Myofibril Fragmentation Research Articles

Meat quality and the calpain system of feedlot steers following a single generation of divergent selection for residual feed intake

Residual feed intake (RFI) is calculated as the difference between an animal’s actual feed intake and its expected feed intake based on its size and growth over a specified test period. Following a single generation of divergent selection for postweaning RFI, Angus steers and Angus × Hereford, Angus×Poll Hereford and Angus × Shorthorn crossbred steers born in 1996 and 1997 were fed in a feedlot. Cohorts of steers were slaughtered at the same age and had attained similar (P>0.05) final liveweights: 467 kg for steers selected for low RFI (high efficiency; HE, n = 91) and 459 kg for steers selected for high RFI (low efficiency; LE, n = 98). The HE and LE steers had similar (P>0.05) carcass weight (247 and 244 kg), dressing percentage (53.1 and 53.2%) and eye-muscle area (58.9 and 60.3 cm 2 ). The HE steers had slightly less subcutaneous fat over the rib than the LE steers (9.2 v. 10.1 mm, P<0.05), and there was a trend towards less fat over the rump of HE steers (11.5 v. 12.1 mm, P = 0.10). For meat samples taken from the M. longissimus dorsi (LD) there were no differences (P>0.05) between the HE and LE steers in content of intramuscular fat (5.4 and 5.3% fresh weight), marbling scores, meat colour and fat colour. There were also no differences (P>0.05) between HE and LE steers in shear force and compression values for samples of LD aged for 1 day (4.6 and 4.6 kg shear force, 1.45 and 1.44 kg compression), or for 14 days (3.8 and 3.5 kg, 1.36 and 1.32 kg). Myofibril fragmentation index (MFI) measures the breakdown of these structural elements which occurs as an initial step in the process of protein degradation and meat tenderisation. MFI was lower (i.e. less fragmentation; P<0.05) in LD samples from HE steers than from LE steers, both in samples aged for 1 day (67.7 v. 72.5 units) and in samples aged for 14 days (87.8 v. 91.1 units). The rate of decline in MFI between 1 and 14 days post slaughter was similar in the LD samples from both lines of steers. There were no differences (P>0.05) between HE and LE steers in the activity of m-calpain and µ-calpain in LD immediately after slaughter (HE steers: 1.9 and 2.3 units, LE steers: 1.8 and 2.1 units). The level of calpastatin in LD from the HE steers was 13% higher than in the LD from the LE steers (5.2 and 4.6 units respectively, P<0.05). Rate of myofibril fragmentation was positively correlated (P<0.01) with the ratios of both m-calpain and µ-calpain to calpastatin, but not (P>0.10) with levels of either calpain or calpastatin. A single generation of divergent selection for RFI produced differences in calpastatin and myofibril fragmentation that may, with on-going selection for low RFI, negatively affect meat tenderness.

The calpain system in three muscles of normal and callipyge sheep.

Activities of mu- and m-calpain and of calpastatin were measured at four different times during postmortem storage (0, 1, 3, and 10 d) in three muscles from either callipyge or noncallipyge (normal) sheep. The weights of two muscles, the biceps femoris and the longissimus, are greater in the callipyge phenotype, whereas the weight of the infraspinatus is not affected. The activity of m-calpain was greater (P < 0.05) in the biceps femoris and longissimus from callipyge than in those from normal sheep, but it was the same in the infraspinatus in the two phenotypes. The extractable activity of m-calpain did not change (biceps femoris and infraspinatus) or decreased slightly (longissimus) during postmortem storage. Extractable activity of mu-calpain decreased to zero or nearly zero after 10 d postmortem in all muscles from both groups of sheep. The rate of decrease in mu-calpain activity was the same in muscles from the callipyge and normal sheep. At all time points during postmortem storage, calpastatin activity was greater (P < 0.05) in the biceps femoris and longissimus from the callipyge than from the normal sheep, but it was the same in the infraspinatus from callipyge and normal sheep. Calpastatin activity decreased (P < 0.05) in all three muscles from both phenotypes during postmortem storage; the rate of this decrease in the callipyge biceps femoris and longissimus and in the infraspinatus from both the callipyge and normal sheep was slow, especially after the first 24 h postmortem, whereas calpastatin activity in the biceps femoris and longissimus from the normal sheep decreased rapidly. During postmortem storage, the 125-kDa calpastatin polypeptide was degraded, but the 80-kDa subunit of mu-calpain was cleaved only to 76- and 78-kDa polypeptides even though extractable mu-calpain activity declined nearly to zero. Approximately 50 to 60% of total mu-calpain became associated with the nonextractable pellet after 1 d postmortem. The myofibril fragmentation index for the biceps femoris and longissimus from normal sheep increased significantly during postmortem storage. The fragmentation index for the infraspinatus from the callipyge and normal sheep increased to an intermediate extent, whereas the index for the biceps femoris and longissimus from the callipyge did not change during 10-d postmortem storage. The results suggest that postmortem tenderization is related to the rate of calpastatin degradation in postmortem muscle and that calpastatin inhibition of the calpains in postmortem muscle is modulated in some as yet unknown manner.

Meat tenderization by proteolytic enzymes after osmotic dehydration

The treatment of proteolytic enzymes is one of the popular methods for meat tenderization. In this case, it is very important how to introduce the enzymes into the meat cut. This paper describes meat tenderization by dipping the meat cut in a solution containing proteolytic enzymes after contact-osmotic dehydration. After the dehydration of each piece of meat from culled cow for 18 h by contact-dehydration sheet, each sample was dipped for 3 h in a solution containing papain or proteinases from Aspergillus traditionally used for soysauce production in Japan. It was stored at 3∼4°C for 24, 48 and 168 h, and subjected to texture measurement, sensory evaluations, biochemical analysis and histological observations. The penetration efficiency of the enzyme solution (of around 80%) after the contact-osmotic dehydration seemed to be sufficient. A marked decrease in hardness by texture measurements was observed in the meats treated with proteolytic enzymes and higher sensory scores for tenderness were observed in the meats treated with enzymes as compared with the untreated meat. The papain-treated meat received the highest score in tenderness, but the scores given to juiciness and taste were lower than that of the control. The rapid increases of the fragmentation of myofibrils from the enzyme-treated meat were observed at first 24 h of storage as compared with that of the control. Remarkable degradation of myosin molecule in the myofibrils from the enzyme-treated meats was observed on SDS-PAGE profiles. Considerable degradation of myofibrilar structure especially due to proteolytic removal of Z-lines, was observed among the myofibrils from enzyme-treated meats by electronmicroscopy. The remarkable deformation and disruption of honeycomb-like structure of endomysium were also observed in the meats treated with enzymes. From these results, it was shown that treatment after osmotic dehydration, was effective in tenderizing.

Postmortem Changes in Mule Duck Muscle Marinated in Red Wine

Postmortem changes in duck breast muscle as affected by red wine marination at 5 degrees C were studied. Myofibrils were purified from the control (CON) and the red wine marinated muscle (RW) after 0, 1, 3, 7, and 14 d storage. The results showed that myofibril fragmentation index (MFI) was significantly (p < 0.05) higher in RW than in CON samples. Myosin heavy chain, alpha-actinin, troponin-T, titin, and nebulin were degraded more rapidly as seen on SDS-PAGE in RW than in CON samples. Our results suggested that red wine marination can cause postmortem changes in mule duck breast muscle.

A fatal case of oral ingestion of benzine

A young woman committed suicide by ingesting benzine. We report the findings obtained at autopsy and the chemical analyses of the gastric contents, blood, and tissues in this case. Fatal concentrations of n-hexane, benzene, toluene and m-, p-xylene were detected. Pulmonary edema and hemorrhage were caused by the primary effect of the chemicals or secondarily by respiratory depression, suffocation due to volatile fluid, or heart failure. Mild hemorrhage around arterioles and venules in the brain cortex suggest hyperpermeability of the vessels. The fragmentation and waviness of the cardiac myofibrils indicate the presence of hypercontraction and possibly arrhythmia.

Influence of feeding intensity, grazing and finishing feeding on meat and eating quality of young bulls and the relationship between muscle fibre characteristics, fibre fragmentation and meat tenderness

Forty-one autumn-born Friesian bull calves were allocated to two production systems (Extensive=‘E'and Intensive=‘I'). In the E-system, animals were loose-housed and fed a roughage-based diet from October to May, followed by a grazing period from May to October. Ten animals were slaughtered directly from pasture in October [360 kg body weight (BW)] and 11 after a 10-week finishing period in tie-stalls (460 kg). The E-bulls were compared with intensively-fed tie-stall-housed young bulls (I) slaughtered at comparable weights (360 kg, n=11 and 460 kg, n=9). The myofibril fragmentation index (MFI) was measured 24 h post mortem in semitendinosus (ST), longissimus dorsi (LD), and supraspinatus (SU) muscles, and meat quality characteristics and sensory evaluation of LD were performed on aged meat. Intramuscular fat content was lower ( P<0.001) in all three muscles of E- compared with I-bulls. MFI of ST and LD was lower in E-bulls compared with I-bulls, but only at 360 kg. In contrast, MFI of SU was higher in E- compared with I-bulls at 360 kg. In E- compared with I-bulls, shear force value of ST was higher ( P<0.003) at 360 kg, but not at 460 kg. Panel scores for tenderness, taste and juiciness were all lower ( P<0.006 to 0.001) and remarks for off-flavour higher in E- compared with I-bulls, the effects being most pronounced at 360 kg. A 10-week finishing period improved all meat and eating quality characteristics of E-bulls. In LD, the correlation between MFI and tenderness was 0.79 ( P<0.001), which indicates a potential of MFI as an early predictor of tenderness.

Structural features of acute focal metabolic injuries to somatic muscle fibers caused by dimethylparaphenylenediamine

The pathological picture of an acute disorder of cell metabolism caused by dimethylparaphenylenediamine consists of typical focal reactions of striated muscles to injury: myofibril contractures and intracellular myocytolysis. Analysis of the pathological process demonstrates the time course of contracture injuries as a succession of overcontracture (first-third degree contractures) and necrobiotic phases (fourth degree contracture), followed by lump degradation and macrophagal resorption. Two polar types of contractures are clearly differentiated by the size, shape and structural and metabolic characteristics of target fibers: “ribbons“ and ”medallions”. Disappearance of Z strips, disaggregation, disorientation, and fragmentation of myofibrils are typical of intracellular myocytolysis. The observed changes form the morphological basis for acute disease of striated muscles.

Hind-limb protein metabolism and calpain system activity influence post-mortem change in meat quality in lamb

This study is concerned with the rate of protein turnover in the hind limb muscle bed of intact lambs, the activity of calpain proteolytic system in the M. biceps femoris, and subsequent rates of myofibre breakdown and tenderisation in the M. longissimus dorsi. Feed restriction increased protein degradation in hind-limb muscle of lambs ( p < 0.1), with a concominant decrease in the extractable activity of calpastatin ( p < 0.01), the endogenous inhibitor of calpain. IGF-1 analog treatment decreased both protein degradation and assayed μ-calpain activity ( p < 0.05) with no effect on the activity of calpastatin. β-Agonist treatment increased hind-limb protein synthesis ( p < 0.01), calpastatin activity ( p < 0.1) and decreased ( p < 0.01) μ-calpain activity, but did not effect protein degradation. Significant correlations were observed between Myofibril Fragmentation Index (MFI) values during post-mortem storage and initial post-slaughter calpastatin activity at days 3 ( r=−0.34, p < 0.1), 5 ( r=−0.58, p < 0.01) and 9 ( r=−0.58, p < 0.1), and μ-calpain activity at days 5 ( r=0.35, p < 0.1) and 9 ( r=0.41, p < 0.05). However, stronger correlations were observed between the ratio of μ-calpain to calpastatin, an estimate of potential μ-calpain proteolytic activity, and the rate of myofibril fragmentation ( r=0.75, p < 0.001) and tenderisation ( r=−0.64, p < 0.01) during aging. These results are consistent with the calpain system being the major proteolytic system involved in myofibril fragmentation and hence aging-related tenderisation of meat.

The effects of age at slaughter, genotype and finishing system on the biochemical properties, muscle fibre type characteristics and eating quality of bull beef from suckled calves

AbstractMuscle fibre characteristics and biochemical properties of muscle recovered from young bulls of two genotypes (Aberdeen Angus × and Charolais ×), reared on two different diets (silage-based and barley-based) and slaughtered at varying ages between 10 and 19 months of age were established. These analyses were restricted to samples ofm. longissimus lumborum (LI) recovered at 48 h post mortem, vacuum packed and stored at 2°C for 14 days. Biochemical measurements included intramuscular fat content, intramuscular collagen content and its solubility, haem pigment concentration, sarcomere length and myofibril fragmentation. Muscle fibre type was classified according to the contractile nature of thefibres and their metabolic properties.Intramuscular fat content increased (P &lt; 0·01) with age at slaughter and at a fixed age was greater for Angus × than Charolais × bulls (211·5 v. 295·8 mg/g dry matter, P &lt; 0·01). Total intramuscular collagen and its solubility tended to decrease with age (P &lt; 0·01). Differences in haem pigment concentration in samples of LI were detected between genotype (3·99 v. 3·59 mg/g for Angus × and Charolais × bulls; P × 0·01) and diet (3·97 v. 3·62 mg/g for bulls given barley and silage; P &lt; 0·01), and increased with age at slaughter (P &lt; 0·01). There was a significant increase in eye muscle cross-sectional area with increasing slaughter date (P &lt; 0·01) and this was paralleled by an increase in cross-sectional area of individual muscle fibres (P &lt; 0·001). Differences in cross-sectional area of individual muscle fibres between genotype and diet were small and inconsistent. Charolais × bulls had a greater percentage area of fast twitch glycolytic fibres than Angus × bulls (54·3 v. 49·3%; P &lt; 0·01) and a smaller percentage area of slow twitch oxidative fibres (15·8 v. 18·9%; P &lt; 0·05). Beef tenderness was positively correlated (r = 0·48; P &lt; 0·01) with the frequency of slow twitch oxidative fibres and negatively correlated (r = -0·38; P &lt; 0·05) with the frequency offast twitch glycolytic fibres.

Effects of age and/or weight at slaughter on longissimus dorsi muscle: Biochemical traits and sensory quality in pigs

The effect of increasing either age alone through feed restriction, or both age and weight at slaughter, on the quality of the longissimus dorsi muscle (LM) was investigated. Starting at 83 days of age and 32 kg, 80 pigs were allotted within litter to four experimental groups. All pigs were free of RYR1 mutated gene. Pigs were fed either ad libitum (A100, A130) or restricted 30% (R100, R130) and slaughtered at either 100 kg (A 100, R100) or 130 kg (A130, R130) body weight. Restricting feed intake in order to increase age at the same weight resulted in slower growth, better feed efficiency and increased leanness, whereas increasing age and weight simultaneously elicited slower growth, reduced feed efficiency and fatter carcasses. Intramuscular fat (IMF) and muscle collagen concentration were reduced by restricted feeding. Increase in both age and weight of pigs resulted in lower water, and higher protein and IMF concentrations. Although pigs were free of RYR1 gene, the PSE condition (defined as pH1 ≤ 5.9) developed in 25 carcasses, with a higher incidence in restricted pigs. PSE animals were excluded from the subsequent analysis of meat quality data. Feed restriction resulted in higher drip loss and lower a ∗ and c ∗ (saturation index) values. Longer myofibril fragments in muscle of restricted pigs on day 1 post mortem are indicative of slower maturation, while longer fragments on day 4 in heavier pigs, suggest that the extent of post mortem tenderisation could be negatively affected by the elevation of slaughter weight. Feed restriction had no significant effect on meat sensory quality, whereas increase in both age and weight resulted in lower tenderness, chewiness and mouth coating scores. Our results indicate that increasing age at a given body weight, via feed restriction, reduced IMF and collagen concentrations, and the rate of post mortem proteolysis, however, this had no significant impact on pork quality assessed after 4 days of ageing. On the other hand, increasing both age and weight at slaughter could alter pork texture, in spite of elevated IMF concentration.

Acceleration of post‐mortem changes in Tsaiya duck (Anas platyrhynchos) breast muscle by lactic acid marination

1. The effect of lactic acid marination at 5°C on post mortem changes in breast muscle pectoralis major of spent layer Tsaiya duck was studied. 2. Myofibrils were prepared from 0.1 M and 0.2 M lactic acid marinated muscle and control (non‐marinated samples) sampled at 0, 1, 3, 7 and 14 d post mortem. 3. Changes in myofibril fragmentation index (MFI), myofibrillar proteins and Z‐line structure were examined. 4. Marination of duck breast muscle in lactic acid at 5°C enhanced fragmentation of myofibrils and degradation of myofibrillar proteins and Z‐line structure as compared to control samples. 5. In summary, lactic acid marination at 5°C can accelerate the post mortem degradation of myofibrils in Tsaiya duck breast muscle.

Changes affecting the Longissimus dorsi, Triceps brachii caput longum and Rectus femoris muscles of young Friesian bulls during meat ageing

The chemical composition and post-mortem changes during 3–14 days of ageing were studied on three muscles ( Longissiums dorsi, Triceps brachii caput longum, Rectus femoris) from 13 young Friesian bulls. Chemical composition varied widely between animals ( p < 0.001) and muscles ( p < 0.001), and did not change during post-mortem storage. Significant changes affecting the non-protein nitrogen and soluble protein nitrogen contents were similar in all three muscles but differed from animal to animal. The increase in non-protein nitrogen can be considered as an indicator of proteolysis. Proteolysis extended to 14 days post mortem. The myofibril fragmentation index increased significantly ( p < 0.001) between 3 and 7 days post mortem along the same pattern, irrespective of the muscle and animal. A ceiling was reached at around 7 days post mortem, by which time maximum breakdown of the structure had probably occurred. No significant relationship was observed between chemical composition, changes in the soluble protein nitrogen, breakdown of structures and carcass characteristics.

Postmortem Changes in Breast Muscles of Mule Duck

Post-mortem changes in myofibril fragmentation index and degradation of myofibrillar proteins of duck breast muscles at 5°C was investigated. Muscle samples were collected immediately after killing and from the stored carcasses at 5°C for 1, 3, 7, and 14 days post mortem. The results showed that the MFI of the breast muscles increased with timepost mortem. SDS-PAGE of myofibrils indicated that the disappearance of troponin-T accompanied concurrently with the appearance of 32–30 kDa components. After 7 days of storage, α-actinin was degraded, and a 98 kDa component appeared. Titin 1 and nebulin also disappeared after post-mortem storage for 3 days.

Post-mortem Changes in Breast Muscles of Mule Duck

Post-mortem changes in myofibril fragmentation index and degradation of myofibrillar proteins of duck breast muscles at 5°C was investigated. Muscle samples were collected immediately after killing and from the stored carcasses at 5°C for 1, 3, 7, and 14 days post mortem. The results showed that the MFI of the breast muscles increased with timepost mortem. SDS-PAGE of myofibrils indicated that the disappearance of troponin-T accompanied concurrently with the appearance of 32–30 kDa components. After 7 days of storage, α-actinin was degraded, and a 98 kDa component appeared. Titin 1 and nebulin also disappeared after post-mortem storage for 3 days.

Biophysical aspects of meat tenderness

Biophysical aspects of meat tenderness is reviewed, where the meat structural origin of variation in meat tenderness is tried to be elucidated. Processes, such as rigor development and ageing, known to influence the properties of the structural components, is covered, and variables that influence those processes, such as chilling, electrical stimulation and stress ante-mortem, are discussed. Meat tenderness can be evaluated both by sensory and instrumental methods. The relationships between mechanical and sensory assessments tend to be non-linear, which can be due to non-linearity in the sensory evaluation and that muscle fibre orientation is easier to control in instrumental than in sensory evaluation. Structural changes of the meat occuring during rigor development are both longitudinal and lateral contraction of the myofibrillar mass. Other structural events, based on the proteolytic action, are the loosing up of the myofibrils held together laterally, weakening of the myofibrillar length and myofibril fragmentation. Using instrumental recordings of meat toughness (Warner-Bratzler (W-B) peak force), it decreases significantly with degree of contraction, when raw, but the reverse is found, when meat is cooked above 60 °C. A structural explanation to this behaviour is suggested to be the following. When meat is raw the lateral contraction of the meat fiber increases with shorter sarcomeres, giving rise to a larger viscous component and hence a lower W-B peak force. On heating, however, with a larger extracellular space, when shortened, there is more room for the connective tissue to contract without being restricted by the myofibrillar mass. This in turn gives a higher number of fibers per unit cross-sectional area, hence a larger elastic modulus and a higher W-B peak force, when cooked. When chilling of muscle during rigor both warm- and cold-shortening occur. Minimal shortening region is for beef M. longissimus dorsi (LD) 10–15 °C and for M. semimembranosus (SM) 7–13 °C. For the SM muscle there is a high correlation between percentage shortening and ultimate tenderness both in the warm- and cold-shortening region. But for the LD muscle this is only the case in the cold-shortening region. This observation suggests that the LD muscle is a more enzymatically active muscle than SM. The influence of low-voltage electrical stimulation (ES) was followed in the cold-shortening region for muscles LD and SM. A significant effect on tenderness 15 days post-mortem was only observed for LD at 1 °C and 4 °C, but not for SM. It was suggested that enhanced proteolysis could be the reason for the improved tenderness on ES of LD, as colds-hortening was not prevented by ES. Long-term and short-term stress ante-mortem can give rise to DFD (dark, firm and dry)-and PSE (pale, soft and exudative)-meat, respectively. DFD-meat (pH u > 6.0 in LD) has relatively short sarcomere lengths, but still it is swollen laterally and has consequently a small extracellular space. Therefore DFD-meat usually is tender. PSE-meat has a large variation in sarcomere length. The long sarcomeres of PSE-meat is suggested to be caused by reduced shortening, due to the denaturation of the sarcoplasmic proteins during rigor. The short sarcomeres can be caused by a higher percentage of rigor development in the warm-shortening region and that the denaturation of the myosin heads cause both longitudinal and lateral contraction of the myofibrillar mass. There is also a large variation in tenderness of PSE-meat, but it has been found that this variation is positively correlated to the sarcomere length (r = 0.52**), as has been shown for the other variables that governs the rigor process.

Effects of a beta-adrenergic agonist (L-644,969) and male sex condition on muscle growth and meat quality of callipyge lambs.

The objective of this study was to determine the effects of dietary administration of a beta-adrenergic agonist (BAA; L-644,969) and male sex condition (ram vs wether) on muscle growth and meat quality of Dorset x Romonov lambs believed to be heterozygous for the callipyge gene. At approximately 17 wk of age, lambs were blocked by weight within each sex condition and randomly assigned to BAA treatment group. The interaction of BAA and male sex condition was not significant for any of the traits measured. Rams had greater initial and final live weights, average daily gain, and hot carcass weight (P < .01). Rams did not differ (P > .05) from wethers with respect to any of the carcass traits, possibly because the wethers were so lean and heavily-muscled that there was little room for improvement. Kidney-pelvic fat weight was reduced 26% by BAA (P < .05). Knife separable lean weight and whole carcass proximate composition were not affected (P > .05) by BAA or male sex condition. Administration of BAA increased calpastatin activity at 20 d (1.1 vs 1.5 units/g), but not at 0 h (3.9 vs 4.8 units/g) postmortem, decreased myofibril fragmentation index (60.7 vs 44.9), and increased shear force (8.2 vs 10.9 kg) at 20 d postmortem (P < .05). These data suggest that muscle growth rates are near maximum in lambs expressing the callipyge gene, regardless of male sex condition or BAA treatment. Therefore, it seems that the callipyge gene exerts most, but not all, of its effect through intracellular events similar to those initiated by administering BAA.

Post‐mortem changes in goose (Anser anser) breast muscles as affected by calcium chloride marination

AbstractEffect of calcium chloride marination at 5°C on post‐mortem changes in goose breast muscles was studied. Purified myofibrils were prepared from 0.1 M CaCl2 marinated muscles and controls (nonmarinated samples) after 0, 1, 3, 7 and 14 days of marination. The changes in myofibril fragmentation index (MFI), myofibrillar proteins and Z‐line structure of goose muscles were examined. Goose breast muscles marinated in 0.1 M CaCl2 at 5°C exhibited a more rapid rate of an increase in MFI, the appearance of 30 kDa component, and the disappearances of troponin‐T, ω‐actinin, titin, nebulin, and Z‐line structure than controls muscles did. It is concluded that 0.1 M CaCl2 marination at 5°C accelerates the post‐mortem changes in goose breast muscles.

Is Z-disk degradation responsible for postmortem tenderization?

A number of studies have suggested that Z-disk degradation is a major factor contributing to postmortem tenderization. These conclusions seem to have been based largely on experimental findings showing that the calpain system has a major role in postmortem tenderization, and that when incubated with myofibrils or muscle strips, purified calpain removes Z-disks. Approximately 65 to 80% of all postmortem tenderization occurs during the first 3 or 4 d postmortem, however, and there is little or no ultrastructurally detectable Z-disk degradation during this period. Electron microscope studies described in this paper show that, during the first 3 or 4 d of postmortem storage at 4 degrees C, both costameres and N2 lines are degraded. Costameres link myofibrils to the sarcolemma, and N2 lines have been reported to be areas where titin and nebulin filaments, which form a cytoskeletal network linking thick and thin filaments, respectively, to the Z-disk, coalesce. Filamentous structures linking adjacent myofibrils laterally at the level of each Z-disk are also degraded during the first 3 or 4 d of postmortem storage at 4 degrees C, resulting in gaps between myofibrils in postmortem muscle. Degradation of these structures would have important effects on tenderness. The proteins constituting these structures, nebulin and titin (N2 lines); vinculin, desmin, and dystrophin (three of the six to eight proteins constituting costameres); and desmin (filaments linking adjacent myofibrils) are all excellent substrates for the calpains, and nebulin, titin, vinculin, and desmin are largely degraded within 3 d postmortem in semimembranosus muscle. Electron micrographs of myofibrils used in the myofibril fragmentation index assay show that these myofibrils, which have been assumed to be broken at their Z-disks, in fact have intact Z-disks and are broken in their I-bands.

Physico-chemical and processing quality of porcine M. longissimus dorsi frozen at different temperatures

Longissimus dorsi muscle from six pigs (24 h post-mortem) was cut into portions of similar size and shape (c. 700 g) and vacuum-packed in polyfilm. The muscle specimens were divided into three samples, one frozen at −20°C, another at −80°C and the third served as the control (not frozen). The meat sample frozen at −80°C was transferred to the −20°C freezer. After one month, both frozen pork samples were thawed at −2°C and drip loss (%) was measured. Hunter colour, metmyoglobin (MetMb) formation (%), water-holding capacity (WHC), TBA value, transmission value (TM) and myofibril fragmentation were also determined. There was no significant difference in drip loss for the two frozen samples. No MetMb formation could be detected and Hunter values were basically the same for all three samples. WHC, TBA value and TM were essentially the same for all three samples. TBA value was quite low for each frozen sample, indicating that lipid oxidation did not occur during freezing. Histological examination of both frozen samples indicated inter- and intracellular ice crystal formation at −20°C, and intracellular ice at −80°C, the extent being less than at −20°C. At −20°C, ice crystals were larger and muscle fibre diameter smaller than for the control or −80°C sample. Myofibril fragmentation in both frozen samples was significantly higher than in the control. Pork sausage was prepared from all three samples by adding 2% NaCl and 100 ppm NaNO 2. Cooking loss and colour forming ratios were essentially the same. The sausage sample made from the −20°C frozen meat was harder than that of the other two samples according to rheological measurement.

Effect of electrical stimulation on post mortem biochemical characteristics and quality of Longissimus dorsi thoracis muscle from buffalo ( Bubalus bubalis)

High voltage electrical stimulation (700 V, 1400 V peak, pulses 1 s on/1 s off, 60 Hz, 2 A) on buffalo carcasses resulted in a significantly more rapid pH fall in Longissimus dorsi thoracis muscle when compared to non stimulated controls ( p < 0.01), during the first 24 h after slaughter. The IMP ATP ratio on the same period showed a much more rapid increase for the stimulated muscles (1.07 and 1.16 at times 1 and 2.5 h post mortem vs control values of 0.77 and 0.83, respectively). Sensory and instrumental evaluation of texture of meat cooled by two distinct processes showed that tenderness at 24 h post mortem was higher in the stimulated muscles compared to non-stimulated controls, irrespective of the cooling process adopted. High voltage stimulation significantly decreases cohesiveness, increases myofibril fragmentation; and SDS polyacrylamide gel electrophoresis of the myofibrillar proteins showed a weakening of Troponin T band during 6 days of ageing in non-stimulated control muscles, whereas electrical stimulation accelerated the process of ageing over 3 days. This is the first report on acceleration of conditioning in buffalo muscle and the conditions described here have a high potential for application in meat industry for buffalo slaughter.