Broiler fatness and meat quality: C. Berri et al.
Effect of selection for or against abdominal fatness on
muscle and meat characteristics of broilers
C. BERRI*, E. LE BIHAN-DUVAL, E. BAÉZA, P. CHARTRIN, N. MILLET and T. BORDEAU
Station de Recherches Avicoles, INRA, 37380 Nouzilly, France
*[email protected]
Keywords: fatness; breast meat quality; pH; glycogen; broiler line
Abstract
Meat quality (pH, colour, drip and cooking loss, Warner-Bratzler shear force) and muscle
characteristics (lipid and glycogen contents) were compared among two experimental divergent lines
of broilers, selected for high abdominal fatness (HF) or low abdominal fatness (LF). By comparison to
the LF line, the HF line exhibited a 2.8 fold higher abdominal fat percentage. It also exhibited a slightly
higher body weight (+5%) and a 10% lower breast yield. The fat content of the breast Pectoralis major
(P. major) muscle was low and similar in the two lines (around 0.9%). By contrast, the P. major muscle
glycogen level at death was higher in the HF than in the LF line (111.6 vs 93.6 µM). There was no
difference between the two lines regarding the rate of early post-mortem pH drop in breast muscle.
However, in accordance with its higher muscle glycogen level at death, the HF line exhibited a lower
ultimate pH than the LF line (5.66 vs 5.79). Moreover, there was a negative correlation between
ultimate pH and abdominal fat yield (-0.52). The consequence for the HF line was a breast meat with a
higher drip loss during storage and a lighter (higher L*) and less coloured (lower a* and b*) aspect.
However, the cooking loss and the Warner-Bratzler shear force of the cooked meat were similar in the
two lines. This study suggested that selection against abdominal fatness modify breast muscle
metabolism by decreasing glycogen reserve, and therefore is likely to improve processing ability of
breast meat by increasing ultimate pH.
Introduction
Selection of broiler chicken has mainly focused on increased growth performances and improved body
composition. Breast meat yield has been increased and abdominal fatness decreased to satisfy both
the consumer and processor demands (Kijowski, 1997). Several studies have already reported that
the breast muscle post-mortem metabolism as well as meat quality could be altered by broiler
selection. Indeed, significant differences in breast initial or ultimate pH were already reported between
broiler chicken lines reared, transported and slaughtered in the same conditions (Gardzielewska et al.,
1995; Xiong et al., 1993; Schreurs et al., 1995; Svalkowska and Meller, 1999). More precisely, Le
Bihan-Duval et al. (1999) and Berri et al. (2001) suggested by comparing 6 week-old experimental
broiler lines that improving meat yield and decreasing abdominal fatness by selection could delay the
onset of rigor mortis, increases the final pH of the meat and as a result improves processing ability of
breast meat. It was also suggested (Berri et al., 2001) that the higher meat ultimate pH of selected
broilers corresponded to lower muscle glycogen level at slaughter, as it was already shown by Warris
et al. (1988). The aim of the present study was to study the specific effect of selection for or against
abdominal fatness on muscle characteristics (lipid and glycogen) and processing ability of breast
meat.
Materials and methods
ANIMALS
The broilers originated from two experimental lines divergently selected at the Poultry Research
Centre (Nouzilly, France) for high abdominal fatness (HF line) or against abdominal fatness (LF line)
(Leclerc et al., 1980). Broilers were reared under similar conditions in a conventional poultry house of
the Poultry Research Centre. Feed and water were provided ad libitum throughout the growth period.
A sample of 60 birds (males and females) in each line was slaughtered at 9 weeks of age after 7-h
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Broiler fatness and meat quality: C. Berri et al.
feed withdrawal in the experimental slaughter plant of the Poultry Research Centre. Broilers did not
undergo transport and were electrically stunned (125 Hz AC, 60mA/bird, 5 S) before killing by ventral
neck cutting. After evisceration, carcasses were air chilled and stored at 2°C until used.
MUSCLE CHARACTERISTICS (DETERMINED FOR 12 BIRDS/LINE)
The lipid content of the P. major muscle was determined from 20 g of frozen tissue according to Folch
et al. (1957). The P. major muscle glycogen, glucose-6-phosphate, and lactate were measured by
enzymatic procedures according to Dalrymple and Hamm (1973) from 1 g of frozen tissue taken at 15
min post-mortem. Results were expressed in micromoles per gram of fresh tissue. Glycolytic potential
(GP), which represents an estimation of resting glycogen level at death, was calculated according to
Monin and Sellier (1985) as follows: GP = 2[(glycogen) + (glucose) + (glucose-6-phosphate)] +
(lactate), and expressed as micromoles of lactate equivalent per gram of fresh tissue.
CARCASS AND MEAT TRAITS (DETERMINED FOR ALL BIRDS)
Carcasses from all broilers were dissected 24 h post-mortem and measured for breast (P. major and
minor) and abdominal fat weights and yields. Yields were calculated in relation to body weight.
The P. major muscle pH was recorded 15 min and 24 h post-mortem with a portable pH-meter
equipped with a xerolyte electrode. At 15 min post-mortem, pH was estimated from 2 g of muscle
mixed in 5 mM iodoacetate-0.15M KCl solution. At 24 h, the ultimate pH was measured by inserting
directly the electrode in the P. major muscle. Colour was measured at 24 h post-mortem on the upper
ventral side of the P. major muscle by using a Miniscan Spectrocolorimeter (Hunterlab, Reston, VA
20190, USA). Colour was measured by the CIELAB trichromatic system as lightness (L*), redness
(a*), and yellowness (b*) values. Drip loss (DL) of the P. major muscle between 24 h and 72 h postmortem was measured in plastic bags as described in Le Bihan-Duval et al. (1999). At 72 h postmortem, the P. major muscle was vacuum-packaged and cooked in a water bath for 10 min at 85°C.
After a 15 min cooling in crushed ice, the cooking loss was determined and the Warner-Bratzler shear
force of the cooked meat was measured on 10 x10 x30 mm samples using an INSTRON machine
(Model 5543, Guyancourt, France).
STATISTICAL ANALYSIS
The effects of the line on carcass and muscle traits were tested by a one-way analysis of variance
using the General Linear Model procedure of SAS (SAS Institute, 1999). Means were compared within
each factor with a significant effect using Newman-Keuls test. In addition, correlations between traits
were calculated using the Pearson’s correlation coefficients of the CORR procedure of SAS (SAS
Institute, 1999).
Results
EFFECT OF SELECTION ON CARCASS COMPOSITION AND BREAST MUSCLE LIPID AND GLYCOGEN
CONTENT
As shown in Table 1, broilers from the HF line exhibited a 2.8 fold higher abdominal fat weight and
yield than broilers of the LF line. The HF line also exhibited slightly higher body weight (+5%) and
lower breast yield (-10%). The lipid content of the P. major muscle was low and similar in the HF and
LF lines. By contrast the glycogen level of the P. major muscle at death (i.e, glycolytic potential) was
higher in the HF birds (+20%) than in the LF birds.
XVII th European Symposium on the Quality of Poultry Meat
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Broiler fatness and meat quality: C. Berri et al.
Table 1 Carcass composition and P. major muscle lipid and glycogen content.
Variables
Carcass traits
Body weight (g)
Breast yield (%) †
Abdominal fat weight (g)
Abdominal fat yield (%) †
LF line
n = 60
2522 ± 193
12.76 ± 0.94
35.7 ± 13.5
1.4 ± 0.5
HF line
n = 60
2627 ± 162
11.51 ± 0.93
103.5 ± 21.6
3.93 ± 0.72
p
***
***
***
***
P. major muscle traits
n = 12
n = 12
Lipid content (%)
0.95 ± 0.15
0.83 ± 0.14
NS
Glycolytic potential ‡
93.65 ± 17.84
111.56 ± 13.10
**
†
Calculated in relation to body weight
‡
Glycolytic potential = 2[(glycogen) + (glucose) + (glucose-6-P)] + (lactate), expressed in µmole of
lactate/g of fresh tissue
NS = non significant; **p ≤ 0.01; ***p ≤ 0.001
EFFECT OF SELECTION ON P. MAJOR MUSCLE PH AND BREAST MEAT TRAITS
As shown in Table 2, the P. major muscle pH recorded 15 min post-mortem was the same in the two
lines. Moreover, at this time, the muscle lactate content did not differed between the HF and the LF
line (58.81 and 63.67 µM/g of fresh tissue, respectively; p = 0.34). By contrast, the ultimate pH (pHu)
of the meat, recorded at 24 h post-mortem, was lower in the HF line than in the LF line. The HF line
exhibited paler (higher L*) and less coloured (lower a* and b*) breast fillet than the LF line. Besides,
the breast meat drip loss during a two-day storage at 2°C was slightly higher for the HL than the FL
line. There was no effect of the line on the cooking loss and the shear force of the cooked meat.
Table 2 P. major muscle pH and breast quality traits (n= 60/line).
Variables
LF line
pH at 15 min post-mortem (pH15)
6.38 ± 0.21
pH at 24 h post-mortem (pHu)
5.79 ± 0.12
L*
44.85 ± 2.64
a*
-0.28 ± 0.68
b*
9.31 ± 1.01
Drip loss (%) †
1.12 ± 0.56
Cooking loss (%) †
7.61 ± 1.75
Warner-Bratzler shear force (N)
22.19 ± 8.80
†
Calculated in relation to the initial weight of the breast fillet
NS = non significant; *p ≤ 0.05; ***p ≤ 0.001
HF line
6.36 ± 0.21
5.66 ± 0.11
47.42 ± 2.65
-1.01 ± 0.70
8.29 ± 1.29
1.35 ± 0.0.59
7.40 ± 2.09
23.62 ± 9.18
p
NS
***
***
***
***
*
NS
NS
WITHIN LINE CORRELATIONS BETWEEN CARCASS, MUSCLE AND MEAT TRAITS
In the LF line, there was significant negative correlations between abdominal fat weight or yield and
breast muscle glycolytic potential (-0.71 and -0.65, respectively). In this line, we also reported a strong
negative correlation (-0.79) between the muscle glycolytic potential and the meat ultimate pH. By
contrast, there was no correlation between abdominal fatness and glycolytic potential as well as
between glycolytic potential and meat ultimate pH in the HL line.
Regardless of the line, there was a strong negative correlation between pHu and lightness (L*) of
the breast meat (Table 3).The pHu also negatively contributed to breast meat yellowness (b*). Only in
the case of the LF line, the meat pHu was negatively correlated to drip and cooking loss as well as
Warner-Bratzler maximal shear force of the cooked meat. Regardless of the line, the pH15 was
moderately positively related to meat breast meat lightness and strongly negatively correlated to
redness. The pH15 was also negatively related to the drip loss and the shear force of breast meat.
XVII th European Symposium on the Quality of Poultry Meat
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Broiler fatness and meat quality: C. Berri et al.
Table 3 Within line correlations between pH and meat traits (n = 60).
L*
a*
b*
LF line
pH15
0.46***
-0.62***
NS
pHu
-0.47***
NS
-0.26*
HF line
pH15
0.31*
-0.59***
NS
pHu
-0.56***
NS
-0.42***
NS = non significant; *p ≤ 0.05; ** p ≤ 0.01; ***p ≤ 0.001
drip loss
cooking
loss
Shear force
-0.46***
-0.55***
NS
-0.33**
-0.54***
-0.42***
-0.52***
NS
NS
NS
-0.56***
NS
Discussion
The two experimental lines used in this study enabled us to assess the specific impact of selection on
abdominal fatness on breast muscle characteristics and meat quality. Indeed, although the LF and HF
lines greatly differed for abdominal fatness, they exhibited similar body weights and breast yield. As
already described on the same experimental lines for thigh muscles (Ricard et al., 1983), selection for
or against abdominal fatness did not affect the breast muscle lipid content. According to Ricard et al.
(1983), it only affected the amount of subcutaneous fat and fat between thigh and drumstick muscles,
the fattiest birds exhibiting more subcutaneous and inter-muscular fat. For the first time, the present
study pointed out that the line selected for abdominal fatness exhibited higher glycogen content in
breast muscle than the line selected for low abdominal fatness. Moreover, in the case of the low fat
line, we reported that the glycogen content of muscle is inversely related to the abdominal fatness of
the bird. From our knowledge, few data are available in poultry regarding the relationship between bird
fatness and glycogen reserve in muscle. Berri et al. (2001) found that the P. major glycolytic potential
tends to be lower and the meat ultimate pH higher in an experimental broiler line selected for breast
yield and against abdominal fatness than in its control unselected line. Moreover, Le Bihan-Duval et al.
(2001) reported in a pure experimental broiler line a negative genetic correlation of -0.54 between
abdominal fatness and ultimate pH of breast meat, suggesting that selection against abdominal
fatness might have contributed to increase breast meat ultimate pH. As in pigs, the ultimate pH of
broiler breast meat is inversely related to the muscle glycolytic potential (Debut et al., 2003; El
Rammouz et al., 2004). In the present study, glycolytic potential explain ultimate pH variation only in
the low fat line which exhibited the lowest level of glycogen at death. The lack of correlation between
abdominal fatness, glycolytic potential and meat ultimate pH in the high fat line would suggest that
muscle glycogen level can not excess a certain amount and that, as already shown in pigs, the meat
ultimate pH can not reached value under 5.5-5.6 because enzyme inactivation.
Because of its higher muscle glycogen reserve at death, the high fat line exhibited lower ultimate pH
than the low fat line. As shown in the present and previous studies (Barbut, 1997; Le Bihan-Duval et
al., 2001; Debut et al., 2003), as the ultimate pH decreased paleness and drip loss of breast meat
increased while yellowness decreased. Therefore, the high fat line produced paler and less yellow
breast meat which exhibited a higher drip loss than the low fat line. However, despite their differences
in ultimate pH, the low and high fat lines exhibited similar cooking loss and toughness (shear force).
These last results corroborate previous results obtained on the same genotypes (Ricard et al., 1983)
which did not report differences in cooking losses and sensory scores of tenderness between the two
lines. In our study, the cooking loss was poorly correlated to muscle ultimate pH. The toughness of the
cooked meat was more related to the muscle pH15 than to the meat ultimate pH. This could explain
why no difference in breast meat cooking loss and toughness was observed between the two lines.
Finally, as already described in broiler (Debut et al., 2003) and turkey (Rathgeber, 1999; Ahn et al.,
2001; Fernandez et al., 2002), the redness of breast meat was chiefly related to the pH15 of muscle.
Despite a similar rate of post-mortem pH drop in the two lines, the redness of breast meat was higher
in the HF line which could suggest that other factors, such as pigment, could explain differences in
breast meat redness between these two lines.
Conclusions
For the first time in broiler, this study clearly showed that selection against fatness could modify breast
muscle metabolism by decreasing glycogen reserve and as a consequence could affect breast meat
quality. Decreasing abdominal fatness of broilers would lead to breast meat exhibiting higher ultimate
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Broiler fatness and meat quality: C. Berri et al.
pH, lower drip loss, less pale and more coloured aspect and potentially a better processing ability.
These results are in agreement with previous studies which already suggested that standard broilers
mainly selected for growth performance and leanness would be well adapted to current processing
practices.
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