Post-mortem changes in cytoskeletal proteins of muscle

Progressive changes have been identified in the solubility of muscle-cell proteins during post-mortem muscle ageing, particularly the cytoskeletal proteins, desmin and connectin. Ox sternomandibularis muscle was sampled immediately post mortem and up to six days later. It was homogenised and separated into three salt-soluble fractions: phosphate soluble, concentrated KI soluble and guanidine-HCl soluble. Proteins in each fraction were analysed on sodium dodecylsulphate polyacrylamide gels. Changes reported previously by other authors were confirmed. In addition desmin, which was restricted to the guanidine fraction, disappeared, apparently due to proteolysis during storage. Connectin was also partly lost from the guanidine fraction, possibly through increased solubility in the KI fraction. In this respect an unidentified polypeptide of 110 000 D appeared during storage. Desmin extracted from ox muscle was partially purified and identified by amino acid analysis. It apparently occurs in vivo as a network of linked collars around the Z-discs and its loss during post-mortem storage probably accounts for the ease with which stored muscle disintegrates into individual myofibrils on homogenisation. The disintegration of the cytoskeletal network can account for the post-mortem changes in the physical properties of muscle for the increased tenderness after cooking of stored meat. However, factors other than those related to changes in cytoskeletal proteins are responsible for the toughness of cooked, cold-shortened muscle since cold shortening prior to storage did not affect the distribution of proteins among the three salt fractions, nor the patterns obtained in gel analyses.     

Endurance-exercised growing sheep: I. Post-mortem and histological changes in skeletal muscles

A study was conducted with Suffolk ram lambs to determine whether chronic endurance exercise would affect post-mortem changes in muscle tissue. Muscle fibre diameters, sarcomere lengths, fibre types, and pH and temperature declines were measured in five skeletal muscles (semimembranosus, SM: vastus lateralis, VL; semitendinosus, ST; psoas major, PM; gastrocnemius, G). The exercise had no significant effect on muscle size or muscle fibre diameter in any of the muscles studied. However, endurance-exercised sheep had significantly shorter sarcomeres in all five muscles than their non-exercised counterparts. The pH decline curves differed among muscles; those having the highest proportion of glycolytic fibres had the slowest rates of pH decline. The increased proportion of slow-twitch fibres in the SM, VL, ST and G associated with the exercise regime had little effect on the post-mortem pH decline. However, the ST also had a significant exercise-associated increase in the proportion of oxidative-glycolytic fibres (intermediate) and was the only muscle in which exercise influenced the rate of pH decline significantly.     

Post-mortem kinetics of meat tenderness and the components of the calpain system in bull skeletal muscle

Eight strip loins (M. longissimus dorsi) from pasture fed Friesian bulls were aged at 15 °C for a range of times from 1 to 120 h. pH declined from 6.29 (SE 0.119) one hour post slaughter to an ultimate pH of 5.48 (SE 0.013). The activities of the components of the calpain system (μ-calpain, m-calpain and calpastatin) were determined after separation on a DEAE-sephacel column. There was a dramatic decline in μ-calpain activity post slaughter with a complete disappearance within 48 h. The rates of decline in m-calpain and calpastatin activity were slower with 30% and 50% remaining 120 h post slaughter, respectively. The rapid decline in μ-calpain activity relative to the calpastatin activity is likely to reduce the degree of tenderisation and ultimate tenderness of the meat.     

Post-mortem changes in myofibrillar protein solubility

Summary. During the ageing of bovine muscle there is an increase in the solubility of the myofibrillar protein as tropomyosin and associated myofibrillar proteins become extractable with the Weber-Edsall solution. This fact agrees with the concomitant structural changes believed to occur in the sarcomere.     

Post-mortem metabolism in fresh porcine, ovine and frozen bovine muscle

After slaughter, beef carcasses (n = 20) in groups of two were subjected to five treatments (one side only) including intermittent spray-chilling using water, 1% acetic acid or 1% lactic acid, or a single spray treatment with 1% acetic acid or 1% lactic acid. Intermittent spray-chilling consisted of two sprays of 30 s duration per hour for 12h. Single spray treatment consisted of one 30 s spray after entering the chill cooler. The other side of each carcass (control) was air chilled (at 2 to 3°C; air velocity 1 to 3 m/s) only. Five subprimal cuts were taken from each side at 48 h post mortem, vacuum packaged and stored for 28 days at 2°C. Intermittent sprays of sides with acetic or lactic acid resulted in significant (1.8-4.3 log/cm(2)) reductions in aerobic plate count of the strip loin, boneless rib and clod over their controls after these subprimal cuts had been vacuum packaged and stored for 28 days at 2°C in high-oxygen barrier (HOB) film. Lactobacillus spp. were dominant in the microflora of the subprimals from the control and treated sides. When sides were treated with a single sprays of acid, significant reductions in APC were noted only for some cuts of sides treated with lactic acid. After 28 days of storage, there were few significant differences in percentage purge, lean color, and off-odor scores between subprimals from control and treated sides.     

Post-mortem changes of muscle from fresh water prawn (Macrobrachium rosenbergii) as influenced by spawning stages

Post-mortem changes of the muscle from pre- and post-spawned fresh water prawn (Macrobrachium rosenbergii) were comparatively monitored during 7 days of iced storage. During the storage, the muscle of pre-spawned prawn had a greater value of trichloroacetic acid (TCA) soluble peptide, heat soluble collagen and pepsin-soluble collagen (PSC) contents than did post-spawned counterpart. Those components in the muscle of both prawns increased markedly after 3 days of storage (p < 0.05). Conversely, insoluble collagen (ISC) content, shear force value and texture liking of both prawns decreased (p < 0.05), indicating the softening of muscle. No changes in protein patterns were observed, except the decreased band intensity of 66 kDa protein in water soluble fraction of both prawns was found after 3 days of storage. T_max and enthalpy of PSC from both prawns decreased during the first 4 days of storage (p < 0.05), suggesting the degradation or denaturation of collagen in the muscle. Light microscopic study showed the lowering of intercellular connection of raw meat and higher gaping in cooked meat when the samples were stored for a longer time. Therefore, post-mortem characteristics of prawn muscle was affected by storage time and spawning stages.     

Pressure-induced changes in the connectin/titin localization in the myofibrils revealed by immunoelectron microscopy

Changes in the connectin/titin localization in post-mortem and pressurized chicken muscles were investigated by immunoelectron microscopy. The anti-connectin monoclonal antibody, 1D11, strongly labeled the sides of thick filaments near the H-zone and weakly labeled the sides of Z-line in the sarcomere prepared immediately after death. With the development of the muscle contraction, the shortening of the sarcomere and the dispersion of the connectin epitope near the H-zone were observed. With the gradual increase of the sarcomere length during further storage, the apparent increase of the width of the epitope in the A-band region stained by the antibody was observed, but the distance from the epitope to M-line remained almost the same length. In the case of high pressure treatment, significant changes in the labeling pattern of the antibody were observed with the increase of the pressure applied. The increase of the distance from the epitope to M-line and dispersion of the epitope were observed in the fiber pressurized at 100 MPa. These phenomena were accelerated with the increase of the pressure applied. The discontinuous dense materials labeled by the antibody at the thick filament near the H-zone were observed in the fiber bundles pressurized at 200 MPa or more. This is probably due to the accumulation of connectin molecule from ordinary location in the sarcomere, because of the pressure-induced destruction of the thick and connectin filaments. In the fiber bundles pressurized at 300 MPa, a significant increase in the distance from the epitope to M-line accompanied with the increase of the sarcomere length was observed. From the results obtained, it was clear that the changes in the location of the connectin epitope induced by the brief exposure to high pressure were drastic in comparison with that in the sarcomere during post-mortem storage.     

Endogenous skeletal muscle antioxidants

Skeletal muscle is susceptible to oxidative deterioration due to a combination of lipid oxidation catalysts and membrane lipid systems that are high in unsaturated fatty acids. To prevent or delay oxidation reactions, several endogenous antioxidant systems are found in muscle tissue. These include α‐tocopherol, histidine‐containing dipeptides, and antioxidant enzymes such as glutathione peroxidase, superoxide dismutase, and catalase. The contribution of α‐tocopherol to the oxidative stability of skeletal muscle is largely influenced by diet. Dietary supplementation of tocopherol has been shown to increase muscle α‐tocopherol concentrations and inhibit both lipid oxidation and color deterioration. Dietary selenium supplementation has also been shown to increase the oxidative stability of muscle presumably by increasing the activity of glutathione peroxidase. The oxidative stability of skeletal muscle is also influenced by the histidine‐containing dipeptides, carnosine and anserine. Whereas carnosine and anserine are affected by diet less than α‐tocopherol and glutathione peroxidase, their concentrations vary widely with species and muscle type. In pigs, beef, and turkey muscle, carnosine concentrations are greater than anserine, while the opposite is true in rabbit, salmon, and chicken muscle. Anserine and carnosine are found in greater concentrations in muscle high in white fibers, with chicken white muscle containing over fivefold more anserine and carnosine than red muscle. Anserine and carnosine are thought to inhibit lipid oxidation by a combination of free radical scavenging and metal chelation.     

草鱼骨髓肌肌球蛋白热隐定性及凝胶化特性的季节变化

对不同季节的草鱼(Ctenopharyngodon idellus)骨骼肌肌球蛋白进行提取和纯化,通过差示扫描量热仪(DSC)和流变仪对它们的热稳定性及动态黏弹性的变化进行了测定和比较.春、夏、秋、冬季鱼肌球蛋白的热转化温度(Tm)分别为42.2、45、41、39.5℃,表明春、夏季鱼较秋、冬季鱼具有更好的肌球蛋白热稳定性;并且四种肌球蛋白的动态黏弹性参数随温度上升的变化趋势是不同的,证明了具有不同热稳定性的肌球蛋白显示不同的热凝胶形成过程;春、夏季草鱼两段形成凝胶:第一段在42℃之前,第二段在44℃之后,而秋、冬季草鱼三段形成凝胶:第一段在30℃之前,第二段在34～39℃,第三段在40℃之后,表明肌球蛋白的热稳定性越差,其形成凝胶的起始温度越低.此外,对不同季节的草鱼鱼糜样品凝胶强度的测定结果显示,秋季鱼较其他三种季节的鱼具有更好的凝胶形成能力.     

Bacterial penetration of chicken breast muscle

Pure cultures of motile, but not non-motile strains of bacteria penetrated blocks of chicken breast muscle, irrespective of ability to hydrolyse gelatin, casein or soluble meat proteins. Penetration occurred as a result of movement of bacteria between the endomysial sheath and associated muscle fibres. Rates of penetration recorded were temperature dependant, affected by tissue moisture content and favoured by proteolytic activity, but were independent of growth rate. In addition, mixtures of proteolytic and non-proteolytic cultures enhanced the penetration rate of the non-proteolytic strains. Other experiments using mixed inocula, indicated some strains of non-motile, non-invasive bacteria may be carried into muscle by motile, invasive strains.     

Influence of caspase3 selective inhibitor on proteolysis of chicken skeletal muscle proteins during post mortem aging

The objective of this study was to investigate the potential contribution of apoptosis related downstream executioner caspase3 to post mortem skeletal muscle proteolysis by use of caspase3 selective inhibitor DEVD–CHO (N-acetyl–Asp–Glu–Val–Asp–CHO). After slaughter, four chicken breast muscles were removed and cut into small pieces, then marinated in treatment solution containing DEVD–CHO, or in control solution, and stored at 4 °C for 1, 3 or 7 d. Meat samples were obtained and used for detecting muscle protein degradation or calpain activity. Results showed that DEVD–CHO had inhibited the degradation of muscle skeletal proteins (titin, nebulin, desmin and troponin-T) significantly, whereas the activity of calpains had not been influenced. Therefore, the degradation of muscle proteins should not been exclusively attributed to the calpain system, and the effector caspase3 may be a new protease involved in meat post mortem tenderization.     

Catechins enhance skeletal muscle performance

Abstract

Muscle-related disorders, such as sarcopenia and cachexia, caused by aging and chronic diseases can lead to the loss of muscle mass and strength to different degrees, severely affecting human health. Globally, tea is one of the three most popular beverages, and its major active ingredient catechins have been reported to delay muscular atrophy and enhance movement. However, currently, there is no systematic review to elaborate its roles and the associated mechanisms. This article reviews the (1) functions and mechanisms of catechins in the differentiation of myogenic stem cells, biogenesis of mitochondria, synthesis and degradation of proteins, regulation of glucose level, and metabolism of lipids in muscle cells; and (2) effect of catechins on the blood vessels, bones, and nerves that are closely related to the skeletal muscles. Catechins could prevent, mitigate, delay, and even treat muscle-related disorders caused by aging and diseases.     

Collagen-bound collagenolytic enzyme in rabbit skeletal muscle

In order to elucidate the changes in connective tissue which occur during meat conditioning, a study was made of the collagenolytic enzyme in muscle.

Collagenolytic enzyme was detected in the collagen fraction of rabbit skeletal muscle. Electrophoretic and electron microscopic studies of the effects of the collagenolytic enzyme on the collagen indicated that this enzyme could digest the β-subunit of the soluble collagen and cause fragmentation, swelling and splitting of the collagen fibrils.     

Breakdown of connectin during cooking of meat

Light-scattering studies on extracts of meat have confirmed the heat-induced breakdown of connectin previously observed by SDS gel electrophoresis. Because of the high subunit MW (～10(6)) of connectin, the weight-average molecular weight of whole muscle undergoes a relatively large decrease when connectin is broken down during heating of meat. In cold-shortened muscle, breakdown of connectin by proteolysis was as rapid as in control samples, suggesting that connectin exists in an exposed environment rather than as a core to thick filaments. The breakdown of connectin during heating at 60 or 80°C for 40 min was more extensive than during ageing for 3 weeks at 2°C. Hence, the partial proteolysis of connectin during storage at 2°C is unlikely to be responsible for tenderisation induced by ageing.     

The detection of polyphosphate in broiler chicken breast muscle

The relationship between the concentration of sodium and phosphorus (as P₂O₅) in commercially processed broiler chicken breast muscle as a result of injection of various levels of sodium polyphosphate and sodium chloride has been studied and a routine analytical method which can confirm the presence or absence of the addition of these chemicals has been developed. The method is applicable to frozen, thawed or cooked broilers and is independent of moisture and protein content. Since polyphosphates may contain potassium as well as sodium salts, the relationship between these two elements in untreated commercially processed broiler breast muscle has also been measured and compared with treated birds. The analytical procedure has been applied to a survey of deep frozen broilers purchased from three local supermarkets.     

Iron solubilisation by chicken muscle protein digests

The objective of this work was to compare the solubilisation of iron by in vitro digests of soluble and insoluble protein fractions from chicken muscle. Chicken breast muscle was extracted to provide dilute salt-soluble protein (DSSP) and dilute salt-insoluble protein (DSIP) fractions. These fractions together with casein and ovalbumin were subjected to in vitro digestion in the presence of ferric iron. After proteolytic digestion, soluble iron increased fourfold for DSSP, 20-fold for DSIP, twofold for casein and 0.5-fold for ovalbumin. 64% of the soluble iron in the DSSP digest and 30% of the soluble iron in the DSIP digest were ferrous; in the casein and ovalbumin digests, less than 6% was ferrous. Dialysable iron was less than 5% of the soluble iron for all proteins and was mostly ferric iron. DSIP solubilised twice as much iron as DSSP but much less than casein or ovalbumin digests. It was concluded that muscle proteins solubilise iron by reduction and chelation to mostly large (non-dialysable) peptides resulting from digestion. © 1999 Society of Chemical Industry     

Cooking effects on sulfonamide residues in chicken thigh muscle

This paper presents the net change by cooking on residues of sulfadiazine (SDZ), sulfamethoxazole (SMX), sulfamonomethoxine (SMM) and sulfaquinoxaline (SQ) in chicken muscles. These sulfonamides (SAs) were fed to chickens at a dietary concentration of 100 mg/kg (each drug) for 7 successive days. On the 7th day of feeding, they were killed and thigh muscles were collected. Muscle was ground, mixed and formed into 10-g “meatballs”. SA residues were determined by high-performance liquid chromatography. By using the usual cooking methods, boiling, roasting and microwaving, the muscles containing SAs were treated for the specified times. Net residues in the muscles cooked by boiling were reduced 45–61% in 12 min. In roast cooking, the SMX, SMM and SQ residues, except for SDZ, were reduced 38–40% in 12 min. No significant reduction of SDZ was found. By the microwave cooking, the four SAs residues were reduced 35–41% in 1 min. Reducing half-lives of SAs in chicken muscles cooked were estimated as follows: 9.3 min for SDZ and 13.2 min for SMX, SMM and SQ in boiling; 18.3 min for SMX, SMM and SQ in roasting; 1.6 min for all the SAs in microwaving.     

Post-mortem metmyoglobin reduction in fresh venison

The accumulation of metmyoglobin (MetMb) at the surface of meat during storage contributes significantly to its discolouration. Under appropriate conditions it may be possible to utilise residual meat MetMb reducing activity to maintain fresh colour. Venison meat colour stability is poorer compared with other species. Hence, we evaluated the capacity of completely discoloured venison (n=12 animals) to reduce MetMb under anaerobic conditions in order to decipher more clearly the role MetMb reducing activity may play. The reducing capacity of venison (1 day, 3, and 6 weeks post-mortem), electrical stimulation, surface location (top and bottom) and rigor temperature (15 and 35°C) on MetMb were evaluated. Surface MetMb decreased (P<0.001) during storage while deoxymyoglobin increased (P<0.001) demonstrating MetMb reduction. Metmyoglobin reduction was greater (P<0.001) in venison which entered rigor at 15°C, the reduction at the bottom surface of the steaks was greater (P<0.001) compared with the top surface, and electrical stimulation had no affect (P>0.05). These data demonstrate that metmyoglobin reducing activity occurs anaerobically in completely discoloured venison following storage display. The practical application for this finding needs to be determined.     

Apparent viscosity of chicken muscle homogenates. Influence of pH and muscle type

The effect of pH and type of muscle on apparent viscosity of chicken breast, thigh and combined B/T muscles was investigated. The apparent viscosity of thigh muscle homogenate at pH from 5.8 to 6.6, and combined B/T muscle homogenate at pH from 5.8 to 6.3 was increasing. The apparent viscosity of breast muscle homogenate increased with pH increase, reaching a maximum at pH 6.3 and then decreased. When pH raised from 5.8 to 6.3, breast muscle homogenate apparent viscosity increased 3.5-6.0 times more than apparent viscosity of thigh muscle homogenate. An increase of combined B/T muscle homogenate apparent viscosity under shear rate 0.3333-48.6 (s-1) was approximately an average of increases for its individual muscles. At pH 5.8 and 6.0, apparent viscosity of thigh muscle homogenate was approximately two times higher than that of breast muscle homogenate, and reversibly, at pH 6.3, breast muscle homogenate apparent viscosity was about 20% higher than that of thigh muscle homogenate. The apparent viscosity of combined B/T muscle homogenate at pH 5.8 and 6.0, was greater than apparent viscosity of breast muscle homogenate, and at pH 6.3, was greater than apparent viscosity of thigh muscle homogenate. The present data extend the results reported by other researches that there are remarkable differences not only in functional and rheological properties of myofibrillar proteins (SSP, myosin) but also in those of homogenates from chicken white and red muscles.