processing technology ii - woolwise · web viewthis chapter discusses the application of pre-rigor...

23 Processing Technology II

Diana Perry

Learning objectives

By the end of this topic you should be able to:

1. Describe the biochemical causes of myofibrillar shortening

2. Understand the relationship between sarcomere length and tenderness

3. Describe the processes by which muscles may be stretched pre-rigor

4. Discuss how stretching the muscle pre-rigor impacts on palatability

23.1 Introduction

The period immediately following slaughter can have a dramatic effect on meat quality. Consequently, considerable effort has been expended in the development of specifications and control measures that can be reliably used in the abattoir to ensure that eating quality, particularly tenderness is maximised. The focus has centred on minimising the degree of myofibrillar shortening and optimising the degree of proteolysis. However, this is by no means simple, as some of the practices that minimise against myofibrillar shortening (eg. electrical stimulation, as presented in the previous topic) may not always be conducive to optimal proteolytic activity. The understanding of this interrelationship is further complicated by the variability in cooling rates between different regions in the carcase.

This chapter discusses the application of pre-rigor stretching of muscles to minimise myofibrillar shortening. In conventionally hung (Achilles tendon) carcases, some muscles are free to shorten in adverse chilling conditions, because their skeletal attachments do not hold them taut. Alternative systems rely on increasing the tension on these muscles so that they become taut and are no longer free to shorten. This can be done by hanging from the pelvic area, or by a process called Tendercut.

23.2 Muscle biochemistry and post-mortem shortening

In a muscle undergoing contraction and relaxation, the cycle depends upon the availability of chemical energy (in the form of ATP). The muscle structural apparatus converts this chemical energy to mechanical energy and powers the contraction. Heat is produced as a by-product. Initiation of contraction results from a nerve impulse. The chemical mechanism involves the release of Ca++ from the muscle cell membranes and this triggers a conformational response in a key structural protein that initiates contraction.

MEAT418/518 Meat Technology - 23 - 1

©2009 The Australian Wool Education Trust licensee for educational activities University of New England

The exact point after death at which the conversion of muscle to meat is complete is difficult to assess, but it is usually accepted to be the establishment of rigor mortis at which time the muscle has �set� and is no longer able to contract.

However while function of the muscle ceased at death, metabolic activity in the muscle tissue does not. Various biochemical events may still occur. Rigor mortis is characterised by progressive stiffening of the muscle and is related to the availability of ATP. As long as ATP is present, crossbridge cycling between myosin and actin molecules can occur. When ATP is exhausted, the myosin and actin molecules remain locked together and cause the stiff nature of rigor muscle.

23 - 2 – MEAT418/518 Meat Technology


23.3 Toughness induced by muscle shortening

There are two components of the muscle that affect toughness, the muscle fibres and the connective tissue. However connective tissue toughness can be regarded as constant in terms of processing technology - it is a function of the live animal (particularly its age) and of the muscle and is not significantly altered by shortening. Toughness of a muscle can be very significantly affected by the state of contraction of that muscle at the time that it goes into rigor. Diagrammatic representation of the contraction and extension of a sarcomere is shown in Figure 23.1.

Figure 23.1 Contraction and extension of a sarcomere –from a stretched sarcomere (top), through relaxed, contracted, and fully contracted (bottom). The area between 2 Z discs is

represented, with actin (shaded) and myosin (black) shown. Source: Perry, (2006).

The extent of toughening induced by shortening will depend upon the muscle under consideration

o if the muscle is free to shorten on the carcase then it can potentially be affected by shortening —eg. striploin (m. longissimus dorsi).

o if the muscle is restrained and unable to shorten because of the nature of its skeletal attachments, it cannot be affected by shortening — eg, eye round (m. semitendinosus), fillet (m. psoas major).

The relationship between toughness (resistance to shear) and sarcomere length is shown in Figure 23.2 (Marsh and Carse, 1974). The diagram of the sarcomere length against the toughness trace in this diagram demonstrates the relative longitudinal positions of the thick and thin filaments at different degrees of sarcomere contraction and extension. At length x 1 the muscle is neither stretched nor shortened. At length * -5 it is fully contracted.

Figure 23.2 Relationship between toughness (shear force) and sarcomere length. Tenderness/toughness is on the Y axis, tender being at the bottom, tough at the top.

Sarcomere decreases from left to right. Source: Marsh and Carse (1974).



23.4 The effect of temperature on shortening

The degree of shortening of muscle is a function of the temperature at which it sets or goes into rigor (when ATP is no longer available to energise the system). The relationship between muscle shortening and temperature is shown in Figure 23.3. Shortening is at a minimum at about 15-20oC.

Figure 23.3 Relationship between muscle shortening and temperature. Source: Locker and Hagyard, (1963)

This type of data is obtained by studying muscles excised from hot carcases and held at constant temperatures. The effect is a result of the temperature dependence of the biochemical events in muscle post-mortem. In general an increase of 10oC results in a doubling of the reaction rate. During meat production, muscle is cooled from 38-40oC down to about 5oC or even lower. The rate of carcase cooling will influence the degree to which post-mortem glycolysis reactions are slowed up and the time course of rigor onset.

The relationship between percent shortening, sarcomere length and toughness can be summed up as follows:

The degree of shortening is a function of the time/temperature history of the muscle. The toughening that results is a function of the degree of shortening.

23.5 Chilling induced cold shorteningIn commercial practice a chiller is normally set to a specific program, which is rarely varied. Factors to be considered in setting the program include microbiological quality and weight loss. When chillers are loaded with carcases of various sizes, these will become colder at varying rates depending upon carcase weight and dimensions, and the extent and depth of fat cover. Heavy, fat carcases will chill more slowly than light lean ones.

Individual muscles will chill at a rate that reflects their position in the carcase, with muscles at or near the surface chilling more rapidly. If the muscle cools quickly and its temperature falls to below about 12oC while ATP is still present, significant cold shortening may result. For cold shortening to occur:

ATP must be present to energise contraction. This will occur if chilling is rapid because the rapid fall in muscle temperature reduces the rate of glycolysis, glycogen is depleted more slowly and ATP continues to be available.



Ca++ must be released from the sarcoplasmic reticulum in the absence of a nerve impulse. The membrane will still retain functionality for some time after slaughter but cold temperatures shock the membrane and cause the irreversible release of Ca++ . This drives the muscle to maximum contraction provided ATP is present.

Cold shortening has been reported to increase the toughness of some muscles up to four fold.

Cold shortening is a problem for lighter lean carcases more typical of the domestic market.

23.6 Minimising shortening - tenderstretch

A means of avoiding the problems of myofibrillar shortening is to hang the carcase in such a way that there is maximum tension on the muscles and they cannot shorten. This can be achieved using a procedure called tenderstretch, which was investigated a number of years ago. To tenderstretch a side, a hook or string is passed through either the obturator foramen or the pelvic ligament to hang the side, rather than the conventional hook through the Achilles tendon (Figure 23.4). This allows the hind limb to hang down thereby placing more tension on the major leg muscles, and the backbone straightens and maximum tension is placed on these muscles. This hanging position has a positive effect on the palatability of the striploin and most leg muscles, with little on no effect on forequarter muscles and a small negative effect on the tenderloin fillet (m psoas major).

Figure 23.4. Normally hung (right) and tenderstretched (left) carcases. Hatched areas = relaxed or stretched and tender muscles, dark cross-hatched areas = contracted and tough

muscles. Source: Harris (1974).

23.7 The effect of tenderstretch on microscopic muscle structure

Tenderstretch is essentially a mechanical effect, whereby the muscle is stretched and physically stopped from shortening during rigor. There are few studies which have examined the impact of tenderstretch on the structure of the myofibre. In a study by Hopkins et al (2000) the effect of tenderstretch on the myofibre structure was examined in the M. longissimus muscle in sheep carcases which had been either normally hung or super stretched (achieved by hanging the



carcase with a hook through the pubic symphysis and weighting the hind-limbs so that the stretching effect on the loin muscle was increased).

The effect of tenderstretch on muscle structure is twofold. Firstly tenderstretching has been shown to reduce the overlap of actin and myosin in the sarcomere as evidenced by the shorter A-bands, compared with the samples from the normally hung carcases (Hopkins et al 2000). Tenderstretching also resulted in clear breaks in the I-band and disassembly of the Z disks (Figure 23.5). Damage to the sarcomere in the I-band/Z disk attachment indicates disruption of proteins such as actin, titin and nebulin. This is likely to weaken the sarcomere, increasing tenderness and suggests that the decreased fibre density, which occurs in cooked tenderstretched muscle, is not the only explanation for the large increase in tenderness in such muscle. The disrupted Z disks in tenderstretched samples meant a larger variation in sarcomere length, compared with normally hung samples.



Figure 23.5. Electron microscope images of the m. longissimus muscle in lamb from carcases which were normally hung and super tenderstretched.

Source: Hopkins et al (2000a).

23.8 The effect of tenderstretch on ageing rates in muscle

One of the other advantages of tenderstretch is that it minimises the need for ageing meat. In a CRC experiment striploin samples from tenderstretched beef carcases were as tender after 7 days ageing as samples from normally hung carcases which had been aged for 14 days. (O’Halloran et al 1998 – see Figure 23.6).

There are several theories on the mechanism by which ageing is accelerated in tenderstretched muscle. One theory is that tenderstretching places the actin/Z disk junction under tension and changes the configuration of the proteins, thereby making them more susceptible to proteolysis. There may also be effects on the connective tissue matrix, which is obviously under more tension in a tenderstretched muscle.

Figure 23.6. Mean tenderness scores for tenderstretched (TS) and normally hung (AH) carcases after ageing for 1, 7 and 14 days. Source: O’Halloran et al. (1998). Tenderness

score ranges from 0 (tough) to 100 (tender).



23.9 The effect of tenderstretch on variation within the muscle

In addition to generating large differences in palatability for the hindquarter muscles, tenderstretching also has the effect of reducing variation within the muscle. As part of the MSA testing procedures the striploin was divided into anterior and posterior sections to generate enough product for testing using different cooking procedures or different ageing periods. In these cases the different treatment were randomised across the anterior and posterior sections. When this term was included as a fixed effect in the statistical model it was found to interact with hanging position (hanging by the sacral ligament). The magnitude of the interaction is shown in the following diagram. In the normally hung carcase the cranial portion (ie the anterior section) of the striploin had a palatability score which was 8 CMQ4 units better than the posterior section. Tenderstretching resulted in a marked increase in palatability in both the cranial and caudal sections, but it was greater in the caudal section, thus decreasing the difference between the sections to about 3 CMQ4 palatability units (Figure 23.7).

Figure 23.7. The effect of loin position on the palatability of beef in tenderstretched (i.e. carcases hung by the sacral ligament) and normally hung carcases.

Unpublished MSA data.

23.10 The effect of tenderstretch on palatability

MSA results have shown a highly significant hanging method x muscle interaction (Ferguson et al 1999). Eating quality was significantly improved by tenderstretch in the majority of the hindquarter muscles. The notable exceptions to this trend were the Mm. psoas major and semitendinosus, both of which are stretched in conventionally hung sides. The M. Psoas major is more likely to shorten in the tenderstretched state, although the sarcomere length is still generally above the threshold of 2.0. As expected, there was no effect of tenderstretch on the forequarter muscles with the exception of the M. longissimus thoracis. Table 23.1 shows the results from this experiment.

The greatest response to tenderstretch occurs in carcases with the poorer eating quality. In matched sides the variance in tenderstretched sides was approximately half that in normally hung treatments. Thompson (2002) examined the MSA database to quantify the magnitude of the tenderstretch response in matched carcases where grilled striploin steaks from tenderstretched and normally hung sides had been aged for 14 days prior to consumer evaluation. There were a total of 195 carcases drawn from 14 different tenderstretch experiments conducted in 8 different abattoirs. The variance in tenderstretch sides was 9 palatability units compared with 12 in the normally hung sides. The improvement in palatability from tenderstretching was greater in those



carcases with a low palatability score in the normally hung side. This suggests that there is a maximum potential palatability for a muscle, regardless of hanging technique.



Table 23.1. Mean CMQ4 score (standard errors and significance) for different cuts from electrically stimulated tenderstretched and normally hung (Achilles tendon) sides. Source: Ferguson et al (1999).Primal Cut Muscle Hanging Method SE of the

differenceSignif

Tenderstretch Achilles Tendon

Forequarter

Brisket Pectoralis profundus

31.9 34.7 1.7 ns

Blade Triceps brachii 55.3 55.8 1 ns

Oyster Blade Infraspinatus 61.3 62.4 1.2 ns

Cube Roll Longissimus thoracis

65.2 62.9 1.1 <P0.05

Spinalis dorsi 74.6 75.6 1.8 ns

Hindquarter

Striploin Longissimus lumborum

61.2 55.3 0.8 <P0.001

Tenderloin Psoas major 70.9 73.5 1 <P0.01

Rump Gluteus medius 63.9 56.9 0.9 <P0.001

Topside Semimembranosus

44.9 37.8 0.8 <P0.001

Outside flat Biceps femoris 50.4 46.7 0.8 <P0.001

Eye Round Semitendinosus 48.3 47.3 1 ns

Knuckle Rectus femoris 50.3 48 0.9 <P0.05

Figure 23.8. The relationship between the increment in striploin palatability resulting from tenderstretching one side, as a function of the palatability score of the normally hung side

Striploins had been aged for 14 days Source: Thompson (2002). Printed with permission from Elsevier.



23.11 Operational issues associated with tenderstretch

Carcase sides must be in the tenderstretched position during rigor for it to impact on palatability. In most plants which tenderstretch, sides are suspended by the Achilles tendon during the dressing procedure and then hung in the tenderstretch position at some stage after the hot sides go over the scales and before they are moved into the chiller.



Supporting the side through the obturator foramen is not as secure as hanging through the Achilles tendon. As a safety measure most plants therefore re-hang tenderstretched sides by the Achilles tendon when they are loaded out of the chiller for processing through the boning room. For most sides this re-hanging means that they partially revert to the normally hung position. With light bodies the re-hanging can also result in some distortion and twisting of the loin region, which can be a problem in the boning room (Figure 23.9).

Fig. 23.9. A tenderstretched carcase (left), which has been re-hung after an overnight chill. Note how the leg position has not returned to the same shape as a carcase hung by the

Achilles tendon (right). Photograph supplied by D. Perry.

Lost chiller space. An argument often quoted against tenderstretching is the loss of chiller space due to tenderstretching. In reality the space lost from tenderstretching is generally small with most processors quoting figures less than 13%. To achieve this small loss it is essential that carcases be loaded onto rails with sides on alternate rails having backs or legs together. The legs need to be interleaved, which makes loading and unloading the chiller more difficult.

As already mentioned some abattoirs hang using strings whilst others use long stainless steel hooks to hang the carcases in the tenderstretch position. The latter technique, although more expensive since a large number of stainless steel hooks are required, does allow more control over the position of the carcase during chilling to avoid contact with adjoining carcases.

Hanging by the obturator foramen or the pelvic ligament?The majority of research has examined the impact of tenderstretching on palatability when carcases were suspended by a hook through the obturator foramen. More recently several researchers suggested that a greater effect could be obtained by hanging the carcase through the sarcal ligament as this effectively moved the fulcrum and the loin and leg muscles had a greater tension placed on them during rigor. This was recently investigated by MSA where it was shown that although there was a slightly greater effect for the loin the impact was reduced for the majority of the leg muscles.



Torn tenderloinsOne of the problems with re-hanging tenderstretched carcases is that the tenderloin which is on the inside of the spine curvature in a tenderstretched carcase is stretched further by re-hanging the carcase by the Achilles tendon. In a number of Australian plants re-hanging the tenderstretched sides was found to tear a small proportion of tenderloins (generally less than 5%). One option of 'freeing' the head of the tenderloin just prior to re-hanging out of the chiller was investigated as a means of reducing the tension on the tenderloin. This was found to be too difficult and not pursued further. A further option was to 'free' or 'nick' the head of the tenderloin in the hot carcase prior to tenderstretching. This was examined in 9 sides where one tenderloin was 'nicked' and the other left as a control prior to tenderstretching the hot side. After re-hanging the carcases the next morning both tenderloins were collected from the nine bodies and prepared for MSA consumer testing. The results are shown in Table 23.2.

Table 23.2. CMQ4 scores for tenderloins (psoas major) from tenderstretched carcases where the caudal end of the tenderloin had been 'nicked' prior to tenderstretching the hot carcase. Source: MSA.

Control tenderloins 'Nicked' tenderloins

Mean CMQ4 score 68.0 68.1

Standard deviation 5.54 7.49

Boning room difficulties with tenderstretch carcasesOne often quoted problem with tenderstretch is that tenderstretch carcases are more difficult to bone than conventionally hung carcases. The steps in breaking a carcase down differ slightly between tenderstretch and normally hung carcases. However recent experience in a number of boning rooms has shown that once boning room teams become accustomed to the differences they can process tenderstretch sides as quickly as normally hung sides. Differences in boning procedure include a change in the shape of the cap of the knuckle, which means that the round cannot be boned as such. Also it is easier if the silverside and rump are removed as one cut from the carcase and separated on the boning table.

TendercutThe tendercut process is an alternative means of improving tenderness to the tenderstretch method. The process results in stretching the muscles of the loin and hind-limb so that they go into rigor in the stretched state. Whilst the tenderstretch process uses the pelvic hanging position to increase the tension on the loin and hind-limb muscles, the tendercut process applies a similar tension on the muscles by breaking the vertebrae and pelvic bones in the hot carcase, so that the weight of the forequarter or hind limb itself stretches the relevant muscles.

The tendercut process was initiated by Drs Claus and Marriott in 1991, where they tested four carcases in the meat abattoir at Virginia Polytechnic Institute and State University in the US. Based on data from in-plant testing conducted in a major commercial facility, Claus and Marriott have reported improvements in tenderness of over 35% in the loin muscle using the tenderstretch process, particularly in beef animals with inherently less tenderness meat (Ludwig et al 1997, Claus et al 1997).

The tendercut process involves sawing the vertebral column at the 12th/13th-rib junction (Figure 23.10) and the ischium at the rump/butt junction



Figure 23.10. A diagram showing the method of breaking the vertebrae and severing the connective tissue attachments to achieve the 5cm drop necessary to stretch the loin muscle

in tendercut sides. Source: http://www.ansci.wisc.edu/facstaff/Faculty/pages/claus/tenderct/tc.html.



In addition to breaking the vertebrae at the 12/13th rib junction, all tissues surrounding the loin are cut, such that it is the only dorsal component holding the forequarter to the hindquarter. The breaking of the bone and cutting of the muscles surrounding the loin is shown in. Figure 23.10. the adipose tissue dorsal to the longissimus muscle is also cut to expose the epimysium. This cut is then continued around the medial side of the loin muscle and the M. multifidus dorsi completely severed. Intercostal connective tissue and muscle are then cut between the 12 th and 13th costal bones. This latter cut is extended approximately 12 cm from the lateral edge of the loin muscle. A photo of the tendercut break at the loin is shown below (Figure 23.11).

Figure 23.11. Photograph of tendercut process showing the break and incision at the 12/13th

rib junction. Note the distance the forequarter drops resulting in a 5cm stretch of the loin muscle. The multifidius dorsi and the fat dorsal to the longissimus dorsi has also been cut.

Source: http://www.ansci.wisc.edu/facstaff/Faculty/pages/claus/tenderct /tcphot2.htm

The second treatment site involves sawing the ischium at the same site used to separate the butt/rump joints. To minimise this damage the fillet muscle during sawing it must be freed from its attachment and deflected forward. Also care must be taken whilst sawing the ischium to minimise damage to the rump cut. A photo of the tendercut break at the butt/rump joint is also shown (Figure 23.12).

The tendercut process overcomes some of the problems of tenderstretching, particularly the problem of carcases breaking the pelvic bone or the ileo-sarcal ligament, and dropping, the extra chiller space required and the need to perhaps re-hang the carcase if prior to boning.

Figure 23.12 . A photograph of a Tendercut carcase showing the break in the ischium at the normal point of separation of the limb primals from the loin.

Source: http://www.ansci.wisc.edu/facstaff/Faculty/pages/claus/tenderct/tcphot3.htm



http://www.ansci.wisc.edu/facstaff/Faculty/pages/claus/tenderct

However recent MSA experiments (unpublished) have concluded the effect is generally midway between the Achilles hung and tenderstretch treatments. In addition to a reduced effect tendercut is rather difficult to do, particularly on-line. The breaking of the vertebral column and freeing the muscles and connective tissue around the loin muscle must be done with care. The pelvic bone is rather difficult to break and again care must be taken not to damage the rump primal.

Marking outTo increase boning yield and to assist carcase chilling, a number of processors have adopted the practice of 'marking out' the vertebral spines and removing the paddy wack on the hot carcase. A marked out side is shown below (Figure 23.13). There was concern that severing the insertion of the Mm. spinalis dorsi and the longissimus thoracics et lumborum to the paddy wack and dorsal spines of the vertebrae could allow the myofibres in the cube roll to shorten during rigor, thereby increasing the risk of cold shortening. An experiment was undertaken by MSA (S. Skinner, unpublished data) to examine the effect of 'marking out' the forequarter on sarcomere length of the myofibres in the cube roll. Alternate left and right sides from six domestic bodies were 'marked out' on the hot carcase from the 1st thoracic vertebrae until the 10th rib. Carcases were stimulated using the high voltage on-line stimulator. Cube rolls were collected at boning and samples collected from the Mm. spinalis dorsi and longissimus thoracics et lumborum for sarcomere measurement.��

Figure 23.13. An example of a marked out side showing the removal of the paddy wack and separation of the muscle fibres of the cube roll from the vertebral column.

Photograph supplied by D. Perry.



The results showed the sarcomere length of marked out cube� rolls was 1.87 microns compared with 1.83 for cube rolls that were not marked out – that is, there was no apparent effect of marking out on sarcomere length, and thus it was unlikely that there would be a greater likelihood of cold shortening in sides which wee treated in this manner.

23.12 Topic summary

There is a strong relationship between sarcomere length and tenderness/toughness. The optimal processing environment is one which minimises muscle shortening and maximises the ageing potential of the meat. This is influenced by the following factors.

Biochemical changes post-mortem Whether or not a muscle is free to shorten

Tenderstretch

Prevents shortening by maintaining tension on muscles that are free to shorten in normally hung (Achilles tendon) carcases.

Improves palatability more in poorer quality carcases

Shortens the ageing process

Decreases variability within muscle

Has some operational issues



Tendercut

Prevents shortening by using weight of forequarter and hind-limb to stretch muscles in the hind quarter.

Is more difficult to implement than tenderstretch

May cause damage to primals if poorly done

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References

Claus, J.R., Wang, H. and Marriot, N.G., 1997. Prerigor muscle stretching effects on tenderness of grain-fed beef under commercial conditions. Journal of Food Science vol 62 pp 1231-1243

Ferguson, D., Thompson, J., and Polkinghorne, R. 1999. Meat Standards Australia, A 'PACCP' based beef grading scheme for consumers. 3) PACCP requirements which apply to carcase processing. Presented at the 45th International Congress of Meat Science and Technology, Yokohama, Japan. Vol 45 pp18-19.



Harris, P.V., 1974. Meat Chilling. Proceedings of Advances in Science and Technology, Meat Research Laboratory. Cannon Hill, QLD, 1974.

Hopkins, D.L., Garlick, P.R. and Thompson, J.M., 2000a. The effect on the sarcomere structure of super tenderstretching. Proceedings of the Australian Society of Animal Production. Sydney .

Locker, R.H. and Hagyard, C.J., 1963. A cold shortening effect in beef muscle. Journal of Science Food Agriculture. Vol 14 p787.

Ludwig, C.J., Claus, J.R., Marriot, N.G., Johnson, J. and Wang, H., 1997. Skeletal alteration to improve beef longissimus muscle tenderness. Journal of Animal Science vol 75 pp 2404-2410

Marsh, B.B. and Carse, W.A., 1974. Meat tenderness and the sliding-filament hypothesis. Journal of Food Technology. Vol 9 pp 129-139.

Meat Standards Australia (MSA) unpublished data. Meat and Livestock Australia, Ltd.

O’Halloran, J.M., Ferguson, D.M., Perry, D. and Egan, A.F., 1998. Mechanism of tenderness improvement in tenderstretched beef carcases. Presented at the 44th International Congress of Meat Science and Technology, Barcelona, Spain vol 44 pp 712-713.

Thompson, J.M., 2002. Managing meat tenderness. Meat Science. Vol 62 pp 295-308.

University of Wisconsin, Madison, Animal Sciences, J.R. Clause. Retrieved July 30th, 2006 from http://www.ansci.wisc.edu site.



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