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Lamb meat colour values (HunterLab CIE and reflectance) are influenced by aperture size (5 mm v. 25 mm)
Meat Science 100 (2015) 202–208
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Lamb meat colour values (HunterLab CIE and reflectance) are influenced by aperture size (5 mm v. 25 mm) Benjamin W.B. Holman a,⁎, Eric N. Ponnampalam b, Remy J. van de Ven c, Matthew G. Kerr b, David L. Hopkins a a b c
NSW Department of Primary Industries, Centre for Red Meat and Sheep Development, Cowra, NSW 2794, Australia Agriculture Productivity, Department of Environment & Primary Industries, Attwood, VIC 3049, Australia NSW Department of Primary Industries, Orange Agricultural Institute, Forest Road, Orange, NSW 2800, Australia
a r t i c l e
i n f o
Article history: Received 5 June 2014 Received in revised form 1 October 2014 Accepted 6 October 2014 Available online 29 October 2014 Keywords: Lamb Meat colour stability Aperture
a b s t r a c t The effect of aperture size on the assessment of lamb meat colour values (L*, a*, b* and R630/580) was investigated. Two experiments using 2 HunterLab MiniScan colorimeters (large [25 mm] and small [5 mm] apertures) were conducted: 1) coloured tiles were measured and 2) unaged lamb (n = 65) m. longissimus lumborum (LL) and m. semimembranosus (SM) muscles were measured over 2.5 d under simulated retail display. For Experiment three, 2 different colorimeters were used on lamb (n = 36) LL aged for 6 weeks before measurement over 4 d on simulated retail display. Coloured tile a* and b* values were unaffected by aperture size, but L* values and the R630/580 ratio were influenced by aperture size. The effect of aperture size on lamb meat colour measurements varied with display time and muscle type. The large aperture size generally provided the highest colorimetric values, and is recommended for measuring lamb meat colour. Crown Copyright © 2014 Published by Elsevier Ltd. All rights reserved.
1. Introduction A customer's first appraisal of lamb meat quality is based upon its colour, linking colour to both perceived and actual values. Colour has been the focus of numerous lamb meat studies, generally sharing an aim to achieve acceptable and resilient colour. A bright-red colour is associated with freshness (Carpenter, Cornforth, & Whittier, 2001) and therefore is preferable for retail purposes. Redness and colour in general are a function of deoxymyoglobin, metmyoglobin and oxymyoglobin concentrations. Time on display affects these concentrations, with metmyoglobin levels known to intensify with increased time and subsequent exposure to oxygen (AMSA, 2012; Mancini & Hunt, 2005). Under display, the vitamin E concentration of muscle has been reported vital for the maintenance of redness in lamb meat (Ponnampalam et al., 2010, 2013). Previous reports have indicated that myoglobin oxidation and lipid oxidation are interrelated in relation to meat colour (Chaijan, 2008; Faustman, Sun, Mancini, & Suman, 2010); however, the contribution of vitamin E was shown to be greater than the effect due to iron (myoglobin) or lipids in the maintenance of retail colour (Ponnampalam, Butler, McDonagh, Jacobs, & Hopkins, 2012). Therefore it would be valuable if the assessment of meat colour values influenced by internal and external factors was conducted by a standardised instrument in order for researchers to compare the outcomes between different experimental studies. ⁎ Corresponding author. Tel.: +61 2 6349 9717; fax: +61 2 6342 4543. E-mail address: [email protected] (B.W.B. Holman).
http://dx.doi.org/10.1016/j.meatsci.2014.10.006 0309-1740/Crown Copyright © 2014 Published by Elsevier Ltd. All rights reserved.
There are several ways to evaluate the colour of meat such as visual assessment, use of colour chips or application of instrumentation. Among these, instrumentation has been popular due to time saving, preciseness and reproducibility. Instrumentation has been developed to assess meat colour, for instance HunterLab MiniScan colorimeters (Tapp, Yancey, & Apple, 2011). These apply an illuminant to the surface of a meat sample and record light wavelength reflectance — that is not absorbed or lost with scatter. Information is often reported using 3 CIE tristimulus value coordinates (referred to as colorimetric values from here on): L*, which reports relative lightness or brightness; a*, redgreenness; and b*, yellow-blueness (AMSA, 2012; MacDougall, 1982; Warriss, 2010). Calculation of the wavelength ratio at 630/580 nm (R630/580) provides a useful indication of a decrease in redness and an increase in brownness and has been used in the development of consumer acceptability thresholds (Khliji, van de Ven, Lamb, Lanza, & Hopkins, 2010). Jacob, D'Antuono, Smith, Pethick, and Warner (2007) found that a R630/580 threshold of 3.0 best represented consumer ideals for lamb meat colour, as products below the threshold were observed as unappealing and actively discriminated against. Toohey, Hopkins, Stanley, and Nielsen (2008) since reported a lower threshold value, which depended on lamb cut selection and Morrissey, Jacob, and Pluske (2008) suggested that a higher threshold of 3.5 would be a better representative of consumer ideals. The most comprehensive study by Khliji et al. (2010) found that the threshold value of 3.3 was the appropriate level and for redness (a*) it was 14.8; using illuminant D-65 with 2° standard observer.
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Yancey and Kropf (2008) reported that variation in pork meat colorimetric values occurred as colorimeter aperture size changed. Applying this finding to the aforementioned studies found, Jacob et al. (2007), Morrissey et al. (2008) and Khliji et al. (2010) used HunterLab colorimeters with 25 mm aperture sizes, whereas Toohey et al. (2008) used one with a 5 mm aperture size. Furthermore, applying this outcome to studies investigating CIE colorimetric values demonstrates variation between aperture sizes. For instance, Hulsegge, Engel, Buist, Merkus, and Klont (2001) found veal L* values to be similar to those reported by Eikelenboom, Hoving-Bolink, and Hulsegge (1992) and Klont et al. (1999), whereas a* values from these same rectus abdominis cuts differed. However, as per R630/580 thresholds, aperture sizes differed from those of Hulsegge et al. (2001) using a Minolta colorimeter with a 8 mm aperture size, as opposed to the 50 mm aperture size used by both Eikelenboom et al. (1992) and Klont et al. (1999). This suggests an aperture size effect on colour measurement, which has not been investigated in lamb meat. As 71% of studies investigating meat colour failed to report colorimeter aperture size and 31.6% of studies used HunterLab colorimeters (Tapp et al., 2011), it is crucial to examine whether aperture size is a potential source of variation for colour in lamb studies. Implications for national research programmes, collaborations and project comparisons would be considerable. The objective of this study was to investigate the effect of aperture size in HunterLab instruments on lamb meat colour values, and by doing so, this can contribute to a standardisation of colour measurement protocols and reporting.
aperture sizes of 25 mm and 5 mm, with care to measure the SM superficial surface.
2. Methods
Trait ¼ baseline þ tile þ aperture size þ tile : aperture size þ error:
2.1. Experiment one Twelve (12) tiles of differing solid matt colours (white, purple, blue, teal, dark green, light green, orange, yellow, maroon, ochre, dark red and red) were purchased and cleaned with ethanol. All tiles were then measured using 2 HunterLab meters: Models 45/0-L (Series No. 7237) and 45/0-S (Series No. 6840), with the former instrument having an aperture size of 25 mm and the latter an aperture size of 5 mm. Each HunterLab meter was calibrated with black and white tiles (X = 80.4, Y = 85.3, Z = 91.5) using illuminant D-65 with a 10° standard observer. Tiles were measured twice, on the same flat tile surface with the colorimeter rotated 90° between readings for L*, a*, b*, and the specular component from which R630/580, hue and chroma values were calculated (AMSA, 2012) before all values were then averaged. 2.2. Experiment two Sixty-five (65) lambs, which had been grazed together and then slaughtered as a single group, were used in this study. At 24 h postmortem, the m. longissimus thoracis et lumborum (loin: LL) was removed from each lamb carcase on the left side between the lumbar–sacral junction and the 12th rib. Simultaneously, the m. semimembranosus (topside: SM) was removed from the hind leg. These were then subsampled, with 3–4 cm-thick sections from the LL cranial end and the SM proximal end removed by slicing across the muscle – to expose perpendicular muscle fibre orientation on the measuring surface – before being vacuum-packed (and kept at 3–4 °C for 5 d of ageing). Following their removal from vacuum-packaging, these samples were then placed on individual black Styrofoam trays (13.5 cm × 13.5 cm) and over-wrapped with PVC food film wrap (15 μm thickness). These were allowed to bloom for 30–40 min at 2–3 °C before being assessed with the same meters used in Experiment one. Samples were displayed in a 3–4 °C chiller under-fluorescent lighting (NEC Tubes 58 W delivering 1390 lx for LL and 1000 lx for SM) and periodically measured 5 times over a 2.5 d period (0, 12, 24, 36, 48 and 60 h). Samples were measured twice at each measurement time and as per Experiment 1 using
2.3. Experiment three Thirty-six (36) lambs (3 kill groups of 12 lambs each) had LL samples removed 24 h post-mortem, vacuum packaged and stored at 2–3 °C for 6 weeks (aged meat). After this period, each group of 12 samples was prepared for retail display, by butterflying the LL sample to approximately 10 mm thickness, placing each sample on individual black Styrofoam trays (13.5 cm × 13.5 cm) and over-wrapping these with PVC food film wrap (15 μm thickness) and allowing a bloom time of 30 min in a 2–3 °C chiller under-lighting (1390 lx for LL). Each sample was measured using 2 HunterLab meters (Reston, VA, USA) having aperture sizes of 25 mm and 5 mm respectively, which were different from those used in Experiments one and two. The same protocols with measurements were made in duplicate by removing and replacing the instrument head to a new position on the cut surface and the values were averaged. This technique was repeated at 24, 48, 72 and 96 h following the initial (day of display) measurements. 2.4. Statistical analysis The data in Experiment 1 for each trait (L*, a*, b*, R630/580, hue and chroma) were analysed using a linear mixed model to test differences between aperture sizes:
Tile and aperture size were fitted as fixed effects; tile:aperture size was fitted as a random effect (as these correspond to blocking effects); and error was permitted to have different variation for each aperture size (small and large). Data generated in Experiment two were analysed using a linear mixed model with each trait (L*, a*, b*, R630/580, hue and chroma) analysed separately. The fixed effects in each model were display time (linear effect), cut (loin v. topside), aperture size (large v. small) and all possible interactions between these effects. Random effects were random regressions on display time for each carcase, random regressions on display time for each carcase × cut, and random regressions on display time for each carcase × cut × aperture size. Random effects for each reading display time (denoted by read), read × carcase, and read × carcase × cut were also included in the model. Finally, the random error was allowed to differ in variance for the 2 aperture sizes (small and large). The predicted means, associated standard errors and least significant difference rankings based on the full models were calculated for display times 0 and 48 h. Plots of traits versus display time from the first measurement for each carcase and separately for each cut × aperture size interaction were composed. Data generated in Experiment three were also analysed using linear mixed model analyses. Each trait (L*, a*, b*, R630/580 on the log scale to normalise this dataset, hue and chroma) was analysed separately with each model including as fixed effects separate regression on time for each aperture size (small and large). Random effects were effects for kill group, display date (i.e. four separate day effects within each kill group), random regressions on display time for each carcase, and finally random error. Random errors were modelled as uncorrelated across carcase × display dates, but correlated within carcase × display date. The fixed effects model was simplified where possible by excluding terms not significant (P N 0.05). The results from conditional multivariate normal distributions were used to obtain the regression models for the large aperture size, given the observed value in small aperture size (assuming the predicted result is required for the same carcase on the same day). Models for each experiment were fitted using the package asreml (Butler, 2009) under R (R Core Team, 2013).
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3. Results 3.1. Experiment one The variation within and across tiles for each trait (L*, a*, b*, R630/580, hue and chroma) in Experiment one is shown in Fig. 1. These results were adjusted for average tile effects within each trait and are given in Fig. 2. The average lightness of tiles (L*) for the small aperture size instrument was higher than that for the large aperture size instrument (P b 0.001) by 2.45 ± 0.19 units. However for the large aperture size instrument the average R630/580 was higher than that for the small aperture size instrument (P = 0.04) by 0.15 ± 0.19. Likewise, for the large aperture size instrument the average chroma was higher than that for the small aperture size instrument, having an estimated difference equal to 0.97 ± 0.30 units. No significant difference was found between instruments for average red to greenness (a*), yellow to blueness (b*), and hue results (P N 0.05). 3.2. Experiment two It was shown that irrespective of muscle, the predicted average lightness of the meat (L*) for the large aperture size instrument was significantly less than that for the small aperture size instrument at each display time between 0 h and 60 h (P b 0.05). This difference increased (P b 0.05) with display time due to an increase (P = 0.05) in L* with display time for both cuts using the small aperture size instrument. Hue presented a similar trend to L*, being higher with the small aperture size instrument than the large aperture size instrument (P b 0.05) with this difference observed to increase with display time (P b 0.025) at the estimated rate of 0.00082 ± 0.0003 units per hour. This difference is, however, only apparent in the topside. For redness (a*), yellowness (b*), R630/580 and chroma, on each cut (topside and loin) at each observation time, the results for the large aperture size instrument were significantly larger on average than the results for the small aperture size instrument. For a* and R630/580 the difference declined with display time, whereas chroma differences remain static with display time (P b 0.05). The fitted regression models for each trait for each instrument are given in Table 1 and the predicted
differences for each trait between the large and the small aperture size instrument against display time are presented in Fig. 3, separately for each cut. Also included in Fig. 3 are the approximate 95% confidence intervals for each predicted difference. Redness (a*) for the topside was higher than that for the loin at initial display (0 h) time (P b 0.05) under both aperture sizes and the difference decreased with increasing display time reaching the same values at 60 h. Similar results were observed for yellowness (b*) as for redness (a*) at display time 0 h but, there were no significant changes between cuts. At initial display time, R630/580 values for the large aperture size instrument were higher for both the loin and the topside (P b 0.05). 3.3. Experiment three For traits L*, a*, b*, log(R630/580) and chroma, the large aperture instrument gave significantly higher results than the small aperture instrument at display times up to 4 d (96 h). This difference decreased (significantly at P b 0.001) with display time for each of the traits other than L*. For L*, the differences did not differ significantly (at 0.05 level) with display time. For hue, an inverse response than that observed with the other traits was found as the small aperture instrument gave higher results than the large aperture instrument. This difference was apparent over the same display time, although the difference between the small and the large aperture size instrument's hue reduced as display time increased (P b 0.001). Plots of the trait difference for large minus small aperture instruments are given in Fig. 4. The figure also includes approximate 95% confidence intervals for the predicted differences. The fitted regression models for each trait used in Experiment 3 for each instrument are given in Table 2. 4. Discussion The current study shows a clear difference in lamb meat colour arising from aperture size selection, with a small aperture size producing different L*, a*, b*, R630/580, hue and chroma colorimetric values compared to those using a large aperture size instrument. This outcome was evident across experiments and instruments. Sterrenburg (1989) and
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chroma White Purple Blue Teal Dark green Light green Orange Yellow Maroon Ochre Dark red Red
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Trait Fig. 1. Box-plot of trait (L*, a*, b*, R630/580, hue and chroma) results, irrespective of aperture size, within each coloured tile.
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Trait (adjusted for tile effects within each trait) Fig. 2. Box-plot of trait (L*, a*, b*, R630/580, hue and chroma) results according to aperture size as adjusted for tile effects within each trait.
Yancey and Kropf (2008) also found that meat colorimetric values varied with aperture size, both finding that colorimeters using a small aperture size indicated pork as darker (lower L*), less yellow (b*) and less red (a*) than when a large aperture size instrument was used. This response is the same as that found in the current study for b* and a* values, but not L* values. Brewer, Zhu, Bidner, Meisinger, and McKeith (2001) found that pork yellowness (b*) values were lower, redness (a*) higher and lightness (L*) values unchanged when a 8 mm aperture size was used as opposed to a larger 25 mm aperture size. In the latter study two types of colorimeter were used: Minolta and HunterLab colorimeters, suggesting that colorimetric value variation stems from instrumental differences. As only HunterLab colorimeters were used in the current study, any model differences within an
instrument can be expected as insignificant and therefore variation in observed colorimetric values can be due to aperture size differences. Variation in colorimetric values with aperture size is thought to result from four (4) potential sources: 1) interaction between light wavelength and aperture size, with wavelengths greater than 450 nm and long red wavelengths found to have higher captured reflectance within larger aperture sizes which ultimately affects colorimetric values (Yancey & Kropf, 2008); 2) edge-loss, or the sideward displacement of light outside of the aperture window which is not measured as reflectance but instead as absorbed (Sterrenburg, 1989), is thought to be increased with large aperture sizes (Eikelenboom et al., 1992; Hulsegge et al., 2001); 3) large aperture sizes permit a greater area of meat surface to contribute to colorimetric value calculation providing
Table 1 The fitted regression model (parameter estimates ± standard error) for each trait for each aperture size under Experiment two, together with the estimate of the random error variance (after removal of sources of variance associated with kill group, random display time (hours) and carcase effects over display time). Please note: m. longissimus lumborum = loin and m. semimembranosus = topside. Trait
Cut
Aperture size
Model
Error variance
L*
Loin
Large Small Large Small Large Small Large Small Large Small Large Small Large Small Large Small Large Small Large Small Large Small Large Small
41.04 (±0.30) − 0.00 (±0.02) h 42.66 (±0.33) + 0.04 (±0.02) h 37.29 (±0.33) + 0.00 (±0.02) h 41.32 (±0.37) − 0.04 (±0.02) h 18.08 (±0.21) + 0.00 (±0.01) h 10.06 (±0.21) + 0.01 (±0.01) h 20.34 (±0.23) − 0.04 (±0.01) h 11.77 (±0.23) − 0.01 (±0.01) h 16.06 (±0.16) + 0.000 (±0.003) h 10.98 (±0.15) − 0.000 (±0.003) h 17.97 (±0.19) − 0.009 (±0.004) h 11.47 (±0.18) − 0.007 (±0.003) h 4.44 (±0.06) − 0.026 (±0.003) h 2.59 (±0.05) − 0.015 (±0.003) h 5.40 (±0.07) − 0.043 (±0.003) h 2.74 (±0.06) − 0.019 (±0.003) h 0.726 (±0.006) + 0.00015 (±0.00032) h 0.838 (±0.006) + 0.00015 (±0.00032) h 0.718 (±0.006) + 0.00083 (±0.00032) h 0.774 (±0.006) + 0.00083 (±0.00032) h 24.19 (±0.27) + 0.000 (±0.014) h 14.92 (±0.26) + 0.000 (±0.014) h 27.16 (±0.30) − 0.031 (±0.015) h 16.47 (±0.29) − 0.013 (±0.015) h
2.31 (±0.14) 4.78 (±0.29) 2.31 (±0.14) 4.78 (±0.29) 1.10 (±0.07) 0.91 (±0.06) 1.10 (±0.07) 0.91 (±0.06) 1.59 (±0.10) 1.18 (±0.07) 1.59 (±0.10) 1.18 (±0.07) 0.18 (±0.01) 0.04 (±0.003) 0.18 (±0.01) 0.04 (±0.003) 0.00072 (±0.00004) 0.00099 (±0.00006) 0.00072 (±0.00004) 0.00099 (±0.00006) 2.28 (±0.14) 1.88 (±0.11) 2.28 (±0.14) 1.88 (±0.11)
Topside a*
Loin Topside
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Loin Topside
R630/580
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Loin Topside
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Loin Topside
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Display time (Hour) Fig. 3. Predicted differences (large minus small aperture instruments) for traits L*, a*, b*, R630/580, hue and chroma versus display time (hours) on loin (m. longissimus lumborum) and topside (m. semimembranosus) (solid lines) together with an approximate 95% point-wise confidence interval for each predicted value (dotted lines). Please note that solid lines refer to loin and dashed lines refer to topside.
better representation of the actual colour of a complex heterogeneous conglomeration such as lamb meat; and 4) meat is a translucent substrate which alters light reflectance and scatters more so than opaque substrates (Sterrenburg, 1989). In combination with the presented research, these promote the use of larger aperture size instruments over small aperture size instruments when assessing lamb meat colour, a sentiment shared in recommendations from the AMSA Meat Colour Guidelines (AMSA, 2012). The current research confirmed this conclusion by assessing coloured tile colorimetric values as affected by aperture size. Opaque ceramic tile L*, R630/580, hue and chroma values depended on aperture size, but not a* or b* values. This finding highlighted that a* and b* values vary with aperture size as specific to meat samples, and proposes that wavelength interactions with a translucent substrate are
important for any aperture size effect. Sterrenburg (1989) measured Teflon tile light reflectance to permit better comparison of the aperture size effect on a translucent material (unlike the opaque tiles tested in this research) and found L* values unchanged. However, a* and b* values increased with aperture size. L* and R630/580 divergence on the same tiles in combination with the above findings indicates the effect of aperture size on colour measurement regardless of the substrate tested. Aperture size affects the decline of colorimetric values as time on display increases, with the exception of L* values for which variable results were found between experiments. There is no apparent explanation for this finding, but since the R630/580 and a* values have been found to be related to consumer acceptability (Khliji et al., 2010) the consistent effect for these two traits across experiments and
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Display time (Hour) Fig. 4. Predicted differences (large minus small aperture instruments) for traits L*, a*, b*, log(R630/580), hue and chroma versus display time (hours) on loin (m. longissimus lumborum) (solid lines) together with an approximate 95% point-wise confidence interval for each predicted value (dotted lines).
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Table 2 The fitted regression model (parameter estimates ± standard error) for each trait for each aperture size under Experiment three measured on the loin (m. longissimus lumborum), together with the estimate of the random error variance (after removal of sources of variance associated with kill group, random display time (hours) and carcase effects over display time). Trait
Aperture size
Model
Error variance
L*
Large Small Large Small Large Small Large Small Large Small Large Small
36.10 (±0.66) + 0.42 (±0.16) h 32.12 (±0.66) + 0.42 (±0.16) h 22.47 (±0.34) − 2.61 (±0.10) h 12.22 (±0.31) − 1.20 (±0.09) h 19.21 (±0.39) − 0.86 (±0.07) h 13.77 (±0.38) − 0.42 (±0.06) h 2.17 (±0.05) − 0.35 (±0.02) h 1.67 (±0.05) − 0.26 (±0.02) h 0.68 (±0.01) + 0.057 (±0.004) h 0.83 (±0.01) + 0.046 (±0.005) h 29.42 (±0.49) − 2.40 (±0.11) h 18.34 (±0.46) − 1.04 (±0.09) h
0.25 (±0.04) 1.51 (±0.20) 1.05 (±0.16) 0.51 (±0.09) 0.69 (±0.10) 0.52 (±0.08) 0.007 (±0.001) 0.004 (±0.001) 0.00020 (±0.00003) 0.0012 (±0.0002) 1.54 (±0.23) 0.85 (±0.14)
a* b* log(R630/580) Hue Chroma
instruments is of more importance. R630/580 ratio can be used as a proxy for the decline in redness and the buildup of brownness, the latter reflecting metmyoglobin formation initially as a band between oxygenated and deoxygenated layers which increases in thickness with time until reaching the meat surface and causes the ‘unacceptable’ brown surface colour (AMSA, 2012; Channon, Baud, & Walker, 2005). To reiterate, lamb R630/580 threshold synthesis has delivered mixed results with Jacob et al. (2007) suggesting 3.0, Toohey et al. (2008) a lower threshold, Morrissey et al. (2008) a higher threshold of 3.5 and Khliji et al. (2010) who provided the most robust target of 3.3. There was evidence from the current study that differences in aperture size could contribute to the variation in relating observations to consumer preferences. Given the aperture size impacts on the absolute levels recorded, the large aperture size is suggested as providing the best representation of meat colour and it is concluded that any threshold should be developed using these criteria as done by Khliji et al. (2010). HunterLab aperture size selection influenced colorimetric values differently, depending on the lamb cut, as this study demonstrated that redness (a*) declined when a large aperture was used in the topside, but not in the loin. With time on display, the loin of aged meat (Experiment three) showed an increase in brownness formation (R630/580) and a decline in redness (a*) and a large aperture size compared with a small aperture size. Lamb muscles differ in their level of activity and have different oxygen demands, which in turn influences myoglobin concentrations (Judge, Aberle, Forrest, Hedrick, & Merkel, 1989). Therefore, it is reasonable to expect different colorimetric values between cuts as reported by Toohey et al. (2008), with the knuckle (HAM No. 5072) having longer display life than chump (HAM No. 4790) and LL (HAM No. 5109) cuts, sequentially. Different muscles show different colour stability (Ponnampalam, Trout, Sinclair, Egan, & Leury, 2001) due to not only the iron (myoglobin) concentration, but also the concentrations of vitamin E and fatty acid present. The results from the current study demonstrate that in order to relate meat colour values of small aperture to large aperture 1) different equations are needed for different cuts and types of meat and 2) different equations should be used for different time points during retail display. 5. Conclusions Lamb meat colour values for cuts were generally lower when assessed with HunterLab colorimeters with a small aperture size compared to when the same colorimeters were used with a large aperture size. Meat colour values – redness interpreted by a* and brownness interpreted by R630/580 – reported for different cuts differed between large and small aperture size instruments over the display time. Aperture size also influenced colour values from coloured tiles. This research is the first to report the effect of colorimeter aperture size on lamb meat colour values and reveals the significant effect aperture choice has on monitoring colour qualities. Observations from this study emphasise
the need to report colorimeter aperture size in studies of meat colour, without which comparisons between studies are difficult, if not impossible, methodology repeatability is hampered, and the usefulness of information generated regarding acceptability thresholds is lessened. This study recommends the use of large aperture sizes with HunterLab colorimeters to best represent lamb meat colour. Conflict of interest statement The authors declare no conflict of interest. Acknowledgements The contribution of David Stanley, Gordon Refshauge, Edwina Toohey and Susan Langfield (NSW DPI) during sample collection during Experiment two is gratefully acknowledged as is the co-operation of Junee Abattoir (NSW). We would like to thank Wayne Brown for the support provided towards slaughter of lambs and muscle sample collection in Experiment three. The co-operation of staff at the JBS abattoir (Victoria) during slaughter and muscle sample collection is appreciated. This work was funded by the NSW Department of Primary Industries and the Department of Environment and Primary Industries, Victoria. References AMSA (2012). In M. Hunt, & D. King (Eds.), Meat color measurement guidelines (pp. 133) (December 2012 ed.). Champaign, Illinois USA: American Meat Science Association. Brewer, M.S., Zhu, L.G., Bidner, B., Meisinger, D.J., & McKeith, F.K. (2001). Measuring pork color: Effects of bloom time, muscle, pH and relationship to instrumental parameters. Meat Science, 57, 169–176. Butler, D. (2009). asreml: asreml() fits the linear mixed model. R package (3.0-1 ed.). Carpenter, C.E., Cornforth, D.P., & Whittier, D. (2001). Consumer preferences for beef color and packaging did not affect eating satisfaction. Meat Science, 57, 359–363. Chaijan, M. (2008). Review: Lipid and myoglobin oxidations in muscle foods. Songklanakarin. Journal of Science and Technology, 30, 47–53. Channon, H.A., Baud, S.R., & Walker, P.J. (2005). Modified atmosphere packaging improves retail display life of lamb cuts with variation between loin and knuckle. Australian Journal of Experimental Agriculture, 45, 585–592. Eikelenboom, G., Hoving-Bolink, A.H., & Hulsegge, B. (1992). Evaluation of invasive instruments for assessment of veal colour at time of classification. Meat Science, 31, 343–349. Faustman, C., Sun, Q., Mancini, R., & Suman, S. (2010). Myoglobin and lipid oxidation interactions: Mechanistic bases and control. Meat Science, 86, 86–94. Hulsegge, B., Engel, B., Buist, W., Merkus, G.S.M., & Klont, R.E. (2001). Instrumental colour classification of veal carcasses. Meat Science, 57, 191–195. Jacob, R.H., D'Antuono, M.F., Smith, G.M., Pethick, D.W., & Warner, R.D. (2007). Effect of lamb age and electrical stimulation on the colour stability of fresh lamb meat. Australian Journal of Agricultural Research, 58, 374–382. Judge, M.D., Aberle, E.D., Forrest, J.C., Hedrick, H.B., & Merkel, R.A. (1989). Principles of meat science. IA: Kendall/Hunt Dubuque. Khliji, S., van de Ven, R.J., 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. Klont, R.E., Barnier, V.M.H., Smulders, F.J.M., Van Dijk, A., Hoving-Bolink, A.H., & Eikelenboom, G. (1999). Post-mortem variation in pH, temperature, and colour profiles of veal carcasses in relation to breed, blood haemoglobin content, and carcass characteristics. Meat Science, 53, 195–202.
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MacDougall, D.B. (1982). Changes in the colour and opacity of meat. Food Chemistry, 9, 75–88. Mancini, R.A., & Hunt, M.C. (2005). Current research in meat color. Meat Science, 71, 100–121. Morrissey, E.R., Jacob, R.H., & Pluske, J.M. (2008). Perception of red brown colour by consumers. Proceedings of the 54th International Congress of Meat Science and Technology, Cape Town, South Africa (pp. 1–3). Ponnampalam, E.N., Butler, K.L., Burnett, V.F., McDonagh, M.B., Joe, L., Jacobs, J.L., et al. (2013). Aged vacuum packaged lamb cuts are less brown than fresh muscle cuts under simulated retail display. Food and Nutrition Sciences, 4, 147–153. Ponnampalam, E.N., Butler, K.L., McDonagh, M.B., Jacobs, J.L., & Hopkins, D.L. (2012). Relationship between muscle antioxidant status, forms of iron, polyunsaturated fatty acids and functionality (retail colour) of meat in lambs. Meat Science, 90, 297–303. 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.
Ponnampalam, E.N., Warner, R.D., Kitessa, S., McDonagh, M.B., Pethick, D.W., Allen, D., et al. (2010). Influence of finishing systems and sampling site on fatty acid composition and retail shelf-life of lamb. Animal Production Science, 50, 775–781. R Core Team (2013). R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing. Sterrenburg, P. (1989). Influence of sample illumination and viewing on the colour measurement of translucent materials like meat. Proceedings of the 35th International Congress of Meat Science and Technology, Copenhagen, Denmark (pp. 610–613). Tapp, W.N., Yancey, J.W.S., & Apple, J.K. (2011). How is the instrumental color of meat measured? Meat Science, 89, 1–5. 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. Warriss, P.D. (2010). Meat science: An introductory text. New York, USA: CABI Publishing Inc. Yancey, J.W.S., & Kropf, D.H. (2008). Instrumental reflectance values of fresh pork are dependant on aperture size. Meat Science, 79, 734–739.
Contents lists available at ScienceDirect
Meat Science journal homepage: www.elsevier.com/locate/meatsci
Lamb meat colour values (HunterLab CIE and reflectance) are influenced by aperture size (5 mm v. 25 mm) Benjamin W.B. Holman a,⁎, Eric N. Ponnampalam b, Remy J. van de Ven c, Matthew G. Kerr b, David L. Hopkins a a b c
NSW Department of Primary Industries, Centre for Red Meat and Sheep Development, Cowra, NSW 2794, Australia Agriculture Productivity, Department of Environment & Primary Industries, Attwood, VIC 3049, Australia NSW Department of Primary Industries, Orange Agricultural Institute, Forest Road, Orange, NSW 2800, Australia
a r t i c l e
i n f o
Article history: Received 5 June 2014 Received in revised form 1 October 2014 Accepted 6 October 2014 Available online 29 October 2014 Keywords: Lamb Meat colour stability Aperture
a b s t r a c t The effect of aperture size on the assessment of lamb meat colour values (L*, a*, b* and R630/580) was investigated. Two experiments using 2 HunterLab MiniScan colorimeters (large [25 mm] and small [5 mm] apertures) were conducted: 1) coloured tiles were measured and 2) unaged lamb (n = 65) m. longissimus lumborum (LL) and m. semimembranosus (SM) muscles were measured over 2.5 d under simulated retail display. For Experiment three, 2 different colorimeters were used on lamb (n = 36) LL aged for 6 weeks before measurement over 4 d on simulated retail display. Coloured tile a* and b* values were unaffected by aperture size, but L* values and the R630/580 ratio were influenced by aperture size. The effect of aperture size on lamb meat colour measurements varied with display time and muscle type. The large aperture size generally provided the highest colorimetric values, and is recommended for measuring lamb meat colour. Crown Copyright © 2014 Published by Elsevier Ltd. All rights reserved.
1. Introduction A customer's first appraisal of lamb meat quality is based upon its colour, linking colour to both perceived and actual values. Colour has been the focus of numerous lamb meat studies, generally sharing an aim to achieve acceptable and resilient colour. A bright-red colour is associated with freshness (Carpenter, Cornforth, & Whittier, 2001) and therefore is preferable for retail purposes. Redness and colour in general are a function of deoxymyoglobin, metmyoglobin and oxymyoglobin concentrations. Time on display affects these concentrations, with metmyoglobin levels known to intensify with increased time and subsequent exposure to oxygen (AMSA, 2012; Mancini & Hunt, 2005). Under display, the vitamin E concentration of muscle has been reported vital for the maintenance of redness in lamb meat (Ponnampalam et al., 2010, 2013). Previous reports have indicated that myoglobin oxidation and lipid oxidation are interrelated in relation to meat colour (Chaijan, 2008; Faustman, Sun, Mancini, & Suman, 2010); however, the contribution of vitamin E was shown to be greater than the effect due to iron (myoglobin) or lipids in the maintenance of retail colour (Ponnampalam, Butler, McDonagh, Jacobs, & Hopkins, 2012). Therefore it would be valuable if the assessment of meat colour values influenced by internal and external factors was conducted by a standardised instrument in order for researchers to compare the outcomes between different experimental studies. ⁎ Corresponding author. Tel.: +61 2 6349 9717; fax: +61 2 6342 4543. E-mail address: [email protected] (B.W.B. Holman).
http://dx.doi.org/10.1016/j.meatsci.2014.10.006 0309-1740/Crown Copyright © 2014 Published by Elsevier Ltd. All rights reserved.
There are several ways to evaluate the colour of meat such as visual assessment, use of colour chips or application of instrumentation. Among these, instrumentation has been popular due to time saving, preciseness and reproducibility. Instrumentation has been developed to assess meat colour, for instance HunterLab MiniScan colorimeters (Tapp, Yancey, & Apple, 2011). These apply an illuminant to the surface of a meat sample and record light wavelength reflectance — that is not absorbed or lost with scatter. Information is often reported using 3 CIE tristimulus value coordinates (referred to as colorimetric values from here on): L*, which reports relative lightness or brightness; a*, redgreenness; and b*, yellow-blueness (AMSA, 2012; MacDougall, 1982; Warriss, 2010). Calculation of the wavelength ratio at 630/580 nm (R630/580) provides a useful indication of a decrease in redness and an increase in brownness and has been used in the development of consumer acceptability thresholds (Khliji, van de Ven, Lamb, Lanza, & Hopkins, 2010). Jacob, D'Antuono, Smith, Pethick, and Warner (2007) found that a R630/580 threshold of 3.0 best represented consumer ideals for lamb meat colour, as products below the threshold were observed as unappealing and actively discriminated against. Toohey, Hopkins, Stanley, and Nielsen (2008) since reported a lower threshold value, which depended on lamb cut selection and Morrissey, Jacob, and Pluske (2008) suggested that a higher threshold of 3.5 would be a better representative of consumer ideals. The most comprehensive study by Khliji et al. (2010) found that the threshold value of 3.3 was the appropriate level and for redness (a*) it was 14.8; using illuminant D-65 with 2° standard observer.
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Yancey and Kropf (2008) reported that variation in pork meat colorimetric values occurred as colorimeter aperture size changed. Applying this finding to the aforementioned studies found, Jacob et al. (2007), Morrissey et al. (2008) and Khliji et al. (2010) used HunterLab colorimeters with 25 mm aperture sizes, whereas Toohey et al. (2008) used one with a 5 mm aperture size. Furthermore, applying this outcome to studies investigating CIE colorimetric values demonstrates variation between aperture sizes. For instance, Hulsegge, Engel, Buist, Merkus, and Klont (2001) found veal L* values to be similar to those reported by Eikelenboom, Hoving-Bolink, and Hulsegge (1992) and Klont et al. (1999), whereas a* values from these same rectus abdominis cuts differed. However, as per R630/580 thresholds, aperture sizes differed from those of Hulsegge et al. (2001) using a Minolta colorimeter with a 8 mm aperture size, as opposed to the 50 mm aperture size used by both Eikelenboom et al. (1992) and Klont et al. (1999). This suggests an aperture size effect on colour measurement, which has not been investigated in lamb meat. As 71% of studies investigating meat colour failed to report colorimeter aperture size and 31.6% of studies used HunterLab colorimeters (Tapp et al., 2011), it is crucial to examine whether aperture size is a potential source of variation for colour in lamb studies. Implications for national research programmes, collaborations and project comparisons would be considerable. The objective of this study was to investigate the effect of aperture size in HunterLab instruments on lamb meat colour values, and by doing so, this can contribute to a standardisation of colour measurement protocols and reporting.
aperture sizes of 25 mm and 5 mm, with care to measure the SM superficial surface.
2. Methods
Trait ¼ baseline þ tile þ aperture size þ tile : aperture size þ error:
2.1. Experiment one Twelve (12) tiles of differing solid matt colours (white, purple, blue, teal, dark green, light green, orange, yellow, maroon, ochre, dark red and red) were purchased and cleaned with ethanol. All tiles were then measured using 2 HunterLab meters: Models 45/0-L (Series No. 7237) and 45/0-S (Series No. 6840), with the former instrument having an aperture size of 25 mm and the latter an aperture size of 5 mm. Each HunterLab meter was calibrated with black and white tiles (X = 80.4, Y = 85.3, Z = 91.5) using illuminant D-65 with a 10° standard observer. Tiles were measured twice, on the same flat tile surface with the colorimeter rotated 90° between readings for L*, a*, b*, and the specular component from which R630/580, hue and chroma values were calculated (AMSA, 2012) before all values were then averaged. 2.2. Experiment two Sixty-five (65) lambs, which had been grazed together and then slaughtered as a single group, were used in this study. At 24 h postmortem, the m. longissimus thoracis et lumborum (loin: LL) was removed from each lamb carcase on the left side between the lumbar–sacral junction and the 12th rib. Simultaneously, the m. semimembranosus (topside: SM) was removed from the hind leg. These were then subsampled, with 3–4 cm-thick sections from the LL cranial end and the SM proximal end removed by slicing across the muscle – to expose perpendicular muscle fibre orientation on the measuring surface – before being vacuum-packed (and kept at 3–4 °C for 5 d of ageing). Following their removal from vacuum-packaging, these samples were then placed on individual black Styrofoam trays (13.5 cm × 13.5 cm) and over-wrapped with PVC food film wrap (15 μm thickness). These were allowed to bloom for 30–40 min at 2–3 °C before being assessed with the same meters used in Experiment one. Samples were displayed in a 3–4 °C chiller under-fluorescent lighting (NEC Tubes 58 W delivering 1390 lx for LL and 1000 lx for SM) and periodically measured 5 times over a 2.5 d period (0, 12, 24, 36, 48 and 60 h). Samples were measured twice at each measurement time and as per Experiment 1 using
2.3. Experiment three Thirty-six (36) lambs (3 kill groups of 12 lambs each) had LL samples removed 24 h post-mortem, vacuum packaged and stored at 2–3 °C for 6 weeks (aged meat). After this period, each group of 12 samples was prepared for retail display, by butterflying the LL sample to approximately 10 mm thickness, placing each sample on individual black Styrofoam trays (13.5 cm × 13.5 cm) and over-wrapping these with PVC food film wrap (15 μm thickness) and allowing a bloom time of 30 min in a 2–3 °C chiller under-lighting (1390 lx for LL). Each sample was measured using 2 HunterLab meters (Reston, VA, USA) having aperture sizes of 25 mm and 5 mm respectively, which were different from those used in Experiments one and two. The same protocols with measurements were made in duplicate by removing and replacing the instrument head to a new position on the cut surface and the values were averaged. This technique was repeated at 24, 48, 72 and 96 h following the initial (day of display) measurements. 2.4. Statistical analysis The data in Experiment 1 for each trait (L*, a*, b*, R630/580, hue and chroma) were analysed using a linear mixed model to test differences between aperture sizes:
Tile and aperture size were fitted as fixed effects; tile:aperture size was fitted as a random effect (as these correspond to blocking effects); and error was permitted to have different variation for each aperture size (small and large). Data generated in Experiment two were analysed using a linear mixed model with each trait (L*, a*, b*, R630/580, hue and chroma) analysed separately. The fixed effects in each model were display time (linear effect), cut (loin v. topside), aperture size (large v. small) and all possible interactions between these effects. Random effects were random regressions on display time for each carcase, random regressions on display time for each carcase × cut, and random regressions on display time for each carcase × cut × aperture size. Random effects for each reading display time (denoted by read), read × carcase, and read × carcase × cut were also included in the model. Finally, the random error was allowed to differ in variance for the 2 aperture sizes (small and large). The predicted means, associated standard errors and least significant difference rankings based on the full models were calculated for display times 0 and 48 h. Plots of traits versus display time from the first measurement for each carcase and separately for each cut × aperture size interaction were composed. Data generated in Experiment three were also analysed using linear mixed model analyses. Each trait (L*, a*, b*, R630/580 on the log scale to normalise this dataset, hue and chroma) was analysed separately with each model including as fixed effects separate regression on time for each aperture size (small and large). Random effects were effects for kill group, display date (i.e. four separate day effects within each kill group), random regressions on display time for each carcase, and finally random error. Random errors were modelled as uncorrelated across carcase × display dates, but correlated within carcase × display date. The fixed effects model was simplified where possible by excluding terms not significant (P N 0.05). The results from conditional multivariate normal distributions were used to obtain the regression models for the large aperture size, given the observed value in small aperture size (assuming the predicted result is required for the same carcase on the same day). Models for each experiment were fitted using the package asreml (Butler, 2009) under R (R Core Team, 2013).
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3. Results 3.1. Experiment one The variation within and across tiles for each trait (L*, a*, b*, R630/580, hue and chroma) in Experiment one is shown in Fig. 1. These results were adjusted for average tile effects within each trait and are given in Fig. 2. The average lightness of tiles (L*) for the small aperture size instrument was higher than that for the large aperture size instrument (P b 0.001) by 2.45 ± 0.19 units. However for the large aperture size instrument the average R630/580 was higher than that for the small aperture size instrument (P = 0.04) by 0.15 ± 0.19. Likewise, for the large aperture size instrument the average chroma was higher than that for the small aperture size instrument, having an estimated difference equal to 0.97 ± 0.30 units. No significant difference was found between instruments for average red to greenness (a*), yellow to blueness (b*), and hue results (P N 0.05). 3.2. Experiment two It was shown that irrespective of muscle, the predicted average lightness of the meat (L*) for the large aperture size instrument was significantly less than that for the small aperture size instrument at each display time between 0 h and 60 h (P b 0.05). This difference increased (P b 0.05) with display time due to an increase (P = 0.05) in L* with display time for both cuts using the small aperture size instrument. Hue presented a similar trend to L*, being higher with the small aperture size instrument than the large aperture size instrument (P b 0.05) with this difference observed to increase with display time (P b 0.025) at the estimated rate of 0.00082 ± 0.0003 units per hour. This difference is, however, only apparent in the topside. For redness (a*), yellowness (b*), R630/580 and chroma, on each cut (topside and loin) at each observation time, the results for the large aperture size instrument were significantly larger on average than the results for the small aperture size instrument. For a* and R630/580 the difference declined with display time, whereas chroma differences remain static with display time (P b 0.05). The fitted regression models for each trait for each instrument are given in Table 1 and the predicted
differences for each trait between the large and the small aperture size instrument against display time are presented in Fig. 3, separately for each cut. Also included in Fig. 3 are the approximate 95% confidence intervals for each predicted difference. Redness (a*) for the topside was higher than that for the loin at initial display (0 h) time (P b 0.05) under both aperture sizes and the difference decreased with increasing display time reaching the same values at 60 h. Similar results were observed for yellowness (b*) as for redness (a*) at display time 0 h but, there were no significant changes between cuts. At initial display time, R630/580 values for the large aperture size instrument were higher for both the loin and the topside (P b 0.05). 3.3. Experiment three For traits L*, a*, b*, log(R630/580) and chroma, the large aperture instrument gave significantly higher results than the small aperture instrument at display times up to 4 d (96 h). This difference decreased (significantly at P b 0.001) with display time for each of the traits other than L*. For L*, the differences did not differ significantly (at 0.05 level) with display time. For hue, an inverse response than that observed with the other traits was found as the small aperture instrument gave higher results than the large aperture instrument. This difference was apparent over the same display time, although the difference between the small and the large aperture size instrument's hue reduced as display time increased (P b 0.001). Plots of the trait difference for large minus small aperture instruments are given in Fig. 4. The figure also includes approximate 95% confidence intervals for the predicted differences. The fitted regression models for each trait used in Experiment 3 for each instrument are given in Table 2. 4. Discussion The current study shows a clear difference in lamb meat colour arising from aperture size selection, with a small aperture size producing different L*, a*, b*, R630/580, hue and chroma colorimetric values compared to those using a large aperture size instrument. This outcome was evident across experiments and instruments. Sterrenburg (1989) and
L*
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White Purple Blue Teal Dark green Light green Orange Yellow Maroon Ochre Dark red Red
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chroma White Purple Blue Teal Dark green Light green Orange Yellow Maroon Ochre Dark red Red
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Trait Fig. 1. Box-plot of trait (L*, a*, b*, R630/580, hue and chroma) results, irrespective of aperture size, within each coloured tile.
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chroma
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Trait (adjusted for tile effects within each trait) Fig. 2. Box-plot of trait (L*, a*, b*, R630/580, hue and chroma) results according to aperture size as adjusted for tile effects within each trait.
Yancey and Kropf (2008) also found that meat colorimetric values varied with aperture size, both finding that colorimeters using a small aperture size indicated pork as darker (lower L*), less yellow (b*) and less red (a*) than when a large aperture size instrument was used. This response is the same as that found in the current study for b* and a* values, but not L* values. Brewer, Zhu, Bidner, Meisinger, and McKeith (2001) found that pork yellowness (b*) values were lower, redness (a*) higher and lightness (L*) values unchanged when a 8 mm aperture size was used as opposed to a larger 25 mm aperture size. In the latter study two types of colorimeter were used: Minolta and HunterLab colorimeters, suggesting that colorimetric value variation stems from instrumental differences. As only HunterLab colorimeters were used in the current study, any model differences within an
instrument can be expected as insignificant and therefore variation in observed colorimetric values can be due to aperture size differences. Variation in colorimetric values with aperture size is thought to result from four (4) potential sources: 1) interaction between light wavelength and aperture size, with wavelengths greater than 450 nm and long red wavelengths found to have higher captured reflectance within larger aperture sizes which ultimately affects colorimetric values (Yancey & Kropf, 2008); 2) edge-loss, or the sideward displacement of light outside of the aperture window which is not measured as reflectance but instead as absorbed (Sterrenburg, 1989), is thought to be increased with large aperture sizes (Eikelenboom et al., 1992; Hulsegge et al., 2001); 3) large aperture sizes permit a greater area of meat surface to contribute to colorimetric value calculation providing
Table 1 The fitted regression model (parameter estimates ± standard error) for each trait for each aperture size under Experiment two, together with the estimate of the random error variance (after removal of sources of variance associated with kill group, random display time (hours) and carcase effects over display time). Please note: m. longissimus lumborum = loin and m. semimembranosus = topside. Trait
Cut
Aperture size
Model
Error variance
L*
Loin
Large Small Large Small Large Small Large Small Large Small Large Small Large Small Large Small Large Small Large Small Large Small Large Small
41.04 (±0.30) − 0.00 (±0.02) h 42.66 (±0.33) + 0.04 (±0.02) h 37.29 (±0.33) + 0.00 (±0.02) h 41.32 (±0.37) − 0.04 (±0.02) h 18.08 (±0.21) + 0.00 (±0.01) h 10.06 (±0.21) + 0.01 (±0.01) h 20.34 (±0.23) − 0.04 (±0.01) h 11.77 (±0.23) − 0.01 (±0.01) h 16.06 (±0.16) + 0.000 (±0.003) h 10.98 (±0.15) − 0.000 (±0.003) h 17.97 (±0.19) − 0.009 (±0.004) h 11.47 (±0.18) − 0.007 (±0.003) h 4.44 (±0.06) − 0.026 (±0.003) h 2.59 (±0.05) − 0.015 (±0.003) h 5.40 (±0.07) − 0.043 (±0.003) h 2.74 (±0.06) − 0.019 (±0.003) h 0.726 (±0.006) + 0.00015 (±0.00032) h 0.838 (±0.006) + 0.00015 (±0.00032) h 0.718 (±0.006) + 0.00083 (±0.00032) h 0.774 (±0.006) + 0.00083 (±0.00032) h 24.19 (±0.27) + 0.000 (±0.014) h 14.92 (±0.26) + 0.000 (±0.014) h 27.16 (±0.30) − 0.031 (±0.015) h 16.47 (±0.29) − 0.013 (±0.015) h
2.31 (±0.14) 4.78 (±0.29) 2.31 (±0.14) 4.78 (±0.29) 1.10 (±0.07) 0.91 (±0.06) 1.10 (±0.07) 0.91 (±0.06) 1.59 (±0.10) 1.18 (±0.07) 1.59 (±0.10) 1.18 (±0.07) 0.18 (±0.01) 0.04 (±0.003) 0.18 (±0.01) 0.04 (±0.003) 0.00072 (±0.00004) 0.00099 (±0.00006) 0.00072 (±0.00004) 0.00099 (±0.00006) 2.28 (±0.14) 1.88 (±0.11) 2.28 (±0.14) 1.88 (±0.11)
Topside a*
Loin Topside
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Loin Topside
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1 30
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-0.04 -0.06 -0.08 -0.10 -0.12 -0.14 15
15
hue
3
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12 11 10 9 8 0
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Display time (Hour) Fig. 3. Predicted differences (large minus small aperture instruments) for traits L*, a*, b*, R630/580, hue and chroma versus display time (hours) on loin (m. longissimus lumborum) and topside (m. semimembranosus) (solid lines) together with an approximate 95% point-wise confidence interval for each predicted value (dotted lines). Please note that solid lines refer to loin and dashed lines refer to topside.
better representation of the actual colour of a complex heterogeneous conglomeration such as lamb meat; and 4) meat is a translucent substrate which alters light reflectance and scatters more so than opaque substrates (Sterrenburg, 1989). In combination with the presented research, these promote the use of larger aperture size instruments over small aperture size instruments when assessing lamb meat colour, a sentiment shared in recommendations from the AMSA Meat Colour Guidelines (AMSA, 2012). The current research confirmed this conclusion by assessing coloured tile colorimetric values as affected by aperture size. Opaque ceramic tile L*, R630/580, hue and chroma values depended on aperture size, but not a* or b* values. This finding highlighted that a* and b* values vary with aperture size as specific to meat samples, and proposes that wavelength interactions with a translucent substrate are
important for any aperture size effect. Sterrenburg (1989) measured Teflon tile light reflectance to permit better comparison of the aperture size effect on a translucent material (unlike the opaque tiles tested in this research) and found L* values unchanged. However, a* and b* values increased with aperture size. L* and R630/580 divergence on the same tiles in combination with the above findings indicates the effect of aperture size on colour measurement regardless of the substrate tested. Aperture size affects the decline of colorimetric values as time on display increases, with the exception of L* values for which variable results were found between experiments. There is no apparent explanation for this finding, but since the R630/580 and a* values have been found to be related to consumer acceptability (Khliji et al., 2010) the consistent effect for these two traits across experiments and
L*
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4 0
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Display time (Hour) Fig. 4. Predicted differences (large minus small aperture instruments) for traits L*, a*, b*, log(R630/580), hue and chroma versus display time (hours) on loin (m. longissimus lumborum) (solid lines) together with an approximate 95% point-wise confidence interval for each predicted value (dotted lines).
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Table 2 The fitted regression model (parameter estimates ± standard error) for each trait for each aperture size under Experiment three measured on the loin (m. longissimus lumborum), together with the estimate of the random error variance (after removal of sources of variance associated with kill group, random display time (hours) and carcase effects over display time). Trait
Aperture size
Model
Error variance
L*
Large Small Large Small Large Small Large Small Large Small Large Small
36.10 (±0.66) + 0.42 (±0.16) h 32.12 (±0.66) + 0.42 (±0.16) h 22.47 (±0.34) − 2.61 (±0.10) h 12.22 (±0.31) − 1.20 (±0.09) h 19.21 (±0.39) − 0.86 (±0.07) h 13.77 (±0.38) − 0.42 (±0.06) h 2.17 (±0.05) − 0.35 (±0.02) h 1.67 (±0.05) − 0.26 (±0.02) h 0.68 (±0.01) + 0.057 (±0.004) h 0.83 (±0.01) + 0.046 (±0.005) h 29.42 (±0.49) − 2.40 (±0.11) h 18.34 (±0.46) − 1.04 (±0.09) h
0.25 (±0.04) 1.51 (±0.20) 1.05 (±0.16) 0.51 (±0.09) 0.69 (±0.10) 0.52 (±0.08) 0.007 (±0.001) 0.004 (±0.001) 0.00020 (±0.00003) 0.0012 (±0.0002) 1.54 (±0.23) 0.85 (±0.14)
a* b* log(R630/580) Hue Chroma
instruments is of more importance. R630/580 ratio can be used as a proxy for the decline in redness and the buildup of brownness, the latter reflecting metmyoglobin formation initially as a band between oxygenated and deoxygenated layers which increases in thickness with time until reaching the meat surface and causes the ‘unacceptable’ brown surface colour (AMSA, 2012; Channon, Baud, & Walker, 2005). To reiterate, lamb R630/580 threshold synthesis has delivered mixed results with Jacob et al. (2007) suggesting 3.0, Toohey et al. (2008) a lower threshold, Morrissey et al. (2008) a higher threshold of 3.5 and Khliji et al. (2010) who provided the most robust target of 3.3. There was evidence from the current study that differences in aperture size could contribute to the variation in relating observations to consumer preferences. Given the aperture size impacts on the absolute levels recorded, the large aperture size is suggested as providing the best representation of meat colour and it is concluded that any threshold should be developed using these criteria as done by Khliji et al. (2010). HunterLab aperture size selection influenced colorimetric values differently, depending on the lamb cut, as this study demonstrated that redness (a*) declined when a large aperture was used in the topside, but not in the loin. With time on display, the loin of aged meat (Experiment three) showed an increase in brownness formation (R630/580) and a decline in redness (a*) and a large aperture size compared with a small aperture size. Lamb muscles differ in their level of activity and have different oxygen demands, which in turn influences myoglobin concentrations (Judge, Aberle, Forrest, Hedrick, & Merkel, 1989). Therefore, it is reasonable to expect different colorimetric values between cuts as reported by Toohey et al. (2008), with the knuckle (HAM No. 5072) having longer display life than chump (HAM No. 4790) and LL (HAM No. 5109) cuts, sequentially. Different muscles show different colour stability (Ponnampalam, Trout, Sinclair, Egan, & Leury, 2001) due to not only the iron (myoglobin) concentration, but also the concentrations of vitamin E and fatty acid present. The results from the current study demonstrate that in order to relate meat colour values of small aperture to large aperture 1) different equations are needed for different cuts and types of meat and 2) different equations should be used for different time points during retail display. 5. Conclusions Lamb meat colour values for cuts were generally lower when assessed with HunterLab colorimeters with a small aperture size compared to when the same colorimeters were used with a large aperture size. Meat colour values – redness interpreted by a* and brownness interpreted by R630/580 – reported for different cuts differed between large and small aperture size instruments over the display time. Aperture size also influenced colour values from coloured tiles. This research is the first to report the effect of colorimeter aperture size on lamb meat colour values and reveals the significant effect aperture choice has on monitoring colour qualities. Observations from this study emphasise
the need to report colorimeter aperture size in studies of meat colour, without which comparisons between studies are difficult, if not impossible, methodology repeatability is hampered, and the usefulness of information generated regarding acceptability thresholds is lessened. This study recommends the use of large aperture sizes with HunterLab colorimeters to best represent lamb meat colour. Conflict of interest statement The authors declare no conflict of interest. Acknowledgements The contribution of David Stanley, Gordon Refshauge, Edwina Toohey and Susan Langfield (NSW DPI) during sample collection during Experiment two is gratefully acknowledged as is the co-operation of Junee Abattoir (NSW). We would like to thank Wayne Brown for the support provided towards slaughter of lambs and muscle sample collection in Experiment three. The co-operation of staff at the JBS abattoir (Victoria) during slaughter and muscle sample collection is appreciated. This work was funded by the NSW Department of Primary Industries and the Department of Environment and Primary Industries, Victoria. References AMSA (2012). In M. Hunt, & D. King (Eds.), Meat color measurement guidelines (pp. 133) (December 2012 ed.). Champaign, Illinois USA: American Meat Science Association. Brewer, M.S., Zhu, L.G., Bidner, B., Meisinger, D.J., & McKeith, F.K. (2001). Measuring pork color: Effects of bloom time, muscle, pH and relationship to instrumental parameters. Meat Science, 57, 169–176. Butler, D. (2009). asreml: asreml() fits the linear mixed model. R package (3.0-1 ed.). Carpenter, C.E., Cornforth, D.P., & Whittier, D. (2001). Consumer preferences for beef color and packaging did not affect eating satisfaction. Meat Science, 57, 359–363. Chaijan, M. (2008). Review: Lipid and myoglobin oxidations in muscle foods. Songklanakarin. Journal of Science and Technology, 30, 47–53. Channon, H.A., Baud, S.R., & Walker, P.J. (2005). Modified atmosphere packaging improves retail display life of lamb cuts with variation between loin and knuckle. Australian Journal of Experimental Agriculture, 45, 585–592. Eikelenboom, G., Hoving-Bolink, A.H., & Hulsegge, B. (1992). Evaluation of invasive instruments for assessment of veal colour at time of classification. Meat Science, 31, 343–349. Faustman, C., Sun, Q., Mancini, R., & Suman, S. (2010). Myoglobin and lipid oxidation interactions: Mechanistic bases and control. Meat Science, 86, 86–94. Hulsegge, B., Engel, B., Buist, W., Merkus, G.S.M., & Klont, R.E. (2001). Instrumental colour classification of veal carcasses. Meat Science, 57, 191–195. Jacob, R.H., D'Antuono, M.F., Smith, G.M., Pethick, D.W., & Warner, R.D. (2007). Effect of lamb age and electrical stimulation on the colour stability of fresh lamb meat. Australian Journal of Agricultural Research, 58, 374–382. Judge, M.D., Aberle, E.D., Forrest, J.C., Hedrick, H.B., & Merkel, R.A. (1989). Principles of meat science. IA: Kendall/Hunt Dubuque. Khliji, S., van de Ven, R.J., 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. Klont, R.E., Barnier, V.M.H., Smulders, F.J.M., Van Dijk, A., Hoving-Bolink, A.H., & Eikelenboom, G. (1999). Post-mortem variation in pH, temperature, and colour profiles of veal carcasses in relation to breed, blood haemoglobin content, and carcass characteristics. Meat Science, 53, 195–202.
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