Rigor Muscle Research Articles

Differences in eating quality and electronic sense of meat samples as a function of goat breed and postmortem rigor state

Understanding the pre- and post-rigor meat quality characteristics is crucial for the development of featured goat meat products. To evaluate the quality characteristics of goat meat in different rigor states, knuckle muscle in pre-rigor, rigor, and post-rigor states of Taihang and Huanghuai goats were used to analyze chemical characteristics, water mobility, and electronic sense. Results indicated that Taihang and Huanghuai goat meat samples were rich in protein and essential amino acids, especially Lys. Pre-rigor goat meat samples had lower content of free moisture and higher water holding capacity than post-rigor goat meat samples. Furthermore, Taihang and Huanghuai goat meat samples exhibited different odour characteristics. Aromatic constituents content of post-rigor goat meat samples were greater than those of pre-rigor goat meat samples. The sweetness and bitterness of post-rigor goat meat samples were higher than those of pre-rigor goat meat samples. In conclusion, Taihang and Huanghuai goat meat samples have different quality characteristics, which were regulated by rigor state through different texture and flavor profiles.

Determination of pH in Pre rigor Fish Muscle – Method Matters

ABSTRACTThe determination of post mortem muscle pH are often carried out in studies on how pre-slaughter handling influences the development of rigor mortis and the quality of the fish products. The analysis might be performed by inserting a pH-electrode into the intact flesh or using a suspension containing a minced muscle sample. Although it has been known for a long time that mincing muscle tissue accelerates glycolysis and breakdown of adenosine triphosphate (ATP), more recent studies quite commonly determine pH after mincing pre rigor muscle without including an enzyme inhibitor that arrests glycolysis. This may have resulted in anomalously low pre rigor muscle pH. The aim of the present work was to compare the two methods of pH determination in pre rigor fish muscle and to highlight the importance of including the enzyme inhibitor when homogenizing pre rigor fish muscle prior to pH analysis.

X-ray Diffraction Studies on the Structural Origin of Dynamic Tension Recovery Following Ramp-Shaped Releases in High-Ca Rigor Muscle Fibers.

It is generally believed that during muscle contraction, myosin heads (M) extending from myosin filament attaches to actin filaments (A) to perform power stroke, associated with the reaction, A-M-ADP-Pi → A-M + ADP + Pi, so that myosin heads pass through the state of A-M, i.e., rigor A-M complex. We have, however, recently found that: (1) an antibody to myosin head, completely covering actin-binding sites in myosin head, has no effect on Ca2+-activated tension in skinned muscle fibers; (2) skinned fibers exhibit distinct tension recovery following ramp-shaped releases (amplitude, 0.5% of Lo; complete in 5 ms); and (3) EDTA, chelating Mg ions, eliminate the tension recovery in low-Ca rigor fibers but not in high-Ca rigor fibers. These results suggest that A-M-ADP myosin heads in high-Ca rigor fibers have dynamic properties to produce the tension recovery following ramp-shaped releases, and that myosin heads do not pass through rigor A-M complex configuration during muscle contraction. To obtain information about the structural changes in A-M-ADP myosin heads during the tension recovery, we performed X-ray diffraction studies on high-Ca rigor skinned fibers subjected to ramp-shaped releases. X-ray diffraction patterns of the fibers were recorded before and after application of ramp-shaped releases. The results obtained indicate that during the initial drop in rigor tension coincident with the applied release, rigor myosin heads take up applied displacement by tilting from oblique to perpendicular configuration to myofilaments, and after the release myosin heads appear to rotate around the helical structure of actin filaments to produce the tension recovery.

Tension Recovery following Ramp-Shaped Release in High-Ca and Low-Ca Rigor Muscle Fibers: Evidence for the Dynamic State of AMADP Myosin Heads in the Absence of ATP.

During muscle contraction, myosin heads (M) bound to actin (A) perform power stroke associated with reaction, AMADPPi → AM + ADP + Pi. In this scheme, A • M is believed to be a high-affinity complex after removal of ATP. Biochemical studies on extracted protein samples show that, in the AM complex, actin-binding sites are located at both sides of junctional peptide between 50K and 20K segments of myosin heavy chain. Recently, we found that a monoclonal antibody (IgG) to the junctional peptide had no effect on both in vitro actin-myosin sliding and skinned muscle fiber contraction, though it covers the actin-binding sites on myosin. It follows from this that, during muscle contraction, myosin heads do not pass through the static rigor AM configuration, determined biochemically and electron microscopically using extracted protein samples. To study the nature of AM and AMADP myosin heads, actually existing in muscle, we examined mechanical responses to ramp-shaped releases (0.5% of Lo, complete in 5ms) in single skinned rabbit psoas muscle fibers in high-Ca (pCa, 4) and low-Ca (pCa, >9) rigor states. The fibers exhibited initial elastic tension drop and subsequent small but definite tension recovery to a steady level. The tension recovery was present over many minutes in high-Ca rigor fibers, while it tended to decrease quickly in low-Ca rigor fibers. EDTA (10mM, with MgCl2 removed) had no appreciable effect on the tension recovery in high-Ca rigor fibers, while it completely eliminated the tension recovery in low-Ca rigor fibers. These results suggest that the AMADP myosin heads in rigor muscle have long lifetimes and dynamic properties, which show up as the tension recovery following applied release. Possible AM linkage structure in muscle is discussed in connection with the X-ray diffraction pattern from contracting muscle, which is intermediate between resting and rigor muscles.

In vivo myosin step-size from zebrafish skeletal muscle

Muscle myosins transduce ATP free energy into actin displacement to power contraction. In vivo, myosin side chains are modified post-translationally under native conditions, potentially impacting function. Single myosin detection provides the ‘bottom-up’ myosin characterization probing basic mechanisms without ambiguities inherent to ensemble observation. Macroscopic muscle physiological experimentation provides the definitive ‘top-down’ phenotype characterizations that are the concerns in translational medicine. In vivo single myosin detection in muscle from zebrafish embryo models for human muscle fulfils ambitions for both bottom-up and top-down experimentation. A photoactivatable green fluorescent protein (GFP)-tagged myosin light chain expressed in transgenic zebrafish skeletal muscle specifically modifies the myosin lever-arm. Strychnine induces the simultaneous contraction of the bilateral tail muscles in a live embryo, causing them to be isometric while active. Highly inclined thin illumination excites the GFP tag of single lever-arms and its super-resolution orientation is measured from an active isometric muscle over a time sequence covering many transduction cycles. Consecutive frame lever-arm angular displacement converts to step-size by its product with the estimated lever-arm length. About 17% of the active myosin steps that fall between 2 and 7 nm are implicated as powerstrokes because they are beyond displacements detected from either relaxed or ATP-depleted (rigor) muscle.

Myosin S2 Origins Track Evolution of Strong Binding on Actin by Azimuthal Rolling of Motor Domain

Myosin crystal structures have given rise to the swinging lever arm hypothesis, which predicts a large axial tilt of the lever arm domain during the actin-attached working stroke. Previous work imaging the working stroke in actively contracting, fast-frozen Lethocerus muscle confirmed the axial tilt; but strongly bound myosin heads also showed an unexpected azimuthal slew of the lever arm around the thin filament axis, which was not predicted from known crystal structures. We hypothesized that an azimuthal reorientation of the myosin motor domain on actin during the weak-binding to strong-binding transition could explain the lever arm slew provided that myosin’s α-helical coiled-coil subfragment 2 (S2) domain emerged from the thick filament backbone at a particular location. However, previous studies did not adequately resolve the S2 domain. Here we used electron tomography of rigor muscle swollen by low ionic strength to pull S2 clear of the thick filament backbone, thereby revealing the azimuth of its point of origin. The results show that the azimuth of S2 origins of those rigor myosin heads, bound to the actin target zone of actively contracting muscle, originate from a restricted region of the thick filament. This requires an azimuthal reorientation of the motor domain on actin during the weak to strong transition.

The occurrence of giant fibres in different muscles of two chicken genotypes

1. The occurrence of Giant Fibres (GF) in three muscles (Pectoralis major (PM), Iliotibialis lateralis and Semimembranosus) with different types of energy metabolism was studied in slow- and fast-growing chicken strains.2. A total of 20 one-day-old Leghorn chicks (slow-growing) and 20 broiler (Ross 508) chicks (fast-growing) were reared to 100 and 45 d, respectively.3. A small percentage of GF was seen in pre rigor muscle samples even at 3 min post mortem in both genotypes and in all muscle types studied.4. From 3 min to 24 h post mortem GF increased both in Leghorn and broiler chickens but to a different extent according to muscle type and genotype.5. The highest GF 24 h post mortem value was found in the PM muscles belonging to the fast-growing broiler line.6. It was concluded that every type of muscle can develop GF, but this phenomenon is more evident in the PM especially in animals selected for increased growth rate.

Evidence for the Presence of AM-ADP Myosin Heads in Rigor Muscle Fibers: Its Implication of the State of Myosin Heads after the End of Powerstroke

It is generally believed that, during muscle contraction, myosin heads (M) extending from myosin filaments bind with actin filaments (A) and perform powerstrokes associated with reaction, AM-ADP-Pi →AM+Pi + ADP. The presence of rigor or rigor-like myosin heads AM can not, however, be detected by X-ray diffraction studies on contracting muscle. To give information about the state of myosin heads after the end of powerstroke, we studied changes in the state of myosin heads when single Ca-activated skinned muscle fibers were transferred into high-Ca rigor solution (pCa,4), by applying quick releases (0.5-1% of Lo, complete in 1-2ms followed by restretch) at various times after the transfer of the fiber into high-Ca rigor solution. Unexpectedly, the fibers exhibited distinct tension recovery Pr following quick release. The value of Pr relative to the maximum Ca-activated isometric tension Po (Pr/Po) was about 0.4 at 10s after the transfer of the fiber into rigor solution, and decreased with time to completely disappear in 10-20min. In the presence of 5-10mM EDTA, chelating Mg, the amplitude of Pr was markedly reduced, and disappeared in 5-10min. After disappearance of Pr, the fiber only showed tension drop coincident with quick release. These results suggest that AM-ADP myosin heads are responsible for the tension recovery foolowing quick release, If, on the other hand, the ionic strength of rigor solution was reduced from 170 to 50mM by totally removing KCl, the amplitude of Pr was increased appreciably, and did not disappear for 20-30min. Concerning the cyclic actin-myosin interaction, it seems possible that, after the end of powerstroke, myosin heads take the form of AM-ADP having a long average lifetime.

Mesoscopic analysis of motion and conformation of cross-bridges.

The orientation of a cross-bridge is widely used as a parameter in determining the state of muscle. The conventional measurements of orientation, such as that made by wide-field fluorescence microscopy, electron paramagnetic resonance (EPR) or X-ray diffraction or scattering, report the average orientation of 1012-109 myosin cross-bridges. Under conditions where all the cross-bridges are immobile and assume the same orientation, for example in normal skeletal muscle in rigor, it is possible to determine the average orientation from such global measurements. But in actively contracting muscle, where a parameter indicating orientation fluctuates in time, the measurements of the average value provide no information about cross-bridge kinetics. To avoid problems associated with averaging information from trillions of cross-bridges, it is necessary to decrease the number of observed cross-bridges to a mesoscopic value (i.e. the value affected by fluctuations around the average). In such mesoscopic regimes, the averaging of the signal is minimal and dynamic behavior can be examined in great detail. Examples of mesoscopic analysis on skeletal and cardiac muscle are provided.

P-484 - The influence of depot antipsychotic treatment on the occurrence of MB. parkinsoni caused by medicaments- case report

Introduction In everyday psychiatric practice it is often difficult to differentiate primary psychiatric illness of comorbid disease. H.I., 45 years old, laborer, married, graduated on teacher Faculty. CMHC outpatients in three years of depression orally with antipsychotics, antidepressants and fluphenazine depot. Came to the hospital treatmernt with the diagnosis of sch. catatonia. Upon receipt, difficulty speaking, hypomimia, slow gait, upper limb in flexion and rigor muscle. Method Clinical examination, psychiatric interview, psychological testing, biochemical testing, radiographic testing and madopar test. Purpose Faster detection and differentiation of the existence of the clinical picture of primary disease and comorbid disease that was generated polipragmatic medicament approach. Results of the work The rapid differentiation of established diagnosis of primary and secondary neurologic disease. Body symptoms be reduced only after a month of treatment with symptomatic infusion and sedative. benzodiazepine 15 mg pro die. It was madopar test despite clinical neurologists and psychiatrists dilemma contributed fully that this symptom was not about schizophrenia but about medicament parkinsonism caused by various sort of therapy. Conclusion Side effects of depot antipsychotic therapy and pharmacotherapy lead to parkinsonism medicament which is wrongly recognized as depression and, unfortunately, later as an outpatient during the catatonia of schizophrenia. Include depot therapy with extreme caution, only in cases where the pre-clinical detail, examined the patient, especially when there is any organic changes in the brain or suspicion of intellectual inferiority.

Calcium-dependence of Donnan potentials in glycerinated rabbit psoas muscle in rigor, at and beyond filament overlap; a role for titin in the contractile process

In glycerinated rabbit psoas muscle, Donnan potential measurements demonstrated that the net electric charge on the actin–myosin matrix undergoes a sharp switch-like transition at pCa 50 = 6.8. The potentials are 2 mV less negative at the lower pCa 2+ ( P < 0.001). If ATP is present, the muscle contracts and breaks the microelectrode. Therefore the rigor state was studied. There is no reason to suppose a priori that a similar voltage switch does not occur during contraction, however. Calcium dependence is still apparent in muscles stretched beyond overlap (sarcomere length > 3.8 μm) and is also seen in the gap filaments between the A- and I-band ends; further stretching abolishes the dependence. These experiments strongly suggest that calcium dependence is controlled initially by the titin component, and that this control is lost when titin filaments break. We suppose that that effect is mediated by the titin kinase in the M-line region and may involve the extensible PEVK region of titin. There is great interest in the electric charge on proteins in muscle within the structural system. We suggest how changes in these charges may control the calcium activation process. We also suggest some simple experimental approaches that could clarify these effects.

Stiffness and number of crossbridges attached in active frog muscle: a reply to Professor Lombardi

We do not share Professor Lombardi’s confidence that the crossbridge stiffness and the fraction of myosin heads (crossbridges) attached in an isometric contraction are experimentally well established for muscles in these two frog species (Lombardi 2011). In particular we are not persuaded that the crossbridge stiffness is high (*3 pN/ nm) and the fraction of attached heads is low (20% in Rana esculenta and 30% in Rana temporaria). Determination of the crossbridge stiffness in muscle requires knowledge of the fraction of heads attached in an isometric contraction, since it is the product of the crossbridge stiffness and this fraction that is usually determined by subtracting the filament compliance from the half-sarcomere compliance. This inter-relation would cause an overestimate of the crossbridge stiffness to lead to the fraction of crossbridges attached being underestimated. An alternative approach which avoids knowing the fraction of heads attached in an isometric contraction is to determine the crossbridge stiffness in the rigor state. Unfortunately this is subject to large errors because the half-sarcomere compliance in the rigor state is not much larger than the contribution of filament compliance. The thermodynamic approach used for Rana esculenta (Decostre et al. 2005), which appeared at first to offer the hope of determining the crossbridge stiffness directly, is regrettably without foundation as we showed in Appendix 2 of our review (Offer and Ranatunga 2010). The fraction of myosin heads attached in an isometric contraction can be obtained from the ratio of the contribution of crossbridges to the half-sarcomere compliance in rigor to that in the active state. But as the rigor crossbridge compliance contribution can be determined only with a large error, the fraction of heads attached in an isometric contraction also carries a large error. In an earlier study (Linari et al. 1998) thick filament compliance in Rana esculenta was estimated from changes in the spacing of the M3 myosin meridional X-ray reflection. From the ratio of crossbridge compliance contributions in active and rigor muscle, the fraction of heads in isometric contraction may be calculated as 0.43 ± 0.087. But deciding that the M6 reflection should give a more reliable indication of the thick filament compliance, required their estimate of the fraction of heads attached in an isometric contraction to fall to 0.20 ± 0.12 (Linari et al. 2007). Even these large standard errors do not include the errors in determining the thick filament compliance. Moreover, there may be a systematic error in this quantity since it is by no means clear that the M6 reflection is exclusively contributed by detached heads. In our review we discussed the wide range of values that have been reported for the fraction of myosin heads attached (Offer and Ranatunga 2010). In particular, Bershitsky et al. (1997) gauged the number of heads attached in a stereospecific manner in isometrically contracting semitendinosus fibres of Rana temporaria from the intensity of the first actin layer line. At 5–6 C 27% were stereospecifically attached, but after rapidly raising the temperature to 16–19 C by a T-jump, this rose to 46%. This implied that the total fraction of heads attached was more than 46%. Because of this uncertainty, in the main body of the review we were careful to express crossbridge G. Offer K. W. Ranatunga (&) School of Physiology & Pharmacology, The Medical Sciences Building, University of Bristol, Bristol, UK e-mail: k.w.ranatunga@bristol.ac.uk

FRET characterisation for cross-bridge dynamics in single-skinned rigor muscle fibres

In this work we demonstrate for the first time the use of Förster resonance energy transfer (FRET) as an assay to monitor the dynamics of cross-bridge conformational changes directly in single muscle fibres. The advantage of FRET imaging is its ability to measure distances in the nanometre range, relevant for structural changes in actomyosin cross-bridges. To reach this goal we have used several FRET couples to investigate different locations in the actomyosin complex. We exchanged the native essential light chain of myosin with a recombinant essential light chain labelled with various thiol-reactive chromophores. The second fluorophore of the FRET couple was introduced by three approaches: labelling actin, labelling SH1 cysteine and binding an adenosine triphosphate (ATP) analogue. We characterise FRET in rigor cross-bridges: in this condition muscle fibres are well described by a single FRET population model which allows us to evaluate the true FRET efficiency for a single couple and the consequent donor–acceptor distance. The results obtained are in good agreement with the distances expected from crystallographic data. The FRET characterisation presented herein is essential before moving onto dynamic measurements, as the FRET efficiency differences to be detected in an active muscle fibre are on the order of 10–15% of the FRET efficiencies evaluated here. This means that, to obtain reliable results to monitor the dynamics of cross-bridge conformational changes, we had to fully characterise the system in a steady-state condition, demonstrating firstly the possibility to detect FRET and secondly the viability of the present approach to distinguish small FRET variations.Electronic supplementary materialThe online version of this article (doi:10.1007/s00249-010-0624-9) contains supplementary material, which is available to authorised users.

Kinetics of ADP Release From Cycling Cross Bridges In Contracting Skinned Cardiac Muscle Monitored With A Fluorescent Probe

Kinetics of ADP release from cycling cross bridges were studied in Ca activated skinned papillary muscle by displacement of fluorescent ADP bound to the cross bridges in AM*ADP state(s) by non-fluorescent ADP photogenerated from caged ADP. A strip of glycerinated papillary muscle (100um, 2mm) from guinea pig left ventricular in Ca-free solution was loaded with a mixture of non-fluorescent ATP (1mM), fluorescent 3′-amino-deoxy ATP (aminoATP) (50μM) and 5 mM caged ADP in the presence of an ATP back-up system. At the plateau of force at pCa5.8 the muscle was rapidly transferred into the photolysis trough filled with silicone oil and irradiated by a 437 nm laser pulse. Alternatively, a muscle loaded with only fluorescent amino ATP (50μM) was allowed to contract at pCa4.5 in oil and develop rigor with amino ADP bound to the cross bridges. Following photolysis of caged ADP the kinetics of force and fluorescent transients were found markedly different in contracting and rigor muscles. In contracting muscle the force and fluorescence both increased following caged ADP photolysis, while in rigor muscle the photolysis induced an increase in fluorescence, but decrease in force. Kinetics of ADP release estimated by the rate of fluorescence increase was significantly slower in contracting muscle than that in rigor: 2-4 s-1 vs 18-20s-1, suggesting that at least two different AM*ADP states exist during ATP hydrolysis by cycling cross bridge in contracting papillary muscle. Supported by NIH grant R03 AR05 2885 for A.K.

The Fluorescence Lifetime of a Single Actin-bound Fluorophore During Contraction of Skeletal Muscle

During interaction of actin with myosin, cross-bridges impart cyclical impulses to thin filaments. A cross-bridge spends part of cycle time strongly attached to actin (ts) during which it generates force, and remaining time (td) detached from thin filaments. The environment of a binding site on actin is different when a cross-bridge is attached and detached from thin filaments. Here we report, for the first time, measurements of the environment of a single actin binding site in rigor, relaxed and during isometric contraction of skeletal muscle. The environment was monitored by tracking the fluorescent lifetime (τ) of single Alexa488-phalloidin molecule bound to actin. The fluorescent lifetime is the averaged rate of decay of fluorescent species from the excited state. It depends on a variety of environmental factors. Lifetime of a single phalloidin molecule located at the center of the Overlap-band was measured every 50 msec during 60 sec of rigor, relaxation and contraction of muscle. The lifetime of rigor muscle was large when a cross-bridge was bound to actin, low when it was dissociated from it and intermediate during contraction. The “duty cycle” of a cross-bridge (Ψ) - defined as the fraction of the total cross-bridge cycle that myosin spends attached to actin in a force generating state [Ψ=ts/(ts+td)] was calculated from lifetime as 60%.

Orientation of the Essential Light Chain Region of Myosin in Relaxed, Active, and Rigor Muscle

The orientation of the ELC region of myosin in skeletal muscle was determined by polarized fluorescence from ELC mutants in which pairs of introduced cysteines were cross-linked by BSR. The purified ELC-BSRs were exchanged for native ELC in demembranated fibers from rabbit psoas muscle using a trifluoperazine-based protocol that preserved fiber function. In the absence of MgATP (in rigor) the ELC orientation distribution was narrow; in terms of crystallographic structures of the myosin head, the LCD long axis linking heavy-chain residues 707 and 843 makes an angle (β) of 120–125° with the filament axis. This is ∼30° larger than the broader distribution determined previously from RLC probes, suggesting that, relative to crystallographic structures, the LCD is bent between its ELC and RLC regions in rigor muscle. The ELC orientation distribution in relaxed muscle had two broad peaks with β ∼70° and ∼110°, which may correspond to the two head regions of each myosin molecule, in contrast with the single broad distribution of the RLC region in relaxed muscle. During isometric contraction the ELC orientation distribution peaked at β ∼105°, similar to that determined previously for the RLC region.

Myosin cross‐bridges modulate actin‐phalloidin interaction in skeletal muscle myofibrils

By binding to a nebulin site on actin in skeletal myofibrils phalloidin (PH) causes a force decrease (phase 1) followed by an increase in force (phase 2). The initial force decrease likely reflects a disturbance in actin-nebulin interaction. The aim of this work was to determine the role of myosin cross-bridges (XBs) and Ca2+ in PH-induced force decrease in skinned rabbit psoas fibers. Force response to PH was studied in the presence of 30 mM 2,3-Butanedione monoxime (an agent reducing a fraction of strongly bound XBs), where we found that the phase 2 response was suppressed and PH induced 60–70% force decrease. Pretreatment with PH of relaxed (pCa 9, strongly bound XBs are absent) or rigor (in the absence of ATP, all XBs are strongly bound to actin) muscles also resulted in force loss. At the same duration of pretreatment, the remaining force was higher and more sensitive to PH in the latter case. The same properties were found for dethiophalloidin (DTPH), where it was also shown that the force loss was essentially the same at pCa 4 and pCa 9. We concluded that rigor XBs, but not Ca2+, affect the rate of PH binding to actin in myofibrils. The XBs mediated changes in nebulin site on actin are supportive for suggested regulatory nebulin role. Supported by NIH grants HL68555 and HL37680.

Changes in composition and quality characteristics of ovine meat and fat from castrates and rams aged to 2 years

A comprehensive set of quality parameters has been recorded for meat and fat from groups of castrate and ram lambs raised on pasture and slaughtered in groups of six at 91‐day intervals from 122 to 668 days of age. These include mechanical evaluation of meat tenderness, sensory evaluations of meat flavour and fat odour, and measurements of fat colour, fatty acid composition, vitamins C and E, free glucose and iron in the meat, and of the concentrations of the flavour compounds indoles, phenols, and branched chain fatty acids in the fat. There was significant variation in many parameters between slaughter days, including markedly lower meat tenderness in one slaughter group, probably in response to unfavourable pasture conditions. Older ram lambs tended to be less tender than castrates of the same age. However, no longer‐term age‐related trends were observed in tenderness or flavour quality. Concentrations of free glucose in rigor muscle and vitamin C showed a declining trend with age. Concentrations of the branched chain fatty acids 4‐methyloctanoic and 4‐methylnonanoic acids in fat increased with age. Sex category effects were observed for the branched chain fatty acids and for indole and skatole. Higher concentrations were observed in ram lambs. The data indicate there is only a limited decline in lamb meat quality characteristics up to nearly 2 years of age, but that pasture feeding conditions may affect quality significantly.

Protein Osmotic Pressure and Cross-Bridge Attachment Determine the Stiffness of Thin Filaments in Muscle Ex Vivo

The properties of some models of the actin filament are compared with those of the thin filament in muscle. The greater stiffness of thin filaments ex vivo with respect to F-actin in vitro is attributed to the effect of both protein osmotic pressure and the attached cross-bridges. By comparing the stiffness of thin filaments in vitro and in isometric and rigor muscles the stiffness of thin filaments in relaxed muscle is computed. The upper limit of thin filament stretching is deduced to approach approximately 10 nm microm(-1). It is also calculated that, on stretching by 2.02 nm of the fully non-overlapped thin filament or by 1.59 nm of the thin filament on isometric contraction, the energy released on the hydrolysis of one molecule of ATP is fully used up.

Effects of thawing temperature on the physicochemical properties of pre-rigor frozen chicken breast and leg muscles

The objective of this study was to evaluate effects of thawing temperature on the biochemical and physicochemical properties of pre-rigor frozen chicken breast and leg muscles. Breast and leg muscles from 24 broiler chickens were excised within 10 min postmortem. Pre-rigor muscles were frozen at −20 °C and thawed at 0 and 18 °C, and pH, R-value, sarcomere length, muscle shortening, thaw and cook loss, shear force and myofibrillar fragmentation index (MFI) compared with those in pre-rigor or 2 °C chilled muscles. The ultimate pH of 18 °C thawed muscle was lower than that of 0 °C thawed and 2 °C chilled muscles. As expected, the shortening of sarcomere length and muscle length of thaw rigor muscles were more than those of chilled muscle, but there were no significant differences between chilled muscle and 0 °C thawed muscle. Also, there were no significant differences in R-value (Abs 250/Abs 260) and cook loss due to thawing temperature. Samples thawed at 0 °C had higher MFI and lower shear value than samples thawed at 18 °C. Shear force value and MFI were not significantly different between chilled muscle and 0 °C thawed muscle. By thawing at 0 °C, thaw shortening was prevented, and tender meat comparable to the chilled meat was obtained.