SmartStretch™ technology. II. Improving the tenderness of leg meat from sheep using a meat stretching device.

Abstract

This study evaluated the effect of stretching hot-boned sheep hindlegs from 40 sheep carcases, classified as mutton, using a prototype device (SmartStretch™). Left and right legs were collected pre-rigor and randomly allocated to one of four treatments; 0days ageing+SmartStretch™, 0days ageing+no stretch, 5days ageing+SmartStretch™ and 5days ageing+no stretch. There was a significant interaction between stretch treatment and ageing (P<0.05) for shear force of the m. biceps femoris such that stretched and aged samples were the most tender. By contrast stretched m. semimembranosus (SM) had a significantly (P<0.05) lower shear force only at 0days of ageing. Stretching produced longer sarcomeres (P<0.001) for both the SM and m. semitendinosus muscles. Myofibrillar degradation indicated by particle size analysis or histology was not affected by stretching, but there was an ageing effect (P<0.001). SmartStretch™ provided significant improvements in tenderness of the individual muscles.

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SmartStretch™ Technology. II. Improving the tenderness of leg meat from sheep
using a meat stretching device
E.S. Tooheya,⁎, R. van de Venb, J.M. Thompsonc, G.H. Geesinkc, D.L. Hopkinsd
aNSW Department of Primary Industries, PO Box 865, Dubbo, NSW 2830, Australia
bNSW Department of Primary Industries, Orange Agricultural Institute, Forest Road, Orange NSW 2800, Australia
cUniversity of New England, Armidale, NSW 2351, Australia
dNSW Department of Primary Industries, Centre for Red Meat and Sheep Development, PO Box 129, Cowra NSW 2794, Australia
a b s t r a c ta r t i c l ei n f o
Article history:
Received 27 July 2011
Received in revised form 3 November 2011
Accepted 4 January 2012
Keywords:
Stretch
Tenderness
Meat quality
Mutton legs
This study evaluated the effect of stretching hot-boned sheep hindlegs from 40 sheep carcases, classified as
mutton, using a prototype device (SmartStretch™). Left and right legs were collected pre-rigor and ran-
domly allocated to one of four treatments; 0 days ageing+SmartStretch™, 0 days ageing+no stretch,
5 days ageing+SmartStretch™ and 5 days ageing+no stretch. There was a significant interaction between
stretch treatment and ageing (Pb0.05) for shear force of the m. biceps femoris such that stretched and aged
samples were the most tender. By contrast stretched m. semimembranosus (SM) had a significantly
(Pb0.05) lower shear force only at 0 days of ageing. Stretching produced longer sarcomeres (Pb0.001)
for both the SM and m. semitendinosus muscles. Myofibrillar degradation indicated by particle size analysis
or histology was not affected by stretching, but there was an ageing effect (Pb0.001). SmartStretch™
provided significant improvements in tenderness of the individual muscles.
Crown Copyright © 2012 Published by Elsevier Ltd. All rights reserved.
1. Introduction
Given the potential negative effect that hot boning can have on
eating quality, the adoption of hot boning in the Australian sheep
meat processing industry has been limited to adult sheep carcases.
There are many advantages and disadvantages with hot boning
(Devine, Hopkins, Hwang, Ferguson, & Richards, 2004; Jeremiah,
Martin, & Murray, 1985; Pisula & Tyburcy, 1996; Spooncer, 1993).
However, it has also been noted that applying additional processing
interventions such as electrical stimulation and some form of stretching
can improve overall meat quality, in particular tenderness (Davey,
Kuttel, & Gilbert, 1967; Devine, Payne, & Wells, 2002; Herring, Cassens,
Suess, Brungardt, & Briskey, 1967; Locker, 1960; Macfarlane, Harris, &
Shorthose, 1974; Troy, 2006).
The effects of both stretching and ageing on the tenderness of
hot boned sheep topsides (m. semimembranosus) using a prototype
stretching device, SmartStretch™, were outlined by Toohey, van de
Ven, Thompson, Geesink, and Hopkins (this volume). They showed
that tenderness of the m. semimembranosus was improved signifi-
cantly by applying the SmartStretch™ treatment, such that after
both 0 and 5 days of ageing the SmartStretch™ treatment caused a
reduction in shear compared to non-stretched meat. It then was
concluded that the accelerated tenderness achieved by this pre-
rigor stretching device could yield acceptable tenderness levels and
remove the need for aged chiller storage of hot-boned products.
This paper examines the effect of stretching, using a prototype
device (SmartStretch™), and ageing on meat tenderness, of whole,
hot-boned legs from sheep carcases. The intention was to verify if this
additional processing step would further enhance the tenderness of
hottunnelbonedsheeplegsasithaddonewiththem.semimembranosus
(Toohey et al., this volume).
2. Materials and methods
2.1. Animals, experimental design and sample collection
A total of 40 sheep of mixed sex (ewes and wethers) were used
from various consignments over two kill days. The sheep were ran-
domly selected from different consignments and thus were of varying
backgrounds, representing the typical animals processed by the abat-
toir. However, all sheep were of the same breed (Merino) and were
estimated to be between 3 and 5 years old and therefore were classi-
fied as mutton (Anonymous, 2005). Using a randomised complete
block design, the treatment combinations were randomised between
carcases and hindleg within a carcase. The treatment combinations
were: ageing 0 days+no stretch, ageing 0 days+SmartStretch™,
ageing 5 days+no stretch, and ageing 5 days+SmartStretch™.
The carcases were processed under the normal commercial proce-
dures of the abattoir and exposed to a number of electrical inputs rou-
tinely used by the cooperating abattoir, as described by Toohey et al.
Meat Science 91 (2012) 125–130
⁎ Corresponding author. Tel.: +61 2 68 811214; fax: +61 2 68 811295.
E-mail address: edwina.toohey@dpi.nsw.gov.au (E.S. Toohey).
0309-1740/$ – see front matter. Crown Copyright © 2012 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.meatsci.2012.01.003
Contents lists available at SciVerse ScienceDirect
Meat Science
journal homepage: www.elsevier.com/locate/meatsci

Page 2

(this volume). Carcases were then passed through a drying room
for approximately 35 min at an average temperature of 8 °C. Both
the left and right legs (Anonymous, 2005; HAM. 5060) were excised
from the carcases pre-rigor using a tunnel boning technique (n=80).
The boneless legs were trimmed to approximately b10 mm of sub-
cutaneous fat and allocated to their predetermined treatments. The
stretch treatment was applied within 2 h of death to half the legs
using the SmartStretch™ technology. This technology uses air pres-
sure to eject meat into a 100 μm polyethylene packaging tube so
as to constrict the muscle and prevent any subsequent contraction
as previously described by Toohey et al. (this volume). The control
(no stretch) samples were vacuum packed and then frozen after
predetermined ageing periods. The 0 day samples from both treat-
ments were placed in cardboard cartons and stored in a Blast cell
freezer at −22 °C within 4 h of slaughter. The 5 day aged samples
were chilled at an average temperature of 2 °C during ageing, then
were also frozen and stored in a −22 °C Blast cell freezer until
sampling.
2.2. Measurements
Initial measurements taken on each of the legs included initial
length (Li) and circumference (Ci), which were measured at two
different points (Fig. 1). Legs that underwent the SmartStretch™
treatment were re-measured once the treatment was completed and
a final length (Lf) and circumference (Cf) were recorded (Fig. 2).
From these measurements, both the percentage increase in length
and percentage decrease in circumference at sites 1 and 2 were calcu-
lated as:
Length increase %
ð Þ ¼ 100 ? Lf=Li−1
ðÞ
Circumference decrease %
ð Þ ¼ 100 ? 1−Cf=Ci
ðÞ:
The pH and temperature were measured in both the left and right
mm. semimembranosus (SM) and semitendinosus (ST) of each sample
as soon as the legs were collected and just prior to the application
of the stretch treatment. Muscle pH was measured using a meter
with temperature compensation (WP-80, TPS Pty Ltd., Brisbane,
Australia) and a polypropylene spear-type gel electrode (Ionode IJ
44). The pH meter was calibrated before use and at regular intervals
using buffers of pH 4 and pH 6.8 at room temperature.
The 0 day aged frozen whole boneless legs were tempered for
approximately 6 h at an average room temperature of 21 °C to allow
the SM, ST and biceps femoris (BF) to be excised. The 5 day aged
whole boneless legs were thawed to a muscle temperature of approx-
imately 2 °C at a room temperature of 22 °C. This enabled purge to be
measured on the whole leg and the SM, ST and BF to be separated.
Purge was measured in 5 day aged samples only. The initial frozen
leg weight was first recorded. Once samples had thawed (muscle
temperature of approximately 2 °C) they were patted dry using
paper towelling and re-weighed to get a final leg weight. The total
purge percentage was calculated as:
Purge loss %
ð Þ ¼ 100 ? 1−Final leg weight=Initial leg weight
ðÞ:
A 1 g sample was taken also from each muscle for determination
of final pH on 0 and 5 day aged samples. This was determined using
an iodoacetate method adapted from that described by Dransfield,
Wakefield, and Parkman (1992). The 1 g sample was added to 6 ml
of cold iodoacetate (at pH 7) and homogenised at 19,000 rpm for
two bursts of 15 s. Samples were held on ice for 30 s between each
burst. Following this the samples were incubated in a water bath at
20 °C and the pH was measured.
Sarcomere length was measured on the SM and ST 0 day aged sam-
ples using laser diffraction as described by Bouton, Harris, Ratcliff, and
Roberts (1978). Shear force samples were collected from both the
SM and BF after 0 and 5 days of ageing. Shear force samples were cut
into 74±13 gram blocks, with dimensions of 60–70 mm length, 40–
50 mm width, and 20–25 mm thickness. These samples were cooked
for35 mininplasticbagsat71 °Cina90 Lwaterbathwithathermoreg-
ulator and a 2000 W heating element (Ratek Instruments, Boronia,
Victoria, Australia) and measured using a Lloyd Texture analyser
(Hopkins, Toohey, Warner, Kerr, & van de Ven, 2010). Samples used
for shear force determination were weighed pre and post cooking to
measure the amount of cooking loss. After cooking, the samples were
cooled in running water and patted dry using paper towelling before
weighing. Cooking loss percentage was calculated as:
Cooking loss %
ð Þ ¼ 100 ? 1–cooked weight=fresh weight
ðÞ:
A 1–2 g sample was collected from the SM for 0 day and 5 day
aged samples for particle size analysis. The method has been de-
scribed by Karumendu et al. (2009) and used 1 g samples.
2.3. Histology
A 1 g sample was taken from the lateral side of the SM aged for
0 (collected within 2 h of exsanguination) and 5 days. The muscle was
fixed in a solution of 2.5% glutaraldehyde and 2% paraformaldehyde in
0.1 M phosphate buffer and was used to determine the number of
breaks in muscle fibres. The method for determining fibre breaks was
adaptedfromthatreportedbyTaylorandFrylinck(2003).Thisinvolved
fixing, embedding and staining of muscle samples. Digital images of
the stained muscle samples were collected at 40× magnification using
a Leica DMR microscope and Nikon DXM1200F digital camera after
Hopkins et al. (2007). Breaks across the fibres were quantified for 45
Fig. 1. Image of tunnel boned leg. Initial length and circumference measurement sites
are indicated by arrows.
Fig. 2. Image of SmartStretch™ tunnel boned leg. Final length and circumference
measurement sites are indicated by arrows.
126
E.S. Toohey et al. / Meat Science 91 (2012) 125–130

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fibres per sample and if the fibres were not flat, but distorted, this was
also recorded.
2.4. Statistical analysis
Linear mixed model analyses were used to analyse the data for leg
weight, initial pH, initial temperature, shear force (on the log scale),
sarcomere length, purge loss, cooking loss, particle size and fibre
breaks/distortion. For each measurement, the model included stretch
treatment, ageing and their interaction as fixed effects and included
carcase as a random effect. Initial pH was included as a covariate
where appropriate. These analyses were undertaken using ASReml
(Gilmour, Gogel, Cullis, & Thompson, 2006), via the statistical package
asreml (Butler, 2009) under R (R Development Core Team, 2009).
Fixed effects were tested for significance using Wald-related test
statistics developed by Kenward and Roger (1997). Where tabulated,
the denominator degrees of freedom (df) for these Wald tests were
rounded down to be conservative.
Additional regression analyses were undertaken to examine the re-
lationshipbetweensarcomerelengthand shearforce,sarcomere length
and percent increase in length, sarcomere length and initial pH, shear
force and percent increase in length and lastly shear force and initial
pH. The model fitted for the linear mixed model regression analysis
was Y=baseline+X+Carcase+error where the random terms are in
italic,Y=(shearforceorsarcomerelength)and X=(sarcomerelength,
percent increase in length or initial pH). Note that percent increase in
length was only available for stretched samples and sarcomere length
was only available for 0 day aged samples.
3. Results
3.1. Mixed model analysis
The predicted mean, standard error and range for each of the
various carcase characteristics and meat quality traits are shown in
Table 1. There were no significant differences (P>0.05) between
stretch (Table 1) and ageing treatments for any of the traits. Nor
were there any significant interactions, indicating that the random
allocation of muscles to treatment groups was balanced. There was,
however, for final SM pH a significant interaction between stretch
and ageing treatments (P=0.02), such that 0 day control treatment
had a significantly lower pH (5.77) compared to 5 day control (5.87).
Based on the initial pH and temperature, the SM and ST, on aver-
age were still in the pre-rigor phase (Table 1), although given the
range in initial pH for both muscles, it suggests that some carcases
were in stages of rigor. The range in the leg weights of the samples
represented the diversity of the product processed. This was also
evident, based on the random term (carcase) where the variance
component was significant for all traits shown in Table 1. There was
a 14% increase on average in whole leg length (range of 2–24%) as a
result of the SmartStretch™ treatment and an average 44% decrease
in circumference (range of 21–65%) after the SmartStretch™ treat-
ment was applied.
The significance of treatment effects and initial pH on shear force
for the SM and BF muscles is shown in Table 2. There was a significant
interaction between stretching and ageing treatments (Pb0.05) for
the SM shear force. The predicted means for the SM shear force are
shown in Table 3. The interaction for the SM showed that the un-
aged control group (no stretch) meat was the toughest. The benefits
of the stretching treatment diminished after 5 days of ageing.
As shown in Table 2, the SmartStretch™ treatment significantly
(Pb0.01) reduced shear force (36.3±1.57 N) for the BF when com-
pared to the no stretch control (41.8±1.57 N). The initial pH effect
was not significant. As ageing increased, the shear force declined
(Pb0.001) in the BF from a mean 0 day level of 44.8 N (±1.55) to a
5 day level of 33.3 N (±1.59). There was no significant interaction
(P>0.05) between the two treatments (Table 2).
Both stretch (Pb0.05) and ageing (Pb0.05) significantly affected
cooking loss of the BF, but there was no significant interaction
(P>0.05) between the two treatments (Table 4). The cooking loss
of the stretched BF (15.6±0.79%) was lower than non-stretched BF
(17.4±0.79%). The 0 day aged BF had a lower cooking loss (15.5±
0.77%) than 5 day aged BF (17.4±0.77%). There was no significant
difference (P>0.05) between SmartStretch™ and control (no stretch)
treatments for cooking loss of the SM (Table 4). There was, however,
a significant ageing effect (Pb0.05) in the SM. This effect was the
converse to that for the BF with 0 day aged samples having greater
cooking loss when compared to the controls 21.2% (±0.62) and
19.6% (±0.63) respectively. In addition, there was no interaction
(P>0.05) between stretch and ageing treatments (Table 4).
The purge measured on the whole leg was significantly greater
(Pb0.001) for the stretch treatment compared to the control (no
stretch) treatment 1.82% (±0.07) and 1.61% (±0.07) respectively
(Wald statistic F(1,28)=16.4; P=0.001). Analysis of sarcomere
length showed that there was a significant difference (Pb0.05)
between SmartStretch™ treatment and control (no stretch) for both
the SM (Wald Statistic F(1,27)=6.32; P=0.018) and ST (Wald
Table 1
Predicted mean, standard error (s.e.) and range of leg weight, initial pH and temperature
for semimembranosus (SM), semitendinosus (ST) and final pH for semimembranosus (SM),
semitendinosus (ST) and biceps femoris (BF) according to SmartStretch™ and control (no
stretch) treatments.
TraitControl (no stretch)SmartStretch™
Mean (s.e.)RangeMean (s.e.)Range
Leg weight (kg)
Initial pH — SM samples
Initial temperature (°C) —
SM samples
Final pH — SM samples
Initial pH — ST samples
Initial temperature (°C) —
ST samples
Final pH — ST samples
Final pH — BF samples
1.96 (0.05)
6.15 (0.03)
27.8 (0.41)
1.37–2.68
5.91–6.57
20.9–32.1
1.92 (0.05)
6.17 (0.03)
27.5 (0.42)
1.40–2.47
5.77–6.65
21.8–33.4
5.79 (0.05)
6.30 (0.04)
24.7 (0.40)
5.44–6.73
5.68–6.92
18.2–30.4
5.85 (0.05)
6.30 (0.04)
24.6 (0.40)
5.52–6.95
5.91–6.96
20.1–30.2
6.24 (0.05)
5.97 (0.05)
5.59–7.00
5.54–6.73
6.27 (0.05)
6.03 (0.05)
5.65–6.94
5.48–6.77
Table 2
Wald-statistic F-ratio for effects stretch, age, stretch×age and covariate initial pH on
shear force of mm. semimembranosus (SM) and biceps femoris (BF).
TermsShear force SM (N) Shear force BF (N)
df
F-ratiodf
F-ratio
Stretch
Age
Age×stretch
Initial pH
^
^
1,35
1,58
^
^
4.16⁎
2.34ns
1,52
1,50
1,36
1,58
9.51⁎⁎
39.18⁎⁎⁎
2.32ns
2.34ns
^Not tested because there is a significant interaction.
nsP>0.05.
⁎⁎⁎ Pb0.001.
⁎⁎ Pb0.01.
⁎ Pb0.05.
Table 3
Predicted means (s.e.) for shear force in newtons of the m. semimembranosus (SM)
according to treatment groups, ignoring initial pH.
TreatmentsShear force SM (newtons)
SmartStretch™
Control
0 day aged
5 day aged
51.3 (2.87)b
40.6 (2.34)a
60.5 (3.40)c
38.8 (2.12)a
Means in the above table without a trailing letter in common are significantly different
(Pb0.05).
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E.S. Toohey et al. / Meat Science 91 (2012) 125–130

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statistic F(1,19)=15; P=0.001) sarcomere length at 0 days of ageing
(Table 5).
A sample of images of the SM is shown in Fig. 3, where a major
break across a fibre is shown. In contrast, an example image from
muscle subjected to the SmartStretch™ with no ageing (Fig. 4)
shows a wavy pattern indicative of fibres under pressure. These
waves combined with bent fibres were also counted and termed
distorted fibres.
The SmartStretch™ treatment had no effect on myofibrillar degra-
dation of the SM which was measured using particle size analysis
(Table 6). There was a significant difference (Pb0.001) between ageing
treatments. This difference showed that 0 day aged samples had a pre-
dicted mean particle size of 190 μm and after 5 days of ageing it was
140 μm; with the average standard error of the difference equal to
8.3 μm. Stretching did not influence myofibrillar degradation of the
SM measured as breaks in fibres (Table 6) or the distortion of fibres
(Table 6). However, there was a significant (Pb0.001) effect of ageing,
such that as ageing time increased so did the number of fibre breaks
(Tables 6 and 7) and fibre distortion was reduced (Table 7). There was
no significant interaction (P>0.05) between stretching and ageing.
3.2. Regression analysis
Stage of rigor, as measured by initial pH had no significant effect
on shear force (P=0.13). The bi-variate mixed model analysis indi-
cated that there was no relationship (P>0.05) between SM shear
force (SMSF) and SM sarcomere (SMSarc) on 0 day aged samples, at
either the carcase or the residual level. In addition to this, there
were no significant relationships shown of SM initial pH with SM
sarcomere length (P=0.35), the percent increase in muscle length
with sarcomere length (P=0.72) or shear force (P=0.50) and fibre
breaks and particle size (P=0.48). There was, however, a significant
relationship (Pb0.05) between the percentage of fibre breaks and
SM shear force, such that as the percentage of fibre breaks increased
the shear force decreased.
4. Discussion
The SmartStretch™ treatment was effective in reducing shear
force after 0 days of ageing in both the BF and SM. This was despite
the fact that due to the application of electrical stimulation the mus-
cles were on an accelerated path to rigor (Hwang, Devine, & Hopkins,
2003). However, based on the initial pH and temperature, the SM and
ST, muscles were on average still in the pre-rigor phase. Additionally,
there was no significant effect found when initial pH was added as a
covariate in the model for SM shear force, indicating that although
some muscles may have been in stages of rigor they had not completed
rigor mortis (Hwang et al., 2003), thus enabling the stretch treatment
to have an effect.
SmartStretch™causeda13%(5.5 N)reductioninBFshearforceirre-
spective of ageing treatment. As expected, as ageing time increased,
shear force decreased. The benefits were also shown in shear force for
the SM where SmartStretch™ caused a 15.2% (9.2 N) reduction in
shear force at 0 days of ageing. However, after 5 days of ageing the
benefits of SmartStretch™ were nullified. In contrast to the findings for
an individual SM muscle by Toohey et al. (this volume), it appears that
the SmartStretch™ treatment was not as effective when applied to a
whole leg where multiple muscles are involved. This is most likely due
to it being easier to ensure that muscle fibres are aligned longitudinally
in reference to the rubber sleeve inside the SmartStretch™ machine
when an individual muscle is processed, such as the SM, thus allowing
the stretch potential of the muscle to be achieved. In addition to this,
all pressure applied by the SmartStretch™ machine is solely received
by the individual muscle.
Previous work by Thompson et al. (2005) on both lamb and mutton
BF indicated that significant improvements in subjective tenderness
could also be achieved by tenderstretching. These benefits are likely
Table 4
Wald-statistic F-ratio for effects stretch, age, stretch×age on cooking loss % for mm.
semimembranosus (SM) and biceps femoris (BF).
Terms Cooking loss SM (%) Cooking loss BF (%)
df
F-ratio df
F-ratio
Stretch
Age
Age×stretch
1,61
1,65
1,37
1.69ns
4.25⁎
4.11ns
1,59
1,61
1,37
5.50⁎
5.38⁎
2.04ns
nsP>0.05.
⁎ Pb0.05.
Table 5
Predicted means (s.e.) of mm. semimembranosus (SM) and semitendinosus (ST) sarcomere
length (μm) according to treatment.
Muscle Sarcomere length (μm)
SmartStretch™
Control
SM
ST
1.82 (0.05)a
2.12 (0.07)a
1.61 (0.04)b
1.84 (0.03)b
Means in the above table without a trailing letter in common are significantly different
(Pb0.05).
Fig. 3. Imageof muscle fibreswitha major break across the fibre indicated. Muscle came
from non-stretched m. semimembranosus after 5 days of ageing. 40× magnification.
Fig. 4. Image of muscle fibres showing a wave pattern. Muscle came from a stretched
m. semimembranosus after 0 days of ageing. 40× magnification.
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to be a result of the improvements achieved in sarcomere length due to
the increased tension placed on muscle fibres by stretching inhib-
iting the physical ability of muscle fibres to contract Bouton, Fisher,
Harris, and Baxter (1973). The SmartStretch™ treatment applied in the
current study was effective in controlling muscle contraction, as seen by
the increases in sarcomere length for both the SM (1.61 to 1.82 μm) and
ST muscles (1.84 to 2.12 μm). These results support previous findings
reported by Toohey et al. (this volume), where sarcomere length of the
SM increased from 1.54 to 2.19 μm using the SmartStretch™ system,
and Troy (2006), where meat wrapping using the Pi-Vac Elasto Pack
System® was found to be effective in controlling sarcomere shortening.
This meat wrapping method is a similar concept to SmartStretch™, as
the aim is to restrain and potentially stretch the de-boned muscle to
prevent the muscle fibres from contracting. However, work by Devine
et al. (2002) where samples were hand wrapped using polyethylene
cling film 11 μm thick, indicated that the wrapping method employed
only stopped the muscle from shortening rather than applying stretch.
It is apparent that on average SmartStretch™ in the study of Toohey
et al. (this volume) was able to achieve greater difference in sarcomere
lengththaninthecurrentstudy.Itcouldbeconcludedthatbasedonthe
percentage increase in length, on average the SM muscle exhibited
greater stretch in the study of Toohey et al. (this volume). However,
results in the current study show that the changes in the percentage
increase in length are not reflected by those in the sarcomere length
and this outcome is supported by the earlier results of Toohey et al.
(this volume). This indicates that other factors are impacting on sarco-
mere length. There was greater variation in sarcomere length exhibited
for SmartStretch™ treated samples. It was concluded by Hopkins,
Garlick, and Thompson (2000) that the greater variation in sarcomere
length for tenderstretched samples was caused by the disrupted Z
disks, but this is unlikely to be the explanation for the effect found in
the current study.
Particle size analysis is one approach to measuring the degree of
proteolysis that has occurred in meat by examining myofibrillar degra-
dation (Karumendu et al., 2009). In the current study it was shown
that myofibrillar degradation or proteolysis of the SM was not altered
by SmartStretch™, which was consistent with results presented by
Devine, Wahlgren, and Tornberg (1999) and Toohey et al. (this
volume) where the utilisation of SmartStretch™ or hand wrapping
of meat respectively had no effect on proteolysis, but ageing did.
Many studies (e.g. Devine et al., 1999; Hopkins & Thompson, 2001;
Karumendu et al., 2009; Koohmaraie, Doumit, & Wheeler, 1996) have
shown that proteolysis is evident during ageing. The decline in particle
size over time indicates that the fibres had degraded during ageing.
It was concluded by Taylor and Frylinck (2003) that both fibre de-
tachment and fibre breaks affect meat tenderness. The SmartStretch™
treatment applied in the present study did not impact on the number
of fibre breaks or fibre distortion and thus did not accelerate proteol-
ysis, consistent with the particle size results. The significant relation-
ship shown between fibre breaks and shear force in the current
study supported works by Martin, Hopkins, Gardner, and Thompson
(2006) and Taylor and Frylinck (2003). However, it was of interest
that the distortion of fibres decreased significantly with ageing. Pre-
vious work by Taylor and Frylinck (2003) showed that there was no
real effect of ageing and they concluded that this may be an effect of
slaughter. A possible explanation for the different findings could be
that in the present study the fibres sampled at day 0 were not fully
in rigor, as samples were collected and fixed in solution within
approximately 2 h of exsanguination, whereas the aged samples had
been able to fully enter rigor, leading to a straightening of fibres.
Cooking loss was less for BF stretched muscle which is consistent
with that found for the SM by Toohey et al. (this volume). However,
in the current experiment, the stretch treatment had no effect on
cooking loss of the SM, which is similar to the findings of Devine
et al. (2002) and Toohey, Hopkins, and Lamb (2008). In these
studies wrapping and ageing hot-boned sheep m. longissimus had
no effect on cooking loss percent, but it is difficult to compare
stretching with wrapping per se. The percentage of purge lost
after 5 days of ageing was greater for the SmartStretch™ treat-
ment, consistent with the hypothesis developed by Toohey et al.
(this volume) that the SmartStretch™ treatment may lose more ini-
tial purge. This could potentially nullify the differences found in
cook loss. Thus the SmartStretch™ treatment does not appear to
have any significant effect on overall water holding capacity of the
end product.
Given that on average after SmartStretch™ treatment was applied
a 14% increase in leg length and a 45% decrease in circumference
occurred it is clear that the SmartStretch™ treatment transformed
the overall shape of the hindleg, which was consistent with the
overall results presented by Toohey et al. (this volume) for a single
muscle. Although the results of Toohey et al. (this volume) showed
a greater increase in length of 24% the results in the current experi-
ment had a greater decrease in circumference of 45% as opposed to
24%. This is most likely due to the more complex multiple muscle
structure of the hindleg compared to a single muscle. The transforma-
tion of the sheep leg is an important industry outcome and as to our
knowledge there is no other machine that can take a whole sheep
leg and shape it to a consistent size and shape. Results reported
by Taylor et al. pers. comm. (2011) indicated that in beef this shape
retention was maintained after removal from the packaging even
when primals were shaped after cold boning. As outlined by Toohey
et al. (this volume) the ability to produce a consistent shape is con-
sidered a desirable trait by the food service industry (Tarrant, 1998)
irrespective of any potential tenderness benefits.
5. Conclusions
This study has highlighted the potential of the SmartStretch™
technology for improving specifically the tenderness of whole hot
boned hindlegs. However, this benefit was reduced compared to the
improved tenderness achieved from applying the SmartStretch™
technology to individual muscles. Together with the improvements
in sarcomere length, it can be concluded that the SmartStretch™
Table 6
Wald statistic, F-ratio for effects stretch, age and stretch×age on the percentage of
breaks in fibres (fibre break), percentage of either wavy or bent fibres (distorted fibres)
and particle size (μm).
Terms Fibre breaks (%)Distorted fibres (%) Particle size (μm)
df
F-ratiodf
F-ratiodf
F-ratio
Stretch
Age
Age×stretch
1,36
1,50
1,33
1.23ns
33.6⁎⁎⁎
1.59ns
1,74
1,75
1,39
0.109ns
110.0⁎⁎⁎
2.06ns
1,59
1,62
1,40
7.07ns
3.88⁎⁎⁎
2.00ns
nsP>0.05.
⁎⁎⁎ Pb0.001.
Table 7
Predicted means (s.e.) for the percentage of breaks in fibres and the percentage of
either wavy or bentfibres(distorted) for them.semimembranosusaccording totreatment
groups.
TreatmentsFibre breaks (%)Distorted fibres (%)
Stretching
Stretch
Control
Ave S.E.D.
13.5a
19.0a
4.41
45.8a
47.0a
4.33
Ageing
0 day aged
5 day aged
Ave S.E.D.
4.0a
28.5b
4.41
70.6b
22.2a
4.33
Pairs of means for each trait (fibre breaks or distorted fibres) for each treatment
(stretching or ageing) without a trailing letter in common are significantly different
(P=0.05).
129
E.S. Toohey et al. / Meat Science 91 (2012) 125–130

Page 6

treatment was successful in preventing the unrestrained muscle from
shortening. The muscle fibres could have been physically disrupted
by this treatment, but it does not appear that SmartStretch™ causes
more distorted fibres, nor does it cause any acceleration of proteoly-
sis. The lack of relationship between shear force and sarcomere length
indicates that other mechanisms are impacting on the variation in
shear force and a possible explanation is that the SmartStretch™
treatment is altering muscle structure or connective tissue.
Acknowledgements
The financial support of Meat and Livestock Australia, Beef+Lamb
New Zealand and NSW Primary Industries (formerly Industry and
Investment NSW) is gratefully acknowledged, as is the technical
assistance of Tracy Lamb and Matthew Kerr. The assistance of the
management and staff of the co-operating abattoir was paramount
to the success of this work and is acknowledged.
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