P. Henckel1
J.F. Young
H.C. Bertram
A.H. Karlsson
1 Danish Institute of Agricultural Sciences,
Department of Food Science,
Tjele, Denmark
Four different methods of determining water holding capacity (WHC) of meat were compared in chicken muscles. Variation in WHC was induced by supplementation of creatine (CG) and pyruvate (PG) to drinking water 42 hours before slaughter. In the breast muscle, methods were: a bag drip method, a modification of the bag drip method (EZ-method), a compression/filter paper method and application of low field H-NMR.
Of the 'traditional' methods, the compression/filter paper method (relative weight loss) appears to be the most reliable. On the other hand, several of the attributes based on the NMR relaxation data showed significant differences between CG supplemented and control animals. Further validation of this method is needed before it can be practically applicable.
Introduction
PSE and a concomitant reduction in WHC is a growing problem in the poultry industry (Woelfel et al., 2002 in broilers and Sosnicki et al., 1998 in turkey) affecting yield, processing ability and general appearance of the meat (Van Laack et al., 2000).
In poultry meat, several methods have been applied to determine WHC such as the bag drip method either performed on the entire breast muscle (Woelfel et al., 2002) or on slices of breast meat (Wynveen et al., 1999), a filter paper compression method (Urbin et al., 1962). These methods are generally adaptations of methods developed for WHC measurements in pork meat. Determination of WHC is generally subjected to very large variations, which is either due to methodological error or to the existence of large intra-muscular variations. Consequently it is recommended to use large samples and also to perform duplicate or triplicate when possible. None of these recommendations can be met when determining WHC in chicken muscles because of the small muscle size. From our experience, determination of WHC using the bag drip method is not a reliable method. We perform a survey on methods to determine WHC in search for an alternative and more reliable method for further refinement and validation for future use in chicken muscles. We present here the results of this survey. Although breast muscle is the most important muscle in the chicken economically, other muscles like the thigh also substantially contributes to the overall economy. As the breast muscle is characterized as exclusively consisting of white glycolytic type IIB fibres, and M. Iliotibialis of the thigh contains approx. 30% oxido-glycolytic fibres, different response to treatments of the two muscles might be expected.
Material and Methods
One hundred eighty chickens (Ross 208) were used in the experiment. The animals were placed in 9 rooms (1.6m2). Standard procedures were used for feeding, temperature regulation and light exposure. Six days before slaughter a water tank was inserted in each room to get chicken used to drink water by this way. Forty-two hours before slaughter three of the tanks were filled with water (control), three with a solution of water, glucose and pyruvate (50g/l and 9g/l, respectively) and three with a solution of water, glucose and creatine (50g/l and 9g/l, respectively). At the day of slaughter, all birds from the three rooms were caught, placed in boxes and transported to the slaughterhouse on site. The broilers were slaughtered in a rolling order over the three days to compensate for differences in time at the slaughterhouse.
After slaughter, de-feathering, evisceration and chilling, the chickens were stored at 4oC. For all WHC determinations sampling was performed 24 hours after slaughter. For the bag drip method, the Pectoralis major was excised and cut perpendicular to the fibre direction in the widest part.
A slice of one cm was taken from the anterior part, then weighed (weight approx. 25 g), placed in a non-absorbing net mounted in a plastic bag and allowed to hang for 48 hours, then wiped of with a paper towel and weighed again. Water holding capacity is expressed in relative weight loss. A second slice was cut from the posterior part of the breast muscle.
A unique sample from the centre of this slice was punched out in the direction of the fibres using a puncher with a diameter of 10mm. This sample was weighed and placed in a test tube closed with a lid to avoid evaporation. After storage of 48 hours at 4oC reweighed and relative weight loss was used as expression of WHC (Rasmussen and Andersson, 1996).
The controlateral muscle was excised and cut in the same way. A slice of one cm was taken from the anterior part and was used for determination of WHC by the filter paper/compression method. The sample was punched out from the centre as for the EZ-method.
Initial weight was recorded and the sample was placed on filter paper (Whatman 41). On top of the sample was placed a glass and on top of that a weight of 60g, giving a total compression weight of 64.92g. Final weight was recorded and expressed in relation to initial weight. Digital photos were taken of the filters and total area of exudate was measured and likewise the area of the sample from a marked borderline on the filter paper. This was performed by image analyses (Image Pro, Cybernetics, Silver Spring, USA) using a borderline tracking facility.
Total and relative area of exudate was used as indication of water holding capacity.
From the posterior part a sample 1*1*5 cm was cut from the centre of the muscle in the fibre direction and used for NMR measurements. Immediately upon excision the sample was transferred to test tube, transported to the laboratory (within 15 minutes) then allowed to equilibrate to 25oC in a water bath before measurement using a Maran Benchtop pulsed NMR Analyser (Resonance instruments Ltd, Witney, UK) using a magnetic field strengths of 0.47 Tesla and performed according to Bertram et al. (2002).
Calculations included selected T21 and T22 parameters. Because M. Iliotibialis is much smaller than Pectoralis major, only two methods could be used for determination of WHC. The left muscle was excised and the sampling performed as for the EZ method except that punching was performed perpendicular to fibre axis due to the thickness of this muscle and was placed on a metal thread in the tube, so the edges were free and bend downward. The samples for NMR measurements were taken from the right muscle as described for the breast muscle.
Results and discussion
The difference in WHC between the muscles using the EZ-method is shown in Figure 1.
As expected creatine supplementation resulted in a significantly decreased WHC in the breast muscle, whereas no effects were observed in the thigh muscle. Pyruvate supplementation, however, did not increase WHC as it has been demonstrated in earlier experiments. SD is pretty high and CV in the groups amount to 49, 64 and 94% respectively for CG, control and PG in the breast muscle and of a similar magnitude for the thigh muscle. The difference between muscles does not represent a true difference as the sample for determination of WHC in the thigh muscle was cut perpendicular to the fibre axis resulting in less free cut surface of fibres and may therefore account for the major part of the difference, but of course difference in fibre type distribution cannot be ruled out.
Figure 2 shows the mean value of the breast muscle drip loss measured by the four selected methods. All of these methods display a similar response to the treatments, and by none of them were observed differences between the control animals and the PG supplemented.
Based on calculations of CV the filter paper compression/method (relative weight loss) appear to be the most reliable in terms of detecting differences between treatments. However, due to the extra compression force it represents an over-estimation of the true drip loss. The NMR T2 relaxation decay in muscle tissue is multi-exponential, indicating the existence of different water populations in the muscle tissue. This characteristic has been used to determine WHC, and correlations between the slowest T2 component (T22) and WHC of pork has been shown by Tornberg et al. (1993).
In the present survey we have calculated a number of characteristics (area, maximal amplitude, mean and standard deviation) from the relaxation data from the different components T2b, T21, and T22. Twelve different parameters could significantly detect differences between the CG supplemented and the control animals in the breast muscle. Seven parameters (T21 mean, T21 top, T21 SD, T22 area, T22 SD and the parameters derived by exponential fitting T2(1) and T2(2)) could detect significant differences between these two treatments in the thigh muscle.
Surprisingly two of the parameters also derived by bi-exponential fitting, the T21 int and T22 int, only revealed significant differences between controls and CG in the thigh muscle but not the breast. At present the low field proton NMR relaxation appears to be the most promising of methods for determination of water holding capacity in chicken muscles, however, the mechanisms behind the distribution of water within the muscles and their importance to WHC are not fully understood.
References
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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.
