Effects of transport time and season on aspects of rabbit meat quality

MEAT SCIENCE Meat Science 72 (2006) 773–777 www.elsevier.com/locate/meatsci

Effects of transport time and season on aspects of rabbit meat quality

q

G.A. Marı´a *, T. Buil, G. Liste, M. Villarroel, C. San˜udo, J.L. Olleta Department of Animal Production and Food Science, Faculty of Veterinary Medicine, University of Zaragoza, Miguel Servet 177, 50013 Zaragoza, Spain Received 24 March 2005; received in revised form 18 May 2005; accepted 10 October 2005

Abstract The aim of this study was to determine whether transport times of up to 7 h can have a significant effect on instrumental meat quality traits in rabbits. Spain has very hot summers and cold winters; therefore, we performed replicates in two seasons. To evaluate the effect of transport time and season on rabbit meat quality, we assessed four meat quality parameters: pH, water holding capacity (WHC), texture (compression and Warner–Bratzler analyses), and colour (CIEL*a*b*). We also considered the effect of the position of the animals on the transport vehicle. After slaughter, we analysed steaks of Longissimus dorsi from all transported animals (n = 216). Average pH at 24 h and WHC did not differ significantly between transport time treatments. Position on the vehicle did not influence the measures of meat quality. Transport time had a significant effect on all the meat texture parameters measured by compression, but did not affect shear force or toughness. Transport time influenced a* but not L* or b*. Transport time had much less of an effect on meat quality than time of year; therefore the effect of season appeared to be independent of transport time. Position on the vehicle had no effect on meat quality. Based on our results, we conclude that the transport process can affect instrumental meat quality.
2005 Elsevier Ltd. All rights reserved. Keywords: Rabbit; Meat quality; Transport time; pH; Colour; Texture

1. Introduction The chain of events involved in transport can induce stress in rabbits, and affect some aspects of meat quality (Jolley, 1990). Little is known about the effect of transport on the texture and colour of rabbit meat. In studies that consider ante-mortem effects on meat quality, one of the most commonly measured parameters is ultimate meat pH. Even travelling short distances can reduce live weight (shrinkage), decrease glycogen reserves, and increase meat temperature (Jolley, 1990), although changes in ultimate pH do not invariably reflect these effects. The relationship between initial muscle glycogen content and ultimate pH is linear only at very low levels of glycogen (Purchas & Aungsupakorn, 1993). Thus, glycogen concentrations may not q Funded by CICYT Ministry of Science and Technology of Spain. Project AGL 2002-01346 COTRANS. * Corresponding author. Tel.: +34 976 762490; fax: +34 976 761612. E-mail address: [email protected] (G.A. Marı´a). URL: http://www.unizar.es (G.A. Marı´a).

0309-1740/$ - see front matter
2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2005.10.012

decrease enough to have a substantial effect on ultimate pH, especially when the animals can recover during lairage. There are changes in meat texture and colour in response to ante-mortem stress (Gregory, 1998). Transport time has been considered one of the critical points affecting animal welfare during transport from the farm to the abattoir (Buil, Maria, Villarroel, Liste, & Lopez, 2004). It is unclear whether journey duration affects meat quality, particularly in commercial rabbits, for which little information is available. Transportation can increase the ultimate pH and darkness of meat (Masoero, Riccioni, Bergoglio, & Napolitano, 1992), but can improve meat tenderness (Xiccato, Paragini-Bini, & Carazzolo, 1994) and enhance the sensory qualities of rabbit meat by making it more tender and juicy (Dalle Zotte, 2002). The manner in which transport can influence meat quality warrants further investigation. In this study, we determined whether transport times (either 1 or 7 h) and position on the transport vehicle have a significant effect on instrumental meat pH, texture, and colour in two seasons (summer and winter).

774

G.A. Marı´a et al. / Meat Science 72 (2006) 773–777

2. Materials and methods The instrumental meat quality of 216 commercial rabbits was assessed (36 animals per treatment). The animals were transported by road (along with non-target animals), for 1 or 7 h in either winter or summer. The transportation study was performed on three days in January–February (average outside temperature, AOT = 11 C) and in June–July (AOT = 28 C) over three consecutive weeks (i.e., three replicates for each treatment). Every 5 min, average temperature during transport was measured using a Testo thermometer located at the level of the subjects. Three main effects were considered: transport time, season, and position on the truck (top, middle or bottom) in a multi-floor cage rolling stand (MFRS). The stocking rate during transport was 360 cm2 per animal (cage size = 57 · 57 · 25 cm). The overall capacity of the truck was 2400 rabbits. At midday, following 3 h of lairage time housed in MFRS, the rabbits were slaughtered. Average carcass weight (means ± SD) was 1192.50 ± 121 g. Carcasses were chilled under commercial conditions for 24 h (average weight after chilling = 1175.26 ± 120 g). The meat pH was measured at 24 h post-mortem (next day) in the lumbar region (M. Longissimus dorsi lumborum) using a Crison 507 electrode. Meat colour was measured using a MINOLTA portable chromameter (model CR-200b) using the Commission Internationale de LÕEclairage system. Measurements were taken from the surface of a slice of Longissimus dorsi from each animal. Slices were freshly cut at 24 h post-mortem and measured after 24 h blooming. Without touching the sample, we placed each slice on individual plastic foam trays and wrapped them with an O2permeable film at 4 C. The colour was expressed as colour coordinates L* (lightness), a* (redness), and b* (yellowness). Chroma (C*) and hue-angle (h*) values were calculated as C* = (a*2 + b*2)1/2 and h* = tan 1 (b*/a*), respectively. To determine the proportion of muscle, bone, and fat in the carcasses by dissection in the lab, we randomly selected 16 additional rabbits. The Longissimus dorsi was removed from both sides and the right side was sliced into three steaks for instrumental analyses. Water holding capacity (WHC), which we measured 72 h after slaughter, is expressed as percentage (%) of expelled juice after compression, using the Grau and Hamm Method (Boakye & Mittal, 2004; Can˜eque & San˜udo, 2001). For the analyses of meat texture, Longissimus dorsi muscles were vacuumpackaged and frozen at 18 C. Thawed steaks (internal temperature 17–19 C) were cut transversely, and analysed as either raw (compression) or cooked meat (Warner–Bratzler), following the reference methods described by Honikel (1998). We performed compression and Warner–Bratzler (WB) analyses on sample slices using an Instron 4301 (following Campo et al., 2000). The texture of the raw meat was determined using a modified compression device that avoids transversal elongation of the sample (Lepetit & Culioli, 1994). The stress was assessed at 20% (K20), 40% (K40), 60% (K60) and 80% (K80) of the maximum com-

pression (MS, N/cm2). The K20 reflected a progressive tenderization of the meat as ageing progressed. Lepetit and Culioli (1994) observed that low compression values were related to the resistance of myofibrils to deformation (compression). Higher stress compression values are mainly related to the connective tissue components (Lepetit & Culioli, 1994). Vacuum packaged meat was cooked in a water bath at 75 C until the internal temperature reached 70 C. We cut samples (1 cm2 cross-section) in a rectangular shape and with the muscle fibres parallel to the longitudinal axis of the sample. To assess shear force and toughness, samples were sheared until they broke. The sample was 10 mm wide, 10 mm thick and 30 mm long. Load cell was 100 kg (minimum load level = 0.001 kg), crosshead speed was 150 mm/min (high extension limit = 30 mm) and sampling rate was 20 points/s. The data were analysed using the least square method of the GLM procedure in SAS SAS (1988), fitting the data in a three-way model that included the fixed effects of transport time (2), season (2) and position of the cages within the vehicle (3), and the interaction effects. 3. Results Among the rabbits in our study, the average composition of the left middle carcass was 71.58 ± 2.7% muscle, 5.80 ± 1.09% fat, and 16.53 ± 1.8% bone (n = 16 animals) and did not differ significantly between transport times. Average pH 24 (least square means LSM ± S.E. = 5.86 ± 0.02 for 1 h and 5.83 ± 0.02 for 7 h) and water-holding capacity (WHC: 13.77 ± 0.45 for 1 h and 13.57 ± 0.43 for 7 h) did not differ significantly between animals transported for 1 h compared to 7 h. For both transport times and seasons, position on the truck did not influence meat quality measurements (Table 1). Transport time had a significant effect (p 6 0.05) on all of the meat texture parameters measured by compression, but did not affect shear force or toughness. Season had a significant effect (p 6 0.05) on pH 24, WHC and all colour parameters. For meat texture, only shear force, toughness and K20 were affected. In general, transport time had much less of an effect on meat quality than time of year. Rabbits subjected to the short (1 h) journey had higher K20, K40, and K60 values in summer and winter (Table 2). Yield point values were also significantly (p 6 0.001) higher after a 1 h journey in both seasons. Shear force, toughness, 20% compression, and maximum stress values were higher in winter than in summer. For the shear force and toughness, the interaction between transport time and season was significant (p 6 0.05). For short journeys, the meat seemed to be more tender in summer, while meat was more tender after long journeys in winter. Season had a significant affect on all the colour co-ordinates (L*, a*, b*, C* and h*) but transport time only had a significant effect on a* and C* values (Table 1). The effect of transport time on a* values was statistically significant (p 6 0.01) in winter, with the highest values after long jour-

G.A. Marı´a et al. / Meat Science 72 (2006) 773–777

775

Table 1 Summary of significance levels of the main effects and their interactions for instrumental meat quality parameters of commercial rabbits Response variable

Main effects in the full model

Interactions

Season

Time

Position

S*T

S*P

P*S

S*T*P

pH 24 Water holding capacity

*** ***

NS NS

NS NS

NS NS

NS NS

NS NS

NS NS

Warner–Bratzler Shear force (Kgf) Yield point (Kg) Toughness (Kgf/cm2)

*** NS ***

NS *** NS

NS NS NS

*** NS ***

NS NS NS

NS NS NS

NS NS NS

Compression K20 (20%) K40 (40%) K60 (60%) K80 (80%) Maximum stress (N/cm2)

*** NS NS NS NS

*** *** *** * ***

NS NS NS NS NS

NS NS NS NS NS

NS NS NS NS NS

NS NS NS NS NS

NS NS NS NS NS

Colour - CIEL*a*b* L* a* b* C* (Chroma) h* (hue)

* *** *** *** ***

NS * NS ** NS

NS NS NS NS NS

* NS NS NS NS

NS NS NS NS NS

NS NS NS NS NS

NS NS NS NS NS

The levels of significance were *p < 0.05**p < 0.01***p < 0.001. Season refers to summer or winter. Time: journey time (1 or 7 h). Position: position in the multi-floor cage rolling stand (top, middle or bottom cages) during transport.

Table 2 Least square means (±SE) of instrumental meat quality parameters of rabbit in summer and winter at two transport times (1 or 7 h) Response variable

Summer (1)

Winter (2)

1 (h)

7 (h)

1 (h)

7 (h)

pH 24 Water holding capacity

5.75 ± 0.02a 12.61 ± 0.45a

5.77 ± 0.01a 12.12 ± 0.44a

5.97 ± 0.03b 14.93 ± 0.45b

5.90 ± 0.02b 14.57 ± 0.42b

Warner–Bratzler Shear force (Kgf) Yield point (Kg) Toughness (Kgf/cm2)

0.61 ± 0.04a 0.18 ± 0.02a 0.25 ± 0.01a

0.72 ± 0.04a 0.06 ± 0.01b 0.31 ± 0.02b

1.04 ± 0.03b 0.17 ± 0.02a 0.42 ± 0.02c

0.91 ± 0.04c 0.09 ± 0.02b 0.31 ± 0.02b

Compression K20 (20%) K40 (40%) K60 (60%) K80 (80%) Maximum stress (N/cm2)

10.65 ± 0.34a 19.45 ± 0.48a 16.20 ± 0.57a 16.66 ± 0.56a 21.90 ± 0.62a

9.69 ± 0.33b 17.89 ± 0.47b 15.33 ± 0.56a 17.01 ± 0.57a 20.61 ± 0.0.61a

12.32 ± 0.34c 20.88 ± 0.49c 18.02 ± 0.57b 17.36 ± 0.52a 24.02 ± 0.63b

11.39 ± 0.35a 17.73 ± 0.47b 15.44 ± 0.56a 14.92 ± 0.51b 20.74 ± 0.60a

Colour L* a* b* C* (Chroma) h* (hue)

58.46 ± 0.34ab 2.34 ± 0.21a 4.09 ± 0.25a 4.75 ± 0.18a 60.25 ± 3.01a

59.36 ± 0.36b 2.49 ± 0.20a 4.18 ± 0.27a 4.92 ± 0.18a 59.42 ± 3.02a

58.44 ± 0.33ab 3.45 ± 0.22b 2.92 ± 0.20b 5.01 ± 0.19b 40.68 ± 3.01b

57.95 ± 0.31a 4.19 ± 0.26c 3.18 ± 0.22b 5.71 ± 0.18c 37.94 ± 3.00b

Different letters in the same row indicate significant differences, p 6 0.05.

neys. The a* values were higher in winter, while b* was higher in summer (Table 2). Lightness values varied more than the other colour parameters, and values were significantly (p 6 0.05) higher in summer than in winter, being highest on long summer journeys. For L*, the interaction between transport time and season was statistically significant (p 6 0.05). Transport time did not affect hue, but chroma values were significantly (p 6 0.01) higher in meat from rabbits exposed to a long (7 h) journey. Hue values

and chroma values were significantly (p 6 0.001) higher in summer and winter, respectively. 4. Discussion Even under optimum conditions, the multiple potential stressors involved in the transport process might affect the quality of commercial rabbit meat. We performed our study under controlled commercial conditions that

776

G.A. Marı´a et al. / Meat Science 72 (2006) 773–777

included the same type of animal, same age, same production system and same vehicle and driver. The meat quality parameter values fell within the range of what is considered good quality meat and similar to Trocino, Xiccato, Queaque, and Sartori (2002) and Xiccato et al. (1994). Season had a significant effect on meat colour, pH, WHC and a modest influence on WB-derived meat texture parameters. Position on the transport vehicle did not affect meat quality. At the industrial level, ultimate pH is the main parameter used to measure meat quality. In our study, pH 24 values were significantly higher in winter than in summer, but transport time did not appear to influence pH 24. In long and short journeys, pH 24 values were always below 6.0 (hence, within the quality range), which means that transport procedures were appropriate and minimized the risk of DFD or PSE meat. Our findings agree with Trocino et al. (2002). Other studies (Dalle Zotte, 2002; Jolley, 1990; Masoero et al., 1992) found that transport raises pH 24, and Dal Bosco, Castellini, and Berbnardini (1997) reported that pH was higher after long journeys. The same situation (values within the quality range), was observed for WHC, although some studies found that transport affects WHC indirectly, as an increase in ultimate pH produces a rise in the WHC (Jolley, 1990; Trocino et al., 2002). Nevertheless, ultimate pH might be affected by the treatment applied (Ouhayoun & Dalle Zotte, 1996). Solving the problem of inconsistent tenderness is a top priority for the meat industry (Burns, 2005). Eating satisfaction results from the interaction of this quality characteristic with other factors like juiciness and flavour (Koohmaraie, 1996). Texture is a complex concept that includes many different factors, including fibrosity, cohesiveness, chewiness and tenderness. Meat tenderness and texture are important factors for consumers because they determine the commercial value of the meat and the way it will be cooked (tenderized or processed; Lepetit & Culioli, 1994). Texture can be assessed by taste panels or by instrumental analysis (San˜udo et al., 2003) and is influenced by three main factors; sarcomere length, the amount of connective tissue and its degree of cross-linking, and the extent of proteolytic changes that occur during conditioning post-mortem. Large amounts of intramuscular fat, which is scarce in rabbits, will also increase tenderness. The mechanical properties of meat depend on many types of fibres. In order to analyze the role played by each structure in the overall mechanical behaviour of meat, numerous devices and working conditions are used. These methods have been established by correlating a mechanical property with some characteristics of structure analyzed (Lepetit, 1991). Connective and myofibrillar characteristics can be quantified mechanically by testing stress at low and high compression rates in raw meat (Lepetit, 1991). Alternatively, Warner–Bratzler shear force, which has been widely used to evaluate cooked meat, can be considered to reflect both myofibrillar and connective tissue tough-

ness. Warner–Bratzler shear force is accepted as a good predictor of tenderness observed sensorially and could be used as a criterion to determine meat acceptability (San˜udo et al., 2003), at least in species more widely studied than rabbit. The leanness of rabbit meat increases the relative importance of tenderness measurements of rabbit meat quality. This is especially important in the Spanish market since consumers prefer low weight carcasses. In any case, rabbit meat is more tender than meat from other species (Lawrie, 1991). The effect of transport on rabbit meat quality, as measured by a modified compression device (even under optimal transport conditions, as in our study), will have a significant influence on overall appreciation of the meat. It is foreseeable that under sub-optimal conditions, the effect of transport stress on rabbit meat quality should be much higher. In our study, the 7 h journey had a significant effect on the instrumental quality of rabbit meat, as measured by a modified compression device, which reflects the mechanical resistance of the myofibril structure (K20) and connective tissue strength (K80) (Lepetit & Culioli, 1994). Both season and transport time had a significant effect on K20, which was lowest after long journeys in summer. Thus, tenderness is highly related to primary toughness due to myofibril structure resistance. Unlike Dal Bosco et al. (1997), who found a ‘‘greater shear force in animals subjected to long transportation’’, shear force values did not differ with respect to transport times. Our findings agree with other authors (Masoero et al., 1992; Trocino et al., 2002). Season had a significant effect on meat texture parameters measured using a Warner–Bratzler shear device, shear force and toughness. Furthermore, the effect of the transport time on tenderness did not appear to be independent of environmental temperature, as reflected by the significant interaction between transport time and season, with opposite effects of journey length on tenderness evaluated by Warner–Bratzler in summer than winter. This interaction between transport time and season could be related to the seasonal variation of the energy metabolism. Nevertheless, it is a speculation and, clearly, the seasonal effect and its interaction with transport time require further investigation. One of the most important aspects in terms of meat appearance is colour, which the consumer uses as an indicator of quality and freshness (Faustman & Cassens, 1990; Naumann, Rhodes, Brady, & Kiehl, 1957). The quantity of myoglobin in muscle determines colour. The proportion of reduced and oxygenated myoglobin provides a subjective idea of freshness and oxidized myoglobin (grey-brown) or metmyoglobin is undesirable. Colour stability can be associated with pre-slaughter treatment (Renerre, 1990). The potential effects of transportation on the colour of rabbit meat are not well known. Dal Bosco et al. (1997) evaluated the effect of 400 and 15 km transportation on meat from 12-week-old rabbits. In the muscles of animals transported 400 km, L* decreased, and a* and b* increased

G.A. Marı´a et al. / Meat Science 72 (2006) 773–777

significantly. Dal Bosco et al. (1997) suggested that a* values might be a consequence of high pH values. Other studies (Ouhayoun & Lebas, 1994) found that lightness values were lower in meat from animals subjected to long transportation. Jolley (1990) reported that transport time decreases lightness and colour saturation, which makes meat look darker, but with no detrimental effect on quality. In our study, colour values were similar to those reported by Trocino et al. (2002), but higher than in Jolley (1990). Transport time increased a* and C* values, which could be related with higher pigment content (Renerre, 1990). However, transport time did not significantly influence other colour parameters. Time of year affected all meat colour parameters, but the effects were not enough to have a negative effect on meat quality, as colour CIELAB differences (DE*) were small and difficult to distinguish with the naked eye (Abril et al., 2001). Transport and season had significant effects on chroma. Hue did not change with transport time but in terms of season, meat was slightly more red in winter and orange in summer. In general, transport time affected several measures of meat quality and this effect depended on the time of year the rabbits were transported. The effect was higher in summer than in winter, therefore time of year might be a medium stressor that acts independently of transport time. Based on our results, the multifactor stressors involved in the transport process can affect rabbit meat quality even under optimal transport conditions. References ¨ nenc, A., San˜udo, C., Albertı´, P., & Abril, M., Campo, M. M., O Negueruela, A. I. (2001). Beef colour evolution as a function of ultimate pH. Meat Science, 58, 69–78. Boakye, K., & Mittal, G. (2004). Changes in pH and water holding properties of Longissimus dorsi muscle during beef ageing. Meat Science, 12, 269–279. Buil, T., Maria, G. A., Villarroel, M., Liste, G., & Lopez, M. (2004). Critical points in the transport of commercial rabbits to slaughter in Spain that could compromise animalsÕwelfare. World Rabbit Science, 12, 269–279. Burns, R. (2005). The fibrous microstructure of meat. Available from: . Campo, M. M., Santolaria, P., San˜udo, C., Lepetit, J., Olleta, J. L., Panea, B., et al. (2000). Assessment of breed and ageing effects on beef meat quality using different texture devices. Meat Science, 55, 371–378. Can˜eque, V. & San˜udo, C. (2001). Metodologı´a para el estudio de la calidad de la canal y de la carne en rumiantes. Monografı´as INIA, Ganadera No. 1. Ministerio de Ciencia y Tecnologı´a.

777

Dal Bosco, A., Castellini, C., & Berbnardini, M. (1997). Effect of transportation and stunning method on some characteristics of rabbit carcasses and meat. World Rabbit Science, 5(3), 115–119. Dalle Zotte, A. (2002). Perception of rabbit meat quality and major factors influencing the rabbit carcass and meat quality. Livestock Production Science, 75(2002), 11–32. Faustman, C., & Cassens, R. G. (1990). The biochemical basis for discoloration in fresh meat: a review. Journal of Muscle Foods, 1, 217–243. Gregory, N. G. (1998). Animal Welfare and Meat Quality. 085199296X. UK: CABI Publishing. Honikel, K. O. (1998). Reference methods for the assessment of physical characteristics of meat. Meat Science, 49(4), 447–457. Jolley, P. D. (1990). Rabbit transport and its effects on meat quality. Applied Animal Behaviour Science, 28, 119–134. Koohmaraie, M. (1996). Biochemical factors regulating the toughening and tenderization processes of meat. Meat Science, 43, S193–S201. Lawrie, R. A. (1991). Meat Science (5th ed.). Oxford, UK: Permagon Press. Lepetit, J., & Culioli, J. (1994). Mechanical properties of meat. Meat Science, 36, 203–207. Lepetit, J. (1991). Theoretical strain range in raw meat. Meat Science, 29, 271–283. Masoero, G., Riccioni, L., Bergoglio, G., & Napolitano, F. (1992). Implications of fasting and the transportation for a high quality rabbit meat product. Journal of Applied Rabbit Research, 15, 841–847. Naumann, H. D., Rhodes, V. J., Brady, D. E., & Kiehl, E. R. (1957). Discrimination techniques in meat acceptance studies. Food Technology, 2, 123. Ouhayoun, J. & Lebas, F. (1994). Effets de la die´te hydrique, du transport et de lÕattente avan lÕabattage sur les composantes du rendement et sur les caracte´ristiques physicochimiques. In: 6e´ mes Journee´es de la Rechcerche Cunicole. La Rochelle, France (Vol. 2, pp. 443–448). Ouhayoun, J. & Dalle Zotte, A. (1996). Harmonization in rabbit meat research muscle and meat criteria. In: Proceedings of the sixth World Rabbit Congress, Toulouse (Vol. 3, pp. 217–224). Purchas, R. W., & Aungsupakorn, R. (1993). Further investigation into the relationship between ultimate pH and tenderness for beef samples from bulls and steers. Meat Science, 34, 163–178. Renerre, M. (1990). Review: factors involved in the discoloration of beef meat. International Journal of Food Science and Technology, 25, 613–630. San˜udo, C., Alfonso, M., Sanchez, A., Berge, P., Dransfield, E., Zygoyiannis, D., et al. (2003). Meat texture of lambs from different European production systems. Australian Journal of Agricultural Research, 54, 551–560. SAS. (1988). UserÕs guide: statistics. Release 6.03. Cary, NC. Trocino, A., Xiccato, G., Queaque, P. I., & Sartori, A. (2002). Effect of transport duration and sex on carcass and meat quality of growing rabbits. In: Proceedings of the second rabbit congress of the America (pp. 232–235). La Habana, Cuba. Xiccato, G., Paragini-Bini, R., Dalle Zotte a. & Carazzolo, A. (1994). Effect of age, sex and transportation on the composition and sensory properties of rabbit meat. In: Proceedings of the 40th international congress meat science and technology (ICoMST) (pp. W-2.02). The Hague, Netherlands.