The effect of pre-rigor stretch and contraction on the post-rigor geometry of meat samples in relation to meat toughness

The geometry of the muscle fibre and perimysial collagen components of meat subjected to pre-rigor stretch and contraction were examined. The changes in the configurations of these two components accompanying length changes in the muscle were used to explain the reported relationship between raw meat toughness and contraction state. The theory put forward proposes that in raw meat samples the muscle fibre component plays virtually no role in modifying the toughness of the meat sample with contraction state. This theory of the collagen component playing the major role is the same as that reported elsewhere. It is capable of explaining a reverse relationship between meat toughness and contraction state such as is found in cooked meat simply by invoking a firmer consistency for the muscle fibres which then act as fill between the collagen network fibres and hold them at an angle relative to the line of applied force.     

Pig muscle fibre characteristics as a source of variation in eating quality

Despite the application of the MLC Blueprint specifications there is still unacceptable variation in meat eating quality. Evidence from the literature suggests that the intrinsic characteristics of the muscle may be an important source of variation, but there is no indication as to what extent these characteristics may explain the residual variation in eating quality. The purpose of the present study was to quantify the role of muscle fibre characteristics in accounting for eating quality variability. In the study, evaluation of samples from 125 pigs from eight breeding company populations indicated that fibre characteristics, particularly the diameter of the fast twitch oxidative glycolytic fibres, contributed to variation in instrumental texture of meat. In addition, the data suggest that there are genetic differences in fibre type distribution which can be used to segregate populations.     

Relationships of myosin heavy chain fibre types to meat quality traits in traditional and modern pigs

Porcine skeletal muscle fibres were molecularly classified, using in situ hybridisation and immunocytochemistry, into four types, according to the isoform of myosin heavy chain (MyHC) that was present in each fibre (MyHC slow/I, MyHC 2a, MyHC 2x and MyHC 2b). The relationship between MyHC fibre types and meat quality traits between two phenotypically divergent muscles [longissimus dorsi (LD) and psoas], and between the same muscles of different breeds (traditional Berkshire and Tamworth, and modern Duroc-based and Large White-based) were examined. We found that the greater abundance of fast oxidative-glycolytic MyHC 2a and 2x fibres in the psoas was associated with superior meat quality traits, and that the greater presence of fast glycolytic MyHC 2b fibres in the LD could account for less favourable quality traits, both in terms of pH, drip loss, grain, colour, yield force and work done. Although significant correlations were found between specific fibre types and quality traits, within either the psoas or LD muscle of some breeds, no consistent correlation was found across both muscles and all breeds. This finding was in line with the view that a given fibre type could have considerable differences in phenotype between breeds, and between muscles. The observed inverse compositional and functional-meat quality relationship between MyHC 2b and 2x fibres, and MyHC 2b and 2a fibres could form a basis of fibre type manipulation to improve meat quality.     

Muscle fibre orientation and its effect on measurements of tenderness of bovine longissimus dorsi muscle

The muscle fibre orientation within a particular cooked beef steak was found to vary considerably and to be markedly affected by vacuum packaging, freezing and/or cooking. Shear force values, initial-bite tenderness (panel) and cooking loss were highly dependent on, and overall tenderness (panel) was only slightly dependent on muscle fibre orientations. These measures were affected by fibre orientation to a greater extent in tough than in tender meat. At each of three fixed muscle fibre orientation, correlations between tenderness measures were significant (P<0.05), their magnitude depending on the fibre orientation. At a fixed fibre angle correlations of tenderness measures with cooking losses were not significant. However, on a withinanimal basis, cooking loss was related to shear value and to initial-bite tenderness apparently through an effect of fibre orientation. This effect may constitute a major source of variation in the measurement of tenderness and cooking loss.     

The biochemical basis of fibre types in bovine muscle

Recent studies using isolated muscle fibres have established a link between the histochemical fibre types, I, IIA and IIB, which can be defined by myofibrillar ATPase activity, and three forms of myosin heavy chain. This work is reviewed, as is work on metabolic variability within these fibre types. Results are them presented which show that the activity of myofibrillar ATPase in sections, although principally determined by the myosin heavy chain, is modified by other myofibrillar components, as yet unidentified. Evidence is also presented for hybrids of myosin heavy chain in muscle fibres. Finally, metabolic variability within the fibre types is examined for bovine muscle. It is concluded that, in spite of wide metabolic variability within types, a classification based on myofibrillar ATPase activity is still useful.     

Effective Discrimination of Meat Tenderness Using Dual Attribute Time Intensity

We examined the effectiveness of Dual Attribute Time Intensity (DATI) method for assessment of temporal changes in perceived toughness and juiciness, within commercially acceptable meat cuts. Usefulness of DATI in assessing temporal aspects of perception of juiciness and toughness was compared with Single-Attribute Time-Intensity (SATI) and Line Scale Profile. Results showed that DATI provided a good separation of attributes and was equal to or better than SATI in differentiating beef samples based on perceived juiciness and toughness. By reducing the dumping effect and the inherent sample to sample variability, this method enabled more precise assessment of the relationship between juiciness and toughness in meat than SATI.     

The relationship of muscle fibre size to tenderness of beef

Steaks were removed from loins of beef carcasses at 1, 3, 6 or 14 days post mortem for fragmentation index (MFI), Warner-Bratzler Shear Force (SF) and sensory panel tenderness evaluation. Also, after 1 day of storage, samples were removed for histological observations. Greatest improvement in tenderness, SF and MFI occurred within the first 6 days of storage. Sensory panel tenderness was correlated (P < 0·01) with SF and MFI. Average muscle fibre size was correlated (P < 0·01) with tenderness and SF at days 1 and 3, but not at days 6 and 14. Evidently, muscle fibre size is important to tenderness prior to post-mortem storage of meat and proteolysis, but becomes less of a factor in tenderness after 6 days of storage.     

The physical basis of meat texture: Observations on the fracture behaviour of cooked bovine M. Semitendinosus

The fracture behaviour of cooked strips of beef M. semitendinosus was studied by qualitative observation of the manner in which fracture occurred and by quantitative measurements of ultimate tensile strength, work of fracture and notch sensitivity. Qualitative observations showed that fracture started in the perimysial connective tissue in all test configurations used, resulting initially in the separation of intact muscle fibre bundles. The ultimate tensile strength along and across the fibres was ～-300kNm(-2) and ～-25kNm(-2), respectively. The qualitative aspects of fracture were explained on the basis of a uniaxial fibrous composite of strong muscle fibre bundles in a weak connective tissue 'matrix', with poor interfacial strength. Work of fracture through the perimysium was in the range 0·4 to 1·8kJm(-2). The difficulty in propagating fracture across the muscle fibre bundles was explained in terms of the material's complete insensitivity to notches running across the fibres. The results imply that the muscle fibre bundle is an important level of structural organisation as far as fracture is concerned and that the strength of the perimysium, or perimysium/muscle fibre bundle interface, is likely to have a major influence on the toughness of'the cooked meat.     

Development of a system to quantify muscle fibre destructuration

The aim of this study was to set up a method to quantify the loss or modification of muscle fibre structure (destructuration). Thanks to histology and image analysis, we managed to set up a reliable method with an uncertainty of 3.2%. To express the results, a new indicator called MDI (Meat Destructuration Indicator), was calibrated according to mechanically recovered meat market practices. The MDI indicator was strongly correlated (0.95) with the sensory assessment of a European panel (126 professionals). The threshold between raw materials that could be labelled as “meat” in processed products and mechanically separated meat (MSM) has been set at 58.1%, according to the panellist’s judgements. Thus MDI system can be used to characterise meat raw materials from mechanical recovery system according to Regulation (EC) No. 853/2004. It can also be used to study relationships between manufacturing parameters and destructuration or between destructuration of raw materials and processed products characteristics.     

Composition of muscle fibre types and connective tissue in bovine M. semitendinosus and its relation to tenderness

The distribution of muscle fibre types and connective tissue in bovine M. semitendinosus is described. A parallel increase in the volume fraction of type I muscle fibres (from 10% to 30%) and a decrease in the IIB volume fraction (from 58% to 34%) was recorded from superficial to deep layers. A positive correlation was observed between the frequency and the cross-sectional area of both type I and IIB fibres. The elastic fibres formed irregularly shaped bundles that made up about 50% of the volume of the perimysium. Thin elastic fibres extended into the endomysium. The relative proportion of elastic fibres in the perimysial connective tissue increased towards the deeper layers of the muscle. A taste panel evaluation of the sensory properties was performed and the data were correlated to the histological observations. A gradual decrease in scores of four tenderness-related traits was recorded from the superficial to the deep layer of the muscle. The superficial layer was rated as most tender, whereas the consecutive layers were rated less tender. The possible relationship between the composition of muscle and the meat quality is discussed.     

The application of wheat fibre and soy isolate impregnated with iodine salts to fortify processed meats

The aim was to use wheat dietary fibre and soy protein isolate as carriers of KI and KIO₃ for fortification of processed meat with iodine. Products from minced pork were prepared with addition of iodised wheat fibre and soy isolate, and iodised table salt for comparison and the effects of thermal processing and storage on changes in iodine content were determined. It was shown that both alternative carriers limited the iodine changes in meat products compared with iodised table salt. However, wheat fibre was more effective in limiting iodine losses during thermal processing and soy protein during storage of the products. The greatest effect of the carriers was found in meat products fortified with the less stable KI.     

The application of wheat fibre and soy isolate impregnated with iodine salts to fortify processed meats

The aim was to use wheat dietary fibre and soy protein isolate as carriers of KI and KIO₃ for fortification of processed meat with iodine. Products from minced pork were prepared with addition of iodised wheat fibre and soy isolate, and iodised table salt for comparison and the effects of thermal processing and storage on changes in iodine content were determined. It was shown that both alternative carriers limited the iodine changes in meat products compared with iodised table salt. However, wheat fibre was more effective in limiting iodine losses during thermal processing and soy protein during storage of the products. The greatest effect of the carriers was found in meat products fortified with the less stable KI.     

Prediction of lamb meat quality traits based on muscle biopsy fibre typing

The aim of the experiment described in this paper was to determine the relationship between muscle fibre type and meat quality.

Two indicator muscles, the Stylohyoïdeus and the Scutulo auricularis superficialis accessorius, were biopsied on one-month-old lambs and used as an index to select the animals of the redder and of the whiter metabolic types among the lamb population studied. Evaluation of the organoleptic qualities of meats from two groups was performed on the Longissimus dorsi muscle by a taste panel.

The results of the taste panel evaluation suggest, on one hand, that the meat from the redder animals is juicier and has a more intense flavour than that from the whiter. On the other hand, it appears possible to obtain an in vivo prediction of lamb meat quality based on muscle biopsy fibre typing.     

The effects of porcine somatotropin on muscle fibre morphology and meat quality of pigs of known stress susceptibility

To study the effects of porcine somatotropin (pST) administration on muscle fibre characteristics and meat quality, 48 pigs of the Lacombe breed (equal numbers of barrows and gilts) of known halothane genotype (NN, Nn or nn) were randomly assigned to either a control (excipient buffer) or pST (3.0 mg d(-1)) treatment. At a pen average animal weight of 106 kg, pigs were slaughtered and muscle samples were collected post mortem for determination of fibre type, glucidic metabolites and meat quality. There was a 16% increase in muscle weight of the semimembranosus (SM) and psoas major (PM) in pST-treated animals (p ≤ 0.01). However, there was no significant change in fibre type associated with the pST treatment in either the SM or PM (p > 0.05). In the PM muscle there was a 65-70% increase in fast, oxidative, glycolytic (FOG) and fast, glycolytic (FG) fibre areas in pST-treated gilts (p ≤ 0.05). These cellular changes were manifest in meat colour that was lighter and spectrally shifted towards yellow (significantly higher L (?) and hue angle values), higher drip loss, lower moisture content and a tendency towards higher Kramer-Press shears (p = 0.06) in the PM of pST-treated gilts. Although these changes were in the same direction as pale, soft, exudative meat, the average values fell within the normal range. Based on the observed gender by pST treatment interactions, administration of pST (timing, dosage and protein requirements in the feed) may need to be tailored to suit different genders and breeds to achieve the maximal response.     

The effect of cooking temperature on mechanical properties of whole meat, single muscle fibres and perimysial connective tissue

The structural changes in beef semitendinosus caused by cooking were studied by performing tensile tests of the isolated meat components (i.e. single muscle fibres and perimysial connective tissue) and related to the toughness of the whole meat. Whole meat toughness was found to increase in two separate phases upon cooking from 40-50°C, and again from 60 to 80°C with a decrease in meat toughness between 50 and 60°C, in agreement with previous studies. The changes in whole meat toughness at temperatures below 60°C were found to correspond to changes in the mechanical properties of the perimysial connective tissue, whereas changes of whole meat toughness at temperatures above 60°C were found to correspond to increased breaking strength of single muscle fibres. The myofibrillar component explained approximately 47% of the variation in whole meat toughness upon cooking whereas inclusion of the connective tissue component increased the goodness of fit.     

ANALYSING WARNER-BRATZLER CURVES

Forces required to deform and rupture samples of meat were measured in a modified Warner-Bratzler device. A model is proposed to describe the shape of the plot of force against distance. This model was fitted by a least squares method to experimental curves obtained from (1) bovine longissimus dorsi muscles aged at 15°C for 1–7 days and then cooked at 80°C for 4 h, and (2) bovine biceps femoris muscles conditioned at 15°C for 24 h and then cooked at 80°C for 1–22 h. A plot of the variance between replicate forces, as a function of distance, exhibits two prominent peaks, one of which is thought to be associated with rupturing of fibre bundles, and the other with rupturing of perimysial connective tissue. Parameters calculated by fitting the model to replicate curves indicate that muscle fibres rupture in groups of fibre bundles. Hence, contrary to previous interpretations, initial yield involves rupture of connective tissue, as well as myofibrils. However, the number of fibre bundles forming a group capable of independent rupture varies according to the time-temperature history of the sample, as do other parameters. The model permits relative contributions of fibre bundles and perimysial connective tissue to be estimated. In the samples studied here, perimysial connective tissue offered greater resistance to passage of the blade than did the fibre bundles.     

Chemical,microscopic, and instrumental analysis of graded flax fibre and yarn

A series of flax fibre and yarn samples that had been commercially graded low, medium, and high quality were analysed by light microscopy, wet chemical analysis, Raman spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy to determine characteristics which could be related to quality ratings for each sample type. Light microscopy revealed fragments of cuticular and epidermal material bound to the fibres. As the quality ratings improved, fewer of these fragments were found and greater separation of the fibre bundles to smaller bundles and, in some cases, elementary fibres occurred indicating more efficient retting. Chemical evaluation showed that, as quality of the yarns increased, amounts of fatty acid and long‐chain alcohols as well as dihydroxy fatty acids decreased. Chemical data on fibre did not show consistent trends with quality. Raman spectroscopy showed increasing amounts of cellulose and decreasing amounts of aromatics and hydrocarbons with increasing quality, which paralleled the chemical data. NMR analysis showed nearly equal amounts of crystalline cellulose regardless of quality for both fibre and yarn samples. The strengths and weaknesses of each analytical method are discussed. This initial study suggested that chemical constituents characteristic of cutin and waxes could be used as an initial marker of quality. © 1999 Society of Chemical Industry     

Mechanical and structural characteristics of single muscle fibres and fibre groups from raw and cooked pork longissimus muscle

The aim of this study was to analyse the mechanisms that determine why small groups of muscle fibres may have different mechanical properties than single muscle fibres. The method used combined light microscopy and tensile testing on single fibres and small groups of fibres from raw and cooked (80 °C) meat, from both conditioned and unconditioned porcine longissimus muscle. The results showed that small groups of fibres had different breaking properties than constituent single fibres in raw muscle, but that these differences diminished on cooking. Raw groups of fibres showed a more uniform lengthening along their entire length and a higher extension to rupture than single fibres. Conditioning increased maximum strains in both single fibres and small fibre groups. In unconditioned cooked meat, single fibres and fibre groups showed comparable breaking stresses and extensions. Conditioning resulted in a lower strength in fibre groups than in single fibres. These results show that (endomysial) connective tissue linkages between adjacent muscle fibres in a small group significantly alter the breaking behaviour of single fibres. The effects of these connective tissue linkages are not reduced by conditioning alone, but are largely diminished by cooking to 80 °C.     

The role of the endomysium in the salt-induced swelling of muscle fibres

Variable uptake of water is a persistent problem in meat processing. To try to understand the changes that occur during water uptake, and thereby explain this variability, we have measured the swelling of salt-treated single muscle fibres from rabbit longissimus dorsi. By dissolving out the myofibrillar proteins with SDS we have been able to tell whether or not a dissected fibre has an endomysial connective sheath. We find that some fibres do lack a sheath and that these stripped fibres swell on average approximately five times more than intact fibres in 0·25 m KI. This shows that the endomysium limits the swelling of the fibre in salt, as is also shown by the greater swelling of those parts of fibres from which the endomysium has been deliberately removed. On prolonged immersion in 0·25 m KI the stripped parts of fibres shrink after swelling whereas the smaller swelling of unstripped parts is maintained. With careful, slow dissection, the proportion of stripped fibres is low at all times post mortem, but if a quicker method is used, the proportion of stripped fibres increases with time post mortem. As ageing proceeds, an increasing incidence of transverse fractures reduces the productivity of the quicker method, so the slow method has to be used. Regardless of the method of dissection the swelling of stripped and unstripped fibres does not depend on time post mortem. Thus it is the changing proportion of stripped fibres that underlies the earlier report (Wilding et al. Meat Sci., 1986 18, 55) of a dependence of swelling on time post mortem. The ease of stripping of endomysium from muscle fibres may be important in meat processing. Thus whether or not fibres produced during comminution and mixing of meat are stripped directly affects water uptake. The extraction of myofibrillar proteins may also be affected, which would be important for the adhesion of cooked reformed meat products.     

The effect of salt and fibre direction on water dynamics,distribution and mobility in pork muscle: A low field NMR study

The effect of salt concentration and fibre orientation on water within the meat matrix was investigated by low-field nuclear magnetic resonance (LF-NMR), water-binding capacity (WBC), diffusion studies and histological analysis. Pork M. longissimus thoracis et lumborum samples were cured with 5.7, 15.3 or 26.3% w/w NaCl at a parallel or perpendicular fibre direction. NMR transverse (T₂) relaxation identified three water components (T_2b, T₂₁ and T₂₂) which all exhibited characteristics correlated to WBC. Results indicated that T_2b increases with increasing NaCl concentration. Increasing intra-myofibrillar water and decreasing extra-myofibrillar water resulted in the highest WBC. Water diffused more quickly into the extra-myofibrillar space in samples cured at a parallel fibre direction. This water remained loosely bound in samples cured with the saturated solution (26.3% w/w NaCl) leading to decreased WBC. This study provides further information on water binding within the meat matrix by applying the results of LF-NMR to traditional water-binding theories.