C. Molette, H. Rémignon and R. Babilé
ENSAT, Laboratoire Zootechnie et Qualité des Produits,
Toulouse, France
In this study, the properties of fast and normal glycolyzing turkey breast muscles concerning their meat quality and protein alterations are studied. In a commercial processing plant, in a large flock, seventeen breast muscles were selected with a low pH at 20 min post-mortem (fast glycolyzing, FG; pH20min = 6.04 ± 0.09) and seventeen with a normal pH20min (normal glycolyzing, NG; pH20min = 6.47 ± 0.01). Several measurements were done on both groups.
No differences in L* values were measured during a 9-day storage period at 4°C between the 2 groups.
The FG group showed a lower water holding capacity and lower processing yield compared to the NG group.
Warner-Bratzler shear force values of cooked meat were higher for the FG group than for the NG group. The FG meat presented lower protein extractability than the NG one with a low ionic strength (LIS) buffer. However, no differences between the 2 groups were reported in protein extractability with high ionic strength buffer.
LIS protein extract is also studied using 2 dimensional electrophoresis and gels are shown.
Introduction
The pale, soft, exudative (PSE) syndrome leads to meats, which have a paler colour, a higher toughness and a lower water-holding capacity. In pork, this phenomenon has been described a long time ago while it has been reported more recently in poultry. However, in all cases PSE meat appears when a fast pH fall occurs early post-mortem. This fast glycolysis leads to a low muscular pH when the temperature of the muscle is still high.
The combination of these two parameters may lead to the denaturation of muscular proteins. The loss of protein functionality is often suggested to be responsible for the alterations in meat quality.
In turkey, some studies reported that birds with a high rate of pH fall had a lower meat quality (Pietrzak et al., 1997 and Rathgeber et al., 1999a).
The aim of the work is to study the technological properties and some biochemical factors of turkey breast meat showing different rate of pH fall.
Material and methods
In a commercial processing plant, pH of 430 BUT9 tom turkeys was measured at 20 min post-mortem (Jeacocke, 1977). From this, 2 groups of animals were done: the first one (Normal Glycolysis, NG, n = 17) was made up of animals with a "normal" pH20min (6.47 ± 0.01) and the second one (Fast Glycolysis, FG, n = 17) of birds with the lowest pH20min (6.04 ± 0.09). The ultimate pH was 5.67 in the two groups.
At 24 hours post-mortem (D1), scallops were harvested for different measurements during a 9-day storage period at 4°C. The colour of the meat was measured at D1, D3, D6 and D9 on the scallops with a Minolta CR-300.
Drip loss was evaluated at D3, D6 and D9 and is expressed in percent of the weight at D1. Thaw loss was also evaluated after a10-day storage period at –20°C.
Cook loss was measured according to Honikel (1998). Napole yield was determined using the procedure described by Naveau et al. (1985). Objective texture was evaluated according to Honikel, 1998. Buffering capacity was evaluated according to Monin and Sellier (1985). Protein extractabilities were measured using the modified procedures described by Rathgeber et al. (1999a) and Pietrzak et al. (1997). Protein amounts in low ionic strength (LIS) extracts, high ionic strength (HIS) extracts and residual proteins remaining after extraction by HIS (pellet) were determined using BCA Protein Assay Kit (Pierce, Rockford, IL, USA).
Results are expressed as a percentage of total proteins. Two-dimension gels of the LIS extract were performed on immobilized pH gradient (IPG, 7 cm) strips of 7-10 according to Görg et al. (2000). Data were analyzed by analysis of variance using the general linear model procedure of Minitab® software (1994).
Results and discussion
Whatever the time considered, L* values never differ between the two groups. Pietrzak et al. (1997) reported higher L* values for PSE turkey breast meat (pH20min < 5.8) than for normal meat (pH20min > 5.8). However, Rathgeber et al. (1999) did not report such a result for PSE and normal turkey meat. From the present study, L* value of meat is not modified by a higher rate of pH fall.
Drip loss, thawing and cook losses were higher for FG meat than for NG one (Figure 1). Few studies reported the influence of rate of pH fall on drip loss during a 9-d storage period but McKee and Sams (1998) also reported higher cook loss values for PSE turkey meat. Napole yield is an indicator of brine and cook yield. It is similar to conditions encountered in processing plants.
FG meat had a lower Napole yield than NG one (99.2 ± 1.4 and 101.3 ± 1.7%, respectively). Pietrzak et al. (1997) and Rathgeber et al. (1999a) also reported lower processing ability of PSE breast meat compared to normal meat. We conclude that a high rate of pH fall induced a lower water holding capacity of turkey meat.
FG meat had a higher maximum shear force value than NG one, markedly when the meat is cooked (29.4 ±5.8 and 20.9 ±3.5 N, respectively). As in our study, Mc Kee and Sams (1998) reported higher shear force value for cooked meat in PSE turkey. We conclude that tenderness of PSE meat turkey was lower than normal meat.
Buffering capacity of FG meat was lower than for NG meat (48.8 ± 2.4 and 51.4 ± 2.0 meq H+/(pH x kg) respectively, P < 0.01). Monin and Sellier (1985) reported no differences in buffering capacity of muscles from various pork genotypes leading or not to PSE syndrome development. In our study, lower buffering capacity of FG group may be linked with a loss in protein functionality.
LIS protein extractability was lower for FG meat than for NG meat (24.6 ± 1.1 and 25.4 ±0.9% respectively). On the contrary, no differences were found between the two groups for HIS protein extractability. Rathgeber et al. (1999a) reported a lower extractability for sarcoplasmic (similar to our LIS extract) proteins, but also for and myofibrillar (similar to our HIS extract) proteins.
Nevertheless, we conclude that a fast rate of pH fall led to lower protein extractabilities. In order to make a link between buffering capacity, protein extractability and the technological properties, we investigate protein extracts using two dimensional electrophoresis. Figure 2 shows two dimensional gels of LIS extracts from NG and FG animals.
The two groups clearly show different patterns. At least 4 spots located between pHi 8 and 9 and molecular weight around 40-60 kDa can be seen in the NG group whereas it is not in the FG group.
Another spot (pHi around 9 ; molecular weight around 15-20 kDa) can be seen in the FG group only. In this study, two dimensional gels clearly show that there are alterations of LIS extract proteins. We have to better identify these differences and make the link between the observed alterations of meat quality such as water holding capacity, tenderness, processing yield.
Acknowledgements
The authors would like to thank the Groupe Coopératif Occitan (Castelnaudary, France) and Linea Alimentaria (Serinya, Spain) for providing turkey breast muscle.
References
Boles J.A., F.C. Parrish, Jr., T.W. Huiatt and R.M. Robson. 1992. Effect of porcine stress syndrome on the solubility and degradation of myofibrillar/cytoskeletal proteins. J. Anim. Sci. 70:454-464.
Görg A., C. Obermaier, G. Boguth, A. Harder, B. Scheibe, R. Wildgruder and W. Weiss. 2000. The current state of two-dimensional electrophoresis with immobilized pH gradients. Electrophoresis. 21:1037-1053.
Honikel K.O. 1998. Reference methods for the assessment of physical characteristics of meat. Meat Sci. 49(4):447-457.
Jeacocke R.E. 1977. Continuous measurements of the pH of beef muscle in intact beef carcasses. J. Food Technol. 12:375-386.
Mc Kee S.R. and A.R. Sams. 1998. Rigor mortis development at elevated temperatures induces pale exudative turkey meat characteristics. Poultry Sci. 77:169-174.
Minitab .1994. Minitab reference Manual (release 9). State College. PA.
Monin G. and P. Sellier. 1985. Pork of low technological quality with a nomal rate of muscle pH fall in the immediate post-mortem period: the case of the Hampshire breed. Meat Sci. 13:49-63.
Naveau J., P. Pommeret and P. Lechaux. 1985. Proposition d'une méthode de mesure du rendement technologique « le rendement Napole ». TechniPorc. 8(6):7-13.
Pietrzak M., M.L. Greaser and A.A. Sosnicki. 1997. Effect of rapid rigor mortis processes on protein functionality in Pectoralis major muscle of domestic turkeys. J. Anim. Sci. 75:2106-2116.
Rathgeber B.M., J.A. Boles and P.J. Shand. 1999a. Rapid postmortem pH decline and delayed chilling reduce quality of turkey breast meat. Poultry Sci. 78:477-484.
Rathgeber B.M., J.A. Boles and P.J. Shand. 1999b. Rapid postmortem glycolysis and delayed chilling of turkey carcasses cause alterations to protein extractability and degradation of breast muscle proteins. J. Agric. Food Chem. 47:2529-2536.
From Proceedings of the "XVI European Symposium on the Quality of Poultry Meat" and the "X European Symposium on the Quality of Eggs and Egg Products", Saint-Brieuc Ploufragan, France.
