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Significance of storage time on degree of blooming and colour stability of pork loin from different crossbreeds
MEAT SCIENCE Meat Science 72 (2006) 603–612 www.elsevier.com/locate/meatsci
Significance of storage time on degree of blooming and colour stability of pork loin from different crossbreeds Gunilla Lindahl
a,*
, Anders H. Karlsson b, Kerstin Lundstro¨m c, Henrik J. Andersen
a
a
b
Department of Food Science, Danish Institute of Agricultural Sciences, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark Department of Food Science, Meat Science Unit, The Royal Veterinary and Agricultural University, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark c Department of Food Science, Swedish University of Agricultural Sciences, P.O. Box 7051, SE-750 07 Uppsala, Sweden Received 7 May 2005; received in revised form 22 September 2005; accepted 23 September 2005
Abstract The objective was to investigate the effect of ageing time (1 day vs. 8 days postmortem) and sire breed used in the crossbreed (Duroc sired vs. Landrace sired pigs) on blooming ability and colour stability of pork M. longissimus dorsi (LD). The colour was measured during blooming (0, 10, 30, 60, 90 min and 24 h after cutting) and during subsequent display (1, 2, 3 and 6 days) at 3 C. The contents of deoxymyoglobin (Mb), oxymyoglobin (MbO2) and metmyoglobin (MetMb) were calculated. Ageing improved the blooming of LD from both crossbreeds with increased content of MbO2 and decreased content of Mb, resulting in increased lightness, redness and yellowness. Ageing had smaller effect on colour stability with slightly lower MetMb in aged meat. Crossbreed affected both blooming and colour stability. LD from Landrace-sired pigs bloomed more than LD from Duroc-sired pigs, but more MetMb was formed during subsequent storage, although at a low level in both crossbreeds. The present data show superior colour characteristics of fresh pork aged for 8 days. 2005 Elsevier Ltd. All rights reserved. Keywords: Pork; Ageing; Breed; Blooming; Colour stability; Myoglobin species
1. Introduction Many studies have shown that ageing of pork improves the sensory attributes juiciness, tenderness and flavour (Channon, Baud, Kerr, & Walker, 2003; Channon, Kerr, & Walker, 2004; Ellis et al., 1998; Tornberg, von Seth, & o¨ransson, 1994; Wood et al., 1996). For the consumer, optimal pork quality also includes an attractive colour, since it is the only way to assess the quality of packaged meat at the moment of purchase. Pork is often pre-packaged and displayed for several days, thus it is important with a high colour stability. Colour measured 24 h postmortem (pm) is generally included in the assessment of pork quality, but colour stability during retail display is more seldomly studied. There are few studies on the effect of age*
Corresponding author. Present address: Gotlandsgatan 4, SE-244 32 Ka¨vlinge, Sweden. Tel.: +46 46 73 52 52. E-mail address: [email protected] (G. Lindahl). 0309-1740/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2005.09.018
ing on colour stability of pork. Storage of pork pm is reported to influence the colour (Apple et al., 2001; Apple, Stivarius, Reiman, Rakes, & Maxwell, 2002; Frederick, van Heugten, & See, 2004; Rosenvold & Andersen, 2003; Schluter et al., 1994) and the ability of pork to bloom (Zhu, Bidner, & Brewer, 2001). Furthermore, several studies have shown colour differences between pork from purebred Duroc and Landrace pigs (Cameron, Warris, Porter, & Enser, 1990; Newcom et al., 2004) and from Duroc- and Landrace-sired crossbreeds (Blanchard, Warkup, Ellis, Willis, & Avery, 1999; Hammell, Laforest, & Dufour, 1994; Langlois & Minivielle, 1989). However, hardly any knowledge exists regarding the effect of these breeds on colour stability. The colour of pork is influenced by the pigment content, the internal reflectance and the distribution of the myoglobin species, deoxymyoglobin (Mb), oxymyoglobin (MbO2) and metmyoglobin (MetMb) (Lindahl, Lundstro¨m, & Tornberg, 2001). Mb is the purple reduced ferro-species,
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which appear when the meat is freshly cut. Upon exposure to air, Mb rapidly binds oxygen reversibly, forming the bright pink pigment MbO2 (Ledward, 1992) that makes the meat surface to bloom to the characteristic colour of fresh meat, as the small layer of MbO2 diffuses into the meat center (Feldhusen, Warnatz, Erdman, & Wenzel, 1994). The depth to which the oxygen diffuses depends on the enzymatic oxygen consumption rate of the meat, the temperature and the external oxygen pressure (Ledward, 1992). The ferro-species of myoglobin oxidise to the brown ferri-species MetMb upon prolonged exposure to air or at low oxygen pressures (pO2) with a maximum at 1 kPa pO2 at 7 C (Ledward, 1970). MetMb accumulates in the interface between MbO2 and Mb depending on the rates of myoglobin autoxidation, enzymatic MetMb reduction and oxygen consumption (Renerre, 1990). MetMb accumulation in pork changes with ageing time as both MetMb reductase activity (Zhu & Brewer, 1998) and oxygen consumption rate (Atkinson & Follett, 1973) decrease with time pm. Blooming is more efficient under conditions which increase oxygen solubility and discourage enzymatic activity (i.e. low temperatures and low pH values) (Ledward, 1992). Moreover, blooming has been found to be faster and more pronounced in meat that has been aged for several weeks in vacuum packaging prior to exposure to air, owing to some loss of activity of the oxygen-consuming enzymes (Ledward, 1992), and a deeper MbO2 layer is formed (Feldhusen et al., 1994). However, the colour stability of such meat might be impaired depending on the length of the ageing period (Ledward, 1985; OÕKeefe & Hood, 1980–1981). The objective of this study was to investigate the effect of ageing time (1 day vs. 8 days pm) and sire used in the crossbreed (Duroc-sired vs. Landraces-sired pigs) on blooming ability and colour stability of pork loin. 2. Materials and methods 2.1. Animals and treatments The present study was part of an EU project (SUSPORKQUAL) that aimed to evaluate the effect of feeding strategies on pork quality. The animal material consisted of littermate female and castrated male pigs from Landrace* Yorkshire* Duroc (LYD) dams and Landrace (L) or Duroc (D) sires that immediately after weaning (at about 8 weeks of age) were allocated to one of three feeding strategies. The organically grown pigs were kept in indoor pens with deep litter (barley + wheat straw) and with free access to an outside concrete pen, partially roofed. The following feeding strategies were used: (1) basal concentrate diet and red clover silage ad-lib; (2) basal concentrate diet restricted to 70% of ad-lib, red clover silage ad-lib; (3) basal concentrate diet restricted to 70% of ad-lib and red clover silage ad-lib the first 25 experimental days, followed by ad-lib basal concentrate diet and red clover silage. All the pigs received two consecutive basal concentrate diets depending
on their live weight, 30–60 kg and 60–105 kg, and these diets were formulated according to current Danish recommendations (Table 1). An experimental replicate consisted of 30 pigs of each crossbreed, and the pigs were penned in groups of five according to weight and sex. Meat from 12 Duroc-sired and 19 Landrace-sired pigs were used for studies of colour and colour stability. The pigs were slaughtered at approximately 105 kg live weight in the experimental abattoir at Research Centre Foulum. The pigs were stunned with 80% CO2 for 3 min, exsanguinated, scalded at 62 C for 3 min, cleaned and eviscerated within 30 min and chilled at 3 C after 60 min. 2.2. Carcass characteristics, pH and temperature measurements Warm carcass weight was registered by weighing the eviscerated carcass (minus tongue, bristles, genitals, kidneys, diaphragm and front feet) 45 min pm. Lean meat content was estimated from measurements using Fat-O-Meter (SFK Ltd., Hvidovre, Denmark) on the cold carcass (Kempster, Chadwick, & Jones, 1985). Temperature (Testo 110 thermometer, Testo Gmbh 6 Co., Germany) and pH (PHM201 pH Meter, Radiometer, Denmark, equipped with Methrom LL combined pH penetration electrode (Methrohm, Switzerland) were measured in M. longissimus dorsi (LD) at the last rib 1 min, 45 min and 24 h pm. The pH electrode was calibrated in pH 4.01 and 7.00 buffers equilibrated at 35 C for the measurements on the warm carcass 1 and 45 min pm, and at 4 C for the measurement on the cold carcass 24 h pm. 2.3. Colour measurements LD was excised from the carcass 24 h pm, and a piece of 16 cm of the loin (4–20 cm in front of the last rib) was used for colour measurements. These 16 cm were divided into two halves, and the caudale half was used for colour measurements directly, and the cranial half was vacuum-packed and aged at 3 C for 7 days before
Table 1 Feedstuff composition of the diets, kg/100 kg Ingredient
Live weight 30–60 kg
Barley Oats Wheat Peas Rapeseed cake (0 0), Scanola Sweet lupin, Prima Potato protein concentrate Monocalc. Phosphate Aliphos Tess Calcium carbonate Sodium chloride Vitamin and mineral supplement a
Organic.
a
14.08 12.50a 37.39a 5.55a 10.00 12.00a 6.15 0.49 1.26 0.38 0.20
60–105 kg 33.10a 15.00a 15.00a 0 8.00 23.10a 3.70 0.30 1.23 0.37 0.20
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colour measurements. Chops, 2 cm thick, were cut across the fibre direction, wrapped with oxygen permeable film and displayed at 3 C for 6 days. Each colour measurement was done directly on the meat without the covering film. The colour was measured using Minolta CM-2600d spectrophotometer (Minolta Co., Ltd., Osaka, Japan) with specular reflectance excluded, 8 mm diameter measuring aperture, illuminant D65, 10 Standard Observer and CIE (1976) colour scale. The measuring aperture was covered with a glass plate, and the instrument was calibrated against a white plate (L* = 97.30, a* = 0.06, b* = 0.00); the average of four measurements across the surface was used. Blooming was assessed by colour measurements immediately after cutting (0 min) and after 10, 30, 60, 90 min and 24 h of blooming in air at 3 C. Colour stability was assessed by colour measurements after 0 (=blooming for 60 min), 1, 2, 3 and 6 days of display in air at 3 C. The instrument measures reflectance between 400 and 740 nm at 10 nm intervals, and Kubelka-Munk K/S ratios were calculated using SpectraMagic ver. 3.6 software (Minolta Co., Ltd., Osaka, Japan). The relative content of Mb was estimated by the ratio K/S474/525, the relative content of MbO2 by the ratio K/S610/525 and the relative content MetMb by the ratio K/S572/525 (Hunt et al., 1991; Mancini, Hunt, & Kropf, 2003). These ratios decrease when the relative content of the corresponding myoglobin species increases. The K/S-ratios were therefore multiplied by 1 in the diagrams (Figs. 2 and 4) in order to get the right impression when looking at the curves. K/S-ratios at wavelengths not given by the instrument (474, 525, 572 nm) were calculated using linear interpolation. 2.4. Chemical analysis Dry matter (drying for 24 h at 103 C), intramuscular fat (IMF) (NMKL, 1989), protein (NMKL, 1976) and pigment contents (Oksbjerg et al., 2000) were analysed in a 10 cm slice of LD cut just behind the last rib. The pigment content was reported as myoglobin. 2.5. Statistical analysis Statistical analysis was carried out with the Statistical Analysis System version 8.02 (SAS Institute, Cary, NC, USA). The mixed procedure was applied when calculating least squares means (LSM) and standard errors (SE). The statistical model included crossbreed, feeding regimen within crossbreed, ageing time pm, blooming or display time in air and their two-way interactions as fixed effects. Pig nested within crossbreed, feeding regimen and sex were included as random effects, and degrees of freedom were estimated with the Satterthwaite method. The non-significant effect of feeding regimen was ignored in the final model. The GLM procedure was applied on carcass characteristics and meat composition using a model including crossbreed and sex as fixed effects.
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3. Results 3.1. Carcass characteristics and meat composition There were no significant differences between the crossbreeds in carcass weight, pH values, dry matter, IMF or protein contents in LD (Table 2). Duroc-sired pigs had higher lean meat content and slightly higher temperatures at 1 min, 45 min and 24 h pm. The pigment content was higher in LD from Duroc-sired pigs than in LD from Landrace-sired pigs. 3.2. Blooming Blooming of LD was significantly affected by ageing time pm for all the measured colour parameters, with exception of the relative content of MetMb (Table 3). The tristimulus parameters (L*, a* and b*) were all higher 8 days pm compared with 1 day pm. Moreover, the K/Sratios showed a higher relative content of MbO2 and a lower relative content of Mb, indicating a higher degree of blooming after 8 days of ageing. A significant interaction between ageing time pm and blooming time on all tristimulus parameters and myoglobin species was also found. L*, a* and b* values for the two ageing times during blooming are shown in Fig. 1(a)–(c). The L* value was almost constant during the first 90 min, but increased considerably between 90 min and 24 h (Fig. 1(a)). Ageing for 8 days pm resulted in higher L* values and thus lighter meat compared with ageng for 1 day pm. The a* and b* values increased during blooming with the blooming being faster and to a higher level in meat aged for 8 days compared with meat aged for 1 day, resulting in a more red and yellow colour in the former (Fig. 1(b)–(c)). LD aged for 8 days reached the same a* value after 10 min as it took LD aged for 1 day 30–60 min to reach (Fig. 1(b)). A marked increase
Table 2 Effects of crossbreed, Duroc (D · LYD) sires vs. Landrace (L · LYD) sires with Landrace* Yorkshire* Duroc dams, on carcass characteristics, temperature and pH values post mortem and composition of M. Longissimus dorsi Trait
D · LYD (n = 12)
L · LYD (n = 19)
SE
P-valuea
Carcass weight (kg) Lean meat content (%) Temperature1 min, C Temperature45 min, C Temperature24 h, C pH1 min pH45 min pH24 h Dry matter (g/100 g) IMF (g/100 g) Protein (g/100 g) Myoglobin (mg/g)
80.1 61.8 39.6 39.6 3.4 6.60 6.40 5.63 25.1 1.62 23.2 0.78
77.5 60.0 38.7 39.0 2.6 6.56 6.45 5.59 25.0 1.56 23.3 0.59
1.1 0.3 0.2 0.2 0.1 0.06 0.04 0.03 0.1 0.11 0.1 0.024
0.120 0.0004 0.009 0.046 0.0001 0.603 0.375 0.310 0.731 0.723 0.533 0.0001
Least squares mean and standard error (SE). a Significant differences, P 6 0.05, indicated in bold.
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Table 3 Effect of ageing time post mortem (pm) (A), crossbreed (CB), Duroc (D · LYD) sires vs. Landrace (L · LYD) sires with Landrace* Yorkshire* Duroc dams, and time point of blooming (T) on colour parameters during display for 0–24 h at 3 CA Trait
L* value a* value b* value Mb (K/S474/525) MbO2 (K/S610/525) MetMb (K/S572/525)
Ageing time pm
Crossbreed
P-value
1 Day
8 Days
SE
D · LYD
L · LYD
SE
A
CB
T
A*TB
CB*TB
49.3a 0.81a 10.57a 0.802a 0.632a 1.301
51.2b 1.60b 11.83b 0.848b 0.590b 1.300
0.3 0.13 0.11 0.003 0.006 0.003
48.8a 1.04 10.67a 0.817a 0.622 1.306
51.6b 1.36 11.73b 0.834b 0.600 1.296
0.5 0.18 0.15 0.004 0.008 0.004
0.0001 0.0001 0.0001 0.0001 0.0001 0.782
0.0003 0.197 0.0001 0.002 0.058 0.129
0.0001 0.0001 0.0001 0.0001 0.0001 0.0001
0.034 0.0001 0.0001 0.0001 0.0001 0.0028
0.028 0.550 0.640 0.0002 0.596 0.200
Least squares mean and standard error (SE). A Significant differences between LSM with different letters in the same row within the same trait and effect, P 6 0.05; significant P-values indicated in bold. B Presented in Figs. 1 and 2.
the first 24 h after exposure of a fresh surface. The b* value increased only during the first 60 min after 8 days of ageing, but during all 24 h after 1 day of ageing. LD aged
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52
L* value
L* value
in a* value between 90 min and 24 h, with a larger increase for LD aged for 1 day than for LD aged for 8 days, was registered, indicating that blooming proceeds throughout
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44 0
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Blooming time (min)
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1 day pm
8
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8
8 days pm
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c
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3
1
b* value
30
Blooming time (min)
d
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a* value
30
Blooming time (min)
a
30
60
90
Blooming time (min)
1440
0
f
30
60
90
1440
Blooming time (min)
Fig. 1. Blooming of M. longissimus dorsi as reflected in the L*, a* and b* values during 0–24 h of display at 3 C and influenced by ageing time, 1 vs. 8 days post mortem (pm) (a–c) and crossbreed, Duroc (D · LYD) sires vs. Landrace (L · LYD) sires with Landrace* Yorkshire* Duroc dams (d–f), least squares means and standard error (SE).
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increase in the period from the first 90 min to 24 h, however, no effect of ageing time was found (Fig. 2(a)). The smaller crossbreed effect compared with ageing effect was also seen in the myoglobin species (Fig. 2(b)), but the course of the changes during blooming was the same. The higher relative content of Mb and lower relative content of MbO2 in LD from Landrace-sired pigs compared with LD from Duroc-sired pigs indicate a higher degree of blooming in the former. 3.3. Colour stability Ageing time pm significantly affected all the measured colour characteristics of LD during display (Table 4). The L*, a* and b* values were higher for 8 days pm compared with 1 day pm, and the relative content of MetMb was slightly lower after 8 days of ageing. The main effect was a higher degree of blooming in LD aged for 8 days pm, which was reflected both in a higher a* value and a higher formation of the bright pink MbO2. An interaction between ageing time pm and display time on all the colour characteristics was also observed. L*, a* and b* values for the two ageing times during display are shown in Fig. 3(a)– (c). The L* value increased slightly during display and was all the time higher after 8 days compared with 1 day of ageing. The a* value increased markedly during the first day of
Mb - 1 day pm
Mb - D x LYD
Mb - 8 days pm
Mb - L x LYD
MbO2 - 1 day pm
MbO2 - D x LYD
MbO2 - 8 days pm
MbO2 - L x LYD
MetMb - 1 day pm
MetMb - D x LYD
MetMb - 8 days pm
MetMb - L x LYD
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K/S-ratio
K/S-ratio
for 8 days reached the same b* value after 10 min as it took LD aged for 1 day 90 min to reach (Fig. 1(c)). Blooming of LD was significantly affected by crossbreed for the L* and b* values and the relative content of Mb (Table 3). Higher L* and b* values, a lower relative content of Mb and a tendency to a higher relative content of MbO2 (P = 0.058) in LD from Landrace-sired pigs compared with those in LD from Duroc-sired pigs were observed. An effect of interaction between crossbreed and blooming time was observed on the L* value and the relative content of Mb. The L*, a* and b* values for the crossbreeds during blooming are shown in Fig. 1(d)–(f). The course in colour changes during blooming was the same as for the effect of ageing time. However, the crossbreed effect was more pronounced than the ageing effect on the L* value, but it was less pronounced on the b* value. The increase in L* value between 90 min and 24 h was larger for LD from Duroc-sired pigs compared with LD from Landrace-sired pigs. During blooming, the relative content of MbO2 increased with a subsequent decrease in the relative content of Mb (Fig. 2). Eight days of ageing resulted in more rapid and pronounced MbO2 formation and a simultaneous decrease in the relative content of Mb compared with 1 day of ageing. The relative content of MetMb was almost constant during the first 90 min of blooming, with a slight
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a
607
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60
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Blooming time (min)
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Blooming time (min)
Fig. 2. Relative changes in the content of the myoglobin species deoxymyoglobin (Mb), oxymyoglobin (MbO2) and metmyoglobin (MetMb), calculated from Kubelka-Munk K/S-ratios, in M. longissimus dorsi during blooming at 0–24 h of display at 3 C as influenced by ageing time, 1 vs. 8 days post mortem (pm) (a) and crossbreed, Duroc (D · LYD) sires vs. Landrace (L · LYD) sires with Landrace* Yorkshire* Duroc dams (b), least squares means and standard error (SE).
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Table 4 Effect of ageing time post mortem (pm) (A), crossbreed (CB), Duroc (D · LYD) sires vs. Landrace (L · LYD) sires with Landrace* Yorkshire* Duroc dams, and time point of display (T) on colour stability during display at 3 CA Trait
L* value a* value b* value Mb (K/S474/525) MbO2 (K/S610/525) MetMb (K/S572/525)
Ageing time pm
Crossbreed
P-value
1 Day
8 Days
SE
D · LYD
L · LYD
SE
A
CB
T
A*TB
CB*TB
50.7a 2.88a 11.70a 0.904a 0.557a 1.251a
52.0b 3.36b 12.49b 0.927b 0.529b 1.256b
0.3 0.12 0.10 0.002 0.004 0.003
50.2a 3.06 11.70a 0.908a 0.548 1.265a
52.5b 3.18 12.49b 0.924b 0.537 1.242b
0.4 0.16 0.13 0.002 0.006 0.004
0.0001 0.0001 0.0001 0.0001 0.0001 0.0005
0.0006 0.598 0.0002 0.0001 0.235 0.0002
0.0001 0.0001 0.0001 0.0001 0.0001 0.0001
0.039 0.0001 0.0001 0.0001 0.0001 0.0003
0.047 0.0001 0.050 0.020 0.0001 0.0001
Least squares mean and standard error (SE). A Significant differences between LSM with different letters in the same row within the same trait and effect, P 6 0.05; significant P-values indicated in bold. B Presented in Figs. 3 and 4.
no significant difference between the ageing times in a* or b* values after 6 days of display, but the L* value was slightly higher in LD aged for 8 days.
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54
54
52
52
L* value
L* value
display and decreased between 3 and 6 days of display after both ageing times, whereas the b* value only increased during the first day of display after 1 day of ageing. There was
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50 48
1 day pm
D x LYD L x LYD
8 days pm
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46 0
2
3
4
5
6
Storage time (days)
a
0
5
5
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4
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1
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8 days pm
L x LYD
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12 11 1 day pm
10
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6
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b* value
1
Storage time (days)
b
12 11 10
D x LYD
8 days pm
L x LYD
9
9 0
c
6
3
1
1 day pm
5
Storage time (days)
d
a* value
a* value
1
1
2
3
4
5
Storage time (days)
6
0
f
1
2
3
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6
Storage time (days)
Fig. 3. Colour stability of M. longissimus dorsi as reflected in the L*, a* and b* values during 6 days of display at 3 C and influenced by ageing time, 1 vs. 8 days post mortem (pm) (a–c) and crossbreed, Duroc (D · LYD) sires vs. Landrace (L · LYD) sires with Landrace* Yorkshire* Duroc dams (d–f), least squares means and standard error (SE).
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4. Discussion 4.1. Course of colour changes during blooming and display As reflected in a* and b* values and MbO2 formation, blooming was most rapid during the first 30 min of exposure to air, but continued for 24 h. This is in contrast to a previous study, which reported that only 10 min was required for the a* and b* values to stabilise during blooming (Brewer, Zhu, Bidner, Meisinger, & McKeith, 2001),
Mb - 1 day pm
Mb - D x LYD
Mb - 8 days pm
Mb - L x LYD
MbO2 - 1 day pm
MbO2 - D x LYD
MbO2 - 8 days pm
MbO2 - L x LYD
MetMb - 1 day pm
MetMb - D x LYD
MetMb - 8 days pm
MetMb - L x LYD
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a
of MetMb increased during the entire display period with slightly higher MetMb after 6 days of display in LD aged for 1 day compared with LD aged for 8 days (Fig. 4(a)). The crossbreed effect on MetMb formation during display was more pronounced than the ageing effect with a higher level of MetMb in LD from Landrace-sired pigs compared with LD from Duroc-sired pigs (Fig. 4(b)). LD from Landrace-sired pigs reached the same level of MetMb after 3 days of display as LD from Duroc-sired pigs did after 6 days.
K/S-ratio
K/S-ratio
Crossbreed significantly affected all the measured colour characteristics, with exception of the a* value and the relative content of MbO2 (Table 4). The L* and b* values and the relative content of MetMb were higher in LD from Landrace-sired pigs compared with LD from Duroc-sired pigs, whereas the relative content of Mb was lower. An interaction between crossbreed and display time on all the colour characteristics was also observed (Table 4). The L*, a* and b* values during display are shown in Fig. 3(d)–(f). The course in colour changes was the same as for the effect of ageing time. However, the crossbreed effect was more pronounced than the ageing effect on the L* and b* values. Contrary to the ageing effect, there were significant differences between the crossbreeds after 6 days of display with higher L* and b* values and lower a* values in LD from Landrace-sired pigs compared with LD from Duroc-sired pigs. During display, the relative content of MbO2 increased with a subsequent decrease in the relative content of Mb during the first day, and after that both relative contents remained relatively constant (Fig. 4). The relative content
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Storage time (days)
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Fig. 4. Relative changes in the content of the myoglobin species deoxymyoglobin (Mb), oxymyoglobin (MbO2) and metmyoglobin (MetMb), calculated from Kubelka-Munk K/S-ratios, in M. longissimus dorsi during 6 days of display at 3 C as influenced by ageing time, 1 vs. 8 days post mortem (pm) (a) and crossbreed, Duroc (D · LYD) sires vs. Landrace (L · LYD) sires with Landrace* Yorkshire* Duroc dams (b), least squares means and standard error (SE).
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however, it is more in line with the study of Zhu et al. (2001), who concluded that blooming is not completed within 30 min. The difference between these two studies might be due to difference in display temperature, as blooming is more intense at lower temperatures (Ledward, 1992). Millar, Wilson, Moss, & Ledward (1994) found very little formation of MbO2 in pork LD exposed to air for 60 min at 23 C, but blooming was observed, when the meat was transferred to display at 5 C. They observed MetMb at the pork surface after 24 h display at 5 C, contrary to the present study, where the pork was displayed at 3 C, and MetMb was not observed. In the present study, a continuous increase in all three tristimulus parameters lightness (L* value), redness (a* value) and yellowness (b* value) was observed during the first day of display. A similar pattern during blooming has been reported previously (Juncher et al., 2001), whereas only increases in L* value and b* value were reported by Hansen et al. (2004) and Rosenvold & Andersen (2003). The continuous increase in MetMb during an additional 5 days of display in the present study had no dramatic effect on the tristimulus parameters, even though a decrease in redness between days 3 and 6 and a slight increase in lightness were registered. This observation is in agreement with previous reports (Hansen et al., 2004; Juncher et al., 2001; Rosenvold & Andersen, 2003). Consumers are supposed to be able to perceive a difference in a* value of 0.6–0.9 depending on the light source (Zhu & Brewer, 1999). Consequently, the registered increase in a* value during the first day should be perceived by the consumer, whereas the subsequent decrease in a* value during display most probably will not be recognised. 4.2. Effect of crossbreed Equal IMF content in LD from both crossbreeds is in contrast with other studies showing higher IMF content in LD from Duroc compared with Landrace purebreed pigs (Cameron et al., 1990; Candek-Potokar, Zlender, & Bonneau, 1998; Lo, McLaren, McKeith, Fernando, & Novakofski, 1992; Newcom et al., 2004) or Duroc-compared with Landrace-sired crossbreed pigs (Martel, Minivielle, & Poste, 1988; Oliver et al., 1994). The higher myoglobin content in LD from Duroc-sired pigs compared with LD from Landrace-sired pigs is in agreement with Newcom et al. (2004) in a study on purebreed Duroc and Landrace pigs. LD from Duroc-sired pigs was found to be darker and less yellow than LD from Landrace-sired pigs throughout the blooming period and the subsequent display, while no breed effect was registered with regard to degree of redness. The reason for the equal a* values (Table 4) might be that the higher proportion of MetMb counteracts the effect of higher proportion of MbO2 giving the same redness, as the a* value decreases with both increased MetMb and Mb (Johansson, 1989). Other studies have shown
lower lightness and higher redness, but no difference in yellowness (Cameron et al., 1990; Newcom et al., 2004) or lower lightness and redness, but no difference in yellowness (Oliver et al., 1994) on LD from purebreed Duroc pigs compared with Landrace pigs. Hammell et al. (1994) found no differences in lightness, redness or yellowness between Duroc- and Landrace-sired crossbreeds, whereas Langlois & Minivielle (1989) reported lower reflectance (Criterion Reflection Meter) in LD from Duroc- than from Landrace-sired crossbreeds. Blanchard et al. (1999) found darker colour, measured using Japanese colour score and EEL reflectometer, with inclusion of Duroc in the crossbreeds. The higher MetMb content in Landrace-sired pork compared with Duroc-sired pork in the present study indicates higher proneness to discolouration, although the MetMb levels were low in both. The accumulation of MetMb on the meat surface depends on the rates of autoxidation and MetMb reduction. Zhu & Brewer (1998) suggested that the MetMb-reducing capacity controls the rate of MetMb accumulation and discoloration in pork. It is not known whether there are differences between the studied crossbreeds in MetMbreducing activity, which can explain the differences in MetMb accumulation. The colour of pork is influenced by both the pigment content and the relative ratio of the myoglobin species (Lindahl et al., 2001). The registered crossbreed effect on colour can be explained by a combination of higher pigment content and a higher proportion of Mb in pork from Duroc-sired pigs, as this is known to result in a darker and less yellow colour. Surprisingly, no significant difference in redness between breeds was measured, but a numerically slightly lower redness in pork from Duroc-sired pigs. The proportion of Mb is related to both pH within the meat and the rate of the early pm pH decline, as low pH influences oxygen consumption rate within the meat through either decrease in activity or inactivation of enzymatic oxygen consumption systems (Ledward, 1985; Rosenvold & Andersen, 2003). However, as almost identical pH24 h was found in LD from both crossbreeds and the fact that no difference in initial rate of the pH decline was observed between breeds, the progress and final pH in the meat cannot explain the observed colour differences. Muscle temperature pm has also been mentioned as a potential factor of importance for the colour of pork (Rosenvold & Andersen, 2003). A slight, but significant, difference in muscle temperature during the initial pm pH decline was observed. However, this temperature difference was probably too small to explain the observed difference in colour between the pork of the included breeds, especially as the temperature differences was not accompanied by pH differences. Suuronen (1996) reported a tendency to a higher content of fast-twitch oxidative type IIA fibres in LD from DLY pigs compared with LLY pigs. This supports a more oxidative metabolism in LD from DLY pigs, which could explain the registered differences in colour characteristics of pork from the two breeds.
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Acknowledgements
Ageing for 8 days increased lightness, redness and yellowness in the present study due to increased blooming with higher level of MbO2 and lower level of Mb. This is in agreement with a previous study by Zhu et al. (2001), who found that ageing increased the ability of vacuumpackaged pork to bloom, resulting in higher redness. The oxygen consumption rate decreases with time pm and aged meat therefore blooms more rapidly (Ledward, 1992). Apple et al. (2001) reported, in agreement with the present study, increased lightness, redness and yellowness after 4 and 8 weeks of vacuum storage of pork, whereas Apple et al. (2002) found increased lightness, decreased yellowness, but no effect on redness after 3 weeks of vacuum storage. Moreover, Rosenvold & Andersen (2003) reported higher redness and yellowness, however, no difference in lightness after 8 days of vacuum storage. Frederick et al. (2004) found numerically lower lightness and higher redness and yellowness in pork LD after 25 or 50 days of vacuum storage compared with LD 24 h pm. Schluter et al. (1994) reported no difference in lightness and lower redness and yellowness in vacuum-stored LD after 10 days compared with 7 days, but only lower yellowness after 14 days of storage. The present study only showed a minor effect of ageing on myoglobin oxidation, with slightly lower MetMb in aged meat after 6 days of display. This is in contrast to the study of Rosenvold & Andersen (2003), where the higher redness in the aged LD decreased faster during a subsequent 5-day retail display to the same levels as in not aged LD, indicating a more rapid colour-fading in aged pork, which is in agreement with data on colour stability of aged beef (OÕKeefe & Hood, 1980–1981).
The authors wish to thank Jose´ A. Fernandez for animal breeding and Camilla Bjerg Kristensen and Jens Askov Jensen for excellent technical assistance and analysis. The work was part of the project SUSPORKQUAL (QLK52000-00162), financially supported by the European 5th Framework Programme. This paper does not necessarily reflect the EU commissionÕs views and in no way anticipates the commissionÕs future policy in this area. Acknowledgements are also given to the Ministry of Food, Agriculture and Fisheries, Denmark, for financial support.
5. Conclusions Ageing for 8 days in chill improved the blooming of pork loin from both Duroc- and Landrace-sired pigs, resulting in increased lightness, redness and yellowness. The blooming proceeded during all the first day of display, followed by a slow oxidation to MetMb during the subsequent 5 days, with slightly lower MetMb in aged meat. The increased content of MetMb had only minor effect on the colour resulting in a slightly, however, nonsignificant decrease in redness. The colour of pork loin from Duroc-sired pigs was darker and less yellow than that from Landrace-sired pigs due to higher pigment content and less blooming. More MetMb was formed during display of loin from Landrace-sired pigs compared with loin from Duroc-sired, although the levels were low in both crossbreeds. Considering that it is earlier found that texture and flavour improve upon ageing of pork, and that the present data show superior colour characteristics when fresh pork is aged for 8 days, it should be recommended to age pork, if it is intended to be marketed as high quality pork.
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Significance of storage time on degree of blooming and colour stability of pork loin from different crossbreeds Gunilla Lindahl
a,*
, Anders H. Karlsson b, Kerstin Lundstro¨m c, Henrik J. Andersen
a
a
b
Department of Food Science, Danish Institute of Agricultural Sciences, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark Department of Food Science, Meat Science Unit, The Royal Veterinary and Agricultural University, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark c Department of Food Science, Swedish University of Agricultural Sciences, P.O. Box 7051, SE-750 07 Uppsala, Sweden Received 7 May 2005; received in revised form 22 September 2005; accepted 23 September 2005
Abstract The objective was to investigate the effect of ageing time (1 day vs. 8 days postmortem) and sire breed used in the crossbreed (Duroc sired vs. Landrace sired pigs) on blooming ability and colour stability of pork M. longissimus dorsi (LD). The colour was measured during blooming (0, 10, 30, 60, 90 min and 24 h after cutting) and during subsequent display (1, 2, 3 and 6 days) at 3 C. The contents of deoxymyoglobin (Mb), oxymyoglobin (MbO2) and metmyoglobin (MetMb) were calculated. Ageing improved the blooming of LD from both crossbreeds with increased content of MbO2 and decreased content of Mb, resulting in increased lightness, redness and yellowness. Ageing had smaller effect on colour stability with slightly lower MetMb in aged meat. Crossbreed affected both blooming and colour stability. LD from Landrace-sired pigs bloomed more than LD from Duroc-sired pigs, but more MetMb was formed during subsequent storage, although at a low level in both crossbreeds. The present data show superior colour characteristics of fresh pork aged for 8 days. 2005 Elsevier Ltd. All rights reserved. Keywords: Pork; Ageing; Breed; Blooming; Colour stability; Myoglobin species
1. Introduction Many studies have shown that ageing of pork improves the sensory attributes juiciness, tenderness and flavour (Channon, Baud, Kerr, & Walker, 2003; Channon, Kerr, & Walker, 2004; Ellis et al., 1998; Tornberg, von Seth, & o¨ransson, 1994; Wood et al., 1996). For the consumer, optimal pork quality also includes an attractive colour, since it is the only way to assess the quality of packaged meat at the moment of purchase. Pork is often pre-packaged and displayed for several days, thus it is important with a high colour stability. Colour measured 24 h postmortem (pm) is generally included in the assessment of pork quality, but colour stability during retail display is more seldomly studied. There are few studies on the effect of age*
Corresponding author. Present address: Gotlandsgatan 4, SE-244 32 Ka¨vlinge, Sweden. Tel.: +46 46 73 52 52. E-mail address: [email protected] (G. Lindahl). 0309-1740/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2005.09.018
ing on colour stability of pork. Storage of pork pm is reported to influence the colour (Apple et al., 2001; Apple, Stivarius, Reiman, Rakes, & Maxwell, 2002; Frederick, van Heugten, & See, 2004; Rosenvold & Andersen, 2003; Schluter et al., 1994) and the ability of pork to bloom (Zhu, Bidner, & Brewer, 2001). Furthermore, several studies have shown colour differences between pork from purebred Duroc and Landrace pigs (Cameron, Warris, Porter, & Enser, 1990; Newcom et al., 2004) and from Duroc- and Landrace-sired crossbreeds (Blanchard, Warkup, Ellis, Willis, & Avery, 1999; Hammell, Laforest, & Dufour, 1994; Langlois & Minivielle, 1989). However, hardly any knowledge exists regarding the effect of these breeds on colour stability. The colour of pork is influenced by the pigment content, the internal reflectance and the distribution of the myoglobin species, deoxymyoglobin (Mb), oxymyoglobin (MbO2) and metmyoglobin (MetMb) (Lindahl, Lundstro¨m, & Tornberg, 2001). Mb is the purple reduced ferro-species,
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which appear when the meat is freshly cut. Upon exposure to air, Mb rapidly binds oxygen reversibly, forming the bright pink pigment MbO2 (Ledward, 1992) that makes the meat surface to bloom to the characteristic colour of fresh meat, as the small layer of MbO2 diffuses into the meat center (Feldhusen, Warnatz, Erdman, & Wenzel, 1994). The depth to which the oxygen diffuses depends on the enzymatic oxygen consumption rate of the meat, the temperature and the external oxygen pressure (Ledward, 1992). The ferro-species of myoglobin oxidise to the brown ferri-species MetMb upon prolonged exposure to air or at low oxygen pressures (pO2) with a maximum at 1 kPa pO2 at 7 C (Ledward, 1970). MetMb accumulates in the interface between MbO2 and Mb depending on the rates of myoglobin autoxidation, enzymatic MetMb reduction and oxygen consumption (Renerre, 1990). MetMb accumulation in pork changes with ageing time as both MetMb reductase activity (Zhu & Brewer, 1998) and oxygen consumption rate (Atkinson & Follett, 1973) decrease with time pm. Blooming is more efficient under conditions which increase oxygen solubility and discourage enzymatic activity (i.e. low temperatures and low pH values) (Ledward, 1992). Moreover, blooming has been found to be faster and more pronounced in meat that has been aged for several weeks in vacuum packaging prior to exposure to air, owing to some loss of activity of the oxygen-consuming enzymes (Ledward, 1992), and a deeper MbO2 layer is formed (Feldhusen et al., 1994). However, the colour stability of such meat might be impaired depending on the length of the ageing period (Ledward, 1985; OÕKeefe & Hood, 1980–1981). The objective of this study was to investigate the effect of ageing time (1 day vs. 8 days pm) and sire used in the crossbreed (Duroc-sired vs. Landraces-sired pigs) on blooming ability and colour stability of pork loin. 2. Materials and methods 2.1. Animals and treatments The present study was part of an EU project (SUSPORKQUAL) that aimed to evaluate the effect of feeding strategies on pork quality. The animal material consisted of littermate female and castrated male pigs from Landrace* Yorkshire* Duroc (LYD) dams and Landrace (L) or Duroc (D) sires that immediately after weaning (at about 8 weeks of age) were allocated to one of three feeding strategies. The organically grown pigs were kept in indoor pens with deep litter (barley + wheat straw) and with free access to an outside concrete pen, partially roofed. The following feeding strategies were used: (1) basal concentrate diet and red clover silage ad-lib; (2) basal concentrate diet restricted to 70% of ad-lib, red clover silage ad-lib; (3) basal concentrate diet restricted to 70% of ad-lib and red clover silage ad-lib the first 25 experimental days, followed by ad-lib basal concentrate diet and red clover silage. All the pigs received two consecutive basal concentrate diets depending
on their live weight, 30–60 kg and 60–105 kg, and these diets were formulated according to current Danish recommendations (Table 1). An experimental replicate consisted of 30 pigs of each crossbreed, and the pigs were penned in groups of five according to weight and sex. Meat from 12 Duroc-sired and 19 Landrace-sired pigs were used for studies of colour and colour stability. The pigs were slaughtered at approximately 105 kg live weight in the experimental abattoir at Research Centre Foulum. The pigs were stunned with 80% CO2 for 3 min, exsanguinated, scalded at 62 C for 3 min, cleaned and eviscerated within 30 min and chilled at 3 C after 60 min. 2.2. Carcass characteristics, pH and temperature measurements Warm carcass weight was registered by weighing the eviscerated carcass (minus tongue, bristles, genitals, kidneys, diaphragm and front feet) 45 min pm. Lean meat content was estimated from measurements using Fat-O-Meter (SFK Ltd., Hvidovre, Denmark) on the cold carcass (Kempster, Chadwick, & Jones, 1985). Temperature (Testo 110 thermometer, Testo Gmbh 6 Co., Germany) and pH (PHM201 pH Meter, Radiometer, Denmark, equipped with Methrom LL combined pH penetration electrode (Methrohm, Switzerland) were measured in M. longissimus dorsi (LD) at the last rib 1 min, 45 min and 24 h pm. The pH electrode was calibrated in pH 4.01 and 7.00 buffers equilibrated at 35 C for the measurements on the warm carcass 1 and 45 min pm, and at 4 C for the measurement on the cold carcass 24 h pm. 2.3. Colour measurements LD was excised from the carcass 24 h pm, and a piece of 16 cm of the loin (4–20 cm in front of the last rib) was used for colour measurements. These 16 cm were divided into two halves, and the caudale half was used for colour measurements directly, and the cranial half was vacuum-packed and aged at 3 C for 7 days before
Table 1 Feedstuff composition of the diets, kg/100 kg Ingredient
Live weight 30–60 kg
Barley Oats Wheat Peas Rapeseed cake (0 0), Scanola Sweet lupin, Prima Potato protein concentrate Monocalc. Phosphate Aliphos Tess Calcium carbonate Sodium chloride Vitamin and mineral supplement a
Organic.
a
14.08 12.50a 37.39a 5.55a 10.00 12.00a 6.15 0.49 1.26 0.38 0.20
60–105 kg 33.10a 15.00a 15.00a 0 8.00 23.10a 3.70 0.30 1.23 0.37 0.20
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colour measurements. Chops, 2 cm thick, were cut across the fibre direction, wrapped with oxygen permeable film and displayed at 3 C for 6 days. Each colour measurement was done directly on the meat without the covering film. The colour was measured using Minolta CM-2600d spectrophotometer (Minolta Co., Ltd., Osaka, Japan) with specular reflectance excluded, 8 mm diameter measuring aperture, illuminant D65, 10 Standard Observer and CIE (1976) colour scale. The measuring aperture was covered with a glass plate, and the instrument was calibrated against a white plate (L* = 97.30, a* = 0.06, b* = 0.00); the average of four measurements across the surface was used. Blooming was assessed by colour measurements immediately after cutting (0 min) and after 10, 30, 60, 90 min and 24 h of blooming in air at 3 C. Colour stability was assessed by colour measurements after 0 (=blooming for 60 min), 1, 2, 3 and 6 days of display in air at 3 C. The instrument measures reflectance between 400 and 740 nm at 10 nm intervals, and Kubelka-Munk K/S ratios were calculated using SpectraMagic ver. 3.6 software (Minolta Co., Ltd., Osaka, Japan). The relative content of Mb was estimated by the ratio K/S474/525, the relative content of MbO2 by the ratio K/S610/525 and the relative content MetMb by the ratio K/S572/525 (Hunt et al., 1991; Mancini, Hunt, & Kropf, 2003). These ratios decrease when the relative content of the corresponding myoglobin species increases. The K/S-ratios were therefore multiplied by 1 in the diagrams (Figs. 2 and 4) in order to get the right impression when looking at the curves. K/S-ratios at wavelengths not given by the instrument (474, 525, 572 nm) were calculated using linear interpolation. 2.4. Chemical analysis Dry matter (drying for 24 h at 103 C), intramuscular fat (IMF) (NMKL, 1989), protein (NMKL, 1976) and pigment contents (Oksbjerg et al., 2000) were analysed in a 10 cm slice of LD cut just behind the last rib. The pigment content was reported as myoglobin. 2.5. Statistical analysis Statistical analysis was carried out with the Statistical Analysis System version 8.02 (SAS Institute, Cary, NC, USA). The mixed procedure was applied when calculating least squares means (LSM) and standard errors (SE). The statistical model included crossbreed, feeding regimen within crossbreed, ageing time pm, blooming or display time in air and their two-way interactions as fixed effects. Pig nested within crossbreed, feeding regimen and sex were included as random effects, and degrees of freedom were estimated with the Satterthwaite method. The non-significant effect of feeding regimen was ignored in the final model. The GLM procedure was applied on carcass characteristics and meat composition using a model including crossbreed and sex as fixed effects.
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3. Results 3.1. Carcass characteristics and meat composition There were no significant differences between the crossbreeds in carcass weight, pH values, dry matter, IMF or protein contents in LD (Table 2). Duroc-sired pigs had higher lean meat content and slightly higher temperatures at 1 min, 45 min and 24 h pm. The pigment content was higher in LD from Duroc-sired pigs than in LD from Landrace-sired pigs. 3.2. Blooming Blooming of LD was significantly affected by ageing time pm for all the measured colour parameters, with exception of the relative content of MetMb (Table 3). The tristimulus parameters (L*, a* and b*) were all higher 8 days pm compared with 1 day pm. Moreover, the K/Sratios showed a higher relative content of MbO2 and a lower relative content of Mb, indicating a higher degree of blooming after 8 days of ageing. A significant interaction between ageing time pm and blooming time on all tristimulus parameters and myoglobin species was also found. L*, a* and b* values for the two ageing times during blooming are shown in Fig. 1(a)–(c). The L* value was almost constant during the first 90 min, but increased considerably between 90 min and 24 h (Fig. 1(a)). Ageing for 8 days pm resulted in higher L* values and thus lighter meat compared with ageng for 1 day pm. The a* and b* values increased during blooming with the blooming being faster and to a higher level in meat aged for 8 days compared with meat aged for 1 day, resulting in a more red and yellow colour in the former (Fig. 1(b)–(c)). LD aged for 8 days reached the same a* value after 10 min as it took LD aged for 1 day 30–60 min to reach (Fig. 1(b)). A marked increase
Table 2 Effects of crossbreed, Duroc (D · LYD) sires vs. Landrace (L · LYD) sires with Landrace* Yorkshire* Duroc dams, on carcass characteristics, temperature and pH values post mortem and composition of M. Longissimus dorsi Trait
D · LYD (n = 12)
L · LYD (n = 19)
SE
P-valuea
Carcass weight (kg) Lean meat content (%) Temperature1 min, C Temperature45 min, C Temperature24 h, C pH1 min pH45 min pH24 h Dry matter (g/100 g) IMF (g/100 g) Protein (g/100 g) Myoglobin (mg/g)
80.1 61.8 39.6 39.6 3.4 6.60 6.40 5.63 25.1 1.62 23.2 0.78
77.5 60.0 38.7 39.0 2.6 6.56 6.45 5.59 25.0 1.56 23.3 0.59
1.1 0.3 0.2 0.2 0.1 0.06 0.04 0.03 0.1 0.11 0.1 0.024
0.120 0.0004 0.009 0.046 0.0001 0.603 0.375 0.310 0.731 0.723 0.533 0.0001
Least squares mean and standard error (SE). a Significant differences, P 6 0.05, indicated in bold.
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Table 3 Effect of ageing time post mortem (pm) (A), crossbreed (CB), Duroc (D · LYD) sires vs. Landrace (L · LYD) sires with Landrace* Yorkshire* Duroc dams, and time point of blooming (T) on colour parameters during display for 0–24 h at 3 CA Trait
L* value a* value b* value Mb (K/S474/525) MbO2 (K/S610/525) MetMb (K/S572/525)
Ageing time pm
Crossbreed
P-value
1 Day
8 Days
SE
D · LYD
L · LYD
SE
A
CB
T
A*TB
CB*TB
49.3a 0.81a 10.57a 0.802a 0.632a 1.301
51.2b 1.60b 11.83b 0.848b 0.590b 1.300
0.3 0.13 0.11 0.003 0.006 0.003
48.8a 1.04 10.67a 0.817a 0.622 1.306
51.6b 1.36 11.73b 0.834b 0.600 1.296
0.5 0.18 0.15 0.004 0.008 0.004
0.0001 0.0001 0.0001 0.0001 0.0001 0.782
0.0003 0.197 0.0001 0.002 0.058 0.129
0.0001 0.0001 0.0001 0.0001 0.0001 0.0001
0.034 0.0001 0.0001 0.0001 0.0001 0.0028
0.028 0.550 0.640 0.0002 0.596 0.200
Least squares mean and standard error (SE). A Significant differences between LSM with different letters in the same row within the same trait and effect, P 6 0.05; significant P-values indicated in bold. B Presented in Figs. 1 and 2.
the first 24 h after exposure of a fresh surface. The b* value increased only during the first 60 min after 8 days of ageing, but during all 24 h after 1 day of ageing. LD aged
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54
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52
L* value
L* value
in a* value between 90 min and 24 h, with a larger increase for LD aged for 1 day than for LD aged for 8 days, was registered, indicating that blooming proceeds throughout
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44 0
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a
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90
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1440
0
f
30
60
90
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Blooming time (min)
Fig. 1. Blooming of M. longissimus dorsi as reflected in the L*, a* and b* values during 0–24 h of display at 3 C and influenced by ageing time, 1 vs. 8 days post mortem (pm) (a–c) and crossbreed, Duroc (D · LYD) sires vs. Landrace (L · LYD) sires with Landrace* Yorkshire* Duroc dams (d–f), least squares means and standard error (SE).
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increase in the period from the first 90 min to 24 h, however, no effect of ageing time was found (Fig. 2(a)). The smaller crossbreed effect compared with ageing effect was also seen in the myoglobin species (Fig. 2(b)), but the course of the changes during blooming was the same. The higher relative content of Mb and lower relative content of MbO2 in LD from Landrace-sired pigs compared with LD from Duroc-sired pigs indicate a higher degree of blooming in the former. 3.3. Colour stability Ageing time pm significantly affected all the measured colour characteristics of LD during display (Table 4). The L*, a* and b* values were higher for 8 days pm compared with 1 day pm, and the relative content of MetMb was slightly lower after 8 days of ageing. The main effect was a higher degree of blooming in LD aged for 8 days pm, which was reflected both in a higher a* value and a higher formation of the bright pink MbO2. An interaction between ageing time pm and display time on all the colour characteristics was also observed. L*, a* and b* values for the two ageing times during display are shown in Fig. 3(a)– (c). The L* value increased slightly during display and was all the time higher after 8 days compared with 1 day of ageing. The a* value increased markedly during the first day of
Mb - 1 day pm
Mb - D x LYD
Mb - 8 days pm
Mb - L x LYD
MbO2 - 1 day pm
MbO2 - D x LYD
MbO2 - 8 days pm
MbO2 - L x LYD
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K/S-ratio
K/S-ratio
for 8 days reached the same b* value after 10 min as it took LD aged for 1 day 90 min to reach (Fig. 1(c)). Blooming of LD was significantly affected by crossbreed for the L* and b* values and the relative content of Mb (Table 3). Higher L* and b* values, a lower relative content of Mb and a tendency to a higher relative content of MbO2 (P = 0.058) in LD from Landrace-sired pigs compared with those in LD from Duroc-sired pigs were observed. An effect of interaction between crossbreed and blooming time was observed on the L* value and the relative content of Mb. The L*, a* and b* values for the crossbreeds during blooming are shown in Fig. 1(d)–(f). The course in colour changes during blooming was the same as for the effect of ageing time. However, the crossbreed effect was more pronounced than the ageing effect on the L* value, but it was less pronounced on the b* value. The increase in L* value between 90 min and 24 h was larger for LD from Duroc-sired pigs compared with LD from Landrace-sired pigs. During blooming, the relative content of MbO2 increased with a subsequent decrease in the relative content of Mb (Fig. 2). Eight days of ageing resulted in more rapid and pronounced MbO2 formation and a simultaneous decrease in the relative content of Mb compared with 1 day of ageing. The relative content of MetMb was almost constant during the first 90 min of blooming, with a slight
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a
607
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90
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Blooming time (min)
Fig. 2. Relative changes in the content of the myoglobin species deoxymyoglobin (Mb), oxymyoglobin (MbO2) and metmyoglobin (MetMb), calculated from Kubelka-Munk K/S-ratios, in M. longissimus dorsi during blooming at 0–24 h of display at 3 C as influenced by ageing time, 1 vs. 8 days post mortem (pm) (a) and crossbreed, Duroc (D · LYD) sires vs. Landrace (L · LYD) sires with Landrace* Yorkshire* Duroc dams (b), least squares means and standard error (SE).
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Table 4 Effect of ageing time post mortem (pm) (A), crossbreed (CB), Duroc (D · LYD) sires vs. Landrace (L · LYD) sires with Landrace* Yorkshire* Duroc dams, and time point of display (T) on colour stability during display at 3 CA Trait
L* value a* value b* value Mb (K/S474/525) MbO2 (K/S610/525) MetMb (K/S572/525)
Ageing time pm
Crossbreed
P-value
1 Day
8 Days
SE
D · LYD
L · LYD
SE
A
CB
T
A*TB
CB*TB
50.7a 2.88a 11.70a 0.904a 0.557a 1.251a
52.0b 3.36b 12.49b 0.927b 0.529b 1.256b
0.3 0.12 0.10 0.002 0.004 0.003
50.2a 3.06 11.70a 0.908a 0.548 1.265a
52.5b 3.18 12.49b 0.924b 0.537 1.242b
0.4 0.16 0.13 0.002 0.006 0.004
0.0001 0.0001 0.0001 0.0001 0.0001 0.0005
0.0006 0.598 0.0002 0.0001 0.235 0.0002
0.0001 0.0001 0.0001 0.0001 0.0001 0.0001
0.039 0.0001 0.0001 0.0001 0.0001 0.0003
0.047 0.0001 0.050 0.020 0.0001 0.0001
Least squares mean and standard error (SE). A Significant differences between LSM with different letters in the same row within the same trait and effect, P 6 0.05; significant P-values indicated in bold. B Presented in Figs. 3 and 4.
no significant difference between the ageing times in a* or b* values after 6 days of display, but the L* value was slightly higher in LD aged for 8 days.
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52
L* value
L* value
display and decreased between 3 and 6 days of display after both ageing times, whereas the b* value only increased during the first day of display after 1 day of ageing. There was
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8 days pm
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3
4
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6
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12 11 10
D x LYD
8 days pm
L x LYD
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9 0
c
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a* value
1
1
2
3
4
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6
0
f
1
2
3
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Storage time (days)
Fig. 3. Colour stability of M. longissimus dorsi as reflected in the L*, a* and b* values during 6 days of display at 3 C and influenced by ageing time, 1 vs. 8 days post mortem (pm) (a–c) and crossbreed, Duroc (D · LYD) sires vs. Landrace (L · LYD) sires with Landrace* Yorkshire* Duroc dams (d–f), least squares means and standard error (SE).
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4. Discussion 4.1. Course of colour changes during blooming and display As reflected in a* and b* values and MbO2 formation, blooming was most rapid during the first 30 min of exposure to air, but continued for 24 h. This is in contrast to a previous study, which reported that only 10 min was required for the a* and b* values to stabilise during blooming (Brewer, Zhu, Bidner, Meisinger, & McKeith, 2001),
Mb - 1 day pm
Mb - D x LYD
Mb - 8 days pm
Mb - L x LYD
MbO2 - 1 day pm
MbO2 - D x LYD
MbO2 - 8 days pm
MbO2 - L x LYD
MetMb - 1 day pm
MetMb - D x LYD
MetMb - 8 days pm
MetMb - L x LYD
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a
of MetMb increased during the entire display period with slightly higher MetMb after 6 days of display in LD aged for 1 day compared with LD aged for 8 days (Fig. 4(a)). The crossbreed effect on MetMb formation during display was more pronounced than the ageing effect with a higher level of MetMb in LD from Landrace-sired pigs compared with LD from Duroc-sired pigs (Fig. 4(b)). LD from Landrace-sired pigs reached the same level of MetMb after 3 days of display as LD from Duroc-sired pigs did after 6 days.
K/S-ratio
K/S-ratio
Crossbreed significantly affected all the measured colour characteristics, with exception of the a* value and the relative content of MbO2 (Table 4). The L* and b* values and the relative content of MetMb were higher in LD from Landrace-sired pigs compared with LD from Duroc-sired pigs, whereas the relative content of Mb was lower. An interaction between crossbreed and display time on all the colour characteristics was also observed (Table 4). The L*, a* and b* values during display are shown in Fig. 3(d)–(f). The course in colour changes was the same as for the effect of ageing time. However, the crossbreed effect was more pronounced than the ageing effect on the L* and b* values. Contrary to the ageing effect, there were significant differences between the crossbreeds after 6 days of display with higher L* and b* values and lower a* values in LD from Landrace-sired pigs compared with LD from Duroc-sired pigs. During display, the relative content of MbO2 increased with a subsequent decrease in the relative content of Mb during the first day, and after that both relative contents remained relatively constant (Fig. 4). The relative content
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1
2
3
4
Storage time (days)
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6
0
b
1
2
3
4
5
6
Storage time (days)
Fig. 4. Relative changes in the content of the myoglobin species deoxymyoglobin (Mb), oxymyoglobin (MbO2) and metmyoglobin (MetMb), calculated from Kubelka-Munk K/S-ratios, in M. longissimus dorsi during 6 days of display at 3 C as influenced by ageing time, 1 vs. 8 days post mortem (pm) (a) and crossbreed, Duroc (D · LYD) sires vs. Landrace (L · LYD) sires with Landrace* Yorkshire* Duroc dams (b), least squares means and standard error (SE).
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however, it is more in line with the study of Zhu et al. (2001), who concluded that blooming is not completed within 30 min. The difference between these two studies might be due to difference in display temperature, as blooming is more intense at lower temperatures (Ledward, 1992). Millar, Wilson, Moss, & Ledward (1994) found very little formation of MbO2 in pork LD exposed to air for 60 min at 23 C, but blooming was observed, when the meat was transferred to display at 5 C. They observed MetMb at the pork surface after 24 h display at 5 C, contrary to the present study, where the pork was displayed at 3 C, and MetMb was not observed. In the present study, a continuous increase in all three tristimulus parameters lightness (L* value), redness (a* value) and yellowness (b* value) was observed during the first day of display. A similar pattern during blooming has been reported previously (Juncher et al., 2001), whereas only increases in L* value and b* value were reported by Hansen et al. (2004) and Rosenvold & Andersen (2003). The continuous increase in MetMb during an additional 5 days of display in the present study had no dramatic effect on the tristimulus parameters, even though a decrease in redness between days 3 and 6 and a slight increase in lightness were registered. This observation is in agreement with previous reports (Hansen et al., 2004; Juncher et al., 2001; Rosenvold & Andersen, 2003). Consumers are supposed to be able to perceive a difference in a* value of 0.6–0.9 depending on the light source (Zhu & Brewer, 1999). Consequently, the registered increase in a* value during the first day should be perceived by the consumer, whereas the subsequent decrease in a* value during display most probably will not be recognised. 4.2. Effect of crossbreed Equal IMF content in LD from both crossbreeds is in contrast with other studies showing higher IMF content in LD from Duroc compared with Landrace purebreed pigs (Cameron et al., 1990; Candek-Potokar, Zlender, & Bonneau, 1998; Lo, McLaren, McKeith, Fernando, & Novakofski, 1992; Newcom et al., 2004) or Duroc-compared with Landrace-sired crossbreed pigs (Martel, Minivielle, & Poste, 1988; Oliver et al., 1994). The higher myoglobin content in LD from Duroc-sired pigs compared with LD from Landrace-sired pigs is in agreement with Newcom et al. (2004) in a study on purebreed Duroc and Landrace pigs. LD from Duroc-sired pigs was found to be darker and less yellow than LD from Landrace-sired pigs throughout the blooming period and the subsequent display, while no breed effect was registered with regard to degree of redness. The reason for the equal a* values (Table 4) might be that the higher proportion of MetMb counteracts the effect of higher proportion of MbO2 giving the same redness, as the a* value decreases with both increased MetMb and Mb (Johansson, 1989). Other studies have shown
lower lightness and higher redness, but no difference in yellowness (Cameron et al., 1990; Newcom et al., 2004) or lower lightness and redness, but no difference in yellowness (Oliver et al., 1994) on LD from purebreed Duroc pigs compared with Landrace pigs. Hammell et al. (1994) found no differences in lightness, redness or yellowness between Duroc- and Landrace-sired crossbreeds, whereas Langlois & Minivielle (1989) reported lower reflectance (Criterion Reflection Meter) in LD from Duroc- than from Landrace-sired crossbreeds. Blanchard et al. (1999) found darker colour, measured using Japanese colour score and EEL reflectometer, with inclusion of Duroc in the crossbreeds. The higher MetMb content in Landrace-sired pork compared with Duroc-sired pork in the present study indicates higher proneness to discolouration, although the MetMb levels were low in both. The accumulation of MetMb on the meat surface depends on the rates of autoxidation and MetMb reduction. Zhu & Brewer (1998) suggested that the MetMb-reducing capacity controls the rate of MetMb accumulation and discoloration in pork. It is not known whether there are differences between the studied crossbreeds in MetMbreducing activity, which can explain the differences in MetMb accumulation. The colour of pork is influenced by both the pigment content and the relative ratio of the myoglobin species (Lindahl et al., 2001). The registered crossbreed effect on colour can be explained by a combination of higher pigment content and a higher proportion of Mb in pork from Duroc-sired pigs, as this is known to result in a darker and less yellow colour. Surprisingly, no significant difference in redness between breeds was measured, but a numerically slightly lower redness in pork from Duroc-sired pigs. The proportion of Mb is related to both pH within the meat and the rate of the early pm pH decline, as low pH influences oxygen consumption rate within the meat through either decrease in activity or inactivation of enzymatic oxygen consumption systems (Ledward, 1985; Rosenvold & Andersen, 2003). However, as almost identical pH24 h was found in LD from both crossbreeds and the fact that no difference in initial rate of the pH decline was observed between breeds, the progress and final pH in the meat cannot explain the observed colour differences. Muscle temperature pm has also been mentioned as a potential factor of importance for the colour of pork (Rosenvold & Andersen, 2003). A slight, but significant, difference in muscle temperature during the initial pm pH decline was observed. However, this temperature difference was probably too small to explain the observed difference in colour between the pork of the included breeds, especially as the temperature differences was not accompanied by pH differences. Suuronen (1996) reported a tendency to a higher content of fast-twitch oxidative type IIA fibres in LD from DLY pigs compared with LLY pigs. This supports a more oxidative metabolism in LD from DLY pigs, which could explain the registered differences in colour characteristics of pork from the two breeds.
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4.3. Effect of ageing
Acknowledgements
Ageing for 8 days increased lightness, redness and yellowness in the present study due to increased blooming with higher level of MbO2 and lower level of Mb. This is in agreement with a previous study by Zhu et al. (2001), who found that ageing increased the ability of vacuumpackaged pork to bloom, resulting in higher redness. The oxygen consumption rate decreases with time pm and aged meat therefore blooms more rapidly (Ledward, 1992). Apple et al. (2001) reported, in agreement with the present study, increased lightness, redness and yellowness after 4 and 8 weeks of vacuum storage of pork, whereas Apple et al. (2002) found increased lightness, decreased yellowness, but no effect on redness after 3 weeks of vacuum storage. Moreover, Rosenvold & Andersen (2003) reported higher redness and yellowness, however, no difference in lightness after 8 days of vacuum storage. Frederick et al. (2004) found numerically lower lightness and higher redness and yellowness in pork LD after 25 or 50 days of vacuum storage compared with LD 24 h pm. Schluter et al. (1994) reported no difference in lightness and lower redness and yellowness in vacuum-stored LD after 10 days compared with 7 days, but only lower yellowness after 14 days of storage. The present study only showed a minor effect of ageing on myoglobin oxidation, with slightly lower MetMb in aged meat after 6 days of display. This is in contrast to the study of Rosenvold & Andersen (2003), where the higher redness in the aged LD decreased faster during a subsequent 5-day retail display to the same levels as in not aged LD, indicating a more rapid colour-fading in aged pork, which is in agreement with data on colour stability of aged beef (OÕKeefe & Hood, 1980–1981).
The authors wish to thank Jose´ A. Fernandez for animal breeding and Camilla Bjerg Kristensen and Jens Askov Jensen for excellent technical assistance and analysis. The work was part of the project SUSPORKQUAL (QLK52000-00162), financially supported by the European 5th Framework Programme. This paper does not necessarily reflect the EU commissionÕs views and in no way anticipates the commissionÕs future policy in this area. Acknowledgements are also given to the Ministry of Food, Agriculture and Fisheries, Denmark, for financial support.
5. Conclusions Ageing for 8 days in chill improved the blooming of pork loin from both Duroc- and Landrace-sired pigs, resulting in increased lightness, redness and yellowness. The blooming proceeded during all the first day of display, followed by a slow oxidation to MetMb during the subsequent 5 days, with slightly lower MetMb in aged meat. The increased content of MetMb had only minor effect on the colour resulting in a slightly, however, nonsignificant decrease in redness. The colour of pork loin from Duroc-sired pigs was darker and less yellow than that from Landrace-sired pigs due to higher pigment content and less blooming. More MetMb was formed during display of loin from Landrace-sired pigs compared with loin from Duroc-sired, although the levels were low in both crossbreeds. Considering that it is earlier found that texture and flavour improve upon ageing of pork, and that the present data show superior colour characteristics when fresh pork is aged for 8 days, it should be recommended to age pork, if it is intended to be marketed as high quality pork.
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