- Email: [email protected]
Examination of the effect of ageing and temperature at rigor on colour stability of lamb meat
Meat Science 95 (2013) 311–316
Contents lists available at SciVerse ScienceDirect
Meat Science journal homepage: www.elsevier.com/locate/meatsci
Examination of the effect of ageing and temperature at rigor on colour stability of lamb meat D.L. Hopkins a, b,⁎, T.A. Lamb b, M.J. Kerr b, R.J. van de Ven c, E.N. Ponnampalam d a
Sheep CRC, CJ Hawkins Homestead, University of New England, Armidale, NSW 2351, Australia NSW Department of Primary Industries, Centre for Red Meat and Sheep Development, PO Box 129, Cowra, NSW 2794, Australia NSW Department of Primary Industries, Orange Agricultural Institute, Forest Road, Orange, NSW 2800, Australia d Department of Primary Industries, 600 Sneydes Road, Werribee, VIC 3030, Australia b c
a r t i c l e
i n f o
Article history: Received 9 January 2013 Received in revised form 4 April 2013 Accepted 8 April 2013 Keywords: Lamb Colour Ageing Rigor temperature
a b s t r a c t A study of factors (ageing period, rigor temperature and vitamin E level) impacting on the colour stability of lamb m. longissimus thoracis et lumborum (LL) during 3 days of simulated retail display was undertaken. The LL were taken from 84 lambs from 3 slaughters. Slices of LL were measured fresh (24 h post-mortem) or after ageing for 5 days in vacuum packaging. The oxy/met ratio (630/580 nm), declined with display time, and increased with increasing temperature at pH 6.0. Redness (a*) values also declined with display time and a reduction in redness values was observed as LL pH at 24 h post-mortem and/or pH at 18 °C increased. There was no effect of ageing period or vitamin E level on the oxy/met ratio or a* values when the vitamin E level averaged 3.76 mg/kg LL. These results suggest that maximising vitamin E levels in lambs and achieving a moderate rate of pH decline will optimise colour stability irrespective of ageing period. Crown Copyright © 2013 Published by Elsevier Ltd. All rights reserved.
1. Introduction The colour of meat is an extremely important factor that influences consumer purchase decisions as it is deemed a visual measure of freshness and quality (Faustman & Cassens, 1990). Moreover, meat discoloration limits shelf life after retail preparation (Jeyamkondan, Jayas, & Holley, 2000) and this is a significant economic issue for the meat industry. Discoloration occurs over time as oxymyoglobin is converted to metmyoglobin (Faustman & Cassens, 1990; MacDougall, 1982) with consumers rejecting brown meat that has high levels of metmyoglobin (Hood & Riordan, 1973). Hunt (1980) reported that a change in meat colour due to the formation of metmyoglobin can be indicated by the ratio of reflectance for light wavelengths 630 and 580 nm (which will be called oxy/met ratio as a proxy). This measure has been applied in many studies (e.g. Khliji, van de Ven, Lamb, Lanza, & Hopkins, 2010). Some studies have reported that ageing meat in vacuum packs can increase the redness of lamb during the first few days of retail display (Moore & Young, 1991; Ponnampalam, Trout, Sinclair, Egan, & Leury, 2001) compared with non-aged meat. Recently it has been reported that ageing may also delay the onset of metmyoglobin formation as indicated by the oxy/met ratio (Ponnampalam, Butler, Burnett, ⁎ Corresponding author at: NSW Department of Primary Industries, Centre for Red Meat and Sheep Development, PO Box 129, Cowra, NSW 2794, Australia. Tel.: + 61 2 6349 9722; fax: + 61 2 6342 4543. E-mail address: [email protected] (D.L. Hopkins).
McDonagh, Jacobs, & Hopkins, 2012a) in meat that was aged for 4 weeks. It has been postulated that the antioxidant status (e.g. vitamin E concentration) of the meat may be one of the factors causing the difference in colour stability between fresh and vacuum pack aged meat (Ponnampalam et al., 2012a) through an interaction with lipid oxidation. Another factor that has been suggested to impact on colour stability is the temperature at rigor. Jacob and Thomson (2012) found a fast rate of temperature decline resulted in an initial reduction in colour stability that persisted during simulated retail display. However this study only examined aged meat. As part of the Cooperative Research Centre for Sheep Industry Innovation in Australia, each year 2000 progeny are being evaluated for a wide range of meat production and consumer-relevant traits (Hopkins, Jacob, Ball, & Pethick, 2009). This includes colour stability measured with a Hunter Lab Mini Scan (Model no. 45/0-L, aperture size of 25 mm) in lamb meat aged in a vacuum pack for 5 days (Jacob, Mortimer, Hopkins, Warner, & D'Antuono, 2011) then displayed over a period of 4 days. This evaluation will lead to the generation of genetic heritabilites and correlations for colour parameters (Mortimer et al., 2010). Given the potential difference between fresh and vacuum packed aged meat for colour stability it was considered important to confirm whether this is the case and understand whether factors such as rigor temperature were important. This would help in establishing whether the findings for aged meat could be related to fresh meat given the latter is an important commodity on the domestic market. A study was designed to explore colour stability in fresh and aged lamb meat.
0309-1740/$ – see front matter. Crown Copyright © 2013 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.meatsci.2013.04.041
312
D.L. Hopkins et al. / Meat Science 95 (2013) 311–316
2. Materials and methods 2.1. Animal background and slaughter The lambs studied in this work were bred as part of the Sheep CRC Information Nucleus programme at the Cowra and Trangie sites (van der Werf, Kinghorn, & Banks, 2010). Two groups of lambs were slaughtered from the Trangie site in December 2011 (Group 1; n = 27) and January 2012 (Group 2; n = 27) respectively, with the third group from the Cowra site in March 2012 (Group 3; n = 30). Prior to slaughter the lambs were grazed on lucerne based pastures and supplemented with either oats or lupins (Table 1). The feed on offer is shown in Table 1 with an estimate of the pasture composition (based on visual assessment) demonstrating that all lambs had access to green pasture during the pre-slaughter period. The management of the lambs in this study was under the animal ethics approval ORA 10/007 issued by the Orange Animal Ethics Committee of NSW Department of Primary Industries. At each site, lambs were slaughtered to achieve a target carcass weight of approximately 21–22 kg. Lambs were yarded the day before slaughter, held for 6 h, and then weighed and transported to a commercial abattoir, where they were held in lairage overnight and slaughtered the following day. The lambs were slaughtered at 6–9 months of age after head only stunning. All carcases were electrically stimulated pre-dressing with a mid-voltage unit (2000 mA with variable voltage to maintain a constant current, for 25 s at 15 pulses/s, 500 microsecond pulse width, unipolar waveform) (Toohey, Hopkins, Stanley, & Nielsen, 2008). Carcasses were chilled at a mean temperature of 4–5 °C over a 24 h period. All carcasses were trimmed according to AUS-MEAT specifications (Anonymous, 2005). 2.2. Measurements After the commencement of chilling, pH and temperature were measured in the left-hand m. longissimus thoracis et lumborum (LL) at the caudal end over the lumbar–sacral junction and then subsequently three times to ensure that the range in temperature from ~ 35 °C to less than 18 °C was covered. A section of subcutaneous fat and the m. gluteus medius were cut away to expose the LL and after measurement the area was resealed with the overlaying tissue. pH was measured using meters with temperature compensation (WP-80, TPS Pty Ltd., Brisbane, Australia) and a polypropylene spear-type gel electrode (Ionode IJ 44), calibrated at ambient temperature. pH of the LL at 24 h post-mortem (LL24pH) was measured at the 12th/13th rib site after calibrating the meter at chiller temperatures. At 24 h post-mortem the LL muscle was removed (Product identification number HAM 4910; Anonymous, 2005) from both loins. A 3 cm length of muscle was cut from the cranial end of both short loins, the subcutaneous fat removed, and then one sample was randomly allocated for measurement as fresh meat (1 day aged) and the other sample to 5 day ageing. Aged samples were vacuum sealed in gas impermeable plastic bags and held at 3–4 °C. Prior to measurement of colour a fresh surface was cut and for both ageing scenarios the samples were placed on black styrofoam trays (one per tray)
and overwrapped with 15 μ polyvinyl chloride (PVC) film. A sample of LL was also taken from fresh and aged loins at the commencement of the display period and kept frozen at − 20 °C for later measurement of vitamin E content as described by McMurray and Blanchflower (1979). Samples on trays were allowed to bloom for 30–40 min at a temperature of 3–4 °C before making initial colour measurements. Samples were then displayed for 3 days under fluorescent lights set at ~ 1000 lx. Each black tray contained one sample of meat only. A Hunter Lab Mini Scan(tm) XE Plus (Cat. no. 6352, model no. 45/0-L, reading head diameter of 37 mm) was used to measure light reflectance. The light source was set at “D65” with the 10° standard observer. The instrument was calibrated on a black glass then a white enamel tile following the manufacturer's specifications. At each reading the measurement was replicated after rotating the spectrophotometer 90° in the horizontal plane. Measurements for groups 1 and 2 were made at 6 h intervals during the first 24 h of display and daily thereafter. Group 3 measurements were the same as groups 1 and 2, with extra measurements taken every 0.5 h during the first 4 h of display. The oxy/met ratio, was calculated by dividing the percentage of light reflectance at wavelength 630 nm, by the percentage of light reflectance at wavelength 580 nm. 2.3. Statistical analysis The trend for pH with temperature decline across the carcases within each group was modelled using the approach described by van de Ven, Pearce, and Hopkins (in press). That is, the average trend in pH with temperature for each group was modelled using a natural cubic spline, in each case with 3 degrees of freedom, and individual carcases within a group were modelled as deviating linearly, at random, from the average trend. From this modelling, the temperature at pH 6 (Temp@pH6) and the pH at 18 °C (pH@Temp18) were estimated for each carcase (summarised in Table 2). These and the vitamin E concentration of the meat were used as covariates in the analysis of the colour parameters. The level of vitamin E was examined across slaughter groups and ageing periods (fixed effects) using the following model, where Carcase is a random term: VitE ¼ mean þ Slaughter group þ Ageing period þ Slaughter group : Ageing period þ Carcase þ error: Of the colour traits, only log transformed oxy/met ratio (630/ 580 nm), and redness (a*) values were analysed as these have been related to consumer acceptance (Khliji et al., 2010). Fixed effects in the model included, slaughter group, ageing, log of display hours, pH@Temp18, Temp@pH6, LL24pH and vitamin E concentration. The average trends with log of display hours were modelled using splines, which were allowed to differ across ageing periods and groups. Random effects included independent effects associated with each measurement time within each slaughter group × ageing period combination; random regressions about trend for each carcase; random regression
Table 1 Nutritional history of lambs from Cowra and Trangie leading up to slaughter. Date of pasture assessment
1/01/2012 1/02/2012 1/03/2012 1/11/2011 1/12/2011 1/01/2012
Site
Cowra Cowra Cowra Trangie Trangie Trangie
Pasture type
Lucerne Lucerne 65%, weeds 35% Lucerne 75%, weeds 25% Irrigated Lucerne & native pasture Irrigated Lucerne & native pasture Irrigated Lucerne & native pasture
Supplements kg/hd/d
Feed on offer (kg DM/ha)
Pasture composition (%)
Oats
Green
Dead
Total
Grasses %
Legumes %
Other %
kg
kg
kg
1330 1800 1500 1637 1552 2604
70 100 0 269 140 0
1400 1900 1500 1906 1692 2604
0 0 0 13 13 18
80 79 75 76 78 67
20 21 25 11 9 15
0.52 0.52 0.52 0.84 1.32 0.82
Lupins
0.18 0.18 0.18 0 0 0
D.L. Hopkins et al. / Meat Science 95 (2013) 311–316 Table 2 Means and standard error (s.e.) for hot carcase weight, hot GR, pH at 24 h, temperature at pH6.0 ([email protected]) and pH at 18° (pH@18 °C) according to slaughter group. Trait
Hot carcase weight (kg) Hot GR (mm) pH at 24 h [email protected] pH@18 °C
Group 1
Group 2
Group 3
Mean (s.e.)
Mean (s.e.)
Mean (s.e.)
26.1 14.5 5.52 18.8 5.98
25.7 17.3 5.72 28.1 5.77
23.1 15.7 5.77 27.9 5.73
(0.27) (0.56) (0.01) (0.29) (0.01)
(0.53) (0.84) (0.01) (1.12) (0.03)
(0.32) (0.64) (0.02) (1.18) (0.03)
about trend for loins within carcases; and finally random error. Models were fitted using the asreml package (Butler, 2009) in R (R Development Core Team, 2010). 3. Results As shown in Table 2 the carcases used in this study were heavier than the target weight, but there was variation in the rate of pH and temperature decline between groups. The average level of vitamin E mg/kg muscle (Fig. 1) differed across slaughter groups and across ageing periods within slaughter groups, with the ageing period effect differing significantly (P = 0.02) across slaughter groups. 3.1. Oxy/met ratio Display time (as logHours) and Temp@pH6 had a significant effect (P b 0.05) on the oxy/met ratio, with other fixed effects (slaughter
313
group, ageing period and vitamin E level) not significant. The spline deviations associated with the overall trend across time, and the separate spline deviations associated with each ageing category were not significant. The non-significance effect of overall ageing is a result of significant variation in results across slaughter groups and across ageing combinations within slaughter groups. The oxy/met ratio overall declines with time, and the ratio increases with increasing Temp@pH6. The predicted average log oxy/met ratio (averaged over the three groups, the two ageing periods, and across samples) over hours on display is shown in Fig. 2, along with 95% confidence intervals. This shows a rapid decline in the oxy/met ratio during the initial hours of display. For each unit increase in Temp@pH6 it is estimated that the log oxy/met ratio increases by 0.0055 (s.e. = 0.0021). On the original scale, this corresponds to an increase of approximately 0.03 units in oxy/met ratio for every unit increase in Temp@pH6 between 0 and 8 h, and an increase of approximately 0.02 units in oxy/met ratio for ever unit increase in Temp@pH6 between 8 and 72 h as shown in Fig. 3. It should be noted that pH@18 °C is equally significant as a covariate if Temp@pH6 is ignored. It was determined that there is an approximately 50% chance that the oxy/met ratio will be b 3.3 at 72 h. 3.2. Redness (a* values) Display time (as logHours), pH@18 °C and LL24pH had a significant effect (P b 0.05) on redness values with a reduction in values as display time increased. There was, conditional on the other factors being held fixed, a reduction in redness values by 1.9 (s.e. = 0.9) units for a unit increase in pH@18 °C and a 5.4 (s.e. = 2.1) unit reduction for every unit increase in LL24pH (Fig 3). In Fig 4, the
Slaughter group 3, Ageing period 5 days Slaughter group 3, Ageing period 1 day Slaughter group 2, Ageing period 5 days Slaughter group 2, Ageing period 1 day Slaughter group 1, Ageing period 5 days Slaughter group 1, Ageing period 1 day 2
3
4
5
6
Vitamin E (mg/kg muscle) Fig. 1. Box-plots for mean vitamin E levels (mg/kg muscle) for each slaughter group by ageing period combination.
Predicted oxy/met ratio
7 6 5 4 3 0
20
40
60
Hours on display Fig. 2. Predicted oxy/met ratios versus hours on display and the 95% confidence interval for predicted values (dashed lines).
314
D.L. Hopkins et al. / Meat Science 95 (2013) 311–316
7
0 hours
6 5
4 hours
8 hours
24 hours
4
Predicted oxy/met ratio
1 hours
48 hours
3
72 hours
15
20
25
30
35
40
Temperature (°C) at pH = 6 Fig. 3. Predicted oxy/met ratios versus temperature at pH 6 at selected measurement times during display (hours).
predicted redness (a*) values against display time are given at a LL24pH of 5.7, together with approximately 95% pointwise confidence intervals for each predicted value. The confidence interval is for the mean averaged over the two ageing combinations, and all possible slaughter groups and samples (carcases) from which these were sampled. 4. Discussion 4.1. Pattern of decline in colour parameters During the display period colour stability declined as reflected by the oxy/met ratio and redness values. This result is consistent with a large number of studies spanning many years (e.g. Ledward, Dickinson, Powell, & Shorthose, 1968; Khliji et al., 2010). Jacob et al. (2011) showed that in some cases the oxy/met ratio of LL samples (n = 3389) did not in fact exhibit an early decline, but rather increased between the first measurement and the second at 24 h and then declined. For this reason the frequency of measurements was increased during the first 24 h in the current study. This increase in measurement frequency was unable to find a result similar to that reported by Jacob et al. (2011). Any potential effect of delayed blooming (Jacob & Thomson, 2012) was avoided by using more measurement times, because there
was no reliance on a sole measurement at 24 h post-mortem to reflect early changes in colour parameters.
4.2. Effect of ageing on colour parameters In contrast to the results reported previously (Moore & Young, 1991; Ponnampalam et al., 2001), no evidence was found of an overall effect of ageing on redness values. It should be noted that there was a significant interaction with electrical stimulation in the study of Moore and Young (1991) where vacuum pack ageing of unstimulated meat resulted in improved display life assessed by subjective scorers. In the current study all carcases were stimulated so this may explain the contrasting results with these latest results being more relevant because most Australian lamb is now electrically stimulated (Hopkins, 2011). Since Moore and Young (1991) and Ponnampalam et al. (2001) did not measure the oxy/met ratio a direct comparison with the current study is not possible. Ponnampalam et al. (2012a) did however measure the oxy/met ratio and so their results are contrasted with ours. It is of some interest that Ponnampalam et al. (2012a) found a difference in the response of the oxy/met ratio and redness due to the diet fed to the lambs prior to slaughter. So the question arises how to reconcile the different outcomes?
Predicted redness (a*)
19
18
17
16
15 0
10
20
30
40
50
60
70
Hours on display Fig. 4. Predicted redness (a*) values versus hours on display (solid line) with the 95% confidence interval for predicted values (dashed lines).
D.L. Hopkins et al. / Meat Science 95 (2013) 311–316
It would seem that the suggested role of antioxidants such as vitamin E by Ponnampalam et al. (2012a) may provide an explanation. It has been clearly demonstrated that the colour stability of lamb can be improved by the addition of vitamin E to a diet (Wulf, Morgan, Sanders, Tatum, Smith, & Williams, 1995). Vitamin E is a lipid soluble compound that has been shown to protect lipids such as polyunsaturated fatty acids (PUFAs) and myoglobin from oxidation (Faustman, Chan, Schaefer, & Havens, 1998). Recently Ponnampalam, Burnett, Norng, Hopkins, Jacobs, and Dunshea (2012b) reported that if the vitamin E level was above 2.95 mg/kg muscle then lipid oxidation was prevented even if PUFA levels rose and Jose, Pethick, Gardner, and Jacob (2008) also suggested that a level of 3.0 mg/kg muscle will reduce the formation of metmyoglobin as indicated by the oxy/met ratio at 630/580 nm. Based on these findings and because in the current study the mean vitamin E level was 3.8 mg/kg muscle this would suggest that no effect of ageing was observed on indices of colour stability, namely redness and the oxy/met ratio, because of the vitamin E level. This was confirmed by the non-significance of vitamin E when fitted to the model for indices of colour stability and the use of three slaughter groups provides further confidence that this result is real as they represent a form of replication.
4.3. Impact of rigor temperature The impact of rigor temperature on the oxy/met ratio in the current study indicated that after a given time on display, samples that had experienced a higher rigor temperature tended to have a higher oxy/met ratio. The decline with time on display, at a given rigor temperature, was constant on the log oxy/met ratio scale for each rigor temperature. This effect was also evident for the redness of the LL. Conversely Rosenvold and Wiklund (2011) reported that at a very high pre-rigor temperature of 42 °C colour stability was lower, with no major impact at temperatures from 5 °C to 25 °C. It should be noted however that the latter study used excised sections of LL held in water baths until rigor mortis was attained. Thus the temperature profile would be very different to that of the carcases in the current study which are representative of commercial temperature declines. Our results agree with those of Jacob and Thomson (2012) who found that when lambs were chilled rapidly (less than 5 °C deep muscle temperature within 3 h post-mortem) and thus experience a low [email protected] or a high pH@18 °C colour stability was reduced. The pH@18 °C in the current study was at the ‘hot’ end of the temperature decline compared to the study of Jacob and Thomson (2012). However, the effect on colour stability was in the same direction inferring that the effect is not isolated to meat chilled rapidly. Our results were consistent also with the findings of Warner et al. (2010) in meat aged for 5 days and then displayed for 3 days under the same regime as used for our ageing treatment. A high pH in the LL at 24 h reduced redness an effect reported extensively in fresh lamb meat (e.g. Hopkins & Fogarty, 1998; Warner et al., 2010). High pH at 24 h also reduced redness in aged meat held under simulated retail display. It has been reported that breeds with higher ultimate pH in the loin have the lowest redness values (Warner, Ponnampalam, Kearney, Hopkins, & Jacob, 2007).
5. Conclusions The results from this study suggest that no benefit is to be gained from ageing meat in terms of subsequent colour stability. It is postulated that this is driven by vitamin E levels and that at lower levels of this antioxidant this might not be the case. Clearly avoiding a fast rate of rigor onset will provide the best opportunity for maximising colour stability as will a reduction in the final pH of meat which also has benefits for other traits like tenderness.
315
Acknowledgements The CRC for Sheep Industry Innovation is supported by the Australian Government's Cooperative Research Centre's Program, Australian Wool Innovation Ltd. and Meat & Livestock Australia. Staff and resources for this work were provided by NSW Department of Primary Industries (G Refshauge, S Langfield, K Warren, K Bailes and T Bird-Gardiner). The staff of the cooperating abattoir are thanked for their assistance during sample collection.
References Anonymous, (2005). Handbook of Australian meat (7th ed.). AUS-MEAT Limited. Butler, D. (2009). asreml: asreml() fits the linear mixed model. R package version 3.00. Development Core Team, R. (2010). R: A language and environment for statistical computing. R foundation for statistical computing Vienna, Austria. ISBN 3-900051-07-0, URL, http://www.R-project.org/ Faustman, C., & Cassens, R. G. (1990). The biochemical basis for discoloration in fresh meat: A review. Journal of Muscle Foods, 1, 217–243. Faustman, C., Chan, W. K. M., Schaefer, D. M., & Havens, A. (1998). Beef colour update. The role of vitamin E. Journal of Animal Science, 76, 1019–1026. Hood, D. E., & Riordan, E. B. (1973). Discolouration in pre-packaged beef measured by reflectance spectrophotometry and shopper discrimination. Journal of Food Technology, 8, 333–343. Hopkins, D. L. (2011). Processing technology changes in the Australian sheep meat industry: An overview. Animal Production Science, 51, 399–405. Hopkins, D. L., & Fogarty, N. M. (1998). Diverse lamb genotypes—2. Meat pH, colour and tenderness. Meat Science, 49, 477–488. Hopkins, D. L., Jacob, R. H., Ball, A. J., & Pethick, D. W. (2009). The CRC for sheep industry innovation—Measurement of new and novel meat traits. Proceedings of the 55th International Congress of Meat Science and Technology. Session 9 (pp. 23–26) (Copenhagen, Denmark). Hunt, M. C. (1980). Meat colour measurements. Proceedings Reciprocal Meat Conference, 33, 41. Jacob, R. H., Mortimer, S. I., Hopkins, D. L., Warner, R. D., & D'Antuono, M. F. (2011). Opportunities for genetic management of the retail colour stability of lamb meat. Proceedings of the Association for the Advancement of Animal Breeding and Genetics, 19, 446–449. Jacob, R. H., & Thomson, K. L. (2012). The importance of chill rate when characterizing colour change of lamb meat during retail display. Meat Science, 90, 478–484. Jeyamkondan, W., Jayas, D. S., & Holley, R. A. (2000). Review of centralized packaging systems for distribution of retail-ready meat. Journal of Food Protection, 63, 796–804. Jose, C. G., Pethick, D. W., Gardner, G. E., & Jacob, R. H. (2008). The colour stability of aged lamb benefits from vitamin E supplementation. Proceedings of the 54th International Congress of Meat Science and Technology, Session 7B (pp. 1–3) (Cape Town, South Africa). Khliji, S., van de Ven, R., Lamb, T. A., Lanza, M., & Hopkins, D. L. (2010). Relationship between consumer ranking of lamb colour and objective measures of colour. Meat Science, 85, 224–229. Ledward, D. A., Dickinson, R. F., Powell, V. H., & Shorthose, W. R. (1968). The colour and colour stability of beef longissimus dorsi and semimembranosus muscles after effective electrical stimulation. Meat Science, 16, 245–265. MacDougall, D. B. (1982). Changes in the colour and opacity of meat. Food Chemistry, 9, 75–88. McMurray, C. H., & Blanchflower, W. J. (1979). Application of a high-performance liquid chromatographic fluorescence method for the rapid determination of α-tocopherol in the plasma of cattle and pigs and its comparison with direct fluorescence and high-performance liquid chromatography—Ultraviolet detection methods. Journal of Chromatography. A, 178, 525–531. Moore, V. J., & Young, O. A. (1991). The effects of electrical stimulation, thawing, ageing and packaging on the colour and display life of lamb chops. Meat Science, 30, 131–145. Mortimer, S. I., van der Werf, J. H. J., Jacob, R. H., Pethick, D. W., Pearce, K. L., Warner, R. D., Geesink, G. H., Hocking Edwards, J. E., Gardner, G. E., Ponnampalam, E. N., Kitessa, S. M., Ball, A. J., & Hopkins, D. L. (2010). Preliminary estimates of genetic parameters for carcass and meat quality traits in Australian sheep. Animal Production Science, 50, 1135–1144. Ponnampalam, E. N., Burnett, V. F., Norng, S., Hopkins, D. L., Jacobs, J. L., & Dunshea, F. R. (2012a). Is nutritional enrichment of omega-3 fatty acid in meat a concern for quality deterioration of lipid oxidation? Proceedings of the 58th International Congress of Meat Science and Technology, J-98 (pp. 1–4) (Montréal, Canada). Ponnampalam, E. N., Butler, K. L., Burnett, V. F., McDonagh, M. B., Jacobs, J. L., & Hopkins, D. L. (2012b). Change in color stability of lamb: Fresh vs. aged meat. Proceedings of the 58th International Congress of Meat Science and Technology, G-35 (pp. 1–4) (Montréal, Canada). Ponnampalam, E. N., Trout, G. R., Sinclair, A. J., Egan, A. R., & Leury, B. J. (2001). Comparison of the color stability and lipid oxidative stability of fresh and vacuum packaged lamb muscle containing elevated omega-3 and omega-6 fatty acid levels from dietary manipulation. Meat Science, 58, 151–161. Rosenvold, K., & Wiklund, E. (2011). Retail colour display life of chilled lamb as affected by processing conditions and storage temperature. Meat Science, 88, 354–360.
316
D.L. Hopkins et al. / Meat Science 95 (2013) 311–316
Toohey, E. S., Hopkins, D. L., Stanley, D. F., & Nielsen, S. G. (2008). The impact of new generation pre-dressing medium-voltage electrical stimulation on tenderness and colour stability in lamb meat. Meat Science, 79, 683–691. van de Ven, R. J., Pearce, K. L., & Hopkins, D. L. (in press). Post-mortem modelling of pH and temperature in related lamb carcases. Meat Science (in press, http://dx.doi.org/ 10.1016/j.meatsci.2012.10.001) van der Werf, J. H. J., Kinghorn, B. P., & Banks, R. G. (2010). Design and role of an information nucleus in sheep breeding programs. Animal Production Science, 50, 998–1003. Warner, R. D., Jacob, R., Hocking Edwards, J., McDonagh, M., Pearce, K., Geesink, G., Kearney, G., Allingham, P., Pethick, D. W., & Hopkins, D. L. (2010). Quality
of lamb from the Information Nucleus Flock. Animal Production Science, 50, 1123–1134. Warner, R. D., Ponnampalam, E. N., Kearney, G. A., Hopkins, D. L., & Jacob, R. H. (2007). Genotype and age at slaughter influence the retail shelf-life of the loin and knuckle from sheep carcasses. Australian Journal of Experimental Agriculture, 47, 1190–1200. Wulf, D. M., Morgan, J. B., Sanders, S. K., Tatum, J. D., Smith, G. C., & Williams, S. (1995). Effect of dietary supplementation of vitamin E on storage and caselife properties of lamb retail cuts. Journal of Animal Science, 73, 399–405.
Contents lists available at SciVerse ScienceDirect
Meat Science journal homepage: www.elsevier.com/locate/meatsci
Examination of the effect of ageing and temperature at rigor on colour stability of lamb meat D.L. Hopkins a, b,⁎, T.A. Lamb b, M.J. Kerr b, R.J. van de Ven c, E.N. Ponnampalam d a
Sheep CRC, CJ Hawkins Homestead, University of New England, Armidale, NSW 2351, Australia NSW Department of Primary Industries, Centre for Red Meat and Sheep Development, PO Box 129, Cowra, NSW 2794, Australia NSW Department of Primary Industries, Orange Agricultural Institute, Forest Road, Orange, NSW 2800, Australia d Department of Primary Industries, 600 Sneydes Road, Werribee, VIC 3030, Australia b c
a r t i c l e
i n f o
Article history: Received 9 January 2013 Received in revised form 4 April 2013 Accepted 8 April 2013 Keywords: Lamb Colour Ageing Rigor temperature
a b s t r a c t A study of factors (ageing period, rigor temperature and vitamin E level) impacting on the colour stability of lamb m. longissimus thoracis et lumborum (LL) during 3 days of simulated retail display was undertaken. The LL were taken from 84 lambs from 3 slaughters. Slices of LL were measured fresh (24 h post-mortem) or after ageing for 5 days in vacuum packaging. The oxy/met ratio (630/580 nm), declined with display time, and increased with increasing temperature at pH 6.0. Redness (a*) values also declined with display time and a reduction in redness values was observed as LL pH at 24 h post-mortem and/or pH at 18 °C increased. There was no effect of ageing period or vitamin E level on the oxy/met ratio or a* values when the vitamin E level averaged 3.76 mg/kg LL. These results suggest that maximising vitamin E levels in lambs and achieving a moderate rate of pH decline will optimise colour stability irrespective of ageing period. Crown Copyright © 2013 Published by Elsevier Ltd. All rights reserved.
1. Introduction The colour of meat is an extremely important factor that influences consumer purchase decisions as it is deemed a visual measure of freshness and quality (Faustman & Cassens, 1990). Moreover, meat discoloration limits shelf life after retail preparation (Jeyamkondan, Jayas, & Holley, 2000) and this is a significant economic issue for the meat industry. Discoloration occurs over time as oxymyoglobin is converted to metmyoglobin (Faustman & Cassens, 1990; MacDougall, 1982) with consumers rejecting brown meat that has high levels of metmyoglobin (Hood & Riordan, 1973). Hunt (1980) reported that a change in meat colour due to the formation of metmyoglobin can be indicated by the ratio of reflectance for light wavelengths 630 and 580 nm (which will be called oxy/met ratio as a proxy). This measure has been applied in many studies (e.g. Khliji, van de Ven, Lamb, Lanza, & Hopkins, 2010). Some studies have reported that ageing meat in vacuum packs can increase the redness of lamb during the first few days of retail display (Moore & Young, 1991; Ponnampalam, Trout, Sinclair, Egan, & Leury, 2001) compared with non-aged meat. Recently it has been reported that ageing may also delay the onset of metmyoglobin formation as indicated by the oxy/met ratio (Ponnampalam, Butler, Burnett, ⁎ Corresponding author at: NSW Department of Primary Industries, Centre for Red Meat and Sheep Development, PO Box 129, Cowra, NSW 2794, Australia. Tel.: + 61 2 6349 9722; fax: + 61 2 6342 4543. E-mail address: [email protected] (D.L. Hopkins).
McDonagh, Jacobs, & Hopkins, 2012a) in meat that was aged for 4 weeks. It has been postulated that the antioxidant status (e.g. vitamin E concentration) of the meat may be one of the factors causing the difference in colour stability between fresh and vacuum pack aged meat (Ponnampalam et al., 2012a) through an interaction with lipid oxidation. Another factor that has been suggested to impact on colour stability is the temperature at rigor. Jacob and Thomson (2012) found a fast rate of temperature decline resulted in an initial reduction in colour stability that persisted during simulated retail display. However this study only examined aged meat. As part of the Cooperative Research Centre for Sheep Industry Innovation in Australia, each year 2000 progeny are being evaluated for a wide range of meat production and consumer-relevant traits (Hopkins, Jacob, Ball, & Pethick, 2009). This includes colour stability measured with a Hunter Lab Mini Scan (Model no. 45/0-L, aperture size of 25 mm) in lamb meat aged in a vacuum pack for 5 days (Jacob, Mortimer, Hopkins, Warner, & D'Antuono, 2011) then displayed over a period of 4 days. This evaluation will lead to the generation of genetic heritabilites and correlations for colour parameters (Mortimer et al., 2010). Given the potential difference between fresh and vacuum packed aged meat for colour stability it was considered important to confirm whether this is the case and understand whether factors such as rigor temperature were important. This would help in establishing whether the findings for aged meat could be related to fresh meat given the latter is an important commodity on the domestic market. A study was designed to explore colour stability in fresh and aged lamb meat.
0309-1740/$ – see front matter. Crown Copyright © 2013 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.meatsci.2013.04.041
312
D.L. Hopkins et al. / Meat Science 95 (2013) 311–316
2. Materials and methods 2.1. Animal background and slaughter The lambs studied in this work were bred as part of the Sheep CRC Information Nucleus programme at the Cowra and Trangie sites (van der Werf, Kinghorn, & Banks, 2010). Two groups of lambs were slaughtered from the Trangie site in December 2011 (Group 1; n = 27) and January 2012 (Group 2; n = 27) respectively, with the third group from the Cowra site in March 2012 (Group 3; n = 30). Prior to slaughter the lambs were grazed on lucerne based pastures and supplemented with either oats or lupins (Table 1). The feed on offer is shown in Table 1 with an estimate of the pasture composition (based on visual assessment) demonstrating that all lambs had access to green pasture during the pre-slaughter period. The management of the lambs in this study was under the animal ethics approval ORA 10/007 issued by the Orange Animal Ethics Committee of NSW Department of Primary Industries. At each site, lambs were slaughtered to achieve a target carcass weight of approximately 21–22 kg. Lambs were yarded the day before slaughter, held for 6 h, and then weighed and transported to a commercial abattoir, where they were held in lairage overnight and slaughtered the following day. The lambs were slaughtered at 6–9 months of age after head only stunning. All carcases were electrically stimulated pre-dressing with a mid-voltage unit (2000 mA with variable voltage to maintain a constant current, for 25 s at 15 pulses/s, 500 microsecond pulse width, unipolar waveform) (Toohey, Hopkins, Stanley, & Nielsen, 2008). Carcasses were chilled at a mean temperature of 4–5 °C over a 24 h period. All carcasses were trimmed according to AUS-MEAT specifications (Anonymous, 2005). 2.2. Measurements After the commencement of chilling, pH and temperature were measured in the left-hand m. longissimus thoracis et lumborum (LL) at the caudal end over the lumbar–sacral junction and then subsequently three times to ensure that the range in temperature from ~ 35 °C to less than 18 °C was covered. A section of subcutaneous fat and the m. gluteus medius were cut away to expose the LL and after measurement the area was resealed with the overlaying tissue. pH was measured using meters with temperature compensation (WP-80, TPS Pty Ltd., Brisbane, Australia) and a polypropylene spear-type gel electrode (Ionode IJ 44), calibrated at ambient temperature. pH of the LL at 24 h post-mortem (LL24pH) was measured at the 12th/13th rib site after calibrating the meter at chiller temperatures. At 24 h post-mortem the LL muscle was removed (Product identification number HAM 4910; Anonymous, 2005) from both loins. A 3 cm length of muscle was cut from the cranial end of both short loins, the subcutaneous fat removed, and then one sample was randomly allocated for measurement as fresh meat (1 day aged) and the other sample to 5 day ageing. Aged samples were vacuum sealed in gas impermeable plastic bags and held at 3–4 °C. Prior to measurement of colour a fresh surface was cut and for both ageing scenarios the samples were placed on black styrofoam trays (one per tray)
and overwrapped with 15 μ polyvinyl chloride (PVC) film. A sample of LL was also taken from fresh and aged loins at the commencement of the display period and kept frozen at − 20 °C for later measurement of vitamin E content as described by McMurray and Blanchflower (1979). Samples on trays were allowed to bloom for 30–40 min at a temperature of 3–4 °C before making initial colour measurements. Samples were then displayed for 3 days under fluorescent lights set at ~ 1000 lx. Each black tray contained one sample of meat only. A Hunter Lab Mini Scan(tm) XE Plus (Cat. no. 6352, model no. 45/0-L, reading head diameter of 37 mm) was used to measure light reflectance. The light source was set at “D65” with the 10° standard observer. The instrument was calibrated on a black glass then a white enamel tile following the manufacturer's specifications. At each reading the measurement was replicated after rotating the spectrophotometer 90° in the horizontal plane. Measurements for groups 1 and 2 were made at 6 h intervals during the first 24 h of display and daily thereafter. Group 3 measurements were the same as groups 1 and 2, with extra measurements taken every 0.5 h during the first 4 h of display. The oxy/met ratio, was calculated by dividing the percentage of light reflectance at wavelength 630 nm, by the percentage of light reflectance at wavelength 580 nm. 2.3. Statistical analysis The trend for pH with temperature decline across the carcases within each group was modelled using the approach described by van de Ven, Pearce, and Hopkins (in press). That is, the average trend in pH with temperature for each group was modelled using a natural cubic spline, in each case with 3 degrees of freedom, and individual carcases within a group were modelled as deviating linearly, at random, from the average trend. From this modelling, the temperature at pH 6 (Temp@pH6) and the pH at 18 °C (pH@Temp18) were estimated for each carcase (summarised in Table 2). These and the vitamin E concentration of the meat were used as covariates in the analysis of the colour parameters. The level of vitamin E was examined across slaughter groups and ageing periods (fixed effects) using the following model, where Carcase is a random term: VitE ¼ mean þ Slaughter group þ Ageing period þ Slaughter group : Ageing period þ Carcase þ error: Of the colour traits, only log transformed oxy/met ratio (630/ 580 nm), and redness (a*) values were analysed as these have been related to consumer acceptance (Khliji et al., 2010). Fixed effects in the model included, slaughter group, ageing, log of display hours, pH@Temp18, Temp@pH6, LL24pH and vitamin E concentration. The average trends with log of display hours were modelled using splines, which were allowed to differ across ageing periods and groups. Random effects included independent effects associated with each measurement time within each slaughter group × ageing period combination; random regressions about trend for each carcase; random regression
Table 1 Nutritional history of lambs from Cowra and Trangie leading up to slaughter. Date of pasture assessment
1/01/2012 1/02/2012 1/03/2012 1/11/2011 1/12/2011 1/01/2012
Site
Cowra Cowra Cowra Trangie Trangie Trangie
Pasture type
Lucerne Lucerne 65%, weeds 35% Lucerne 75%, weeds 25% Irrigated Lucerne & native pasture Irrigated Lucerne & native pasture Irrigated Lucerne & native pasture
Supplements kg/hd/d
Feed on offer (kg DM/ha)
Pasture composition (%)
Oats
Green
Dead
Total
Grasses %
Legumes %
Other %
kg
kg
kg
1330 1800 1500 1637 1552 2604
70 100 0 269 140 0
1400 1900 1500 1906 1692 2604
0 0 0 13 13 18
80 79 75 76 78 67
20 21 25 11 9 15
0.52 0.52 0.52 0.84 1.32 0.82
Lupins
0.18 0.18 0.18 0 0 0
D.L. Hopkins et al. / Meat Science 95 (2013) 311–316 Table 2 Means and standard error (s.e.) for hot carcase weight, hot GR, pH at 24 h, temperature at pH6.0 ([email protected]) and pH at 18° (pH@18 °C) according to slaughter group. Trait
Hot carcase weight (kg) Hot GR (mm) pH at 24 h [email protected] pH@18 °C
Group 1
Group 2
Group 3
Mean (s.e.)
Mean (s.e.)
Mean (s.e.)
26.1 14.5 5.52 18.8 5.98
25.7 17.3 5.72 28.1 5.77
23.1 15.7 5.77 27.9 5.73
(0.27) (0.56) (0.01) (0.29) (0.01)
(0.53) (0.84) (0.01) (1.12) (0.03)
(0.32) (0.64) (0.02) (1.18) (0.03)
about trend for loins within carcases; and finally random error. Models were fitted using the asreml package (Butler, 2009) in R (R Development Core Team, 2010). 3. Results As shown in Table 2 the carcases used in this study were heavier than the target weight, but there was variation in the rate of pH and temperature decline between groups. The average level of vitamin E mg/kg muscle (Fig. 1) differed across slaughter groups and across ageing periods within slaughter groups, with the ageing period effect differing significantly (P = 0.02) across slaughter groups. 3.1. Oxy/met ratio Display time (as logHours) and Temp@pH6 had a significant effect (P b 0.05) on the oxy/met ratio, with other fixed effects (slaughter
313
group, ageing period and vitamin E level) not significant. The spline deviations associated with the overall trend across time, and the separate spline deviations associated with each ageing category were not significant. The non-significance effect of overall ageing is a result of significant variation in results across slaughter groups and across ageing combinations within slaughter groups. The oxy/met ratio overall declines with time, and the ratio increases with increasing Temp@pH6. The predicted average log oxy/met ratio (averaged over the three groups, the two ageing periods, and across samples) over hours on display is shown in Fig. 2, along with 95% confidence intervals. This shows a rapid decline in the oxy/met ratio during the initial hours of display. For each unit increase in Temp@pH6 it is estimated that the log oxy/met ratio increases by 0.0055 (s.e. = 0.0021). On the original scale, this corresponds to an increase of approximately 0.03 units in oxy/met ratio for every unit increase in Temp@pH6 between 0 and 8 h, and an increase of approximately 0.02 units in oxy/met ratio for ever unit increase in Temp@pH6 between 8 and 72 h as shown in Fig. 3. It should be noted that pH@18 °C is equally significant as a covariate if Temp@pH6 is ignored. It was determined that there is an approximately 50% chance that the oxy/met ratio will be b 3.3 at 72 h. 3.2. Redness (a* values) Display time (as logHours), pH@18 °C and LL24pH had a significant effect (P b 0.05) on redness values with a reduction in values as display time increased. There was, conditional on the other factors being held fixed, a reduction in redness values by 1.9 (s.e. = 0.9) units for a unit increase in pH@18 °C and a 5.4 (s.e. = 2.1) unit reduction for every unit increase in LL24pH (Fig 3). In Fig 4, the
Slaughter group 3, Ageing period 5 days Slaughter group 3, Ageing period 1 day Slaughter group 2, Ageing period 5 days Slaughter group 2, Ageing period 1 day Slaughter group 1, Ageing period 5 days Slaughter group 1, Ageing period 1 day 2
3
4
5
6
Vitamin E (mg/kg muscle) Fig. 1. Box-plots for mean vitamin E levels (mg/kg muscle) for each slaughter group by ageing period combination.
Predicted oxy/met ratio
7 6 5 4 3 0
20
40
60
Hours on display Fig. 2. Predicted oxy/met ratios versus hours on display and the 95% confidence interval for predicted values (dashed lines).
314
D.L. Hopkins et al. / Meat Science 95 (2013) 311–316
7
0 hours
6 5
4 hours
8 hours
24 hours
4
Predicted oxy/met ratio
1 hours
48 hours
3
72 hours
15
20
25
30
35
40
Temperature (°C) at pH = 6 Fig. 3. Predicted oxy/met ratios versus temperature at pH 6 at selected measurement times during display (hours).
predicted redness (a*) values against display time are given at a LL24pH of 5.7, together with approximately 95% pointwise confidence intervals for each predicted value. The confidence interval is for the mean averaged over the two ageing combinations, and all possible slaughter groups and samples (carcases) from which these were sampled. 4. Discussion 4.1. Pattern of decline in colour parameters During the display period colour stability declined as reflected by the oxy/met ratio and redness values. This result is consistent with a large number of studies spanning many years (e.g. Ledward, Dickinson, Powell, & Shorthose, 1968; Khliji et al., 2010). Jacob et al. (2011) showed that in some cases the oxy/met ratio of LL samples (n = 3389) did not in fact exhibit an early decline, but rather increased between the first measurement and the second at 24 h and then declined. For this reason the frequency of measurements was increased during the first 24 h in the current study. This increase in measurement frequency was unable to find a result similar to that reported by Jacob et al. (2011). Any potential effect of delayed blooming (Jacob & Thomson, 2012) was avoided by using more measurement times, because there
was no reliance on a sole measurement at 24 h post-mortem to reflect early changes in colour parameters.
4.2. Effect of ageing on colour parameters In contrast to the results reported previously (Moore & Young, 1991; Ponnampalam et al., 2001), no evidence was found of an overall effect of ageing on redness values. It should be noted that there was a significant interaction with electrical stimulation in the study of Moore and Young (1991) where vacuum pack ageing of unstimulated meat resulted in improved display life assessed by subjective scorers. In the current study all carcases were stimulated so this may explain the contrasting results with these latest results being more relevant because most Australian lamb is now electrically stimulated (Hopkins, 2011). Since Moore and Young (1991) and Ponnampalam et al. (2001) did not measure the oxy/met ratio a direct comparison with the current study is not possible. Ponnampalam et al. (2012a) did however measure the oxy/met ratio and so their results are contrasted with ours. It is of some interest that Ponnampalam et al. (2012a) found a difference in the response of the oxy/met ratio and redness due to the diet fed to the lambs prior to slaughter. So the question arises how to reconcile the different outcomes?
Predicted redness (a*)
19
18
17
16
15 0
10
20
30
40
50
60
70
Hours on display Fig. 4. Predicted redness (a*) values versus hours on display (solid line) with the 95% confidence interval for predicted values (dashed lines).
D.L. Hopkins et al. / Meat Science 95 (2013) 311–316
It would seem that the suggested role of antioxidants such as vitamin E by Ponnampalam et al. (2012a) may provide an explanation. It has been clearly demonstrated that the colour stability of lamb can be improved by the addition of vitamin E to a diet (Wulf, Morgan, Sanders, Tatum, Smith, & Williams, 1995). Vitamin E is a lipid soluble compound that has been shown to protect lipids such as polyunsaturated fatty acids (PUFAs) and myoglobin from oxidation (Faustman, Chan, Schaefer, & Havens, 1998). Recently Ponnampalam, Burnett, Norng, Hopkins, Jacobs, and Dunshea (2012b) reported that if the vitamin E level was above 2.95 mg/kg muscle then lipid oxidation was prevented even if PUFA levels rose and Jose, Pethick, Gardner, and Jacob (2008) also suggested that a level of 3.0 mg/kg muscle will reduce the formation of metmyoglobin as indicated by the oxy/met ratio at 630/580 nm. Based on these findings and because in the current study the mean vitamin E level was 3.8 mg/kg muscle this would suggest that no effect of ageing was observed on indices of colour stability, namely redness and the oxy/met ratio, because of the vitamin E level. This was confirmed by the non-significance of vitamin E when fitted to the model for indices of colour stability and the use of three slaughter groups provides further confidence that this result is real as they represent a form of replication.
4.3. Impact of rigor temperature The impact of rigor temperature on the oxy/met ratio in the current study indicated that after a given time on display, samples that had experienced a higher rigor temperature tended to have a higher oxy/met ratio. The decline with time on display, at a given rigor temperature, was constant on the log oxy/met ratio scale for each rigor temperature. This effect was also evident for the redness of the LL. Conversely Rosenvold and Wiklund (2011) reported that at a very high pre-rigor temperature of 42 °C colour stability was lower, with no major impact at temperatures from 5 °C to 25 °C. It should be noted however that the latter study used excised sections of LL held in water baths until rigor mortis was attained. Thus the temperature profile would be very different to that of the carcases in the current study which are representative of commercial temperature declines. Our results agree with those of Jacob and Thomson (2012) who found that when lambs were chilled rapidly (less than 5 °C deep muscle temperature within 3 h post-mortem) and thus experience a low [email protected] or a high pH@18 °C colour stability was reduced. The pH@18 °C in the current study was at the ‘hot’ end of the temperature decline compared to the study of Jacob and Thomson (2012). However, the effect on colour stability was in the same direction inferring that the effect is not isolated to meat chilled rapidly. Our results were consistent also with the findings of Warner et al. (2010) in meat aged for 5 days and then displayed for 3 days under the same regime as used for our ageing treatment. A high pH in the LL at 24 h reduced redness an effect reported extensively in fresh lamb meat (e.g. Hopkins & Fogarty, 1998; Warner et al., 2010). High pH at 24 h also reduced redness in aged meat held under simulated retail display. It has been reported that breeds with higher ultimate pH in the loin have the lowest redness values (Warner, Ponnampalam, Kearney, Hopkins, & Jacob, 2007).
5. Conclusions The results from this study suggest that no benefit is to be gained from ageing meat in terms of subsequent colour stability. It is postulated that this is driven by vitamin E levels and that at lower levels of this antioxidant this might not be the case. Clearly avoiding a fast rate of rigor onset will provide the best opportunity for maximising colour stability as will a reduction in the final pH of meat which also has benefits for other traits like tenderness.
315
Acknowledgements The CRC for Sheep Industry Innovation is supported by the Australian Government's Cooperative Research Centre's Program, Australian Wool Innovation Ltd. and Meat & Livestock Australia. Staff and resources for this work were provided by NSW Department of Primary Industries (G Refshauge, S Langfield, K Warren, K Bailes and T Bird-Gardiner). The staff of the cooperating abattoir are thanked for their assistance during sample collection.
References Anonymous, (2005). Handbook of Australian meat (7th ed.). AUS-MEAT Limited. Butler, D. (2009). asreml: asreml() fits the linear mixed model. R package version 3.00. Development Core Team, R. (2010). R: A language and environment for statistical computing. R foundation for statistical computing Vienna, Austria. ISBN 3-900051-07-0, URL, http://www.R-project.org/ Faustman, C., & Cassens, R. G. (1990). The biochemical basis for discoloration in fresh meat: A review. Journal of Muscle Foods, 1, 217–243. Faustman, C., Chan, W. K. M., Schaefer, D. M., & Havens, A. (1998). Beef colour update. The role of vitamin E. Journal of Animal Science, 76, 1019–1026. Hood, D. E., & Riordan, E. B. (1973). Discolouration in pre-packaged beef measured by reflectance spectrophotometry and shopper discrimination. Journal of Food Technology, 8, 333–343. Hopkins, D. L. (2011). Processing technology changes in the Australian sheep meat industry: An overview. Animal Production Science, 51, 399–405. Hopkins, D. L., & Fogarty, N. M. (1998). Diverse lamb genotypes—2. Meat pH, colour and tenderness. Meat Science, 49, 477–488. Hopkins, D. L., Jacob, R. H., Ball, A. J., & Pethick, D. W. (2009). The CRC for sheep industry innovation—Measurement of new and novel meat traits. Proceedings of the 55th International Congress of Meat Science and Technology. Session 9 (pp. 23–26) (Copenhagen, Denmark). Hunt, M. C. (1980). Meat colour measurements. Proceedings Reciprocal Meat Conference, 33, 41. Jacob, R. H., Mortimer, S. I., Hopkins, D. L., Warner, R. D., & D'Antuono, M. F. (2011). Opportunities for genetic management of the retail colour stability of lamb meat. Proceedings of the Association for the Advancement of Animal Breeding and Genetics, 19, 446–449. Jacob, R. H., & Thomson, K. L. (2012). The importance of chill rate when characterizing colour change of lamb meat during retail display. Meat Science, 90, 478–484. Jeyamkondan, W., Jayas, D. S., & Holley, R. A. (2000). Review of centralized packaging systems for distribution of retail-ready meat. Journal of Food Protection, 63, 796–804. Jose, C. G., Pethick, D. W., Gardner, G. E., & Jacob, R. H. (2008). The colour stability of aged lamb benefits from vitamin E supplementation. Proceedings of the 54th International Congress of Meat Science and Technology, Session 7B (pp. 1–3) (Cape Town, South Africa). Khliji, S., van de Ven, R., Lamb, T. A., Lanza, M., & Hopkins, D. L. (2010). Relationship between consumer ranking of lamb colour and objective measures of colour. Meat Science, 85, 224–229. Ledward, D. A., Dickinson, R. F., Powell, V. H., & Shorthose, W. R. (1968). The colour and colour stability of beef longissimus dorsi and semimembranosus muscles after effective electrical stimulation. Meat Science, 16, 245–265. MacDougall, D. B. (1982). Changes in the colour and opacity of meat. Food Chemistry, 9, 75–88. McMurray, C. H., & Blanchflower, W. J. (1979). Application of a high-performance liquid chromatographic fluorescence method for the rapid determination of α-tocopherol in the plasma of cattle and pigs and its comparison with direct fluorescence and high-performance liquid chromatography—Ultraviolet detection methods. Journal of Chromatography. A, 178, 525–531. Moore, V. J., & Young, O. A. (1991). The effects of electrical stimulation, thawing, ageing and packaging on the colour and display life of lamb chops. Meat Science, 30, 131–145. Mortimer, S. I., van der Werf, J. H. J., Jacob, R. H., Pethick, D. W., Pearce, K. L., Warner, R. D., Geesink, G. H., Hocking Edwards, J. E., Gardner, G. E., Ponnampalam, E. N., Kitessa, S. M., Ball, A. J., & Hopkins, D. L. (2010). Preliminary estimates of genetic parameters for carcass and meat quality traits in Australian sheep. Animal Production Science, 50, 1135–1144. Ponnampalam, E. N., Burnett, V. F., Norng, S., Hopkins, D. L., Jacobs, J. L., & Dunshea, F. R. (2012a). Is nutritional enrichment of omega-3 fatty acid in meat a concern for quality deterioration of lipid oxidation? Proceedings of the 58th International Congress of Meat Science and Technology, J-98 (pp. 1–4) (Montréal, Canada). Ponnampalam, E. N., Butler, K. L., Burnett, V. F., McDonagh, M. B., Jacobs, J. L., & Hopkins, D. L. (2012b). Change in color stability of lamb: Fresh vs. aged meat. Proceedings of the 58th International Congress of Meat Science and Technology, G-35 (pp. 1–4) (Montréal, Canada). Ponnampalam, E. N., Trout, G. R., Sinclair, A. J., Egan, A. R., & Leury, B. J. (2001). Comparison of the color stability and lipid oxidative stability of fresh and vacuum packaged lamb muscle containing elevated omega-3 and omega-6 fatty acid levels from dietary manipulation. Meat Science, 58, 151–161. Rosenvold, K., & Wiklund, E. (2011). Retail colour display life of chilled lamb as affected by processing conditions and storage temperature. Meat Science, 88, 354–360.
316
D.L. Hopkins et al. / Meat Science 95 (2013) 311–316
Toohey, E. S., Hopkins, D. L., Stanley, D. F., & Nielsen, S. G. (2008). The impact of new generation pre-dressing medium-voltage electrical stimulation on tenderness and colour stability in lamb meat. Meat Science, 79, 683–691. van de Ven, R. J., Pearce, K. L., & Hopkins, D. L. (in press). Post-mortem modelling of pH and temperature in related lamb carcases. Meat Science (in press, http://dx.doi.org/ 10.1016/j.meatsci.2012.10.001) van der Werf, J. H. J., Kinghorn, B. P., & Banks, R. G. (2010). Design and role of an information nucleus in sheep breeding programs. Animal Production Science, 50, 998–1003. Warner, R. D., Jacob, R., Hocking Edwards, J., McDonagh, M., Pearce, K., Geesink, G., Kearney, G., Allingham, P., Pethick, D. W., & Hopkins, D. L. (2010). Quality
of lamb from the Information Nucleus Flock. Animal Production Science, 50, 1123–1134. Warner, R. D., Ponnampalam, E. N., Kearney, G. A., Hopkins, D. L., & Jacob, R. H. (2007). Genotype and age at slaughter influence the retail shelf-life of the loin and knuckle from sheep carcasses. Australian Journal of Experimental Agriculture, 47, 1190–1200. Wulf, D. M., Morgan, J. B., Sanders, S. K., Tatum, J. D., Smith, G. C., & Williams, S. (1995). Effect of dietary supplementation of vitamin E on storage and caselife properties of lamb retail cuts. Journal of Animal Science, 73, 399–405.