Meat tenderness and the gap filaments

A theory is developed relating the myofibrillar component of meat tenderness to a third set of filaments in the sarcomere: the 'gap filaments'. It is prooposed that the gap filaments set the limit to the tensile strength of the raw or heat-denatured myofibril. The basic process of ageing appears to be an attack by 'calcium-activated factor' (CAF) on the integrity of these filaments. An attempt is made to give an integrated picture of the role of both gap filaments and connective tissue in determining the tensile properties of raw, lightly cooked and well cooked meat.     

Yield point in raw beef muscle. The effects of ageing, rigor temperature and stretch

The yield point of raw sternomandibularis muscle of the ox decreased markedly with ageing. This parameter is the most sensitive and selective indicator of ageing since, unlike shear measurements on cooked meat, it is not complicated by heat denaturation or the contribution of the collagen net. Rigor at 2°C with consequent cold shortening has little effect on yield point, but rigor at 37°C diminishes yield values relative to the 15°C controls. Muscles stretched by 40-60% during rigor show higher yield points. Yield was also studied in other muscles. Unaged strips of bull sternomandibularis, or steer psoas and rectus abdominis tended to break rather than yield, but after ageing usually yielded at the same low loads as aged ox sternomandibularis. The histological changes due to yielding varied widely, but stretched, rather than broken, I-bands were the dominant feature. Our interpretation of the electron micrographs is that in rigor muscle, actin filaments fracture while gap filaments stretch, but in aged muscle both sets of filaments fail simultaneously at low loads.     

On the mechanism of water holding in meat: The swelling and shrinking of myofibrils

Water holding in meat has, in the past, been rather poorly understood and has not been explained at all in structural terms. A unifying hypothesis for this phenomenon is that gains or losses of water in meat are due simply to swelling or shrinking of the myofibrils caused by expansion or shrinking of the filament lattice.

Myofibrils have been observed by phase contrast microscopy, and are seen to swell quickly to about twice their original volume in salt solutions resembling those used in meat processing. Such swelling is highly co-operative. Pyrophosphate reduces very substantially the sodium chloride concentration required for maximum swelling. In the absence of pyrophosphate, swelling is accompanied by extraction of the middle of the A-band; in its presence the A-band is completely extracted, beginning from its ends.

We suppose that Cl⁻ ions bind to the filaments and increase the electrostatic repulsive force between them. A crucial factor in swelling is likely to be the removal at a critical salt concentration of one or more transverse structural constraints in the myofibril (probably crossbridges, the M-line or the Z-line) allowing the filament lattice to expand.

We also point out that water losses in rigor, in the PSE condition and on cooking may well result directly from shrinkage of the filament lattice.     

Tenderisation of meat by pressure-heat involves weakening of the gap filaments in the myofibril

These results confirm previous Australian experience that pressure-heat (P-H) treatment tenderises rigor meat effectively only after considerable periods at elevated temperatures; that prior ageing abolishes the effect; and that cold shortened meat is effectively tenderised. Yield point is also profoundly affected by P-H, although this effect is not related to tenderness. As predicted by the new G-filament theory of meat tenderness, P-H greatly weakens the G-filaments. These then break on extension by 50% but not if subsequently cooked. However the tensile properties of cooked meat support the weakening of G-filaments. A problem is that mild P-H treatments which are ineffective at tenderising, produce the same histological damage as harsher tenderising treatments. This paper reviews the considerable body of results on the P-H treatment of rigor meat that have now accumulated. The effects of pressure on the various filaments is discussed. The nature of the changes induced in the G-filaments remains obscure.     

ULTRASTRUCTURAL CHANGES IN BOVINE LONGISSIMUS MUSCLE CAUSED BY THE HYDRODYNE PROCESS

Transmission electron microscopy was used to examine the influence of the Hydrodyne process, a new technology for tenderizing meat in the raw state, on the ultrastructural characteristics of bovine longissimus muscle. Myofibrillar fiagmentation in the region adjacent to the Z-lines was clearly evident. Fragments of Z-lines were attached to the A-band on both sides of the fractures. These fractures resulted in increased intrumyofibrillar spaces with longitudinal gaps or splits in the myofibril lattice (lattice of filaments formed inside the myofibril). These observations offer evidence as to why there is a significant improvement in meat tenderness when meat is treated with the Hydrodyne process.     

Structural changes in meat during ageing

Summary. During the ageing of bovine muscle the most notable changes in the pattern of myofibrillar cross-striations are the complete disappearance of the Z lines and the lengthening of the A bands at the expense of the I zones. It is suggested that with the disintegration of the Z lines, the actin filaments of the I zones collapse onto the myosin rods, leading to apparent A-band lengthening. It is concluded that the weakening of the normally refractory Z lines of the myofibrillar structures is an event closely related to meat ageing.     

Action of NaCl and polyphosphates in meat processing: Responses of myofibrils to concentrated salt solutions

When meat is treated with salt, some parts of the meat are exposed to very high salt concentrations which then fall during equilibration. To gain a better understanding of the consequences of this treatment, we have observed the swelling and extraction of isolated myofibrils treated with series of salt solutions designed to mimic conditions found in salt-treated meat. Myofibrils swelled most in 1m (5·8%) NaCl and hardly at all in 5m (29%) NaCl. Similar results were obtained when the concentration of NaCl was raised in steps to 5m. The pronounced extraction of the A-band that occurs in 1m NaCl was decreased if higher NaCl concentrations were used instead. Lowering the concentration from higher values to 1m caused some swelling and extraction of the A-band, but not as much as when 1m was used directly. Inclusion of pyrophosphate in the solutions had marked effects. There was little swelling in 1m NaCl and none in 5m. Lowering the NaCl concentration to 1m from higher concentrations gave more swelling than observed when 1m was used directly. Extraction of the A-band was greatest in 1m, and was strongly inhibited in 5m. Myofibrils treated with 5m NaCl lost the ability to respond to the presence of pyrophosphate in 1m NaCl. The behaviour of myofibrils in high concentrations of NaCl alone is similar to that of pieces of meat. However, the persistent swelling of meat when the NaCl concentration is slowly raised to 5m is not found with myofibrils, suggesting that significant water compartments exist outside the myofibrils in such meat.     

不同加热处理对牦牛肉风味组成和质构特性的影响

取西藏种萨牦牛肉,研究不同热处理方式(微波加热、高压炖煮和常温水煮)对牛肉风味和质构特性的影响。结果表明：这3种热处理得到的牦牛肉产品风味化合物主要包括脂肪烃、脂环烃、脂肪醛、脂肪酮、芳香烃、含硫化合物和脂肪醇6大类,其中醛类化合物(己醛、壬醛和辛醛等)为熟牦牛肉的特征风味。微波加热形成的风味种类最高,达137种,高压炖煮次之(133种),常温水煮最差(128种),微波加热形成的醛类化合物达10种,高压炖煮形成的醛类化合物为5种,而常温水煮形成醛类化合物为4种。对微波加热、高压炖煮和常温水煮3种加热方式形成的牛肉进行质地剖面分析,表明微波加热形成的牛肉硬度低、弹性高等最佳质感效果。综合风味指标、质构指标和感官评价指标,确认微波加热牦牛肉品质最优。     

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

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

Relationship between the translocation of paratropomyosin and the restoration of rigor-shortened sarcomeres during post-mortem ageing of meat-A molecular mechanism of meat tenderization

The weakening effect of paratropomyosin on rigor linkages formed between actin and myosin was determined by measuring the restoration of rigor-shortened sarcomeres of chicken, pork and beef. We observed the rate of the post-mortem translocation of paratropomyosin from the A-I junction region of sarcomeres onto the thin filaments in the A-band, where rigor linkages had been formed; this agreed well with the rate of increase in length of rigor-shortened sarcomeres. The sarcomere lengths were found to be maximum at 1, 7 and 10 days post-mortem in chicken, pork and beef, respectively. Thus, translocated paratropomyosin weakens rigor linkages and brings about the recovery in the length of rigor-shortened sarcomeres. Paratropomyosin stimulates the resolution of rigor mortis, and is a key factor in meat tenderization during post-rigor ageing. These results powerfully support the ‘Calcium theory of meat tenderization’ which we have proposed.     

Does It Look Cooked? A Review of Factors That Influence Cooked Meat Color

ABSTRACT:  Adequate cooking of meat is necessary to inactivate microbial pathogens. This is particularly important for ground meat products and some variety meats where pathogens can be present internally. Consumers are being advised on appropriate temperatures to which meat products should be cooked, and to use a meat thermometer to ensure these temperatures are reached. However, consumers are more likely to assess cooking status by the color of the meat or juice. This article reviews the factors that can influence the final color of cooked meat. In most instances, these factors influence color by modifying the meat pigment myoglobin prior to and during cooking. Many factors can prolong the pink "uncooked" color in meat, including high pH, modified atmosphere packaging, rapid thawing, low fat content, nitrite, and irradiation. Such factors may lead to overcooking and loss of food quality, and consumer rejection. Alternatively, factors that cause "premature browning" of meat, where the interior of the product looks cooked but a microbiologically safe temperature has not been reached, are food safety issues. Pale, soft exudative meats can prematurely brown, as can meats packaged under oxygenated conditions, frozen in bulk or thawed over long periods, or those that have had salts or lean finely textured beef added. Meats cooked from a frozen state or irradiated in aerobic conditions might also be at risk, but this might depend on meat species. In summary, the color of cooked meat is not a good indicator of adequate cooking, and the use of a food thermometer is recommended.     

RELATIONSHIP OF pH AND TEMPERATURE TO DISRUPTION OF SPECIFIC MUSCLE PROTEINS AND ACTIVITY OF LYSOSOMAL PROTEASES

From a review of the literature, and from specific data presented in this paper, it was concluded that both postmortem temperature and pH have effects on meat tenderness and on disruption of specific myofibrillar proteins. Increased postmortem temperature porduces more tender muscles and increases the disruption of troponin-T, myosin, Z-lines, connectin and gap filaments. Elevated postmortem temperature also increases the activity of enzymes which cause the disruption of myofibrillar proteins. Higher ultimate postmortem pH (above 6.0) produces more tender muscle, but also produces dark-cutting meat Except for one experiment, lower pH in the first few hours postmortem (in muscle with normal ultimate pH; i.e., 5.8 or below) improves meat tenderness. High pH increases the activity of CAF and low pH increases the activity of lsosomal cathepsins. Both high and low pH increase the degradation of troponin-T, Z-lines, gap filaments and connectin, but the degradation of these proteins (except for Z-lines) is greater at a low pH. Low pH increases the degradation of myosin; conversely, high pH retards it degradation.     

The Histology of Pre-Rigor and Post-Rigor Ox Muscle Before and After Cooking and Its Relation to Tenderness

SUMMARY—Pre-rigor and post-rigor semitendinosus muscle was examined under the light microscope and in the electron microscope before and after cooking. During cooking, pre-rigor samples were unrestrained or restrained on stainless-steel frames at normal length and at 130% normal length. Samples which passed at 0°C into rigor unrestrained, or while restrained to the same degrees of stretch as above, were cooked post-rigor without mechanical restraint after various periods of storage. The treatments produced differences in tenderness of the muscle pieces which were related to differences seen in the ultrastructure in the micrographs. It was concluded that, provided the effects of gross connective tissue are small, tenderness in beef muscle is produced by disruption of the actin filaments and by a breaking down of the linkages between the actin and myosin filaments in the sarcomeres.     

兰州市熟肉制品中亚硝酸盐的使用情况及达标检测现状调研

近年来,在食品中添加非食用物质或滥用食品添加剂而导致群体性食物中毒的恶性事件在我国频频发生。作为消费量占肉类产量60%左右的熟肉制品和肉肠类制品[1]其食用是否安全更是各级政府和广大市民关注的焦点。针对兰州市2001～2005年市售熟肉制品中亚硝酸盐合格率较低[2],2008年其检出率高居不下的状况,文章主要讨论了兰州市售熟肉制品的安全现状及可能出现肉制品安全问题的原因,并在此基础上提出了预防肉制品安全问题产生的相关对策。     

Processing characteristics of beef roasts made from high and normal pH bull inside rounds

The processing characteristics of roasts manufactured from either high or normal pH bull inside rounds (semimembranosus and adductor muscles), which had been stored chilled or frozen, were investigated. Roasts were injected with a salt/phosphate brine and cooked to an internal temperature of 63 °C in a 70 °C water bath. High-pH meat that had been frozen had less purge than normal pH meat. However, pH did not affect purge from chilled meat. Meat pH and storage conditions did not affect retention of pumped brine. Cook yields were significantly (P<0.05) higher for roasts made from high pH meat (103.8 vs 98.8%). Raw and cooked meat colour was affected by meat pH but not storage condition. Cooking reduced the effect of pH on meat colour but cooked roasts manufactured from high pH meat were redder than roasts manufactured from normal pH meat.     

MECHANICAL BEHAVIOUR OF COOKED MEAT UNDER SINUSOIDAL COMPRESSION

The rheological behaviour of raw meat, and of meat cooked under different conditions, has been studied with sinusoidal compression in a transient state. Meat samples underwent compression perpendicular to the myofibre axis in a cell equipped with lateral walls that made it possible to limit the free strain of samples to only one direction viz. parallel (longitudinal configuration) or perpendicular (transverse configuration) with respect to the myofibres. Both raw and cooked meat exhibit visco-elastic behaviour with a slight viscous component. Cooking meat results in both increased resistance and more elasticity. The variations in these parameters depend on the configuration and compression ratio used. With raw or slightly cooked meat, myofibrillar and connective structures can be analysed selectively in the longitudinal configuration by using compression ratios that are, respectively, nondestructive and destructive. When cooking is carried out at a high temperature, the myofibrillar resistance can be analysed preferentially in the longitudinal configuration, and connective tissue in the transverse configuration.     

Effect of muscle type, salt and pH on cooked meat haemoprotein formation in lamb and beef

The rate of cooked meat haemoprotein formation, measured as the rate of loss of myoglobin solubility, in lamb was dependent on the muscles anatomical location and temperature. Lamb longissimus dorsi musle at 55 to 70°C formed cooked meat haemoprotein more rapidly than the muscles in the shoulder and leg. The formation in lamb was more rapid than in beef. The rate in high pH beef (7.25) l. dorsi was lower than found in beef l. dorsi of normal pH but in low pH lamb (5.38) l. dorsi the rate was, at most temperatures, also slower than found in this muscle from lamb of normal pH. In the presence of NaCl the rate of cooked meat haemoprotein formation was faster (almost doubled at 2g/100g meat) than found in the corresponding salt free lamb and beef samples. Other additives commonly added to meat products (mechanically recovered meat, oil, polyphosphates, soya, whey and caseinate) had little effect on the rate of cooked meat haemoprotein formation, at the levels normally used in meat products. It is concluded that for lamb products little if any myoglobin will remain soluble, and the products will look cooked before the recommended thermal treatment to inactivate Escherichia coli O157:H7 has been achieved. ?     

The heat pipe and its potential for enhancing the cooking and cooling of meat joints

The rate of cooking and cooling of meat is limited by its poor thermal conductivity. Providing a high conductivity path to the thermal centre of the meat is a potential method of overcoming this problem. The aim of this research was to investigate the feasibility of using heat pipes to increase cooking and cooling rates in meat joints. Three diameters of heat pipe were inserted into 1 kg bacon joints, which were then cooked and cooled under catering/domestic conditions. These results show that the use of heat pipes in the cooking and cooling of meat joints has substantial potential. Heat pipes can halve the cooking time and help guarantee that joints are cooked to a safe internal temperature. They can also reduce the cooling time of joints by over 25%.     

Water characteristics in cooked beef as influenced by ageing and high-pressure treatment-an NMR micro imaging study

The water characteristics in cooked pressure-heat treated (45?°C for 45 min prior to pressurisation at 150 MPa for 30 min) and non-pressurised, cooked (control) samples of beef Longissimus aged for 1, 3, 8 or 16 days were studied by nuclear magnetic resonance microscopy. A multi-echo sequence was used to obtain T2 images, and independent of ageing period, the T2 values were found to be lower in pressure-heat treated meat revealing alterations in water characteristics of pressure-treated, cooked meat compared with cooked meat. With increasing ageing duration, the T2 values in both pressure-treated, cooked and cooked meat decreased indicating that the water became more tightly trapped in the protein network. In addition, independent of length of ageing period the relationship between cooking loss in the cooked meat and transverse relaxation differed between non-pressurised and pressure-treated meat, which reveals that the mechanisms changing the water properties in beef during ageing are different from those occuring during pressure-heat treatment of meat.     

A RESEARCH NOTE EFFECTS OF PRESSURIZATION AND REFRIGERATED STORAGE ON MICROSTRUCTURE OF FISH MUSCLE TISSUE

Fish muscle tissues were subjected to high hydrostatic pressures in the range of 1,000 - 3,000 atm and the tissues subsequently observed using transmission electron microscopy. Pressurization at 1,000 atm caused contraction of the sarcomere with the I-band thin filaments being lost while the A-band was unaffected. On pressurizing the tissues at 2,000 atm, the I-band region became more visible with breakdown of the thin filaments in this region as well as the Z-disks. There was gross disintegration ofmyofibrillar structure with collapse of A-band structure and T-tubular system on subjecting muscle tissue to 3,000 atm of pressure. However, there were no observable changes in myofibrillar structure beyond these initial changes during the subsequent 21 days of storage under refrigerated conditions (4–7C). The results provide the structural basis for pressure-induced changes in fish texture.