ETH-Schriftenreihe zur Tierernährung, Band 35 (M. Kreuzer, T. Lanzini, A. Liesegang, R. Bruckmaier, H.D. Hess, Hrsg.) 2012
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Stunning procedure and carcass chilling regime affect pork quality and post-mortem proteolysis
G. Petca and G. Bee
Agroscope Liebefeld Posieux, Research Station ALP, Posieux, Switzerland Kontakt: Guiseppe Bee, giuseppe.bee@alp.admin.ch
The aim of the study was to compare the impact of two stunning procedures (electrical [ES] vs. CO2
stunning [CS]) and two carcass chilling regimes (conventional [CC: 4°C for 23.5 h] vs. rapid chilling [RC: -30°C for 2.5 h and 4°C for 21 h]) on pork quality traits and potmortem proteolysis in the longissimus muscle. Twenty Swiss Large White × Piétrain crosses were randomly assigned to either ES or CS treatment. Carcasses were then scalded for 7 min at 65°C, eviscerated and split. At 45 min post-mortem, the left and right carcasses were subjected to CC or RC, respectively. The day after slaughter, carcasses were dissected as described previously (Bee et al., 2004). All meat quality traits were assessed in both carcass sides. The pH and temperature of the longissimus dorsi muscle (LM) was monitored at the 10th rib level in each carcass side at 45 min, 3 h and 24 h post-mortem, using a pH-meter (WTW pH197-S, WTW, Weilheim, Germany) equipped with a spearhead elec- trode (Methrom, Herisau, Switzerland). Twenty-four h post-mortem, five 1.5 cm thick LM chops at the 10th to 14th rib level were excised, weighed and labeled 0, A, B, C and D. Drip loss was deter- mined as the proportion of purge generated during 48 h storage at 2°C Honikel 1998 using the A and C chops. After the drip loss measurements, chops were vacuum-packaged and stored at -20°C for further analysis. From the B chop, light reflectance coordinates (L*: lightness, a*: redness and b*: yellowness) of the muscle surface were determined in triplicates following 10 min blooming, using a Chroma Meter CR-300 with a D65 light source (Minolta, Dietikon, Switzerland). After colour measurements were made, B and D samples were vacuum-packed and stored at −20 °C until thaw and cooking losses were assessed and Warner Bratzler shear force measurements were per- formed. Samples from the LM collected at 24 (chop 0) and 72 h (chop A) post-mortem were pre- pared for Western blotting of desmin and talin. Whole-muscle protein extractions and gel prepara- tion, running, transfer, immunoblotting and chemiluminescent of desmin and talin were carried out as previously described by Bee et al. (2006). Gels were loaded with 28 and 32 µg of total protein per lane for desmin and talin, respectively. Primary antibodies included anti desmin (D1033, Sigma, Saint Louis) and anti talin (T3287, Sigma, Saint Louis) both diluted 1:5,000. The second antibody was in both cases goat anti-mouse IgG peroxidase conjugate diluted 1:5,000 (A2554, Sigma, Saint
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Louis). The degradation ratio was calculated as the intensity of each intact desmin (55 kDa) and talin (225 kDa) band over the intensity of the respective bands in a reference sample that was loaded on each gel. Densities of immuno-reactive bands were quantified by densitometry using GeneGnome (Syngene, Cambridge, UK) and Gene Tools Analysis Software (Version 3.02, Syngene).
Compared to ES, the pH of the LM was greater (P < 0.01) at 45 min (6.5 vs. 6.0), 3 h (6.3 vs.
5.6) and 24 h (5.5 vs. 5.4) in CS. Stunning procedure affected muscle temperature being lower in CS at 45 min (38.3 vs. 38.8°C) but greater at 3 (18.8 vs. 16.2°C) and 24 h (1.8 vs. 1.5°C) post- mortem. Regardless of the stunning procedure, pH of the LM was slightly greater (P ≤ 0.03) in RC than CC at both 3 (6.1 vs. 5.9) and 24 h (5.5 vs. 5.4) post-mortem. As expected, RC resulted in lower (P < 0.01) LM temperature at 3 h post-mortem (13.7 vs. 21.4°C). Percentage drip loss was lower (P < 0.01) in loin chops from CS pigs (3.5 vs. 4.5%). Considering the cooling regime, RC resulted in greater (P = 0.04) drip loss than CC (4.3 vs. 3.7%). Maximal shear force was influenced both by stunning procedure (P < 0.01) and chilling regime (P < 0.01), with greater values for CS (6.3 vs. 5.3 kg) and RC (6.4 vs. 5.3 kg). Intact desmin abundance determined at both 24 and 72 h pm was neither affected by the stunning procedure (P ≥ 0.46) nor the chilling regime (P ≥ 0.07).
When CS is followed by CC and when ES is followed by RC, abundance of intact talin in the LM is lower at 24 but not (P ≥ 0.39) at 72 h (stunning procedure × chilling regime interaction; P < 0.01).
Relative abundance of the unautolyzed 80 kDa μ-calpain unit at 24 h pm was influenced by stunning procedure (P < 0.01) and cooling regime (P < 0.05), with greater abundance in the LM of CS and RC. By contrast, the relative abundance of the 78 kDa μ-calpain subunit was lower (P ≤ 0.06) for the CS and RC. The results reveal an overall positive effect of CS, except for the greater shear force values, and CC on LM quality traits.
References
Bee, G., Guex, G. and Herzog, W. (2004): Free-range rearing of pigs during the winter: Adaptations in muscle fiber characteristics and effects on adipose tissue composition and meat quality traits. J.
Anim. Sci. 82: 1206-1218
Honikel, K.O. (1998): Reference methods for the assessment of physical characteristics of meat.
Meat Sci. 49: 447-457.
