Onset Of Rigor Research Articles

Ultrastructural localization of calcium in post-mortem bovine muscle: a cytochemical and X-ray microanalytical study.

Calcium localization was demonstrated in bovine longissimus muscle using the antimonate precipitation technique in combination with electron probe X-ray microanalysis. Samples were taken each hour during the first 24 h post-mortem, and then after a storage period of 8 and 15 days. For all sampling times analysed, heavy precipitates were seen in dense parts of nuclei and on N-lines of myofibrils. Up to 18-20 h post-mortem, deposits were observed in sarcoplasmic reticulum at the level of triads. In comparison with the earlier post-mortem samples, myoplasmic precipitates were strongly increased at 4 h post-mortem, and just before rigor onset, at 19 h where intermyofibrillar spaces were completely blackened and triads were no more visible. These localizations of precipitates were still observed up to 15 days post-mortem. At these storage times, myofibril disruptions were seen at the level of N-lines. Wavelength-dispersive and energy-dispersive spectrometric analyses indicated that significant amounts of calcium occurred in the dense precipitates observed.

Total ischemia III: Effect of inhibition of anaerobic glycolysis

The effect of inhibition of glycolysis with sodium iodoacetate (IAA) on the changes induced by total ischemia was studied in canine left ventricle. Hearts were excised from phenobarbital anesthetized dogs and the circumflex (LCC) and anterior descending (LAD) branches of the left coronary artery were perfused in order to expose the LCC region to 48 μmol of IAA (about 1·5 μmol/g wet wt). The LAD regions of the same hearts served as untreated control myocardium. Hearts then were subjected to total ischemia in vitro at 37°C. Metabolites, ultrastructure, and the capacity of thin incubated slices of heart to maintain volume and ion gradients were studied in the control and IAA-treated regions. Depletion of ATP to levels of 3–4% of control occurred in only 4–5 min of ischemia in the IAA-treated myocardium, but similar depletion required 90 min of total ischemia in untreated myocardium. These low levels of ATP were associated with marked contracture-rigor. Depletion of ATP in the IAA treated region was accompanied by a marked increase in adenosine levels in the tissue at the onset of rigor (∼5 min); at this time, as much as 50% of the adenine nucleotide pool (ΣAd) was in the form of adenosine. In contrast, inosine was the predominant catabolite at 5 min in control myocardium, and only composed 16% of the ΣAd pool. Thus, pretreatment with IAA produced an enormous acceleration in the rate at which the ΣAd pool was consumed in totally ischemic myocardium. Lactate, the principal glycolytic intermediate which accumulates in totally ischemic tissue, was not formed in the IAA-treated heart. Moreover, IAA treatment did not accelerate the rate at which ultrastructural evidence of lethal injury developed in the poisoned myocytes. Thus, in a setting in which lactate accumulation did not occur, totally ischemic myocytes tolerated a very low level of high energy phosphate for a longer period of time than did untreated tissue before ultrastructural signs of cell death developed. The results indicate that marked ATP depletion, pe se, does not necessarity cause prompt sarcolemmal disruption.

Effects of Electrical Stimulation on the Post-Mortem Biochemical Changes and Texture of Broiler Pectoralis Muscle

A study was conducted to determine the influence of electrical stimulation (50, 200, or 350 V ac) on biochemical and textural changes in broiler breast muscle. Sixty-four broilers were stunned (50 V ac) prior to kill, and all but a control group were pulse stimulated during bleeding. After processing, carcasses were held in 10-C water for 1 h, then in 2-C ice/water slush for 1 h prior to muscle removal at 2 h post-mortem (PM). Bagged samples were held at 2 C for 24 h, then cooked. The pH, R value (ratio of adenine nucleotides to inosine nucleotides), cook yield, fluids and solids lost (F&S), and objective texture were measured. In addition, 16 broilers processed in the same manner were used in producing a profile of sarcoplasmic protein/enzyme changes in the breast muscle by cation exchange fast protein-liquid chromatography at 10 min, 2, and 24 h PM. The R values and soluble protein were also determined. Stimulation at 200 and 350 V accelerated the onset of rigor noted by lower pH values at 10 min and 1 h PM, and higher R values at 2 h PM. Muscle stimulated at 350 V exhibited the lowest cook yield and highest percentage of F&S lost, suggesting both the loss of functional properties and muscle integrity due to this treatment. All control and stimulated samples exhibited shear values in excess of what would be considered tender. Hardness and chewiness values increased as stimulation voltage levels increased. Only one of the seven principal chromatographic peaks decreased in response to increased electrical stimulation. Additional separation of the peak suggested that the component was a one active sulfhydryl site monomer of a four subunit lactate dehydrogenase enzyme.

Influence of post‐mortem treatments on turkey and chicken meat texture

SummaryToughness of poultry breast muscle was influenced by the rate of rigor onset, the rate of cooling and chilled storage time. The pH of the breast muscle at 20 min after stunning (pH20) in 52‐day‐old chickens varied from 5.9 to 6.9, and in 70‐day‐old turkeys from 6.2 to 6.8. In turkey meat with pH20 > 6.4, toughening was induced by immersion chilling to 7°C within 65 min post mortem and subsequent ‘tanking’ in iced water. Unaged, thawed meat from chicken carcasses, in which freezing commenced about 2 h after stunning was tougher than that from carcasses chilled for 16 h before freezing. Both were tender after 7 days chilled storage. Electrical stimulation of carcasses using 94 V decreased pH20 by an average of 0.3 unit in turkey, with no overall increase in tenderness. In chicken, it decreased the pH20 by 0.5 unit, but caused an overall toughening due to increased rigor shortening in carcasses with pH20 < 5.8.

Effects of 2,3-butanedione monoxime on the contractile activation properties of fast- and slow-twitch rat muscle fibres.

1. The effects of 2,3-butanedione monoxime (BDM, 0.2-10 mmol/l) have been examined at different temperatures on calcium transients (measured with aequorin) and isometric force in intact bundles of fibres from soleus (slow-twitch) and extensor digitorum longus (EDL; fast-twitch) muscles of the rat and on Ca2+-activated isometric force of mechanically skinned soleus and EDL fibres. Ca2+ release and uptake by the sarcoplasmic reticulum has also been investigated directly on skinned EDL fibres at 1 mmol/l BDM at 23 degrees C. 2. BDM bound calcium with low affinity (KCaBDMapp = 55.9 +/- 4.3 M-1 at 22 degrees C, pH 7.10, ionic strength approximately 155 mmol/l) and did not affect the kinetics and quantum yield of the Ca2+-induced aequorin luminescence. 3. BDM reversibly reduced both force- and Ca2+-dependent aequorin light during the twitch and tetanus of all intact-muscle preparations in a dose-related manner. Twitch responses of soleus fibres were more sensitive to BDM than were EDL fibres. Higher concentrations of BDM were needed to abolish the tetanic force response than the twitch response in both muscle types. 4. The initial rate of rise and the decay rate constants of twitches in both soleus and EDL muscles were increased in the presence of BDM. Accordingly, a higher frequency of stimulation was required to produce fusion of the tetanus. This phenomenon could be explained by the reduced magnitude of the Ca2+ transient. 5. BDM reduced maximal Ca2+-activated force development in mechanically skinned soleus and EDL muscle fibres in a dose-dependent fashion. This depression of force was less sensitive to BDM than were the light transients in intact fibres. Furthermore, BDM affected EDL skinned fibres to a greater extent than soleus skinned fibres, in contrast with its effects on intact fibres. 6. At concentrations of BDM greater than 2.5 mmol/l, BDM significantly decreased the sensitivity of the contractile apparatus to calcium. The relative force-pCa (= -log [Ca2+]) curves for both soleus and EDL skinned fibres were shifted to the right (i.e. to higher calcium concentrations) in a dose-related manner. 7. BDM (10 mmol/l) slowed maximal Ca2+-activated force development of skinned preparations of both fibre types at all temperatures investigated (4-24 degrees C). 8. BDM reduced stiffness in skinned preparations maximally activated by calcium in proportion to the reduction in the isometric force response. BDM also inhibited rigor force of all fibres but only if it was present before the onset of rigor.(ABSTRACT TRUNCATED AT 400 WORDS)

Pectoralis Muscle Shortening and Rigor Development at Different Locations Within the Broiler Breast

Two experiments were conducted to evaluate differences in rigor development that occur as a function of location within the broiler breast muscles, pectoralis major (p. major) and pectoralis minor (p. minor). Three locations were evaluated, corresponding to anterior, middle, and posterior samples taken between the cranial and caudal ends of each muscle. Results of the first experiment indicated that the 1.55-μ sarcomere lengths of hot-boned p. major muscle at the anterior location were significantly shorter than those at the posterior location, which were 1.69 μ. Sarcomere lengths of p. minor were shorter than those of p. major in hot-boned muscles, but longer in those aged intact, indicating a significant muscle × treatment interaction. In the second experiment, the anterior location of hot-boned p. major reached the onset phase of rigor in about 1 h, whereas those at the posterior location required between 2 and 4 h postmortem. Between 1 and 8 h postmortem, sarcomere lengths for the anterior location of p. major were also significantly shorter than lengths in the posterior location, but the differences after 24 h were not significant. Samples at all locations of p. minor reached onset of rigor by 15 to 30 min postmortem, with no locational differences throughout the 24 h period of aging. The results of both experiments generally indicated differences between profiles of rigor development of the two muscles and between samples at different locations of the much larger and more complex p. major.

Cytosolic free Ca2+ in single rat heart cells during anoxia and reoxygenation.

Free Ca2+ in the cytosol ([Ca2+]i) of individual rat ventricle cells injected with aequorin was measured under anoxia. In glucose-free medium myocytes spontaneously shortened after about 60 min, although [Ca2+]i was still at or near resting levels. However, within minutes a net inward movement of Ca2+ across the sarcolemma developed and [Ca2+]i began to rise. Provided oxygen was readmitted before [Ca2+]i exceeded 2-3 microM, cells were able to restore [Ca2+]i to resting levels through caffeine-sensitive sequestration of Ca2+ in the sarcoplasmic reticulum. We suggest that Ca2+-independent shortening of anoxic cardiomyocytes reflects onset of rigor which triggers loss of [Ca2+]i homoeostasis.

Post-mortem evolution of rheological properties of the myofibrillar structure

The post-mortem evolution of the rheological behaviour of beef muscle has been studied with the SATA compressive device. The resistance and elasticity of the muscle tissue, measured at low strain, refer to the myofibrillar structure and provide an indication of the advance of the rigor maturation process. These parameters have been used to quantify the electrical stimulation effect on Longissimus dorsi and Semi-membranosus muscles. An empirical model is proposed for the post-mortem evolution of the resistance and provides three parameters—the initial rate of rigor onset, the time of rigor and the residual stress after ageing. On the other hand, parameters obtained at high strain refer mainly to the connective tissue. The particularly high stress developed by the pre-rigor muscle, however, is presumed to be associated with the myofibrillar component.

Direct observation of the "oxygen paradox" in single rat ventricular myocytes.

By phase contrast microscopy with video length tracking, we followed the sequence of morphological changes in individual isolated rat ventricular myocytes during anoxia followed by reoxygenation. Cells appeared normal during early anoxia. After a duration of anoxia T1, which varied from 17-47 minutes in different cells, each cell abruptly contracted an average of 33% in length to an inert rectangular form presumed to be a rigor state. Cells which were reoxygenated before the onset of rigor showed normal morphology and an unchanged extent of shortening on field stimulation, compared to control. Cells that were reoxygenated after a time in the rigor state, T2, either partially recovered to a shortened rectangular form capable of stimulated twitches or rounded up rapidly to a disordered hypercontracture form. The distribution of T1 was the same for cells which recovered and which hypercontracted. In contrast, the outcome of reoxygenation depended markedly on T2: all cells that were reoxygenated after less than 10 minutes of rigor recovered function, whereas all cells that spent more than 20 minutes in rigor hypercontracted when reoxygenated. The hypercontracture appears to be the cellular analog of the "oxygen paradox" in whole hearts. Its occurrence is reliably related to duration of rigor state but not to duration of hypoxia, because of marked cellular variability in the time of onset of rigor.

Cold-shortening toughness in excised pork M. Longissimus dorsi

Excised pork M. Longissimus dorsi from six Large White Cross pigs were subjected to a range of chilling rates using temperatures between 20°C and -20°C. Onset of rigor at 20°C varied from 3 to 7.5 h between animals and rigor was complete in 6.5 to 15 h. Cold-shortening was induced when samples were chilled in air or liquid at 3°C or below but not at 5°C or ambient. The highest cooling rate, using liquid at -1°C, reduced the meat samples to 10°C in about 1 h and induced 34% shortening. After ageing for 5 days at 3°C in 26 h. Considering all chilling rates, toughness increased as the time to reach 10°C decreased to 3 h or less. Extensive cold-toughening would be unlikely to occur in current UK commerce and any toughening which did occur would be confined to Longissimus dorsi M. in about 20% of carcasses. The projected increased introduction of very rapid cooling, particularly in conjunction with lean pig production and hot deboning of pork, could toughen all cuts in about 60% of carcasses.

Differential Scanning Calorimetry of Beef Muscle: Influence of Sarcomere Length

ABSTRACTContraction state of beef muscle at onset of rigor influences tenderness of cooked meat. Loss in tenderness during cooking has been related, through use of differential scanning calorimetry (DSC), to thermal denaturation of myofibrillar proteins. Contraction of beef sternomandibularis muscle was controlled at sarcomere lengths of 2.4, 2.1, 1.9, 1.7, and 1.4 μm. Samples were scanned from 25‐ 105°C at 10°C/min; ΔH (change in heat of transition) between 45° and 92°C dropped from ca. 4 J/g muscle at 2.4 μm to ca. 3 J/g at 1.4 μm. This difference (P < 0.05) amounts to less than 1% of the total energy resuired to heat meat from 45° to 92°C. The decrease is attributed to a greater actomyosin contribution to the overall thermal curve resulting from increased overlap of the filaments.

Effects of Brain Destruction on Post Harvest Muscle Metabolism in the Fish Kahawai (Arripis trutta)

Brain destruction followed by immediate chilling of troll-caught kahawai delayed the onset of rigor by 73 min. It also resulted in the lowest measured pH in white muscle during rigor being reached after 1500 min compared with only 500 min for untreated fish. This difference in pH appeared to correlate with differences in lactic acid levels during rigor. Brain destruction also considerably increased the time at which significant amounts of ATP could be found in white muscle. High pH and ATP levels particularly during the chilling phase may contribute to retention of flesh translucency for longer periods.

The kinetics of rigor onset in beef muscle fibres

Force and stiffness were investigated as beef muscle fibre preparations entered rigor mortis. The results show that single fibres enter rigor rapidly (exhibit a small t 10–90) whilst fibre bundles exhibit a much slower rate of entry into rigor (larger t 10–90). The mean ‘rigor time’ in both cases is, however, similar. The difference in kinetics is probably due to the fact that individual fibres within a bundle enter rigor at different times. Effectively anaerobic fibre bundles treated with iodoacetate exhibit a t 10–90 almost as short as do single fibres when similarly treated, suggesting that much of the inferred heterogeneity of response amongst fibres in a bundle arises from differences between fibres in the ability of glycolysis to sustain ‘relaxing’ concentrations of ATP. Fibres have been chemically ‘skinned’ after entering the rigor state. Measurements of the relationship between stiffness and tension in the skinned fibres indicate that there are two readily distinguishable rigor ‘states’ depending upon whether rigor is entered from the relaxed of from the contracting state. By contrast, the rigor state achieved by intact fibres is similar to that attained in skinned fibres via the contracted state, suggesting that the ‘natural’ rigor state is preceded by a calcium-activated contraction. Interconversion of the two rigor states generated in vitro requires an intermediary relaxed state.

Pre‐ and Post‐Rigor Sectioned and Formed Beef Steaks Manufactured with Different Salt Levels, Mixing Times and Tempering Times

ABSTRACTThis study was designed to identify processing parameters necessary for the incorporation of pre‐rigor beef in sectioned and formed steaks. Meat logs were prepared from pre‐ or post‐rigor beef muscle with 0.0, 0.5 or 1.0% salt, mixed for 0, 6, 12 or 18 min, frozen and tempered to —3°C. Logs were pressed and cleaved after 0, 24, 48 or 72 hr tempering. Tempering at ‐3°C resulted in sufficient metabolic activity (as measured by pH and R‐value) to deplete the ATP content of pre‐rigor muscle. The presence of salt hastened the onset of rigor, maintained a higher ultimate muscle pH and improved cooking yields, bind (adhesion) and tenderness. Longer mixing times enhanced bind. These data suggest that, with appropriate modification in the processing procedure, pre‐rigor muscle can be incorporated into sectioned and formed products.

The influence of temperature on shortening and rigor onset in beef muscle

At sufficient ATP concentration and temperatures below about 15°C, pre-rigor beef muscles (neck muscles) contract; this phenomenon is known as cold shortening. There is also a contracture at higher temperatures occurring just before rigor onset which is called rigor shortening. While rigor shortening starts in neck muscles at pH around 6·3–6·0 and at about 2 μMol ATP/g muscle, cold shortening can begin at pH around 7·0 and the full ATP concentration (4 μMol ATP/g) in the muscle. Shortening can take place as long as there is no irreversible formation of the actomyosin complex in the muscle, i.e. before rigor onset occurs, which can be measured by intermittent loading of the muscle. The degree of extensibility which follows starts to decrease at the moment of rigor onset. This irreversible loss of extensibility at temperatures between the freezing point (−1°C) and physiological temperatures (38°C) starts at various pH values and ATP concentrations in the muscle. At 38°C the rigor onset occurs at pH 6·25 and about 2 μMol ATP/g muscle, dropping at 15°C to pH 5·75 and 1 μMol ATP/g muscle. At 0°C, as at all temperatures below 10°C, the loss of extensibility at medium loads (about 250 g/cm 2) begins shortly after cold shortening. This loss of extensibility is reversible by increasing the load or raising the temperature. The irreversible loss, or rigor onset, however, occurs at 0°C with pH of 6·1–6·2 and 1·8–2·0 μMol ATP/g muscle. Thus, the onset of rigor is influenced by more than one factor. Temperature, pH and ATP concentration each play a rôle. Maximum loss of extensibility or completion of rigor is reached between 10°C and 38°C at pH 5·5–5·6 and less than 0·5 μMol ATP/g muscle. At 0°C the completion of rigor takes place at pH 6·0, but still at 0·5 μMol ATP/g muscle. The latter fact shows that the completion of rigor is solely dependent on the ATP concentration in the muscle; nevertheless, the pH of rigor completion is higher in the extreme cold shortening range. This is apparently due to a different pH/ATP relationship in muscles at low temperatures. The results are discussed in terms of changes in the concentration of Ca 2+ ions and ATP. The results are of particular interest for the handling of hot-boned meat; that is, for both the cooling of pre-rigor muscle and the use of hot-boned meat for processing.

Biochemical and technological characteristics of hot chicken meat

SummaryIn the hot breast and leg muscles of broiler chicken the level of ATP, the ‘R’ value, the lactic acid content, the pH value, the length of sarcomers, the water and fat retention capacity, the fat emulsion stability, thermal drip, and the extractability of protein fraction were investigated. It was found that in the breast muscles the onset of rigor mortis commenced within 30–60 min, and in the leg muscles as early as 15–30 min after killing of the birds. The deepest rigor mortis occurred between the first and fourth hour, and then gradually declined, sooner in the leg than in the breast muscles. The addition of sodium chloride (2.0–2.5%) to the minced pre‐rigor meat not later than 40 min after slaughter, or better, an injection of NaCl brine into intact muscles 15 min after slaughter of birds, preserved their good technological properties.The tenderness and the thermal drip of hot salted and chilled salted muscles showed no significant differences, but water retention and fat emulsifying capacity were better in the hot salted meat samples. The hot salted and cooked muscles were preferred by the sensory panel to corresponding samples of chilled muscles.From the hot salted chicken meat more sarcoplasmic and myofibrillar proteins were extracted than from meat salted after chilling. However, after frozen storage the extractability of myofibrillar proteins were higher in the salted chilled meat.

Influence of temperature on the rate of post-mortem metabolism and water-holding capacity of bovine neck muscles

Strips of forty bovine neck muscles were placed at temperatures in the range −1° to +30°C within 45 min of slaughter and stored for up to 24 h. Strips were taken at various times during storage and assayed for pH, ‘R’ value (degree of transformation of ATP to IMP) and ATP concentration. The water-holding capacity (WHC) of the intact muscle was compared with the WHC of a salted muscle homogenate prepared at each sampling time. The rate of pH fall post mortem was relatively low around +5°C and increased at lower or higher temperatures. ATP concentration showed a delay phase dependent on storage temperature and a subsequent rate of depletion which was also temperature dependent. The patterns of change in WHC of the muscle samples and the salted homogenates differed, the former showing a rapid fall to a fairly steady level shortly after initiation of storage, the latter showing no appreciable change until the onset of rigor. It is suggested that salting meat at any time prior to the onset of rigor will confer improved WHC and that the temperature of storage post mortem should be chosen to induce low rates of ATP turnover so as to prolong the feasible delay between slaughter and salting.

Influence of Postmortem Changes in Bovine Muscle on the Water‐Holding Capacity of Beef. Postmortem Storage of Muscle at Various Temperatures Between 0 and 30°C

ABSTRACTBovine neck muscles were incubated between 0° and 30°C soon after slaughter. At different times postmortem biochemical and physical parameters and cooking loss in homogenates with or without salt were measured. The rate of pH fall in muscle depends on the incubation temperature. At 0.5°C the pH drops fast at first, leveling off afterwards but between 7° and 14°C there is an initial lag period of 2‐3 hr. At 30°C no lag phase occurs. The increased rate of postmortem metabolism at 0.5°C is accompanied by cold shortening which occurs before onset of rigor and is followed by little rigor shortening. Above 16°C rigor shortening increases with rising temperature without prerigor contraction. Neither shortening nor development of rigor have an immediate influence of WHC of muscle and unsalted muscle homogenates; the small decrease of WHC postmortem is due to pH fall only and independent of temperature. Salted homogenates prepared from muscles at different time postmortem show above pH 6.0 a similar relationship between pH and WHC. At the onset of rigor mortis (pH 5.9), however, the WHC of the salted homogenate decreases strongly. The practical consequences of these results with regard to processing of beef are discussed.

Influence of Postmortem Changes in Bovine Muscle on the Water‐Holding Capacity of Beef. Postmortem Storage of Muscle at 20°C

ABSTRACTRigor mortis occurs in bovine neck muscles as soon as pH 5.9 and an ATP level of about 1 μMol/g are reached. At 20°C muscle contraction does not occur before the onset of rigor. Postmortem changes in water‐holding capacity (WHC) were followed by measuring the cooking loss of unsalted and salted (2% NaCl) muscle homogenates prepared after storage of the intact muscle tissue at 20°C for different periods postmortem. At tissue pH above 5.9 addition of salt causes a strong increase of WHC of muscle homogenates. There is a small decrease of WHC of both unsalted and salted homogenates during the prerigor phase which is apparently caused by the postmortem fall of pH. Rigor mortis does not influence the WHC of unsalted muscle homogenates but causes a strong decrease of WHC of salted homogenates. The reason for this difference is discussed. No more than one‐third of the total postmortem decrease of WHC and protein solubility in salted muscle homogenates was attributed to the fall of pH, so at least two‐thirds were due to the development of rigor.

The Effects of Dietary Selenium and Vitamin E on Avian White Muscle Disease as Measured by Both Chemical and Physical Parameters

Commercial chicken broilers were fed a semipurified diet deficient in vitamin E and selenium from day 1 to day 13 ex ova and subsequently fed varying levels of dietary selenium and vitamin E. All birds were sacrificed on the 28th day, stored for 36 hr at 2 C to allow the onset and resolution of rigor, and frozen at −32 C until needed. Total cathepsin content of the Pectoralis major depended upon dietary vitamin E for birds receiving 0 to 12 IU/kg, whereas selenium administered at .05 to .16 ppm in the diet showed no statistically significant effect. Similary, total protein content of P. major increased with increasing level of dietary vitamin E, but the level of dietary selenium had no effect. Muscle break strength was significantly affected by dietary selenium and vitamin E (P = .0092) interacting together. Catheptic activity and muscle protein explained 6.36% and 3.58% of the variability in muscle break strength. Birds with more advanced avian hite muscle disease showed higher break strength values. Ultrastructural deterioration of the myopathic muscle included disintegration of blood vessel walls, transverse tubules, and mitochondrial membranes as well as the obvious disruption of the myofibrillar components. Myelin figures were present in diseased, but not in normal, muscle. Accumulation of adipocytes both extracellularly and intracellularly occurred in selenium and vitamin E-deficient birds.