on pH, water holding capacity (WHC, %) cooking losses (CL, %), drip losses (DL, %) and shear force (SF, N/cm2 ) of light lamb meat. The type of modified atmosphere had no effect on the lamb meat quality (pH, WHC, CL, DL) for the different stunning groups (G1–G5) except for SF values with significant differences at 14 and 21 days post-packing (both P < 0.001). In general, the modified atmosphere MA-O2 (70% O2 + 30% CO2 ) promoted higher shear force values (less tenderness) than the MA-CO (69.3% N2 + 30% CO2 + 0.7% CO) in all stunning treatment groups (P < 0.05). Some authors (Lund et al., 2007) observed that pork stored under 70% O2 + 30% CO2 exhibited higher shear force values (less tenderness) than vacuum packed meat. Recently, other authors (Kim et al., 2010) have confirmed that the oxidative conditions promoted by high oxygen concentrations in the gas mixture negatively affect colour, flavour stability and also meat tenderness during storage. Since oxidation development could play an important role in meat tenderness, the lipid and myoglobin oxidation and cross-linking/aggregation of myosin could explain the increase of shear force values in samples under high-oxygen modified atmosphere packaging systems, as previously reported by Zakrys et al. (2008) for beef. In addition, the increased oxygen levels could inhibit calpain activity, which directly influences meat tenderness (Guttmann et al., 1997). On the other hand, GLM procedures showed a significant effect of the type of stunning on pH values starting from 14 days post-packing (P < 0.01) in Manchego light lamb meat packed under modified atmosphere. In the present paper (for light-lamb), the lower pH was found in G1 and G3 groups (with significant differences according to a Tukey’s test only at 21 days and in MA-CO) while in a previous study in suckling lamb meat (Bórnez et al., 2010) the lower values of pH were found in G4 and G5 groups. The difference on pH value was also reported in a previous paper in light lamb with higher pH described for
89
gas-stunned lambs meat than in the electrically samples (Linares and Vergara, 2009), thus pointing to the existence of an intense slaughter weight/age effect for meat quality ˜ parameters in sheep (Sanudo et al., 1998; Martínez-Cerezo et al., 2005). Regarding meat tenderness, higher Warner Bratzler shear force values (N/cm2 ) were found in the G1 stunning group (80% CO2 90 s) in both types of modified atmosphere packaging systems (MA-O2 and MA-CO) in comparison to the other stunning groups. On the other hand, the lower SF in the G1 group even after ageing could be related with the highest fall in pH (pH0 –pH24 ) at the initial time after slaughter (Vergara et al., 2009) and an increase in the catecholamines level at this time (Bórnez et al., 2009a), which can produce a low calpain activity. Curiously, at 7 days post-mortem, in light lamb meat packed under aerobic conditions (Vergara et al., 2009) no significant differences were found between the G1 and G5 groups, contrary to the present study, although the values in G1 were slightly higher (74.8 vs 51.1 N/cm2 respectively) and this tendency continued in meat packed under modified atmosphere until significant values. The type of stunning affected drip losses (DL) and cooking losses (CL). In general the electrical stunning method (G5) showed higher CL values in comparison to the G1 and G2 groups (both 90 s). However it should be pointed out that in this study the G3 and G4 stunning group (both 60 s) showed CL similar to the G5 group, as previously described by Bórnez et al. (2009b) in suckling-lamb meat. It seems that not only the gas concentration but also the time of exposure to the gas in the bottom of the pit can imply changes in the meat quality parameters, mainly in relation to water losses. Furthermore the type of stunning did not affect the water holding capacity although this parameter significantly varied with storage time in all the stunning groups (P < 0.05), except for G2. During the ageing process of meat, a tendency to expel more water (higher WHC values) has been described in the literature as occurring under aerobic conditions (Vergara and Gallego, 2000) and also under modified atmosphere packaging systems (Vergara and Gallego, 2001), which is in agreement with the results of the present study. A similar trend was shown for the drip losses (DL) occurring during ageing, as reported in other studies (Sekar et al., 2006; Vergara and Gallego, 2000). Table 2 shows the effect of the type of modified atmosphere packing system and the type of stunning on the colour coordinates of light lamb-meat. The type of gas mixture affected the colour coordinates for L* and b* values, while the h* angle was the highest in the MA-O2 for all the stunning groups (P < 0.001). Likewise, the a* and C* values were the lowest in MA-O2 , while the meat packed under the MA-CO (P < 0.001) reached the maximum levels. This tendency was previously reported in other papers on suckling lamb meat packed under modified packing systems (Bórnez et al., 2010). MA-CO that included a low level of carbon monoxide (0.7%) preserved colour stability longer than the highoxygen gas mixture such as that found in MA-O2 in the present research. This has been extensively reported in literature since the greater stability of the carboxymyoglobin,
90 Table 1 Effect of the type of stunning and modified atmosphere in meat pH, water holding capacity (WHC, %), cooking losses (CL, %) drip losses (DL, %) and shear force (SF, N/cm2 ) (mean ± s.d) from Spanish Manchego light lamb meat. G1 (n = 10)
pH
7d 14 d 21 d
WHC%
7d 14 d 21 d
CL%
DL%
SF N/cm2
G2 (n = 10)
G3 (n = 10)
MA
TS
MA × TS
5.64 ± 0.03
5.59 ± 0.01
5.61 ± 0.02
5.64 ± 0.00
5.64 ± 0.01
5.62 ± 0.01
5.62 ± 0.01
NS
5.57 ± 0.01
5.59 ± 0.01
5.61 ± 0.02
5.63 ± 0.03 5.59 ± 0.02d,e
5.57 ± 0.01
5.58 ± 0.01 5.56 ± 0.01d
5.62 ± 0.01
5.62 ± 0.02
5.61 ± 0.01
5.65 ± 0.01
NS
NS **
NS
5.64 ± 0.01e
5.54 ± 0.01 21.05 ± 1.77x 23.06 ± 0.91x,y 25.94 ± 1.05y
5.55 ± 0.01d 20.31 ± 0.82x 22.77 ± 0.6x,y,d,e 23.93 ± 0.78y
5.57 ± 0.02 22.44 ± 0.74 24.23 ± 1.01 25.76 ± 1.5
MA-CO
22.7 ± 1.03 24.61 ± 0.86e 25.98 ± 1.42
4.54 ± 0.24d 5.19 ± 0.23d,e
4.86 ± 0.2a,b 4.95 ± 0.2a
4.19 ± 0.36d 4.48 ± 0.28d
21 d
5.83 ± 0.24y,a,b
5.43 ± 0.28d,e
5.08 ± 0.27a
4.77 ± 0.27d
7d
2.16 ± 0.16x,e 2.65 ± 0.2x,y
2.16 ± 0.11x,b 2.83 ± 0.07y,b
2.22 ± 0.13e
14 d
2.12 ± 0.1x,b 2.48 ± 0.15x,y,b
21 d
2.68 ± 0.14y,a,b
3.11 ± 0.18y
3.08 ± 0.09y,b
3.03 ± 0.23
14 d 21 d
Significance
5.63 ± 0.02
MA-O2
4.21 ± 0.35x,a 4.92 ± 0.3x,y,a
7d
G5 (n = 10)
5.58 ± 0.02
MA-CO
14 d
7d
G4 (n = 10)
5.6 ± 0.02
MA-O2
63.70 ± 0.86 64.58 ± 0.76b 52 ± 0.68
61.83 ± 0.93 52.43 ± 0.84e 38.80 ± 0.6e
48.90 ± 0.47y 35.96 ± 0.24x,a,g 36 ± 0.26x,g
2.8 ± 0.2
MA-O2
5.55 ± 0.01 22.03 ± 0.39x 23.72 ± 0.7x 26.45 ± 0.8y
MA-CO
21.35 ± 0.83x 23.2 ± 0.79x,y,d,e 25.34 ± 1y
MA-O2
5.61 ± 0.01 20 ± 0.68x 23.21 ± 0.84y 25 ± 0.65y
MA-CO
5.59 ± 0.01d,e 20.46 ± 0.78x 22.51 ± 0.81x,y,d,e 24.54 ± 0.45y
MA-CO
NS
NS
***
NS
21.53 ± 0.46x 23.03 ± 0.63x,y 24.74 ± 0.77y
20.93 ± 0.46x 21.33 ± 0.75x,y,d 23.63 ± 0.57y
NS
*
NS
NS NS
* NS
NS NS
5.6 ± 0.01
5.9 ± 0.18c 5.92 ± 0.35a,b 6.58 ± 0.32b
5.33 ± 0.56d,e 6.08 ± 0.47e
5.86 ± 0.26x,c 6.52 ± 0.27x,y,b
5.54 ± 0.19b,c 6.16 ± 0.29b
5.54 ± 0.16d,e 6.06 ± 0.19e
NS
***
NS
6.17 ± 0.2e
NS
***
NS
6.18 ± 0.25e
6.72 ± 0.15y,b
6.44 ± 0.28e
6.27 ± 0.17b
6.26 ± 0.28e
NS
***
NS
2.04 ± 0.09x,b 2.36 ± 0.14x,y,a,b
2.12 ± 0.17x,e 2.71 ± 0.2x,y
1.56 ± 0.11x,a 1.86 ± 0.15x,y,a
1.46 ± 0.11x,d 2.21 ± 0.21y
1.81 ± 0.14x,a,b,g 2.56 ± 0.21x,y,b
1.42 ± 0.11x,d,h 2.5 ± 0.26y
NS
***
NS
NS
**
NS
2.62 ± 0.12y,a,b
2.85 ± 0.2y
2.52 ± 0.16y
3.03 ± 0.37y,b
2.68 ± 0.41y
NS
**
NS
*
NS
***
NS
**
NS
2.2 ± 0.12y,a
6.07 ± 0.28e
MA-O2
41.65 ± 0.54y 27.53 ± 0.17x,d,h
51.35 ± 0.51 44.29 ± 0.37a,g
45.17 ± 0.45y 30.28 ± 0.1x,d,h
51.94 ± 0.6 43.15 ± 0.4a
48.11 ± 0.63y 34.3 ± 0.32x,d,e
25.28 ± 0.08x,d,h
37.73 ± 0.21g
25.97 ± 0.08x,d,h
37.43 ± 0.38g
27.14 ± 0.2x,d,e,h
49.78 ± 0.55 41.84 ± 0.46a 37.43 ± 0.42g
49 ± 0.69y NS 36.16 ± 0.54x,y,d,e *** 24.3 ± 0.16x,d,h
***
G1: 80% – 90 s; G2: 90% – 90 s; G3: 90% – 60 s; G4: 80% – 60 s; G5: electrical. TS: type of stunning; MA-O2 : modified atmosphere with high oxygen level (MA-O2 : 70% O2 + 30% CO2 ); MA-CO: modified atmosphere with a low carbon monoxide level (69.3% N2 + 30% CO2 + 0.7% CO). a,b : different superscripts in the same row indicate significant differences in MA-O2 due to the type of stunning; d,e : different superscripts in the same row indicate significant differences in MA-CO due to the type of stunning; x,y,z : different superscripts in the same column indicate significant differences due to the storage time; g,h : different superscripts in the same row indicate significant differences among MA-O2 and MA-CO for the same type of stunning group. * P ≤ 0.05. ** P ≤ 0.01. *** P ≤ 0.001. NS: P > 0.05.
M.B. Linares, H. Vergara / Small Ruminant Research 108 (2012) 87–94
Time
Table 2 Effect of the type of stunning and modified atmosphere in colour coordinates (L*, a*, b*, C*, h*; means ± s.d.) on Spanish Manchego light lamb meat.
L
a*
h*
G5 (n = 10)
G4 (n = 10)
Significance MA × TS
MA-CO
MA-O2
MA-CO
MA-O2
MA-CO
MA-O2
MA-CO
MA-O2
MA-CO
MA
47.04 ± 0.54d,e 47.14 ± 0.74h
45.54 ± 0.73x 49.93 ± 1.16y
45.34 ± 0.85d
47.98 ± 1x
47.17 ± 0.72d,e 47.33 ± 0.61h
46.31 ± 1.27x 49.67 ± 1.21x,y
NS ***
52.96 ± 1.1y,g
47.25 ± 1.02h
53.3 ± 1.38y,g
51.21 ± 0.5y,g 55.58 ± 0.7z,g
47.13 ± 0.85x 50.26 ± 0.6x,y,g
21 d
46.74 ± 1.03 47.04 ± 0.88h
48.38 ± 0.96e 48.43 ± 0.8h
46.55 ± 0.35d,e
14 d
46.96 ± 1.05x 49.62 ± 0.87x,y,g
47.91 ± 0.89
51.29 ± 1.23y,g
47.81 ± 0.58h
***
7d
15.59 ± 1.34y,a,g 11.02 ± 1.57x,g
24.79 ± 0.83h 26.08 ± 0.72h
19.91 ± 0.77z,b,g 10.35 ± 1.31y,g
25.64 ± 0.72h 26.25 ± 0.55h
17.25 ± 1.04z,a,b,g 12.15 ± 1.43y,g
25.68 ± 0.43h 26.77 ± 0.73h
16.85 ± 0.38z,a,g 11.5 ± 1.76y,g
23.57 ± 0.67h 25.45 ± 0.9h
***
**
NS
***
NS
NS
6.97 ± 0.83x,g
6.48 ± 0.83x,g
25.75 ± 0.45h
7d
24.3 ± 0.9h 26.12 ± 0.8h
50.8 ± 1.41y 19.64 ± 0.48y,b,g 10.55 ± 1.34x,g
NS NS
5.37 ± 0.67x,g
6.01 ± 0.63x,g
26.07 ± 0.62h
***
NS
NS
9.16 ± 0.56h 9.56 ± 0.3h
12.6 ± 0.18x,b,g 14 ± 0.3y,g
9.19 ± 0.32x,h 10.34 ± 0.27x,y,h
12.81 ± 0.25x,b,g 14.16 ± 0.55x,y,g
9.07 ± 0.22x,h 10.18 ± 0.26y,h
10.74 ± 0.4x,a,g 12.85 ± 0.38y,g
8.3 ± 0.4x,h 9.47 ± 0.19y,h
***
**
NS
14 d
12.72 ± 0.4x,b,g 13.27 ± 0.62x,g
***
*
NS
21 d
15.33 ± 0.68y,g
10.4 ± 0.16h
15.68 ± 0.47y,g
9.89 ± 0.27h
16.1 ± 1.43z,g
10.48 ± 0.38y,h
14.92 ± 0.63y,g
10.56 ± 0.38y,h
15.09 ± 0.7z,g
9.97 ± 0.13y,h
***
NS
NS
7d 14 d
19.57 ± 1.26a,g 17.86 ± 0.43g
26.57 ± 0.9h 28.05 ± 0.81h
23.64 ± 0.84y,b,g 17.3 ± 0.57x,g
27.25 ± 0.86h 27.95 ± 0.52h
23.45 ± 0.5y,b,g 18.02 ± 0.82x,g
27.24 ± 0.43h 28.65 ± 0.75h
21 d
17.11 ± 0.4g
28.43 ± 0.81h
16.71 ± 0.41x,g
28.24 ± 0.54h
17.3 ± 0.39x,g
26 ± 0.9h 28.1 ± 0.81h 28.13 ± 0.6h
17.48 ± 0.79x,g
7d
21.1 ± 0.38
14 d
37.38 ± 2.55x 51.18 ± 5.56y,g
32.66 ± 0.53x,g 53 ± 4.37y,g
19.52 ± 0.6h 20.05 ± 0.71h
36.84 ± 2.06x,g 50.34 ± 3.5y,g
20.82 ± 0.74h 21.65 ± 0.48h
33.16 ± 0.57x,g 54.32 ± 3.63y,g
21 d
65.23 ± 3.38z,g
71.1 ± 2.46z,g
20.5 ± 0.38h
69.55 ± 2.21z,g
21.95 ± 0.87h
64.19 ± 5.11y,g
21.5 ± 0.54h 21.56 ± 0.54h
27.44 ± 0.8h
NS NS
9.56 ± 0.37h 10.3 ± 0.45h
21.45 ± 0.83y,a,b,g 18.86 ± 0.88x,g
7.68 ± 1.7x,g
46.78 ± 0.79
NS
26.45 ± 0.84h
7d
26.44 ± 0.5h
48.8 ± 0.96h
TS *
11.57 ± 0.67x,a,b,g 13.21 ± 0.75x,y,g
21 d
C*
G3 (n = 10)
G2 (n = 10)
MA-O2
14 d
b*
G1 (n = 10)
20 ± 0.45y,a,g
25.01 ± 0.74x,h
***
**
NS
27.17 ± 0.9x,y,h 27.62 ± 0.43y,h
***
NS
NS
29.41 ± 0.86h
17.84 ± 0.97x,y,g 16.64 ± 0.61x,g
***
NS
NS
19.46 ± 0.48x,h 20.85 ± 0.37y,h
32.46 ± 0.92x,g 50.43 ± 5.05y,g
19.32 ± 0.62x,h 20.52 ± 0.46x,y,h
***
*
NS
***
NS
NS
21.01 ± 0.27y,h
66.67 ± 3.03z,g
21.21 ± 0.35y,h
***
NS
NS
G1: 80% – 90 s; G2: 90% – 90 s; G3: 90% – 60 s; G4: 80% – 60 s; G5: electrical. TS: type of stunning; MA-O2 : modified atmosphere with high oxygen level (MA-O2 : 70% O2 + 30% CO2 ); MA-CO: modified atmosphere with a low carbon monoxide level (69.3% N2 + 30% CO2 + 0.7% CO). a,b : different superscripts in the same row indicate significant differences in MA-O2 due to the type of stunning; d,e : different superscripts in the same row indicate significant differences in MA-CO due to the type of stunning; x,y,z : different superscripts in the same column indicate significant differences due to the storage time; g,h : different superscripts in the same row indicate significant differences among MA-O2 and MA-CO for the same type of stunning group. * P ≤ 0.05. ** P ≤ 0.01. *** P ≤ 0.001. NS: P > 0.05.
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Time
91
* ***
G1: 80% – 90 s; G2: 90% – 90 s; G3: 90% – 60 s; G4: 80% – 60 s; G5: electrical. TS: type of stunning; MA-O2 : modified atmosphere with high oxygen level (MA-O2 : 70% O2 + 30% CO2 ); MA-CO: modified atmosphere with a low carbon monoxide level (69.3% N2 + 30% CO2 + 0.7% CO). a,b : different superscripts in the same row indicate significant differences in MA-O2 due to the type of stunning; d,e : different superscripts in the same row indicate significant differences in MA-CO due to the type of stunning; x,y,z : different superscripts in the same column indicate significant differences due to the storage time; g,h : different superscripts in the same row indicate significant differences among MA-O2 and MA-CO for the same type of stunning group. * P ≤ 0.05. *** P ≤ 0.001. NS: P > 0.05.
***
NS NS NS
TS MA
***
0.73 ± 0.05x,g 1.03 ± 0.09d,e,y,g 1.32 ± 0.08d,z,g
MA-CO MA-O2 MA-CO MA-O2 MA-CO MA-O2
2.46 ± 0.11x,h 0.82 ± 0.05x,g 1.94 ± 0.29x,h 0.74 ± 0.11x,g 2.43 ± 0.12x,h 3.74 ± 0.19y,h 0.99 ± 0.07d,e,x,g 4.27 ± 0.65y,h 1.33 ± 0.17e,x,y,g 3.19 ± 0.12y,h 4.51 ± 0.27a,b,z,h 1.39 ± 0.07d,e,y,g 5.39 ± 0.75a,b,y,h 1.44 ± 0.25d,e,y,g 5.82 ± 0.24b,z,h 0.96 ± 0.13x,g 1.37 ± 0.06e,y,g 1.93 ± 0.15e,y,g
MA-CO MA-O2 MA-CO MA-O2
2.05 ± 0.39x,h 0.57 ± 0.14x,g 1.97 ± 0.17x,h 3.64 ± 0.35y,h 0.86 ± 0.12d,x,y,g 3.89 ± 0.38y,h 5.51 ± 0.24a,b,z,h 1.27 ± 0.09d,y,g 4.14 ± 0.27a,y,h 7d 14 d 21 d
Significance G5 (n = 10) G4 (n = 10) G3 (n = 10) G2 (n = 10) G1 (n = 10) Time
Table 3 Effect of the type of stunning and modified atmosphere in lipid oxidation level (malondialdehyde/kg of meat) (means ± s.d) on Spanish Manchego light lamb meat.
NS NS
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MA × TS
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a stable chemical state of myoglobin, promoted a desirable bright cherry-red colour in meat that also helped in preservation (Jeong and Claus, 2011). The type of stunning did not affect the colour coordinate values although the G5 (electrically) showed the lowest b* value at 7 days post-storage, possibly related to the increased muscular activity and the final glycogen content which is comparable to that indicated by Roselvold et al. (2001). In general, no significant differences were found due to the effect of storage time in any of the colour coordinate values for MA-CO with some exceptions in b* for G3; b* and h* for G4 and b*, C* and h* for G5 (P < 0.05). Other studies reported that the increase in L* coordinate would be related to protein degradation changes which increases light scattering properties of meat like in samples from modified atmosphere MA-O2 (Vergara et al., 2009). 3.2. Lipid oxidation The effects of the type of modified atmosphere packing system and the type of stunning on lipid oxidation values of light-lamb meat are shown in Table 3, with the MDA values higher in modified atmosphere with high oxygen concentration (MA-O2 ) (P < 0.001). Such levels were three times higher in MA-O2 samples than in those packed under a low CO concentration (P < 0.001). Under a low carbon monoxide level (MA-CO), even after 21 days post-storage, meat samples did not exceed the threshold of 2 mg of MDA/kg of meat proposed as the limit to perceive oxidised odour and flavours in lamb meat (Camo et al., 2008). It has been extensively reported in literature that highoxygen gas mixtures increase the lipid oxidation of meat and meat products, negatively affecting its organoleptic characteristics (Livingston et al., 2004; Lagerstedt et al., 2011). Thus, from day 7 to 21 of storage the increase in TBARS values were approximately 3 units and about 0.5–1 point for the same interval time in MA-O2 and MA-CO, respectively. Carbon monoxide is considered as an inhibitor on the heme a3 group in the oxidase cytochrome which blocks the interaction with oxygen (Alvarez et al., 1994) and can displace the O2 from the oxymyoglobin (MbO2 ), with carboxymyoglobin conforming a very stable pigment in meat (Sorheim et al., 1997, 1999). The type of stunning had no effect on the lipid oxidation values in any of the established stunning groups. Previous works on suckling lamb meat (Bórnez et al., 2009c) pointed out significant differences among stunning groups attributed to the hypoxia generated by the CO2 gas concentration applied. This fact confirms the importance of the slaughter weight/age in the lipid oxidation development in this breed as was previously pointed out in a preliminary study (Linares et al., 2007b), where different weight–age relationships were tested with regards to meat quality, including the lipid oxidation index. 4. Conclusions According to the results found in the present study on light-lamb meat quality characteristics, we can conclude the following: (1) in general, this study support the well
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known effects of modified atmosphere type on SF values, colour coordinates and lipid oxidation since MA-CO promoted more tender meat, with the highest lipid and colour stability. (2) The type of stunning affected the physical characteristics (pH, losses water and SF) and for light lamb meat stunned with a minor CO2 concentration (80%) and longer time (90 s), less tenderness in both types of packaging in all ageing times analysed was reported. (3) In general, the gas stunning system did not affect lipid oxidation a fact which contrasts with the results found in meat packed under aerobic conditions (Vergara et al., 2009). (4) Finally, we conclude that the results of the present study and previous ones on suckling lamb (Bórnez et al., 2009c, 2010) indicated that the developments of the main characteristics depend on the lamb age at slaughter, especially for pH, lipid oxidation and SF. Acknowledgements The authors would like to thank the slaughter-men at the Municipal Abattoir in Albacete (Spain). We are also grateful to Prof. K. Walsh and to P. Wolder for assistance with the preparation of this manuscript in English. This work had been made possible by financial help from the Ministerio de Educación y Ciencia (Project: AGLl-200761110). References Alvarez, S., Novoa, M.J., Boveris, A., 1994. La mitocondria. Estructura, función y especies reactivas del oxígeno. http://www.antioxidantes. com.ar/FrArt084.htm. Bórnez, R., Linares, M.B., Vergara, H., 2009a. Systems stunning with CO2 gas on Manchego light lambs: physiologic responses and stunning effectiveness. Meat Sci. 82, 133–138. Bórnez, R., Linares, M.B., Vergara, H., 2009b. Effects of stunning with different carbon dioxide concentrations and exposure times on suckling lamb meat quality. Meat Sci. 81, 493–498. Bórnez, R., Linares, M.B., Vergara, H., 2009c. Microbial quality and lipid oxidation of Manchega breed suckling lamb meat: effect of stunning method and modified atmosphere packaging. Meat Sci. 83, 383– 389. Bórnez, R., Linares, M.B., Vergara, H., 2010. Effect of different gas stunning methods on Manchega suckling lamb meat packed under different modified atmospheres. Meat Sci. 84, 727–734. Camo, J., Beltrán, J.A., Roncales, P., 2008. Extension of the display life of lamb with an antioxidant active packaging. Meat Sci. 80, 1086– 1091. 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 Sci. 65, 1325–1333. Directive 65/2003/EC, 2003. Protection of animals designated for experimentation and scientific experiments. Directive 1009/2009/EC, 2009. On the protection of animals at the time of slaughter or killing. Off. J. Eur. Commun., L 303, 1–30. Grau, R., Ham, R., 1953. Muscle as Food, Food Science and Technology. A Series of Monographs (1985). Academic Press, New York. Gregory, N.G., 2005. Recent concerns about stunning and slaughter – a review. Meat Sci. 70, 481–491. Guttmann, R.P., Elce, J.S., Bell, P.D., Isbell, J.C., Johnson, G.V.W., 1997. Oxidation inhibits substrate proteolysis by calpain I but not autolysis. J. Biol. Chem. 272, 2005–2012. Jakobsen, M., Bertelsen, G., 2000. Colour stability and lipid oxidation of fresh beef. Development of a response surface model for predicting the effects of temperature, storage time and modified atmosphere composition. Meat Sci. 54, 49–57. Jayansingh, P., Cornforth, D.P., Carpenter, C.E., Whittier, D., 2001. Evaluation of carbon monoxide treatment in modified atmosphere packaging or vacuum packaging to increase color stability of fresh beef. Meat Sci. 59, 317–324.
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Jeong, J.Y., Claus, J.R., 2011. Colour stability of ground beef packaged in a low carbon monoxide atmosphere or vacuum. Meat Sci. 87, 1–10. Kennedy, C., Buckley, D.J., Kerry, J.P., 2004. Display life of sheep meats retail packaged under atmospheres of various volumes and compositions. Meat Sci. 68, 649–658. Kim, Y.H., Huff-Lonergan, E., Sebranek, J.G., Lonergan, S.M., 2010. High oxygen modified atmosphere packaging system induces lipid and myoglobin oxidation and protein polymerization. Meat Sci. 85, 759–767. Lagerstedt, A., Lundstrom, K., Lindahl, G., 2011. Influence of vacuum or high-oxygen modified atmosphere packaging on meat quality of beef M. longissimus dorsi steaks after different ageing times. Meat Sci. 87, 101–106. ˜ Lauzarica, S., de la Fuente, J., Díaz, M.T., Alvarez, I., Pérez, C., Caneque, V., 2005. Effect of dietary supplementation of vitamin E on characteristics of lamb meat packed under modified atmosphere. Meat Sci. 70, 639–646. Linares, M.B., Vergara, H., 2009. Light lamb meat quality packed under modified atmospheres: effect of stunning systems (electrically vs gas). Animal 3, 1763–1771. Linares, M.B., Berruga, M.I., Bórnez, R., Vergara, H., 2007b. Lipid oxidation in lamb meat: effect of the weight, handling previous slaughter and modified atmospheres. Meat Sci. 76, 715–720. Linares, M.B., Bórnez, R., Vergara, H., 2007a. Effect of different stunning systems on meat quality of light lamb. Meat Sci. 76, 675–681. Linares, M.B., Bórnez, R., Vergara, H., 2008. Effect of stunning systems on meat quality of Manchego suckling lamb packed under modified atmospheres. Meat Sci. 78, 279–287. Livingston, M., Brewer, S., Killifer, J., Bidner, B., Mckeith, F., 2004. Shelf life characteristics of enhanced modified atmosphere packaged pork. Meat Sci. 68, 115–122. Lund, M.N., Lametsch, R., Hviid, M.S., Jensen, O.N., Skibsted, L.H., 2007. High oxygen packaging atmosphere influences protein oxidation and tenderness of porcine Longissimus dorsi during chill storage. Meat Sci. 77, 295–303. ˜ C., Panea, B., Medel, I., Delfa, R., Sierra, I., Martínez-Cerezo, S., Sanudo, Beltrán, J.A., Cepero, R., Olleta, J.L., 2005. Breed, slaughter weight and ageing time effects on physico-chemical characteristics of lamb meat. Meat Sci. 69, 325–333. Pexara, E.S., Metaxopoulos, J., Drosinos, E.H., 2002. Evaluation of shelf life of cured cooked sliced turkey fillets and cooked pork sausages-piroskistored under vacuum and modified atmospheres at 4 and 10 ◦ C. Meat Sci. 62, 33–43. Roselvold, K., Petersen, J.S., Lwerke, H.N., Jensen, S.K., Therkildsen, M., Karlssom, A.H., Moller, H.S., Andersen, H.J., 2001. Muscle glycogen stores and meat quality as affected by strategic finishing feeding of slaughter pigs. J. Anim. Sci. 79, 382–391. ˜ Sanudo, C., Sanchez, A., Alfonso, M., 1998. Small ruminant production and factors affecting lamb meat quality. Meat Sci. 49, S29–S64. Sekar, A., Dushyanthan, K., Radhakrishnan, K.T., Narendra, R., 2006. Effect of modified atmosphere packaging on structural and physical changes in buffalo meat. Meat Sci. 72, 211–215. Sorheim, O., Aune, T., Nesbakken, T., 1997. Technological hygienic and toxicological aspects of carbon monoxide used in modified-atmosphere packaging of meat. Trends Food Sci. Technol. 8, 307–312. Sorheim, O., Nissen, H., Nesbakken, T., 1999. The storage life of beef and pork packaged in an atmosphere with low carbon monoxide and high carbon dioxide. Meat Sci. 52, 157–164. Sorhein, O., Langsrud, O., Cornforth, D.P., Johannessen, T.C., Slinde, E., Berg, P., Nesbakken, T., 2006. Carbon monoxide as a colorant in cooked or fermented sausages. J. Food Sci. 71, 549–555. Statistical Package for the Social Sciences (SPSS), 2005. SPSS for Windows 14.0. User’s Guide. SPSS Inc., Chicago, IL. Tarladgis, B.G., Pearson, A.M., Dugan, R., 1964. Chemistry of the 2-thiobarbituric test for determination of oxidative rancidity in foods II. Formulation of the TBA–malonaldehyde complex without acid-heat treatment. J. Sci. Food. Agric. 15, 602–604. Vergara, H., Gallego, L., 2000. Effect of electrical stunning on meat quality of lamb. Meat Sci. 56, 345–349. Vergara, H., Gallego, L., 2001. Effects of gas composition in modified atmosphere packaging on the meat quality of Spanish Manchega lamb. J. Sci. Food Agric. 81, 1353–1357. Vergara, H., Berruga, M.I., Linares, M.B., 2005. Effect of gas composition on rabbit meat quality in modified atmosphere packaging. J. Sci. Food Agric. 85, 1981–1986.
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Contents lists available at SciVerse ScienceDirect
Small Ruminant Research journal homepage: www.elsevier.com/locate/smallrumres
Effect of gas stunning and modified-atmosphere packaging on the quality of meat from Spanish Manchego light lamb María Belén Linares a , Herminia Vergara b,c,∗ a
Department of Food Science and Technology, Faculty of Veterinary, University of Murcia, 30100 Espinardo, Spain Department of Agroforestal Science, Technology and Genetics, Escuela Técnica Superior de Ingenieros Agrónomos, University of Castilla-La Mancha, Campus Universitario, 02071 Albacete, Spain c Food Quality Division, Instituto de Desarrollo Regional, University of Castilla-La Mancha, Campus Universitario, 02071 Albacete, Spain b
a r t i c l e
i n f o
Article history: Received 20 December 2011 Received in revised form 22 June 2012 Accepted 29 June 2012 Available online 21 July 2012 Keywords: Gas stunning Meat quality Light lamb Modified atmosphere Carbon monoxide Shelf life
a b s t r a c t The aim of the present study was to evaluate the effect of different stunning methods (using two different CO2 concentrations and exposure times) and modified atmosphere packaging systems (MA-O2 : 70 O2 + 30 CO2 vs MA-CO: 69.3% N2 + 30% CO2 + 0.7% CO) on the meat quality of Manchego Spanish male light lambs (n = 50). One electrically stunned control group was used. The type of stunning affected pH value, meat tenderness and water losses (P < 0.05) but did not modify most of the colour coordinates or the lipid oxidation level. Furthermore the modified atmosphere with a low CO level (MA-CO) promoted more tender meat with higher oxidative stability than the high-oxygen packed meat (MA-O2 ). Most likely both the CO2 gas concentration and the exposure time are relevant in the evolution of meat quality from light lambs stunned with different gas stunning systems. In addition, the use of a low CO level to pack lamb meat permits to remove the oxygen from the pack, which improves meat tenderness and the oxidative stability. © 2012 Elsevier B.V. All rights reserved.
1. Introduction The current European law to protect animals at slaughter (EU Council Directive 1009, 2009) requires electrical stunning of sheep in order to guarantee that these animals are unconscious and insensitive. Although the gas method is not considered under the present law for sheep slaughter, this system should be seen as an alternative in ovine specie since important advantages have been reported (Linares and Vergara, 2009). In previous works (Linares et al., 2007a; Bórnez et al., 2009a) authors found the gas system to be more effective since it enables to reduce the stun–stick
∗ Corresponding author at: Departamento de Ciencia y Tecnología Agroforestal y Genética, ETSIA, University of Castilla-La Mancha, Campus Universitario s/n, 02071, Albacete, Spain. Tel.: +34 967599200. E-mail address: [email protected] (H. Vergara). 0921-4488/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.smallrumres.2012.06.015
interval with almost not any handling of animals, thus improving welfare. Furthermore, since less kicking is described during the exsanguinations, the gas method is much safer for the slaughterer (Bórnez et al., 2009b), while fewer haemorrhages and blood spots were observed in carcasses, hence improving meat quality. In other species such as pig (Channon et al., 2003) or poultry (Gregory, 2005) the electrical method has been replaced by the gas system due to the numerous favourable effects observed. On the other hand, meat preservation under modified atmosphere systems and the effect of gases commonly used in the gas mixture have been extensively studied in lamb (Vergara and Gallego, 2001; Kennedy et al., 2004; Lauzarica et al., 2005; Linares et al., 2008) as in many other species (Jakobsen and Bertelsen, 2000; Livingston et al., 2004; Vergara et al., 2003, 2005; Sekar et al., 2006). In fact, the high oxygen concentration in packs can help to preserve colour while also promoting the development of important
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oxidative processes (Livingston et al., 2004). The use of a low carbon monoxide concentration (less than 1%) in the gas blends could be an option to pack red meat due to the increase in the oxidative stability and colour in lamb meat (Linares et al., 2007b). Similar conclusions regarding the use of this gas have been observed in pork (Wilkinson et al., 2006), beef (Jayansingh et al., 2001) or turkey (Pexara et al., 2002). In addition, the use of this gas at low levels, similar to those proposed in the present study (0.7%), is completely safe for consumers (Sorhein et al., 2006). The packing of fresh meat under modified atmosphere systems by adding carbon monoxide (<1%) has been allowed in countries such as the United States, New Zealand and Australia since 2004. By other side, previous papers, which evaluated the effect of the gas stunning systems on initial meat quality (24 h and 7 days post-mortem, packed under aerobic conditions) from Manchego Spanish breed lamb, showed that results depend on the lamb age. Thus, in light lamb (Vergara et al., 2009) the main finding was that the application of a low CO2 concentration (80%) for an extended time (90 s) could cause lower values of lipid oxidation, pH, cooking loss, and tenderness. In suckling lamb (Bórnez et al., 2009b), however, the same gas concentration at stunning was related to more drip loss and greater tenderness. In addition, studies (Bórnez et al., 2009c, 2010) concerning the effect of these same gas stunning methods on the quality of suckling-lamb meat packed under different modified atmospheres showed that the use of low CO in packing could increase oxidative stability and tenderness in all the stunning groups, even though it does not improve microbial quality. However, the effect of both factors, gas stunning typemodified atmosphere, is unknown for light lamb meat and, as authors has pointed out in previous studies (Linares et al., 2008), the evolution of meat quality could vary in accordance with the slaughter weight/age of lambs in this breed. Therefore the aims of this study were (1) to examine the effect of gas stunning systems using different concentrations/time of exposure on physic-chemical characteristics and lipid oxidation of light lamb meat and (2) to determine optimal gas stunning system-modified atmosphere combinations for light-lamb meat quality. 2. Materials and methods The research protocol used in this study was previously approved by the Animal Ethics Committee of the University of Castilla-La Mancha, according to guidelines regarding the protection of animals used in research and for scientific purposes (Directive 65/2003 EC). 2.1. Animals In this trial 50 male Spanish Manchego light lambs were used. Animals were fed with milk up to 12 kg of weight (30 days old) and after that a commercial concentrate (16% crude protein; 12.443 kJ/kg dry matter) and cereal straw ad libitum were provided until slaughter time at 25 kg live weight (70 days old). According to the type of stunning, lambs were distributed into five groups (n = 10): - Four groups were stunned with gas using different CO2 concentrations and exposure times [G1: 80% – 90 s; G2: 90% – 90 s; G3: 90% – 60 s;
G4: 80% – 60 s] using a gondola dip-lift system (G van Wijnsberghe & Co. NV, Veurne, Belgium) generally used to stun pigs (3 m long × 1.5 m wide × 1 m high). This system indicates the concentration of CO2 in the pit, a factor which was tested every day during the experiment by authorised personnel. Groups of three or four lambs were placed in the box. The motor of the gondola transporter was set to reach the bottom of the pit in 10 s and to return to the ejection level 16 s after restarting. The lambs were shackled by the leg and hoisted onto the overhead rail where they were bled by cutting the blood vessels in the neck between 25 and 35 s after removal from the gondola. - One control group (G5) was electrically stunned at 110 V, 50 Hz for 5 s (plate electrodes applied on both sides of the head, behind the ears; Electronarcosis Panel, MAC-01, Bernard, S.L. Albacete, Spain). Immediately after stunning, lambs were slaughtered and dressed using standard commercial procedures. All carcasses were chilled at 4 ◦ C for 24 h in a conventional chiller. 2.2. Sampling After this period, the Longissimus dorsi from both sides of the carcasses was removed and cut into similarly sized portions (8 per lamb). Two samples were used to determine initial meat quality (at 24 h and 7 days) and results were shown by Vergara et al. (2009). The remaining samples were placed in clear trays (LINPAC Packaging West Yorkshire, UK) with an oxygen permeability rate of 3.2 cm3 m−2 day−1 atm−1 at 23 ◦ C, and covered by a film with transmission rates of 1 cm3 m−2 day−1 atm−1 for oxygen (23 ◦ C; 50% RH); 5.5 cm3 m−2 day−1 for CO2 (23 ◦ C; 0% RH) and 2.2 g m−2 day−1 for H2 O (25 ◦ C; 90% RH) and packed under modified atmosphere using a packaging machine (Efabind L-650, Efabind, Murcia, Spain). All samples remained in a conventional chiller at 2 ◦ C in the dark. The following modified atmospheres (MA) were compared: MA-O2 : 70% O2 + 30% CO2 MA-CO: 69.3% N2 + 30% CO2 + 0.7% CO Gas composition was tested in the packs by using a ChecMate machine (PBI Dansensor, Ringsted, Denmark). Samples from each lamb were packed under both types of modified atmosphere (MA-O2 , MA-CO) and analysed at 7, 14, 21 days post-packing. 2.3. Analysis The following characteristics were assessed: A. Physical and chemical characteristics - pH was measured using a Crison 507 (Barcelona, Spain, Crison Instruments, S.A.) equipment with a penetrating electrode. - Cooking losses (CL), expressed as the percentage of weight after cooking relative to the initial weight (before cooking). Each meat sample (approximately 40 g) was weighed and individually placed in polyethylene bags in a water bath at 70 ◦ C for 15 min. After surfacedrying of the cooked samples with filter paper samples were again weighed. - Water holding capacity (WHC), calculated as the percentage of free water in accordance with the procedure established by Grau and Ham (1953). - Drip losses (DL), expressed as a percentage of the initial portion weight (Vergara et al., 2005). - Shear force (SF) was analysed with a TA.XT2 texture analyser equipped with a Warner-Bratzler device with 50 mm/min test speed. For the analysis, each meat sample (40 g) was individually placed in polyethylene bags in a water bath at 70 ◦ C for 15 min. The cooked samples were cooled for 30 min at 20 ◦ C room temperature and maintained at 4 ± 1 ◦ C until the texture analysis. At this time the samples were cut into three (1 cm cross-section and 2–3 cm length) and the SF was by triplicate recorded. The pieces were cut in a perpendicular position as respect to the orientation fibres. - Colour coordinates (L, a*, b* values) were measured on the surface of the Longissimus dorsi muscle (80 mm diameter), immediately after the packs were opened, with a colorimeter Minolta CR-400 (Osaka, Japan) using illuminant D65 and 10◦ standard
M.B. Linares, H. Vergara / Small Ruminant Research 108 (2012) 87–94 observer after standardisation with respect to the white calibration plate. Chroma [C* = (a* + b*)1/2 ] and Hue angle [h* = arctan (b*/a*)] were also calculated. All measurements were carried out by triplicate. B. Lipid oxidation 2-Thiobarbituric acid reactive substances were determined (Tarladgis et al., 1964) and results were expressed as mg of malonaldehyde (MDA) per kg of meat. The absorbance at 532 nm was read with a 140 Helios alfa spectrophotometer (Thermo, Electron Corporation, Leicester, England). 2.4. Statistical analysis Statistical analyses were performed using the Statistical Package SPSS 15.0 version (SPSS Inc., Chicago, USA, 2005). A General Lineal Model procedure was used to examine the effect of the stunning method and the type of modified atmosphere at 7, 14 and 21 days post-packaging on meat quality parameters. An ANOVA was carried out to check the effect of time (7, 14, 21) in each stunning method-modified atmosphere group and when the differences were statistically significant a Tukey’s test was carried out.
3. Results and discussion 3.1. Physical and chemical parameters Table 1 shows the effect of the modified atmosphere and the stunning method on pH, water holding capacity (WHC, %) cooking losses (CL, %), drip losses (DL, %) and shear force (SF, N/cm2 ) of light lamb meat. The type of modified atmosphere had no effect on the lamb meat quality (pH, WHC, CL, DL) for the different stunning groups (G1–G5) except for SF values with significant differences at 14 and 21 days post-packing (both P < 0.001). In general, the modified atmosphere MA-O2 (70% O2 + 30% CO2 ) promoted higher shear force values (less tenderness) than the MA-CO (69.3% N2 + 30% CO2 + 0.7% CO) in all stunning treatment groups (P < 0.05). Some authors (Lund et al., 2007) observed that pork stored under 70% O2 + 30% CO2 exhibited higher shear force values (less tenderness) than vacuum packed meat. Recently, other authors (Kim et al., 2010) have confirmed that the oxidative conditions promoted by high oxygen concentrations in the gas mixture negatively affect colour, flavour stability and also meat tenderness during storage. Since oxidation development could play an important role in meat tenderness, the lipid and myoglobin oxidation and cross-linking/aggregation of myosin could explain the increase of shear force values in samples under high-oxygen modified atmosphere packaging systems, as previously reported by Zakrys et al. (2008) for beef. In addition, the increased oxygen levels could inhibit calpain activity, which directly influences meat tenderness (Guttmann et al., 1997). On the other hand, GLM procedures showed a significant effect of the type of stunning on pH values starting from 14 days post-packing (P < 0.01) in Manchego light lamb meat packed under modified atmosphere. In the present paper (for light-lamb), the lower pH was found in G1 and G3 groups (with significant differences according to a Tukey’s test only at 21 days and in MA-CO) while in a previous study in suckling lamb meat (Bórnez et al., 2010) the lower values of pH were found in G4 and G5 groups. The difference on pH value was also reported in a previous paper in light lamb with higher pH described for
89
gas-stunned lambs meat than in the electrically samples (Linares and Vergara, 2009), thus pointing to the existence of an intense slaughter weight/age effect for meat quality ˜ parameters in sheep (Sanudo et al., 1998; Martínez-Cerezo et al., 2005). Regarding meat tenderness, higher Warner Bratzler shear force values (N/cm2 ) were found in the G1 stunning group (80% CO2 90 s) in both types of modified atmosphere packaging systems (MA-O2 and MA-CO) in comparison to the other stunning groups. On the other hand, the lower SF in the G1 group even after ageing could be related with the highest fall in pH (pH0 –pH24 ) at the initial time after slaughter (Vergara et al., 2009) and an increase in the catecholamines level at this time (Bórnez et al., 2009a), which can produce a low calpain activity. Curiously, at 7 days post-mortem, in light lamb meat packed under aerobic conditions (Vergara et al., 2009) no significant differences were found between the G1 and G5 groups, contrary to the present study, although the values in G1 were slightly higher (74.8 vs 51.1 N/cm2 respectively) and this tendency continued in meat packed under modified atmosphere until significant values. The type of stunning affected drip losses (DL) and cooking losses (CL). In general the electrical stunning method (G5) showed higher CL values in comparison to the G1 and G2 groups (both 90 s). However it should be pointed out that in this study the G3 and G4 stunning group (both 60 s) showed CL similar to the G5 group, as previously described by Bórnez et al. (2009b) in suckling-lamb meat. It seems that not only the gas concentration but also the time of exposure to the gas in the bottom of the pit can imply changes in the meat quality parameters, mainly in relation to water losses. Furthermore the type of stunning did not affect the water holding capacity although this parameter significantly varied with storage time in all the stunning groups (P < 0.05), except for G2. During the ageing process of meat, a tendency to expel more water (higher WHC values) has been described in the literature as occurring under aerobic conditions (Vergara and Gallego, 2000) and also under modified atmosphere packaging systems (Vergara and Gallego, 2001), which is in agreement with the results of the present study. A similar trend was shown for the drip losses (DL) occurring during ageing, as reported in other studies (Sekar et al., 2006; Vergara and Gallego, 2000). Table 2 shows the effect of the type of modified atmosphere packing system and the type of stunning on the colour coordinates of light lamb-meat. The type of gas mixture affected the colour coordinates for L* and b* values, while the h* angle was the highest in the MA-O2 for all the stunning groups (P < 0.001). Likewise, the a* and C* values were the lowest in MA-O2 , while the meat packed under the MA-CO (P < 0.001) reached the maximum levels. This tendency was previously reported in other papers on suckling lamb meat packed under modified packing systems (Bórnez et al., 2010). MA-CO that included a low level of carbon monoxide (0.7%) preserved colour stability longer than the highoxygen gas mixture such as that found in MA-O2 in the present research. This has been extensively reported in literature since the greater stability of the carboxymyoglobin,
90 Table 1 Effect of the type of stunning and modified atmosphere in meat pH, water holding capacity (WHC, %), cooking losses (CL, %) drip losses (DL, %) and shear force (SF, N/cm2 ) (mean ± s.d) from Spanish Manchego light lamb meat. G1 (n = 10)
pH
7d 14 d 21 d
WHC%
7d 14 d 21 d
CL%
DL%
SF N/cm2
G2 (n = 10)
G3 (n = 10)
MA
TS
MA × TS
5.64 ± 0.03
5.59 ± 0.01
5.61 ± 0.02
5.64 ± 0.00
5.64 ± 0.01
5.62 ± 0.01
5.62 ± 0.01
NS
5.57 ± 0.01
5.59 ± 0.01
5.61 ± 0.02
5.63 ± 0.03 5.59 ± 0.02d,e
5.57 ± 0.01
5.58 ± 0.01 5.56 ± 0.01d
5.62 ± 0.01
5.62 ± 0.02
5.61 ± 0.01
5.65 ± 0.01
NS
NS **
NS
5.64 ± 0.01e
5.54 ± 0.01 21.05 ± 1.77x 23.06 ± 0.91x,y 25.94 ± 1.05y
5.55 ± 0.01d 20.31 ± 0.82x 22.77 ± 0.6x,y,d,e 23.93 ± 0.78y
5.57 ± 0.02 22.44 ± 0.74 24.23 ± 1.01 25.76 ± 1.5
MA-CO
22.7 ± 1.03 24.61 ± 0.86e 25.98 ± 1.42
4.54 ± 0.24d 5.19 ± 0.23d,e
4.86 ± 0.2a,b 4.95 ± 0.2a
4.19 ± 0.36d 4.48 ± 0.28d
21 d
5.83 ± 0.24y,a,b
5.43 ± 0.28d,e
5.08 ± 0.27a
4.77 ± 0.27d
7d
2.16 ± 0.16x,e 2.65 ± 0.2x,y
2.16 ± 0.11x,b 2.83 ± 0.07y,b
2.22 ± 0.13e
14 d
2.12 ± 0.1x,b 2.48 ± 0.15x,y,b
21 d
2.68 ± 0.14y,a,b
3.11 ± 0.18y
3.08 ± 0.09y,b
3.03 ± 0.23
14 d 21 d
Significance
5.63 ± 0.02
MA-O2
4.21 ± 0.35x,a 4.92 ± 0.3x,y,a
7d
G5 (n = 10)
5.58 ± 0.02
MA-CO
14 d
7d
G4 (n = 10)
5.6 ± 0.02
MA-O2
63.70 ± 0.86 64.58 ± 0.76b 52 ± 0.68
61.83 ± 0.93 52.43 ± 0.84e 38.80 ± 0.6e
48.90 ± 0.47y 35.96 ± 0.24x,a,g 36 ± 0.26x,g
2.8 ± 0.2
MA-O2
5.55 ± 0.01 22.03 ± 0.39x 23.72 ± 0.7x 26.45 ± 0.8y
MA-CO
21.35 ± 0.83x 23.2 ± 0.79x,y,d,e 25.34 ± 1y
MA-O2
5.61 ± 0.01 20 ± 0.68x 23.21 ± 0.84y 25 ± 0.65y
MA-CO
5.59 ± 0.01d,e 20.46 ± 0.78x 22.51 ± 0.81x,y,d,e 24.54 ± 0.45y
MA-CO
NS
NS
***
NS
21.53 ± 0.46x 23.03 ± 0.63x,y 24.74 ± 0.77y
20.93 ± 0.46x 21.33 ± 0.75x,y,d 23.63 ± 0.57y
NS
*
NS
NS NS
* NS
NS NS
5.6 ± 0.01
5.9 ± 0.18c 5.92 ± 0.35a,b 6.58 ± 0.32b
5.33 ± 0.56d,e 6.08 ± 0.47e
5.86 ± 0.26x,c 6.52 ± 0.27x,y,b
5.54 ± 0.19b,c 6.16 ± 0.29b
5.54 ± 0.16d,e 6.06 ± 0.19e
NS
***
NS
6.17 ± 0.2e
NS
***
NS
6.18 ± 0.25e
6.72 ± 0.15y,b
6.44 ± 0.28e
6.27 ± 0.17b
6.26 ± 0.28e
NS
***
NS
2.04 ± 0.09x,b 2.36 ± 0.14x,y,a,b
2.12 ± 0.17x,e 2.71 ± 0.2x,y
1.56 ± 0.11x,a 1.86 ± 0.15x,y,a
1.46 ± 0.11x,d 2.21 ± 0.21y
1.81 ± 0.14x,a,b,g 2.56 ± 0.21x,y,b
1.42 ± 0.11x,d,h 2.5 ± 0.26y
NS
***
NS
NS
**
NS
2.62 ± 0.12y,a,b
2.85 ± 0.2y
2.52 ± 0.16y
3.03 ± 0.37y,b
2.68 ± 0.41y
NS
**
NS
*
NS
***
NS
**
NS
2.2 ± 0.12y,a
6.07 ± 0.28e
MA-O2
41.65 ± 0.54y 27.53 ± 0.17x,d,h
51.35 ± 0.51 44.29 ± 0.37a,g
45.17 ± 0.45y 30.28 ± 0.1x,d,h
51.94 ± 0.6 43.15 ± 0.4a
48.11 ± 0.63y 34.3 ± 0.32x,d,e
25.28 ± 0.08x,d,h
37.73 ± 0.21g
25.97 ± 0.08x,d,h
37.43 ± 0.38g
27.14 ± 0.2x,d,e,h
49.78 ± 0.55 41.84 ± 0.46a 37.43 ± 0.42g
49 ± 0.69y NS 36.16 ± 0.54x,y,d,e *** 24.3 ± 0.16x,d,h
***
G1: 80% – 90 s; G2: 90% – 90 s; G3: 90% – 60 s; G4: 80% – 60 s; G5: electrical. TS: type of stunning; MA-O2 : modified atmosphere with high oxygen level (MA-O2 : 70% O2 + 30% CO2 ); MA-CO: modified atmosphere with a low carbon monoxide level (69.3% N2 + 30% CO2 + 0.7% CO). a,b : different superscripts in the same row indicate significant differences in MA-O2 due to the type of stunning; d,e : different superscripts in the same row indicate significant differences in MA-CO due to the type of stunning; x,y,z : different superscripts in the same column indicate significant differences due to the storage time; g,h : different superscripts in the same row indicate significant differences among MA-O2 and MA-CO for the same type of stunning group. * P ≤ 0.05. ** P ≤ 0.01. *** P ≤ 0.001. NS: P > 0.05.
M.B. Linares, H. Vergara / Small Ruminant Research 108 (2012) 87–94
Time
Table 2 Effect of the type of stunning and modified atmosphere in colour coordinates (L*, a*, b*, C*, h*; means ± s.d.) on Spanish Manchego light lamb meat.
L
a*
h*
G5 (n = 10)
G4 (n = 10)
Significance MA × TS
MA-CO
MA-O2
MA-CO
MA-O2
MA-CO
MA-O2
MA-CO
MA-O2
MA-CO
MA
47.04 ± 0.54d,e 47.14 ± 0.74h
45.54 ± 0.73x 49.93 ± 1.16y
45.34 ± 0.85d
47.98 ± 1x
47.17 ± 0.72d,e 47.33 ± 0.61h
46.31 ± 1.27x 49.67 ± 1.21x,y
NS ***
52.96 ± 1.1y,g
47.25 ± 1.02h
53.3 ± 1.38y,g
51.21 ± 0.5y,g 55.58 ± 0.7z,g
47.13 ± 0.85x 50.26 ± 0.6x,y,g
21 d
46.74 ± 1.03 47.04 ± 0.88h
48.38 ± 0.96e 48.43 ± 0.8h
46.55 ± 0.35d,e
14 d
46.96 ± 1.05x 49.62 ± 0.87x,y,g
47.91 ± 0.89
51.29 ± 1.23y,g
47.81 ± 0.58h
***
7d
15.59 ± 1.34y,a,g 11.02 ± 1.57x,g
24.79 ± 0.83h 26.08 ± 0.72h
19.91 ± 0.77z,b,g 10.35 ± 1.31y,g
25.64 ± 0.72h 26.25 ± 0.55h
17.25 ± 1.04z,a,b,g 12.15 ± 1.43y,g
25.68 ± 0.43h 26.77 ± 0.73h
16.85 ± 0.38z,a,g 11.5 ± 1.76y,g
23.57 ± 0.67h 25.45 ± 0.9h
***
**
NS
***
NS
NS
6.97 ± 0.83x,g
6.48 ± 0.83x,g
25.75 ± 0.45h
7d
24.3 ± 0.9h 26.12 ± 0.8h
50.8 ± 1.41y 19.64 ± 0.48y,b,g 10.55 ± 1.34x,g
NS NS
5.37 ± 0.67x,g
6.01 ± 0.63x,g
26.07 ± 0.62h
***
NS
NS
9.16 ± 0.56h 9.56 ± 0.3h
12.6 ± 0.18x,b,g 14 ± 0.3y,g
9.19 ± 0.32x,h 10.34 ± 0.27x,y,h
12.81 ± 0.25x,b,g 14.16 ± 0.55x,y,g
9.07 ± 0.22x,h 10.18 ± 0.26y,h
10.74 ± 0.4x,a,g 12.85 ± 0.38y,g
8.3 ± 0.4x,h 9.47 ± 0.19y,h
***
**
NS
14 d
12.72 ± 0.4x,b,g 13.27 ± 0.62x,g
***
*
NS
21 d
15.33 ± 0.68y,g
10.4 ± 0.16h
15.68 ± 0.47y,g
9.89 ± 0.27h
16.1 ± 1.43z,g
10.48 ± 0.38y,h
14.92 ± 0.63y,g
10.56 ± 0.38y,h
15.09 ± 0.7z,g
9.97 ± 0.13y,h
***
NS
NS
7d 14 d
19.57 ± 1.26a,g 17.86 ± 0.43g
26.57 ± 0.9h 28.05 ± 0.81h
23.64 ± 0.84y,b,g 17.3 ± 0.57x,g
27.25 ± 0.86h 27.95 ± 0.52h
23.45 ± 0.5y,b,g 18.02 ± 0.82x,g
27.24 ± 0.43h 28.65 ± 0.75h
21 d
17.11 ± 0.4g
28.43 ± 0.81h
16.71 ± 0.41x,g
28.24 ± 0.54h
17.3 ± 0.39x,g
26 ± 0.9h 28.1 ± 0.81h 28.13 ± 0.6h
17.48 ± 0.79x,g
7d
21.1 ± 0.38
14 d
37.38 ± 2.55x 51.18 ± 5.56y,g
32.66 ± 0.53x,g 53 ± 4.37y,g
19.52 ± 0.6h 20.05 ± 0.71h
36.84 ± 2.06x,g 50.34 ± 3.5y,g
20.82 ± 0.74h 21.65 ± 0.48h
33.16 ± 0.57x,g 54.32 ± 3.63y,g
21 d
65.23 ± 3.38z,g
71.1 ± 2.46z,g
20.5 ± 0.38h
69.55 ± 2.21z,g
21.95 ± 0.87h
64.19 ± 5.11y,g
21.5 ± 0.54h 21.56 ± 0.54h
27.44 ± 0.8h
NS NS
9.56 ± 0.37h 10.3 ± 0.45h
21.45 ± 0.83y,a,b,g 18.86 ± 0.88x,g
7.68 ± 1.7x,g
46.78 ± 0.79
NS
26.45 ± 0.84h
7d
26.44 ± 0.5h
48.8 ± 0.96h
TS *
11.57 ± 0.67x,a,b,g 13.21 ± 0.75x,y,g
21 d
C*
G3 (n = 10)
G2 (n = 10)
MA-O2
14 d
b*
G1 (n = 10)
20 ± 0.45y,a,g
25.01 ± 0.74x,h
***
**
NS
27.17 ± 0.9x,y,h 27.62 ± 0.43y,h
***
NS
NS
29.41 ± 0.86h
17.84 ± 0.97x,y,g 16.64 ± 0.61x,g
***
NS
NS
19.46 ± 0.48x,h 20.85 ± 0.37y,h
32.46 ± 0.92x,g 50.43 ± 5.05y,g
19.32 ± 0.62x,h 20.52 ± 0.46x,y,h
***
*
NS
***
NS
NS
21.01 ± 0.27y,h
66.67 ± 3.03z,g
21.21 ± 0.35y,h
***
NS
NS
G1: 80% – 90 s; G2: 90% – 90 s; G3: 90% – 60 s; G4: 80% – 60 s; G5: electrical. TS: type of stunning; MA-O2 : modified atmosphere with high oxygen level (MA-O2 : 70% O2 + 30% CO2 ); MA-CO: modified atmosphere with a low carbon monoxide level (69.3% N2 + 30% CO2 + 0.7% CO). a,b : different superscripts in the same row indicate significant differences in MA-O2 due to the type of stunning; d,e : different superscripts in the same row indicate significant differences in MA-CO due to the type of stunning; x,y,z : different superscripts in the same column indicate significant differences due to the storage time; g,h : different superscripts in the same row indicate significant differences among MA-O2 and MA-CO for the same type of stunning group. * P ≤ 0.05. ** P ≤ 0.01. *** P ≤ 0.001. NS: P > 0.05.
M.B. Linares, H. Vergara / Small Ruminant Research 108 (2012) 87–94
Time
91
* ***
G1: 80% – 90 s; G2: 90% – 90 s; G3: 90% – 60 s; G4: 80% – 60 s; G5: electrical. TS: type of stunning; MA-O2 : modified atmosphere with high oxygen level (MA-O2 : 70% O2 + 30% CO2 ); MA-CO: modified atmosphere with a low carbon monoxide level (69.3% N2 + 30% CO2 + 0.7% CO). a,b : different superscripts in the same row indicate significant differences in MA-O2 due to the type of stunning; d,e : different superscripts in the same row indicate significant differences in MA-CO due to the type of stunning; x,y,z : different superscripts in the same column indicate significant differences due to the storage time; g,h : different superscripts in the same row indicate significant differences among MA-O2 and MA-CO for the same type of stunning group. * P ≤ 0.05. *** P ≤ 0.001. NS: P > 0.05.
***
NS NS NS
TS MA
***
0.73 ± 0.05x,g 1.03 ± 0.09d,e,y,g 1.32 ± 0.08d,z,g
MA-CO MA-O2 MA-CO MA-O2 MA-CO MA-O2
2.46 ± 0.11x,h 0.82 ± 0.05x,g 1.94 ± 0.29x,h 0.74 ± 0.11x,g 2.43 ± 0.12x,h 3.74 ± 0.19y,h 0.99 ± 0.07d,e,x,g 4.27 ± 0.65y,h 1.33 ± 0.17e,x,y,g 3.19 ± 0.12y,h 4.51 ± 0.27a,b,z,h 1.39 ± 0.07d,e,y,g 5.39 ± 0.75a,b,y,h 1.44 ± 0.25d,e,y,g 5.82 ± 0.24b,z,h 0.96 ± 0.13x,g 1.37 ± 0.06e,y,g 1.93 ± 0.15e,y,g
MA-CO MA-O2 MA-CO MA-O2
2.05 ± 0.39x,h 0.57 ± 0.14x,g 1.97 ± 0.17x,h 3.64 ± 0.35y,h 0.86 ± 0.12d,x,y,g 3.89 ± 0.38y,h 5.51 ± 0.24a,b,z,h 1.27 ± 0.09d,y,g 4.14 ± 0.27a,y,h 7d 14 d 21 d
Significance G5 (n = 10) G4 (n = 10) G3 (n = 10) G2 (n = 10) G1 (n = 10) Time
Table 3 Effect of the type of stunning and modified atmosphere in lipid oxidation level (malondialdehyde/kg of meat) (means ± s.d) on Spanish Manchego light lamb meat.
NS NS
M.B. Linares, H. Vergara / Small Ruminant Research 108 (2012) 87–94
MA × TS
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a stable chemical state of myoglobin, promoted a desirable bright cherry-red colour in meat that also helped in preservation (Jeong and Claus, 2011). The type of stunning did not affect the colour coordinate values although the G5 (electrically) showed the lowest b* value at 7 days post-storage, possibly related to the increased muscular activity and the final glycogen content which is comparable to that indicated by Roselvold et al. (2001). In general, no significant differences were found due to the effect of storage time in any of the colour coordinate values for MA-CO with some exceptions in b* for G3; b* and h* for G4 and b*, C* and h* for G5 (P < 0.05). Other studies reported that the increase in L* coordinate would be related to protein degradation changes which increases light scattering properties of meat like in samples from modified atmosphere MA-O2 (Vergara et al., 2009). 3.2. Lipid oxidation The effects of the type of modified atmosphere packing system and the type of stunning on lipid oxidation values of light-lamb meat are shown in Table 3, with the MDA values higher in modified atmosphere with high oxygen concentration (MA-O2 ) (P < 0.001). Such levels were three times higher in MA-O2 samples than in those packed under a low CO concentration (P < 0.001). Under a low carbon monoxide level (MA-CO), even after 21 days post-storage, meat samples did not exceed the threshold of 2 mg of MDA/kg of meat proposed as the limit to perceive oxidised odour and flavours in lamb meat (Camo et al., 2008). It has been extensively reported in literature that highoxygen gas mixtures increase the lipid oxidation of meat and meat products, negatively affecting its organoleptic characteristics (Livingston et al., 2004; Lagerstedt et al., 2011). Thus, from day 7 to 21 of storage the increase in TBARS values were approximately 3 units and about 0.5–1 point for the same interval time in MA-O2 and MA-CO, respectively. Carbon monoxide is considered as an inhibitor on the heme a3 group in the oxidase cytochrome which blocks the interaction with oxygen (Alvarez et al., 1994) and can displace the O2 from the oxymyoglobin (MbO2 ), with carboxymyoglobin conforming a very stable pigment in meat (Sorheim et al., 1997, 1999). The type of stunning had no effect on the lipid oxidation values in any of the established stunning groups. Previous works on suckling lamb meat (Bórnez et al., 2009c) pointed out significant differences among stunning groups attributed to the hypoxia generated by the CO2 gas concentration applied. This fact confirms the importance of the slaughter weight/age in the lipid oxidation development in this breed as was previously pointed out in a preliminary study (Linares et al., 2007b), where different weight–age relationships were tested with regards to meat quality, including the lipid oxidation index. 4. Conclusions According to the results found in the present study on light-lamb meat quality characteristics, we can conclude the following: (1) in general, this study support the well
M.B. Linares, H. Vergara / Small Ruminant Research 108 (2012) 87–94
known effects of modified atmosphere type on SF values, colour coordinates and lipid oxidation since MA-CO promoted more tender meat, with the highest lipid and colour stability. (2) The type of stunning affected the physical characteristics (pH, losses water and SF) and for light lamb meat stunned with a minor CO2 concentration (80%) and longer time (90 s), less tenderness in both types of packaging in all ageing times analysed was reported. (3) In general, the gas stunning system did not affect lipid oxidation a fact which contrasts with the results found in meat packed under aerobic conditions (Vergara et al., 2009). (4) Finally, we conclude that the results of the present study and previous ones on suckling lamb (Bórnez et al., 2009c, 2010) indicated that the developments of the main characteristics depend on the lamb age at slaughter, especially for pH, lipid oxidation and SF. Acknowledgements The authors would like to thank the slaughter-men at the Municipal Abattoir in Albacete (Spain). We are also grateful to Prof. K. Walsh and to P. Wolder for assistance with the preparation of this manuscript in English. This work had been made possible by financial help from the Ministerio de Educación y Ciencia (Project: AGLl-200761110). References Alvarez, S., Novoa, M.J., Boveris, A., 1994. La mitocondria. Estructura, función y especies reactivas del oxígeno. http://www.antioxidantes. com.ar/FrArt084.htm. Bórnez, R., Linares, M.B., Vergara, H., 2009a. Systems stunning with CO2 gas on Manchego light lambs: physiologic responses and stunning effectiveness. Meat Sci. 82, 133–138. Bórnez, R., Linares, M.B., Vergara, H., 2009b. Effects of stunning with different carbon dioxide concentrations and exposure times on suckling lamb meat quality. Meat Sci. 81, 493–498. Bórnez, R., Linares, M.B., Vergara, H., 2009c. Microbial quality and lipid oxidation of Manchega breed suckling lamb meat: effect of stunning method and modified atmosphere packaging. Meat Sci. 83, 383– 389. Bórnez, R., Linares, M.B., Vergara, H., 2010. Effect of different gas stunning methods on Manchega suckling lamb meat packed under different modified atmospheres. Meat Sci. 84, 727–734. Camo, J., Beltrán, J.A., Roncales, P., 2008. Extension of the display life of lamb with an antioxidant active packaging. Meat Sci. 80, 1086– 1091. 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 Sci. 65, 1325–1333. Directive 65/2003/EC, 2003. Protection of animals designated for experimentation and scientific experiments. Directive 1009/2009/EC, 2009. On the protection of animals at the time of slaughter or killing. Off. J. Eur. Commun., L 303, 1–30. Grau, R., Ham, R., 1953. Muscle as Food, Food Science and Technology. A Series of Monographs (1985). Academic Press, New York. Gregory, N.G., 2005. Recent concerns about stunning and slaughter – a review. Meat Sci. 70, 481–491. Guttmann, R.P., Elce, J.S., Bell, P.D., Isbell, J.C., Johnson, G.V.W., 1997. Oxidation inhibits substrate proteolysis by calpain I but not autolysis. J. Biol. Chem. 272, 2005–2012. Jakobsen, M., Bertelsen, G., 2000. Colour stability and lipid oxidation of fresh beef. Development of a response surface model for predicting the effects of temperature, storage time and modified atmosphere composition. Meat Sci. 54, 49–57. Jayansingh, P., Cornforth, D.P., Carpenter, C.E., Whittier, D., 2001. Evaluation of carbon monoxide treatment in modified atmosphere packaging or vacuum packaging to increase color stability of fresh beef. Meat Sci. 59, 317–324.
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