Effects of rigor temperature and electrical stimulation on venison quality

MEAT SCIENCE Meat Science 75 (2007) 564–574 www.elsevier.com/locate/meatsci

Effects of rigor temperature and electrical stimulation on venison quality A.E.D. Bekhit b, M.M. Farouk b

a,*

, L. Cassidy a, K.V. Gilbert

a

a AgResearch Limited, Ruakura MIRINZ Centre, Private Bag 3123, Hamilton, New Zealand Agriculture and Life Sciences Division, Lincoln University, PO Box 84, Canterbury, New Zealand

Received 2 May 2006; received in revised form 11 September 2006; accepted 11 September 2006

Abstract The effects of rigor temperature and electrical stimulation on venison quality were assessed using venison longissimus dorsi muscle. In the first trial, effect of rigor temperature (0, 15, 25, 30, 35 and 42 C) and time post-mortem (at rigor, 3, 7 and 14 days) on drip and cooking losses, % expressible water (water holding capacity, WHC), sarcomere length, protein solubility, meat tenderness and colour were investigated. In the second trial, the effects of rigor temperature (15 and 35 C), electric stimulation (stimulated or not stimulated) and time (at rigor, 3 and 6 weeks post-mortem) on tenderness and colour were further investigated. Results of the first trial showed no clearly established trends of the effect of rigor temperature and time on the cooking and drip losses and protein solubility except venison muscles that went into rigor at 42 C tended to have higher drip loss and lower protein solubilities compared to muscles that went into rigor at the other temperatures. Venison water holding capacity (WHC) decreased with the increase in rigor temperature (P < 0.001) and venison became more tender with time post-mortem. Venison colour improved with increasing rigor temperature. During display, samples that went into rigor at 15, 25 and 35 C had the lowest and those at 0 and 42 C had the highest rate of change of redness (a*) value with time. In the second trial, tenderness was improved by stimulation (P = 0.01). Redness (a*) values were affected by rigor temperature (P < 0.01) and post-mortem time (P < 0.001) but not by electrical stimulation. It is concluded that venison tenderness can be improved via the manipulation of rigor temperature to obtain acceptable level of tenderness early post-mortem with less damaging effect on colour stability.  2006 Elsevier Ltd. All rights reserved. Keywords: Venison; Electrical stimulation; Rigor temperature; Protein solubility; Meat quality; Colour

1. Introduction Over 90% of New Zealand venison is exported (Wiklund, Stevenson-Barry, Duncan, & Littlejohn, 2001), thus close attention to its quality remain a focus and a priority for New Zealand meat industry. The temperature at which a muscle enters rigor has a profound effect on the quality of meat produced (Chrystall & Devine, 1985; Hertzman, Olsson, & Tornberg, 1993; Ledward, 1985). The temperaturedependent pH decline (glycolysis) has been widely reported in the literature. As rigor temperature increases, the rate of pH decline increases. However, the outcome of the temperature–pH decline relationship is quite complex. For exam-

*

Corresponding author. Tel.: +64 7 838 5260; fax: +64 7 838 5625. E-mail address: [email protected] (M.M. Farouk).

0309-1740/$ - see front matter  2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2006.09.005

ple, when a muscle enters rigor at high temperature, the activity of the proteolytic enzymes is stimulated (Dutson, Yates, Smith, Carpenter, & Hostelter, 1977; Moeller, Fields, Dutson, Landmann, & Carpenter, 1976; Zeece & Katoh, 1989). Also, the fast rate of rigor development can lead to the release of calcium ions and to an increase in the calcium-dependent proteases, calpains, (Dransfield, 1994). However, at high temperature and rapid pH decline, the calpains activity and stability is greatly compromised (Simmons, Singh, Dobbie, & Devine, 1996; Thompson, Goll, & Kleese, 1990). Meat tenderness can be negatively affected under the aforementioned conditions due to the tightly packed structure resulting from heat shortening. This could prevent the proteases the access to their substrates (Rees, Trout, & Warner, 2002b). The effect of rigor temperature on the quality of meat at the onset of rigor and during post-mortem storage have

A.E.D. Bekhit et al. / Meat Science 75 (2007) 564–574

been reported for lamb (Devine et al., 2002; Geesink, Bekhit, & Bickerstaffe, 2000), beef (Babiker & Lawrie, 1983; Farouk & Swan, 1998; Hertzman et al., 1993; Rhee & Kim, 2001; Simmons et al., 1996) and pork (Rees, Trout, & Warner, 2002a, 2002b). Such information for venison, to the best of our knowledge, is not available. This is important as previous research on different species reported differing conclusions in regard to the effect of rigor temperature on the quality of meat, hence, extrapolating information from other species to venison would not be appropriate. The objectives of the present study were to investigate the effects of rigor temperature (0, 15, 25, 30, 35 and 42 C) and the combined effects of rigor temperature (15 and 35 C) and electrical stimulation on the quality of venison. 2. Material and methods 2.1. Animals Eighteen female red deer (Cervus elaphus; age 2–3 years) were used in two experiments to study the effects of a range of rigor temperatures (0–42 C) and the combined effects of rigor temperature (15 or 35 C) and electrical stimulation on the quality of venison. 2.1.1. Experiment 1: effects of rigor temperature on venison quality Animals (n = 6) were slaughtered in a processing plant licensed for export following the standard practices (captive bolt stunning, no electrical stimulation). The longissimus muscles from the right and left sides of the carcass were removed (about 20 min from slaughter) after dressing. The muscles were quickly transferred to an insulated box and conveyed to the MIRINZ centre (30 min from kill) where further processing took place. The muscles were trimmed of visible fat and were each divided into three portions (each 682 ± 145 g) yielding six portions per animal. Portions were double bagged and immersed in water baths with controlled temperatures set at 0, 15, 25, 30 35 and 42 C to represent the rigor temperatures. The portions were assigned to rigor temperatures in such a way that muscle sides (left, right) and positional effects (top, middle or bottom) were removed. The pH decline in the muscles at each rigor temperature were monitored until a pH of <5.8 was reached, then the portions were sliced into steaks (2.5 cm thick) and assigned to tenderness (at rigor, 3, 7 and 14 days post-mortem), colour stability (at rigor and 7 days post-mortem only), sarcomere length (at rigor and 7day post-mortem only) and water holding capacity (rigor, 7 and 14 days post-mortem) measurements. The samples assigned to 3, 7 and 14 days postmortem measurements were vacuum packed and stored at 1.5 C. Cooking and drip losses were determined on these samples.

565

2.1.2. Experiment 2: effects of rigor temperature and electrical stimulation on venison quality Twelve female red deer were slaughtered in two groups of 6 (1 week apart) as described in experiment 1. The carcasses were randomly allocated to entering rigor at either 15 or 35 C (n = 3 for each rigor temperature and in each group). Longissimus thoracis et lumborum muscle from the left side of each carcass (n = 6 in each group) was excised immediately and transferred to a chilly bin maintained at the assigned rigor temperatures (no electrical stimulation, non-ES). The right side was treated in the same manner after receiving low voltage electrical stimulation (square wave with 7.5 ms width, rate 15 pulses per second with voltage peak derived from 90 V and current of 125 mA, ES). Carcasses were stimulated with a battery clip attached to the neck and a stainless steel hook contacting the anus. The samples were transferred to MIRINZ centre within 1 h of kill. Loins allocated to 15 C rigor treatment were transferred to a water bath maintained at 15 ± 1 C until the samples reached their ultimate pH (pHu). Loins assigned to 35 C rigor treatment were transferred to hot air tunnel maintained at 35 C until the loins reached their pHu. When each loin reached pHu, it was transferred to a 4 C chiller until further processed at 24 h post-mortem. The four treatment combinations were: no electrical stimulation and rigor temperature 15 C (non-ES 15 C); electrical stimulation and rigor temperature 15 C (ES 15 C); no electrical stimulation and rigor temperature 35 C (non-ES 35 C); and electrical stimulation and rigor temperature 35 C (ES 35 C). Samples for tenderness and colour measurements (Day 1, 3 and 6 weeks post-mortem) were obtained and 3 and 6 weeks samples were treated as described above. 2.1.3. pH and temperature measurements The loins’ pH declines were measured at 1.5 hr postmortem and then every 30 min for the first 6 h of immersion then every 2 h until rigor. For the aged samples (3, 7 and 14 days post-mortem), the pH was determined upon opening the bags. Measurements were carried out using Mettler-Toledo pH electrode and meter (model MP125, Mettler-Toledo, Schwerzenbach, Switzerland). Temperature was monitored using kooltrak standard unmounted temperature loggers (model 214002, KoolTrak GmbH, Geisenheim, Germany). 2.1.4. Tenderness measurements Tenderness of steaks was determined objectively by measuring the force required to shear through a cooked sample. Samples were cooked individually in plastic bags immersed in a temperature-controlled water bath until internal temperature of 75 C was recorded by probe thermometer (Eirelec MT130TC, Amber Instruments Ltd., Chesterfield, UK). The cooked samples were cooled on ice and pieces (10 · 10 · 25 mm) were removed parallel to the muscle fibre. The pieces were placed separately in a

566

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MIRINZ tenderometer (Chrystall & Devine, 1991) and the shear force (N) required to cut across the fibres was determined. 2.1.5. Colour measurements Objective colour measurements were obtained for steaks light-exposed surfaces twice daily during 6 days of retail display using MiniScan XE (Model 45/0-L, Hunter Associates Laboratary Inc., Reston, VA). The unit was calibrated using a black standard plate and a white standard C236852. Measurements were CIE L*, a* and b* values and spectral reflectance (400–700 nm) using illuminant C and a 10 observer with an aperture size of 3.5 cm. The chroma (C = [a*2+b*2][1/2]), and hue angle (HA = tan 1 b*/a*) were calculated (AMSA, 1991). 2.1.6. Drip and cooking losses Venison samples at 3, 7 and 14 days post-mortem were used for the determination of drip and cooking losses as described by Farouk and Swan (1998). 2.1.7. Water holding capacity The filter-paper press method developed by Grau and Hamm (1957) was used to measure the amount of expressible water from meat held under pressure (60 kg pressure). The amount of expressed water is inversely proportional to the meat’s water holding capacity (WHC). 2.1.8. Sarcomere length Sarcomere length was determined using the phase contrast microscopy method as described by Wiklund et al. (2001). 2.1.9. Protein solubility measurements Protein solubility was determined as described by Helander (1957) and modified by Farouk and Swan (1998). 2.1.10. Statistical analysis Data from experiment 1 were analysed using an analysis of variance (ANOVA) for 6 (rigor temperatures) · 6 (locations) completely randomised block design. When there were significant effects for the model terms and their interactions, mean separation was accomplished using least squares F-test procedures. Means were separated using least significant differences (P < 0.05, unless stated differently in the text) based on standard errors of differences of means (SED). Data from experiment 2 were analysed as a completely randomised split–split–strip plot design where the carcasses were the whole plot and rigor temperature was the whole plot treatment. Loins from the carcasses were the split plots and electrical stimulation was the split plot treatment. Post-mortem ageing was the split–split–plots and steaks for various measurements were the split–split–strip plots. The analysis was performed using Genstat software (7th edition, release 7.1, Lawes Agricultural Trust, VSN International Ltd., UK). Colour results were tested for repeated measurement effects; how-

ever, the uniformity of the residuals at different times meant that the colour data could be treated as a general ANOVA. It was unfortunate that the animals from the two kills in the second experiment displayed some significant differences in some of the measured parameters, which could be attributed to on farm effects as the two groups were from different farms,. The analysis was accommodated to that effect and will be highlighted where appropriate. The pH decline was fitted by SigmaPlot (version 7.0, SPSS Inc., Chicago, IL). 3. Results and discussion 3.1. pH and temperature measurements The time it took for the temperature of the pre-rigor muscles to equilibrate with the set rigor temperatures increased with the decrease in rigor temperature. Venison muscles reached 42, 35, 30, 25, 15 and 0 C after 2.5, 1, 1, 2, 4 and 9 h, respectively. Except at 15 C, the pH decline in venison muscles was temperature-dependent (Fig. 1a). These results are similar to those reported by Jeacocke (1977) and Farouk and Lovatt (2000) for beef muscles. The lower pH decline at 15 C compared to 0 C could be explained by the increase in glycolysis at temperatures below 10 C due to the increased activity of the contractile actomyosin ATPase of muscles at low temperatures (Jeacocke, 1977). The pH decline was very rapid in muscles at 35 and 42 C compared with the other temperatures reflecting the higher rate of glycolytic changes. The ultimate pH (pHu) for those muscles held at 35 and 42 C was reached after 4.6 ± 0.40 and 2.7 ± 0.21 h, respectively (Fig. 1a). Samples held at 30, 25, 15 and 0 C rigor temperatures reached pHu after 7.5 ± 0.50, 9.5 ± 0.70, 13.3 ± 0.86 and 14.3 ± 0.45 h, respectively. As was earlier reported for beef (Farouk & Swan, 1998; Marsh, 1954) and lamb (Geesink et al., 2000), samples of venison that entered rigor at low rigor temperature (0 C) had higher (P < 0.05) pHu compared to high rigor temperature, 35 and 42 C in the present study (Fig. 1a). This probably reflects differences in time needed to complete glycolysis (Jeacocke, 1977). At 3 days post-mortem, the pHu for all the treatments were lower than at rigor; and samples held at 15 and 42 C had lower (P < 0.05) pHu than those held at 0 and 35 C (Fig. 1a and Table 1). The increased in pH with time post-mortem for all treatments (Table 1) is likely to be due to proteolysis of muscle proteins resulting in the increase in free amino acids and dipeptides in particular carnosine which has notable buffering capacity (Braggins, Frost, Agnew, & Podmore, 1999; Davey, 1960). Similar increase in pHu with post-mortem time has been reported in chicken (Craig, Fletcher, & Papinaho, 1999), lamb (Braggins et al., 1999) and beef (Farouk & Wieliczko, 2003). As expected, the combination of electrical stimulation and high rigor temperatures (15 and 35 C) resulted in fas-

0.45 0.48 0.47 0.54 0.61 0.66

SED

6.0

2

4

6

8

10

12

14

16

T4

T3

6.2

14 d

**

1.50 1.56 0.61 1.0 1.90 2.24 19.51 19.95 20.01y 18.55 17.97 18.06 1.32 ns

x, y

21.76 17.66 17.35x 17.24 17.43 18.56 1.56 ns 20.08 18.35 20.04y 19.70 21.13 14.44 2.54 ns * *

ter rates of pH decline (Fig. 1b). Electrical stimulation had an effect on 15 C rigor temperature samples only. Samples from 15 C NS treated samples exhibited higher (P < 0.05) pH values during rigor and eventually had higher pHu compared with 15 C ES (Fig. 1b). The results suggest that at high rigor temperature (e.g. 35 C) any role for ES will be suppressed by the overwhelming glycolysis rate caused by high temperature whereas at lower rigor temperature (e.g. 15 C), when the glycolysis is not at its maximum rate, an electrical input can significantly contribute to the glycolysis process. Rigor pH was negatively correlated with the development of a* (redness) and % expressible water (Table 3). Also, rigor pH was correlated with shear force values at rigor, 3 and 7 days post-mortem (Table 3). Time to rigor was highly correlated to shear force values and negatively correlated to % expressible water (Table 1). When regression was performed, both time to rigor and pHu accounted for 40% of the variability of meat tenderness. These results underscore the importance of both ultimate pH and the rate of pH decline in regulating the biochemical pro-

0.03 0.03 0.03 0.02 0.03 0.03

Fig. 1. Effects of rigor temperatures (0, 15, 25, 30, 35 and 42 C) (a), and rigor temperature (15 and 35 C) combined with electrical stimulation (b) on pH decline in venison during rigor. ES is electrical stimulation and nonES is non electrical stimulation.

5.58b 5.51a 5.57ab 5.57aby 5.62by 5.56aby 0.03

30

5.60b 5.51a 5.57ab 5.57aby 5.61bxy 5.53xy 0.04 ns

25

5.55a 5.45b 5.50ab 5.50abx 5.55ax 5.46bx 0.02

20

0 15 25 30 35 42 SED Degree of significance, rigor temperature

15

7d

10

Postmortem time (hours)

Cooking loss

5

3d

0

SED

5.4

14 d

5.6

7d

5.8

pH

T1

3d

6.0

SED

T2

Table 1 Effects of rigor temperature and post-mortem time on pH, cooking loss and drip loss in venison longissimus muscle

pH

6.4

*

Drip loss

6.6

3d

6.8

7d

T1 (15˚C Non-ES) T2 (15 ˚C ES) T3 (35 ˚C Non-ES) T4 (35 ˚C ES)

7.0

6.43abxy 5.99abxy 5.28axy 5.61ab 6.04ab 7.16b 0.79

7.2

Rigor temperature (C)

b

5.52abx 5.21abx 4.65ax 5.23ab 5.48ab 6.41b 0.38

Postmortem time (hours)

ns = not significant; SED = standard errors of the difference; * = P < 0.05; ** = P < 0.01; ***;= P < 0.001. a, b Within a column, means that do not have a common script letter differ, P < 0.05;

0

**

5.0

7.02aby 6.57aby 5.76by 6.03b 6.38ab 7.64a 0.35

14 d

5.5

Within a row for each measured parameter, means that do not have a common script letter differ, P < 0.05.

*

*

pH

6.5

*

7.0

*

0 ˚C 15 ˚C 25 ˚C 30 ˚C 35 ˚C 42 ˚C

*

7.5

567

*

a

Degree of significance, post-mortem time

A.E.D. Bekhit et al. / Meat Science 75 (2007) 564–574

568

A.E.D. Bekhit et al. / Meat Science 75 (2007) 564–574

cesses during rigor mortis that dictate meat colour and tenderness.

65

3.2. Drip and Cooking losses Venison samples at 42 C rigor temperature consistently exhibited higher (P < 0.05) drip loss post-mortem than 25 C treated samples (Table 1). There were no differences in drip loss at the other temperatures (0–35 C) in this study. The effect of rigor temperature on drip loss seems to be dependent on species and muscle type under investigation. For instance, in beef (Farouk & Swan, 1998) and lamb (Geesink et al., 2000) post-mortem drip loss increased with increasing rigor temperature (5–35 C range) whereas in pork (Rees et al., 2002) significant decrease in drip loss was found at intermediate temperatures (7 and 14 C) compared with lower and higher temperature (0 and 21 C), which did not differ. Also, Molette, Re´mignon, and Babile´ (2003) found more drip loss in turkey breasts which entered rigor at 40 C compared with 4 and 20 C. This underscores the sensitivity of different species for conditions causing protein denaturation. Cooking losses post-mortem were not affected by temperature treatment (Table 1) which is in agreement with published reports on various species (Devine et al., 2002; Geesink et al., 2000; Molette et al., 2003) but in contrast with the results of Farouk and Swan (1998) who found that cooking losses tended to decrease in fresh unfrozen samples and increase in frozen samples with the increase in rigor temperature (5–35 C) in beef. This might be due to differences in muscle type and the sample size used in the present study and that in Farouk and Swan (1998) rather than differences in species. 3.3. Water holding capacity Venison % expressible water increased (water holding capacity decreased) with the increase in rigor temperature (P < 0.001, Fig. 2). Venison muscles held at 42 C had the lowest (P < 0.001) water holding capacity throughout the storage time, while those held at 0 C exhibited the highest (P < 0.01) WHC at rigor. This effect is likely as a result of protein denaturation resulting from fast pH decline coupled with high muscle temperature especially at temperature above 35 C (Hamm, 1960; Scopes, 1964). Wiklund et al. (2001) reported that WHC in electrically stimulated red deer carcasses was not different from nonelectrically stimulated carcasses. They suggested that the lack of obvious effect for ES on the WHC in venison compared with beef may be due to sufficient cooling rate during the fast pH decline that minimised denaturation or that venison has a greater resistance to the effects of denaturing conditions compared with meat from other species. Our results seem to support the second reasoning because 35 C rigor temperature had a great impact on the WHC in lamb (Geesink et al., 2000) and beef (Farouk & Swan, 1998), but did not have such effect on venison. The percent

% expressible water

60

55

Rigor 3 days PM 7 days PM 14 days PM

cz

50

cx

35

bx

bx

by

bx

45

40

cy

w w

bw

awx aw

wx

ay

bw

aw

bw

bwx aw

aw ax aw

ax 30 0

10

20

30

40

50

Rigor temperature (˚C) Fig. 2. Effects of rigor temperatures (0, 15, 25, 30, 35 and 42 C) on the amount of expressible water (%) of venison at rigor and after post-mortem vacuum storage (3, 7 and 14 days) at 1.5 C. The amount of expressed water is inversely proportional to the meat‘s water holding capacity (WHC). Means with different letters are significantly different (P < 0.05). Letters a–c is for comparison within same rigor temperature. Letters w–z is for comparison within post-mortem time.

expressible water decreased (P < 0.001) with post-mortem time. This is due to the increase in drip loss during storage which resulted in less free water available for expression. This phenomena was found with high rigor temperatures in meat from various species (Farouk, Wieliczko, & Merts, 2003; Geesink et al., 2000; Molette et al., 2003). 3.4. Sarcomere length There was no effect of rigor temperature on the sarcomere length (SL) of venison (P > 0.05; data not shown). It is generally accepted that: (1) rigor temperature affects the degree of muscle fibre shortening, (2) temperatures 65 C and P25 C increase muscle shortening (Geesink et al., 2000; Honikel, Kim, Hamm, & Roncales, 1986; Locker & Hagyard, 1963) and (3) manipulating the rate of glycolysis can produce wide range of sarcomere lengths (Smulders, Marsh, Swartz, Russell, & Hoenecke, 1990). However, reports on the effect of rigor temperature on SL are not consistent. Some investigators have found minimal muscle shortening to occur at 15 C and significant decrease in SL (shortening) at extreme temperatures, e.g. 0 and P35 C (Devine, Wahlgren, & Tornberg, 1996; Geesink et al., 2000; Locker & Hagyard, 1963), while others found an effect only at 0 C and no effect of rigor temperature at the 5–35 C range on SL (Farouk & Lovatt, 2000; Farouk & Swan, 1998; Rees et al., 2002). Our results are in agreement with those of Farouk and Swan (1998), Rees et al. (2002) and Farouk and Lovatt (2000). However, in the present study, it was observed that muscles from different animals reacted differently toward the effects of rigor temperatures in the range 15–35 C, which may indicate that an animal based susceptibility for shortening is present that is normally ignored when the mean values of results

* *** *** *

SP = sarcoplasmic protein solubility; MP = myofibrillar protein solubility; TP = total protein solubility; ns = not significant; SED = standard errors of the difference. * = P < 0.05, ** = P < 0.01, *** = P < 0.001. 1 = standard errors of difference for SP; 2 = standard errors of difference for MP. a–c Within a column, means that do not have a common script letter differ, P < 0.05.; x,y Within a row for each parameter measured at different post-mortem times, means that do not have a common script letter differ, P < 0.05.

*

*

**

**

**

**

ns ns ns ns

0.281 – – – – 0.932 19.48b 19.64b 18.73b 18.30ab 17.05a 16.47a 1.11 13.00b 13.53b 12.60ab 11.85a 10.54a 10.65axy 1.04 6.48by 6.11ab 6.13ab 6.45b 6.50b 5.82a 0.31 18.70b 17.35ab 18.62b 18.46ab 17.11ab 16.80a 0.88

12.31 11.28 12.29 12.19 10.96 11.60y 0.78 ns 6.40ay 6.06ab 6.33a 6.27a 6.16ab 5.21b 0.24 19.18a 19.05a 19.31a 18.18a 18.17a 13.83b 0.61 14.18a 12.83ab 13.38ab 11.62b 12.30ab 8.60cx 0.49

TP MP

5.00bx 6.22ab 5.93ab 6.56a 5.87ab 5.22b 0.33

0 15 25 30 35 42 SED Degree of significance, rigor temperature

MP SP

14 days post-mortem

TP SP SP

MP

7 days post-mortem Rigor

The effect of rigor temperature on venison tenderness is shown in Fig. 3a. There was no effect of rigor temperature on meat tenderness at rigor (P < 0.05). Venison samples that entered rigor at 42 C reached acceptable level of tenderness in 3 days. In fact, 42 C rigor temperature produced more tender venison than the other treatments at all storage times except at 25 C on day 7 and 35 C on day 4 in which the tenderness levels did not differ with that at 42 C. Muscle shortening (cold or heat shortening) and decreased proteolytic activity are the main factors ascribed for meat toughness especially in hot-boned meat (Dutson & Pearson, 1985; Hertzman et al., 1993; Rees et al., 2002a, 2002b). In the present study, venison at 15 C rigor temperature produced tougher meat compared with higher temperatures (e.g. 25, 35 and 42 C). This is consistent with the findings of (Davey & Gillbert, 1976), who demonstrated that the rate of meat tenderisation increased with the increase in temperature up to 60 C. For lamb and pork, it was found that rigor temperature of 14–18 C (Devine et al., 2002; Geesink et al., 2000; Rees et al., 2002b) to be optimal rigor temperature for longissimus muscle as it produced the most tender meat. As in the first trial, venison tenderness in the second experiment was not affected by rigor temperature (P < 0.05) (Fig. 3b). However, kill group had a significant effect on tenderness, with the tenderness of the first kill group significantly affected by temperature while that of the second group was not. Tenderness was affected by

Rigor temperature (C)

3.6. Meat tenderness

Table 2 Effect of rigor temperature and post-mortem time on mean values for protein solubility in venison longissimus muscle

Sarcoplasmic protein solubility at rigor was higher (P < 0.05) in samples held at 30 C rigor temperature compared to those held at 0 and 42 C (Table 2). During postmortem storage, samples held at 42 C had the lowest (P < 0.05) sarcoplasmic protein solubility and it was not different from 15 to 35 C samples at 7 days or 15 and 25 C at 14 days post-mortem. Similarly, myofibrillar and total protein solubilities were lower (P < 0.001) for 42 C treated samples at rigor and during post-mortem. These results are consistent with what has been reported earlier (Farouk & Swan, 1998; Molette et al., 2003). According to Joo, Kauffman, Kim, and Park (1999), sarcoplasmic protein solubility had a strong negative relation with L* and b* values throughout meat display times (r values ranged from 0.406 to 0.646; P < 0.01). In this study, sarcoplasmic and total protein solubility at rigor were highly and negatively correlated to percent expressible water (Table 3), thus % expressible water also can be used as an indicator of protein denaturation.

TP

3.5. Protein solubility

Degree of significance, post-mortem time

from different animals are reported. This variability resulted in high standard deviation and the loss of the ability to detect any effect for rigor temperature although it was clear that 0 and 42 C treatments caused numerically lower SL with very small variability.

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SED

A.E.D. Bekhit et al. / Meat Science 75 (2007) 564–574

0.63 (0.000) 0.46 (0.005) 0.38 (0.024)

0.36 (0.030) 0.46 (0.005)

0.524 (0.001)

0.34 (0.041)

SP 7 d

SP 14 d

SL

0.39 (0.019) 0.47 (0.004) 0.38 (0.024)

0.40 (0.014) 0.49 (0.002) 0.56 (0.000) 0.434 (0.008) 0.36 (0.02) %EW rigor %EW3 d %EW 7 d %EW 14 d TP Rigor

0.381 (0.022)

0.42 (0.011) Time to a* = 12

0.34 (0.041)

0.46 (0.004) 0.35 (0.036) 0.33 (0.052) pH Rigor

250

0˚C 15˚C 25˚C 30˚C 35˚C 42˚C

200

Shear force (N)

0.37 (0.026) 0.66 (0.000) 0.45 (0.006) 0.522 (0.001) 0.51 (0.001) 0.56 (0.000) 0.618 (0.000)

0.33 (0.050) 0.32 (0.055) 0.63 (0.000) 0.35 (0.039) 0.44 (0.007) 0.45 (0.005) 0.50 (0.002) 0.31 (0.071) 0.46 (0.005) Time to rigor

a

b b

150

c b

ab

bc

100

ab a

ab a a

50 SED 0

RIGOR

b

3 DAYS 7 DAYS Post-mortem time

14 DAYS

160 160

B

140 140

stim ES Unstim Non-ES

120 120

Shearforce force(N) (N) Shear

0.40 (0.015)

0.31 (0.066)

0.56 (0.000) 0.314 (0.06) 0.33 (0.046)

0.48 (0.003)

TP 14 d %EW 14 d %EW 7 d %EW 3 d %EW rigor SF 14 d SF 7 d SF 3 d SF Rigor pH Rigor a* 4 h a* 2 h

Table 3 Pearson‘s correlation coefficients for quality indicators of venison entered rigor at different temperatures1

SF = Shear force (N); a* = relative redness (CIE L*a*b* system); %EW = % expressible water; TP = total protein solubility; SP = sarcoplasmic protein solubility; SL = sarcomere length; d = day; 1 Temperatures were 0, 15, 25, 30, 35 and 42 C. P values are in brackets.

A.E.D. Bekhit et al. / Meat Science 75 (2007) 564–574 Time to rigor

570

100 100 80 80 60 60 40 40 20 20 0 0

1 1

15˚C 2 15˚C 2

11 day day

35˚C 3 35˚C 3

4 15˚C 4 15˚C

35˚C 5 35˚C 5

33 weeks weeks Post-mortem Post-mortem time time

15˚C 6 15˚C 6

35˚C 7 35˚C 7

66 weeks weeks

Fig. 3. Effects of rigor temperatures (0, 15, 25, 30, 35 and 42 C) (a), and rigor temperature (15 and 35 C) combined with electrical stimulation (b) on venison shear force at rigor and during post-mortem ageing. ES is electrical stimulation and non-ES is non electrical stimulation. Means within each post-mortem time with different letters (a–c) are significantly different (P < 0.05). Standard error of differences (SED) for B is 8.95.

stimulation (P = 0.01), post-mortem storage (P < 0.001) and their interactions (P < 0.05). Electrical stimulation made venison more tender particularly at 1 day post-mortem (Fig. 3b). The tenderness level at 1 day post-mortem was more pronounced in samples held at 35 C compared to 15 C which was equivalent to the tenderness achieved in venison samples that entered rigor at 42 C at 3 days post-mortem. However, the rate of tenderisation was 40, 45, 60 and 66% for ES 35 C, non-ES 35 C, ES 15 C and non-ES 15 C, respectively, after 3 weeks post-mortem storage relative to the values at 1 day post-mortem. The higher rate of tenderisation in 15 C treatment (ES and non-ES) is likely to be the result of the apparent higher shear forces at 1 day post-mortem in those samples, which signifies that more substrates were available for the proteolytic enzymes to act on. This is supported by the observation that not

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much improvement in tenderness occurred beyond 3 weeks of post-mortem storage (Fig. 3b). Electrical stimulation was reported to enhance proteolysis (Babiker & Lawrie, 1983; Davey & Gillbert, 1976). Although it was speculated that ES may cause some changes in the muscle system which help to protect its protein from the effects of exposure to high temperature (Babiker & Lawrie, 1983) and that high temperature may negatively affect the calpain system (Geesink et al., 2000; Simmons et al., 1996), it is possible that the positive enthalpy required for activation could be derived either through high temperature treatment (Davey & Gillbert, 1976; Fig. 3a) or a combination of intermediate temperature and ES (Fig. 3b); regardless, an effect for ES per se can not be ruled out as it has been shown that ES beef incubated at 2 C was more tender than ES beef incubated at 40 C (Babiker & Lawrie, 1983). 3.7. Colour Colour parameters (L*, a* and b*) were affected by rigor temperature (P < 0.001), storage (P < 0.001) and display (P < 0.001) times. At rigor, all the colour parameters increased with the increase in temperature (Fig. 4). After blooming, venison samples that entered rigor at 42 C were lighter and redder and those that went into rigor at 0 C were darker and less red compared to samples that went into rigor at the other temperatures (Fig. 4). This is most likely as a result of protein denaturation at 42 C (Swatland, 1984) and the reduced activity of enzyme system responsible for oxygen depletion at that temperature (Ledward, 1992). These results are in agreement with those in beef (Farouk & Swan, 1998; Young, Prioli, Simmon, & West, 1999) and lamb (Bekhit, Geesink, Morton, & Bickerstaffe, 2001; Geesink et al., 2000). During display, 15, 25 and 35 C treated venison exhibited the lowest rate of change of a* value whereas 0 and 42 C treatments had the highest. This was clearly demonstrated by the time to achieve a* value equal to 12 (the cut off level of acceptable colour, Wiklund et al., 2001). The average time of acceptable colour was 6, 8.5, 9.5, 6.5, 8.5 and 6 days for 0, 15, 25, 30, 35 and 42 C, respectively. Unlike in beef and lamb (Geesink et al., 2000), there was an effect for rigor temperature on the colour of 7 days post-mortem venison (P < 0.001). The initial a* values of 7 days post-mortem venison sample were higher (P < 0.01) for all treatments compared with rigor samples (Fig. 4). This increase in a* could be attributed to the diminished mitochondrial respiration and reduced oxygen consumption after 7 days of vacuum packaging storage (Bendall, 1972; Bendall & Taylor, 1972; DeVore & Solberg, 1974). However, a faster rate of discolouration was found in 7 days post-mortem samples compared with rigor samples. The time (in days) to a* equal 12 was half that found with at rigor samples (3, 4.3, 5.8, 2.5, 2.5 and 3 days for 0, 15, 25, 30, 35 and 42 C, respectively). Ledward (1992) suggested that oxygen consumption rate dictates the colour stability of meat early post-mortem while MetMb reducing activity is the dominant factor for colour stability after ageing. That

571

view, however, ignored the disrupted balance between proand anti-oxidants in meat during post-mortem ageing. During post-mortem aging, the balance between pro-oxidative and antioxidative factors favours oxidation (Morrissey, Sheehy, Galvin, Kerry, & Buckley, 1998). Moreover, as any role for MetMb reducing activity during aerobic display is limited by rapid catabolism of NADH during post-mortem storage (Echeverne, Renerre, & Labas, 1990), and that oxidative processes are propagated due to ageing (Renerre, 1999), it is logical to account for the fast rate of discolouration post-mortem in venison at high temperatures (>25 C) to increased oxidative processes. Venison muscles that entered rigor at 25 C, exhibited the longest acceptable display time at rigor and at 7 days post-mortem. Early post-mortem colour measurements (e.g. a* at 2 and 4 h of display) were correlated with venison colour shelf-life, WHC and protein solubility (Table 3). In the first trial, tenderness of samples that went into rigor at 35 C did not differ from the samples that entered rigor at 42 C. The 35 C samples had good display time at rigor, but very low colour shelf-life upon vacuum storage. We hypothesised that by applying ES, the colour stability in 35 C could be improved as it has been shown that ES treated meat accumulates less MetMb (Renerre, 1984) and exhibited more appealing colour (Eikelenboom, Smulders, & Ruderus, 1985; Savell, Smith, & Carpenter, 1978; Smith, 1985; Tang & Henrickson, 1980; Unruh, Kastner, Kropf, Dikeman, & Hunt, 1986). Also, the tenderness in 15 C treatment, which had high shelf-life, probably could benefit from ES treatment (Chrystall & Devine, 1983; Drew, Crosbie, Forss, Manley, & Pearse, 1988). In this study, a* values were affected by rigor temperature (P < 0.01) and post-mortem storage (P < 0.001) and no effects were found for ES. The effect of ES on meat colour is dependent on the pH–temperature relationship, ES intensity and, the muscle tissue structure. Electrical stimulation has generally been associated with improvement of the fresh meat appearance by imparting a lighter bright red colour on the meat surface (Eikelenboom et al., 1985; Savell et al., 1978; Smith, 1985; Tang & Henrickson, 1980; Unruh et al., 1986) and reduced MetMb accumulation (Renerre, 1984). However, the advantage of electrical stimulation disappeared after vacuum packaged ageing (Geesink et al., 2000; Moore & Young, 1991). Also, the effect seems to be dependent on ES intensity (Mareko, 2000) and muscle type (Ledward, 1985). For example, while a reduction in the colour stability of deep muscles such as semimembranosus is caused by ES, a surface muscle such as LD was unaffected (Ledward, 1985). Giving that all the samples in the present study were derived from LD muscles and exposed to same ES conditions, it is reasonable to assume that any effects for ES on the pH–temperature profile was superseded by the constant temperature effects. That was clear from the effects of rigor temperature at different post-mortem times (Table 4). The display-life of venison that went into rigor at 35 C was half that at 15 C for 1 day and 3 weeks post-mortem times.

572

35

35

35

36

35

35

35

Rigor temperature (˚C)

34 33 33

35 35 35

34

35 35

32 20 32 34

34 33 15 33

35 34

35 35 35

35 35

14

14

16

25 12

14

14

16 20 14

12

14

12

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10

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12

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6 6

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4

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6

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6 7

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0 20

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5 34

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25

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Rigor temperature (˚C)

30

0 20

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120

140

20

40

60

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120

140

Display time (hrs)

Fig. 4. Contour maps represents the changes in colour parameters (L*, a* and b*) during retail display for venison at rigor (top row) and 7 days (bottom row) post-mortem. Venison muscles entered rigor at different temperatures (0, 15, 25, 30, 35 and 42 C).

A.E.D. Bekhit et al. / Meat Science 75 (2007) 564–574

34

36

35

35

12 30

35

25

7

7

8

35

35 36

36

7 6

16

35 35

35

35

34

7

40 12

16

35 35

12

14

14

35

35 34

30

18

40

35

Rigor temperature (˚C)

36 37 36

35

36

Rigor temperature (˚C)

38

40

b*

a*

L*

16.90a 18.64ab 20.50b 19.10abc 18.17ab 22.11d 22.16d 21.84cd 20.37bcd 19.14abc 20.95bcd 19.40abc d 1.48 SED

35 C

15 C 6 weeks

35 C

15 C 3 weeks

35 C

ES Non-ES ES Non-ES ES Non-ES ES Non-ES ES Non-ES ES Non-ES 15 C 1 day

ES = Electrical stimulation; Non-Es = no electrical stimulation. a–d Within a column, means that do not have a common script letter differ, P < 0.05. Shaded area represent the time when the samples colour will not be acceptable (a* 6 12).

13.55e 12.64e 6.69ab 7.24bc 8.22cd 8.92d 6.21ab 6.21ab 5.67a 5.69a 5.85a 5.80a 0.69 13.93d 12.78d 8.30b 8.53b 9.00bc 10.19c 6.87a 6.58a 6.28a 6.56a 6.12a 5.74a 0.67 14.44c 13.35c 10.33b 10.40b 9.54b 10.56b 6.8a 6.98a 7.01a 7.65a 6.57a 6.42a 0.84 14.86d 14.75d 12.59c 12.47c 10.71b 11.26bc 7.94a 8.11a 8.22a 8.37a 8.08a 7.32a 0.83 18.31a 19.80ab 21.78bc 20.37ab 21.15bc 22.38bc 23.47c 21.82bc 21.22bc 20.43ab 22.10bc 19.89ab 1.40

14.77a 15.48a 17.86bc 17.56b 20.25b 21.78d 21.75d 20.32cd 20.74d 19.58bcd 21.69d 20.20bcd 1.36

18.52d 17.49bcd 18.62d 18.14cd 15.80ab 17.16bcd 16.62bcd 15.32ab 14.30a 14.00a 15.82abc 14.22a 1.17

16.16h 15.78eh 14.92deh 14.12de 12.1bc 13.62cd 11.67ab 10.72ab 10.8ab 10.48ab 11.5ab 10.03a 0.89

120 100 75 55 30 6

1

2 1

Display time (h) Treatment Rigor temperature Post-mortem time

Table 4 Effects of electrical stimulation, rigor temperature and post-mortem storage on redness (a*) of venison during retail display at 4 C

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4. Conclusion and implications In the present study, we have shown that venison tenderness can be improved via the manipulation of rigor temperature to obtain acceptable level of tenderness early post-mortem with less damaging effect on the colour stability. Venison seems to be more resistant to conditions causing denaturation compared to beef and lamb. Early measurements of venison quality indicators can be utilised at rigor to predict the quality at later storage periods. This would need to be confirmed with a larger trial. Acknowledgements The financial support of the New Zealand Foundation of Research Science & Technology and the technical assistance of AgResearch MIRINZ Centre Meat Science team and John Waller of AgResearch for statistical analyses is much appreciated. References AMSA. (1991). Guidelines for meat color evaluation. The American Livestock and Meat Board, Chicago, IL. Babiker, S. A., & Lawrie, R. A. (1983). Post-mortem electrical stimulation and high temperature ageing of hot-deboned beef. Meat Science, 8, 1–20. Bekhit, A. E. D., Geesink, G. H., Morton, J. D., & Bickerstaffe, R. (2001). Metmyoglobin reducing activity and colour stability of ovine longissimus muscle. Meat Science, 57, 427–435. Bendall, J. R. (1972). Consumption of oxygen by the muscles of beef animals and related species and it‘s effect on the colour of meat. I: Oxygen consumption in pre-rigor muscle. Journal of the Science of Food and Agriculture, 23, 61–72. Bendall, J. R., & Taylor, A. A. (1972). Consumption of oxygen by the muscles of beef animals and related species. II Consumption of oxygen in post-rigor muscle. Journal of the Science of Food and Agriculture, 23, 707–719. Braggins, T. J., Frost, D. A., Agnew, M. P., & Podmore, C. (1999). Changes in pH and free amino acides in sheep meat during extended chilled storage. In: Proceedings of the 45th international congress of meat science and technology (pp. 416–417). Yokohama, Japan. Chrystall B. B., & Devine, C. E. (1991). Quality assurance for tenderness. Publication No. 872. Meat Industry Research Institute of New Zealand, Hamilton. Chrystall, B. B., & Devine, C. E. (1983). Electrical stimulation of deer carcasses. New Zealnad Journal of Agricultural Research, 26, 89–92. Chrystall, B. B., & Devine, C. E. (1985). Electrical stimulation Its early development in New Zealand. Advances in Meat Research. (pp. 73–119). Westport, CT: AVI Publishing Co. Craig, E. W., Fletcher, D. L., & Papinaho, P. A. (1999). The effects of ante-mortem electrical stunning and post-mortem electrical stimulation on biochemical and textural properties of broiler breast meat. Poultry Science, 78, 490–494. Davey, C. L. (1960). The effect of carnosine and anserine on glycolytic reactions in skeletal muscle. Archives of Biochemistry and Biophysics, 89, 296–302. Davey, C. L., & Gillbert, K. V. (1976). The temperature coefficient of beef ageing. Journal of the Science of Food and Agriculture, 27, 244–250. Devine, C. E., Wahlgren, M. A., & Tornberg, E. (1996). The effects of rigor temperature on shortening and meat tenderness. In: Proceedings of the 42nd international congress of meat science and technology (pp. 396–397). Lillehammer, Norway.

574

A.E.D. Bekhit et al. / Meat Science 75 (2007) 564–574

Devine, C. E., Steven, R. P., Peachey, B. M., Lowe, T. E., Ingram, J. R., & Cook, C. J. (2002). High and low rigor temperature effects on sheep meat tenderness and ageing. Meat Science, 60, 141–146. DeVore, D. P., & Solberg, M. (1974). Oxygen uptake in post-rigor muscle. Journal of Food Science, 39, 22–28. Dransfield, E. (1994). Optimisation of tenderisation, ageing and tenderness. Meat Science, 36, 105–121. Drew, K. R., Crosbie, S. F., Forss, D. A., Manley, T. R., & Pearse, A. J. (1988). Electrical stimulation and aging of carcasses from red, fallow and New Zealand wapiti-type male deer. Journal of the Science of Food and Agriculture, 43, 245–259. Dutson, T. R., & Pearson, A. M. (1985). Postmortm conditioning of meat. In A. M. Pearson & T. R. Dutson (Eds.). Advances in meat research eletrical stimulation (vol. 1, pp. 45–72). Connecticut: AVI Publishing Company. Dutson, T. R., Yates, L. D., Smith, G. C., Carpenter, Z. L., & Hostelter, R. L. (1977). Rigor onset before chilling. Proceedings of Reciprocal Meat Conference of the American Meat Science Association, 30, 79–86. Echeverne, C., Renerre, M., & Labas, R. (1990). Metmyoglobin reductase activity in bovine muscles. Meat Science, 27, 161–172. Eikelenboom, G., Smulders, F. J. M., & Ruderus, H. (1985). The effects of high and low voltage electrical stimulation on beef quality. Meat Science, 15, 247–254. Farouk, M. M., & Lovatt, S. J. (2000). Initial chilling rate of pre-rigor beef muscles as an indicator of colour of thawed meat. Meat Science, 56, 139–144. Farouk, M. M., & Swan, J. E. (1998). Effect of rigor temperature and frozen storage on functional properties of hot-boned manufacturing beef. Meat Science, 49, 233–247. Farouk, M. M., & Wieliczko, K. J. (2003). Effect of diet and fat content on the functional properties of thawed beef. Meat Science, 64, 451–458. Farouk, M. M., Wieliczko, K. J., & Merts, I. (2003). Ultra-fast freezing and low storage temperatures are not necessary to maintain the functional properties of manufacturing beef. Meat Science, 66, 171–179. Geesink, G. H., Bekhit, A. D., & Bickerstaffe, R. (2000). Rigor temperature and meat quality characteristics of lamb longissimus muscle. Journal of Animal Science, 78, 2842–2848. ¨ ber das Wassesbindungsvermo¨gen des Grau, R., & Hamm, R. (1957). U ¨ ber die Bestimmung der Wasserbindung Sa¨ugetiermuskels. II Mitt. U des Muskels. Z. Lebensm. Untersuch. Forsch., 105, 446–460. Hamm, R. (1960). Biochemistry of meat hydration. In C. O. Chichester, E. M. Mrak, & G. F. Stewart (Eds.). Advances in food research (Vol. 10, pp. 356–463). New York: Academic Press. Helander, E. (1957). On quantitative muscle protein determination. Acta Physiologica Scandinavica, 41(Suppl.), 141. Hertzman, C., Olsson, U., & Tornberg, E. (1993). The influence of high temperature, type of muscle and electrical stimulation on the course of rigor, ageing and tenderness of beef muscles. Meat Science, 35, 119–141. Honikel, K. O., Kim, C. J., Hamm, R., & Roncales, P. (1986). Sarcomere shortening of prerigor muscle and its influence on drip loss. Meat science, 16, 267–282. Jeacocke, R. E. (1977). The temperature dependence of anaerobic glycolysis in beef muscle held in a linear temperature grident. Journal of the Science of Food and Agriculture, 28, 551–556. Joo, S. T., Kauffman, R. G., Kim, B. C., & Park, G. B. (1999). The relationship of sarcoplasmic and myofibrillar protein solubility to colour and water-holding capacity in porcine longissimus muscle. Meat Science, 52, 291–297. Ledward, D. A. (1985). Post-slaughter influences on the formation of metmyoglobin in beef muscles. Meat Science, 15, 149–171. Ledward, D. A. (1992). Colour of raw and cooked meat. In D. A. Ledward, D. E. Johnston, & M. K. Knight (Eds.), The chemistry of muscle-based foods (pp. 33–68). Cambridge: The Royal Society of chemistry. Thomas Graham House, Science Park. Locker, R. H., & Hagyard, C. J. (1963). A cold shortening effect in beef muscles. Journal of the Science of Food and Agriculture, 14, 787–793.

Mareko, M. H. D. (2000). Effects of pre-slaughter stress and electrical stimulation intensity on meat tenderness. MSc Thesis, Lincoln University, New Zealand. Marsh, B. B. (1954). Rigor mortis in beef. Journal of the Science of Food and Agriculture, 5, 70–75. Moeller, P. W., Fields, P. A., Dutson, T. R., Landmann, W. A., & Carpenter, Z. L. (1976). High temperature effects on lysosomal enzyme distribution and fragmentation of bovine muscle. Journal of Food Science, 42, 510–512. Molette, C., Re´mignon, H., & Babile´, R. (2003). Maintaining muscles at a high post-mortem temperature induces PSE-like meat in turkey. Meat Science, 63, 525–532. Moore, V. J., & Young, O. A. (1991). The effects of electrical stimulation, thawing, aging and packaging on the colour and display life of lamb chops. Meat Science, 30, 131–145. Morrissey, P. A., Sheehy, P. J. A., Galvin, K., Kerry, J. P., & Buckley, D. J. (1998). Lipid stability in meat and meat products. Meat Science, 49, S73–S86. Rees, M. P., Trout, G. R., & Warner, R. D. (2002a). Tenderness, ageing rate and meat quality of pork M. longissimus thoracis et limborum after accelerated boning. Meat Science, 60, 113–124. Rees, M. P., Trout, G. R., & Warner, R. D. (2002b). Tenderness of pork M. longissimus thoracis et lumborum after accelerated boning. Part I. Effect of temperature conditioning. Meat Science, 61, 205–214. Renerre, M. (1984). Effect of electrical stimulation on meat colour. Science. Renerre, M. (1999). Biochemical basis of fresh meat colour. In: Proceedings of the 45th international conference of meat science and technology (ICoMST) (pp. 344–353). Yokohama, Japan. Rhee, M. S., & Kim, B. C. (2001). Effect of low voltage electrical stimulation and temperature conditioning on post-mortem changes in glycolysis and calpains activities of Korean native cattle. Meat Science, 58, 231–237. Savell, J. W., Smith, G. C., & Carpenter, Z. L. (1978). Beef quality and palatability as affected by electrical stimulation and cooler aging. Journal of Food Science, 43, 1666–1668. Scopes, R. K. (1964). The influence of post-mortem conditioning on the solubilities of muscle proteins. Biochemical Journal, 91, 201–207. Simmons, N. J., Singh, K., Dobbie, P. M., & Devine, C.E. (1996). The effect of pre-rigor holding temperature on calpain and calpastatin activity and meat tenderness. In: Proceedings of the 42nd international congress of meat science and technology (pp. 414–415). Lillehammer, Norway. Smith, G. C. (1985). Effects of electrical stimulation on meat quality, color, grade, heat ring and palatability. In J. A. M. Pearson & T. R. Dutson (Eds.), Advances in meat research electrical stimulation. Connecticut: AVI Publishing Company. Smulders, F. J. M., Marsh, B. B., Swartz, D. R., Russell, R. L., & Hoenecke, M. E. (1990). Beef tenderness and sarcomere length. Meat Science, 28, 349–363. Swatland, H. J. (1984). Structure and development of meat animals. Englewood Cliffs, NJ: Prentice-Hall. Tang, B. H., & Henrickson, R. L. (1980). Effect of post-mortem electrical stimulation on bovine myoglobin and its derivatives. Journal of Food Science, 45, 1139–1156. Thompson, V. F., Goll, D. E., & Kleese, W. C. (1990). Effects of autolysis on the catalytic properties of the calpains. Biological Chemistry. HoppeSeyler, 371(Suppl.), 177–185. Unruh, J. A., Kastner, C. L., Kropf, D. H., Dikeman, M. E., & Hunt, M. C. (1986). Effects of low-voltage electrical stimulation during exsanguination on meat quality and display colour stability. Meat Science, 18, 281–293. Wiklund, E., Stevenson-Barry, J. M., Duncan, S. J., & Littlejohn, R. P. (2001). Electrical stimulation of red deer (Cervus elaphus) carcasses – effects on rate of pH –decline, meat tenderness, colour stability and water-holding capacity. Meat Science, 59, 211–220. Young, O. A., Prioli, A., Simmon, N. J., & West, J. (1999). Effects of rigor attainment temperature on meat blooming and colour on display. Meat Science, 52, 47–56. Zeece, M. G., & Katoh, K. (1989). Cathepsin D and its effects on myofibrillar proteins: a review. Journal of Food Biochemistry, 13, 157–178.