The action of a muscle proteinase on the myofibrillar proteins of bovine muscle

Myofibrillar proteins from bovine muscle have been treated with a Ca²⁺ activated muscle proteinase and the consequent changes in these proteins have been examined by various techniques. Tropomyosin, α-actinin and troponin were substrates for the enzyme, the last losing its property of inhibiting actomyosin ATPase in the absence of Ca²⁺ ions. Actin and actomyosin were apparently not digested but the Mg²⁺-activated ATPase activity of actomyosin was less after treatment whereas the Ca²⁺-activated ATPase was unaffected. It is suggested that the observed destruction of the Z-bands of the myofibrils by this proteinase is due to its digestion of the α-actinin, rather than the actin component.     

Factors affecting the colour of lamb meat from the longissimus muscle during display: The influence of muscle weight and muscle oxidative capacity

Spectrophotometric measures were used to determine the redness:browness (R630/R580) of 4238 lamb longissimus muscle after 3 days under simulated display. The results were analysed using linear mixed effects models. Environmental factors represented by effects such as kill group and site of production produced the greatest variation of up to 2.76 units in R630/R580. Isocitrate dehydrogenase activity, reflecting muscle oxidative capacity, reduced R630/R580 by 0.5 units. Selection for high muscling sires increased R630/R580 by 0.27 units, likely due to changes in muscle oxidative capacity. Lamb carcass weight also increased R630/R580 by 0.5 units. Analysis of genotypic factors influencing lamb size and growth rate such as sire type and dam breed further supported that increased growth rate improves meat R630/R580. Our findings suggest that breeding for increased growth rate and increased muscle weight could result in Australian lamb meat retaining its red colour for extended periods whilst on display.     

Modelling muscle energy-metabolism in anaerobic muscle

A mathematical model of anaerobic muscle energy-metabolism was developed to predict pH and the concentrations of nine muscle metabolites over time. Phosphorous-31 Nuclear Magnetic Resonance was used to measure time-course data for some phosphate metabolites and pH in anoxic M. semitendinosus taken from three slaughtered sheep. Muscles were held at 35 °C during the experiment. Measurement commenced 25 min post mortem and concluded before rigor mortis. The model was fitted to these data within experimental error, by simultaneously varying model parameter values and initial substrate concentrations.     

The influence of the collagen fibre network of muscle on the compliance and tensile strength of muscle samples subjected to loads at right angles to the muscle fibre axis

The pattern of subdivision of a muscle into fibre bundles by the perimysium was examined as a possible source of within sample variability of meat toughness attributable to the connective tissue component. It was shown that the pattern of subdivision into fibre bundles relates to the tendom surfaces and influences the compliance and toughness of a meat sample. In addition it was shown that greater plasticity of raw meat samples results in greater compliance under load. The procedure of defining sample orientation relative to the geometry of the component parts enables some of the within sample variability to be explained and controlled.     

The flexibility of the collagen compartment of muscle

Collagen, the major connective tissue protein, is an integral constituent of muscle and, because of its occurrence and characteristics, is a factor contributing to the texture of meat. This brief review focuses on aspects of collagen biosynthesis and experimental data which indicate the collagens of muscle possess remarkable capacity for change. Over 90% of the intramuscular collagen of meat is located in the perimysium. This fibrillar collagen is comprised predominantly of two collagen phenotypes, types I and III, whose proportions vary with animal age, muscle type, gender and probably rate of collagen synthesis. Collagen in muscle can differ additionally in crosslinking profile. Collagen crosslinks are structures arising from the condensation of lysine or hydroxylysine residues and their aldehydes. Crosslinks link two or three collagen molecules or (collagen fibrils) together. Both the tensile strength of collagen and the toughening of meat due to its connective component are related to collagen crosslink type and concentration. With age and maturation there is a general and progressive shift in collagen type (toward more type I) and an increase in the concentration of mature crosslinks. Such alterations in collagen characteristics, rather than significant changes in collagen concentrations, are responsible for the toughening of meat as animals age. Data also suggest that management practices which alter growth and muscle accretion rates can have a profound affect on collagen characteristics. Increasing or decreasing plane of nutrition, compensatory growth, testosterone- and somatotropin-mediated growth, and exercise alter collagen crosslink and/or type proportionally. Such changes can sometimes be associated with increased shear force scores for cooked meat. Alterations in muscle collagen characteristics are linked directly or indirectly to perturbations in collagen synthesis and turnover rates accompanying growth and muscle accretion. The concept that collagen does not change once deposited extracellularly or that changes in its characteristics are unidirectional does not appear to be valid in muscle tissues. Rather collagen appears to be a very flexible component of the extracellular matrix. Potential for management practices to alter collagen characteristics therefore exists.     

Some observations on the histology of cold-shortened muscle

Summary. Changes in the histology of muscles subject to temperatures just above freezing-point while in the pre-rigor condition are described. Observations are based on the study of sectioned tissue by optical and electron microscopy, and by scanning electron microscopy. the presence of 'active' and 'passive' fibres is noted. These are defined by their contractile state. the appearance of the surface membrane of the active fibres is also described and its influence on the texture of cold-shortened muscle as meat is discussed.     

Ultrasonic scanning measurements of the longissimus thoracis et lumborum muscle to predict carcass muscle content in sheep

Nineteen Omani sheep (average 26 kg body weight) were scanned over the 6th rib, 12th rib and the second-last lumbar vertebra, to determine the maximum depth (B), circumference, area of the cross-section and volume of the longissimus thoracis et lumborum (LD) muscle. The volume of the muscle was estimated by multiplying the average area of its cross-section obtained at the three sites by its length. After slaughter, the LD muscle was dissected out, frozen, and its maximum depth, circumference, length, weight and volume were determined. Correlation and regression analyses were carried out to evaluate relationships between scanning and real measurements and between scanning measurements and carcass total muscle content. Generally there were positive correlations (r = 0.43-0.66) between the LD scanning measurements made at the 12th rib and the corresponding measurements made on the dissected muscle. The volume of the LD muscle estimated from scanning was positively correlated (r = 0.59) with its real volume which was correlated with its weight (r = 0.51) and consequently with the total carcass muscle content (r = 0.69). Ultrasonic scanning can be used to predict the circumference and volume of the LD muscle. These may be used for prediction of total carcass muscle content in sheep in addition to traditional measurements of the muscle (the maximum depth B) and area.     

肉蛋白氧化帆制及氧化对肉制品品质和功能性的影响

肉蛋白氧化及功能性和品质变化目前已经引起国内外关注.本文从氨基酸残基侧链的改变、羰基衍生物的产生、蛋白质聚合物的形成三方面阐述了肉中蛋白氧化的机理,同时对氧化给肉蛋白品质和功能性带来的影响进行了概括性论述.     

Elastography of beef muscle

Elastography, a technique that uses ultrasonic pulses to track the internal displacements of small tissue elements in response to an externally applied stress, has been applied to beef muscle. Beef longissimus (1 day post mortem) and semimembranosus (5 days post mortem) muscles were obtained from A maturity beef carcasses. Samples were vacuum-packaged and frozen to -20°C. For elastography measurements, muscles were equilibrated to a constant temperature (30° C± 0·5) in a water tank. Custom transmitters and receivers were used in conjunction with a 2·25 MHz medical transducer. The transducer was driven by a 286 PC, and the radio-frequency echoes digitized at 50 MHz and 8 bits. The pre- and post- compression echo trains (A-lines) were subjected to cross-correlation analysis. Visual interpretation of beef elastograms demonstrate circular areas of relatively inelastic tissues and smaller, banding areas of elastic tissues in the cross-section of beef longissimus muscle. The dark inelastic areas from the elastograms may be related to myofibrilar areas from the same muscle sections; the light, elastic band areas from the elastograms may be related to perimysiaal connective tissue or intramuscular fat. Fatty septa and a calcified abscess could be easily identified on the elastogram. These preliminary results demonstrate that elastography may have potential as a non-intrusive method of visualizing tissue components of beef muscle.     

Tensile strength and the tenderness of beef sternomandibularis muscle

In their relationship to shortening, the tensile strength of cooked meat along the fibres and the shearing force measured across them are strikingly similar. Both increase to maximum values at 40% shortening before falling by a half with an approach to 60% shortening. A high correlation (r = 0·81) exists between the two sets of values, whether toughness is increased by cold shortening or reduced by ageing. The mechanical strength of meat along its fibres is therefore a simple measure of tenderness and a useful basis for relating muscle structure to stength.     

Phosphorus content of muscle tissue and muscle function in dairy cows fed a phosphorus-deficient diet during the transition period

Phosphorus (P) deficiency and hypophosphatemia are believed to be associated with muscle function disturbances in dairy cows, particularly around parturition. The objective of this study was to determine the effect of dietary P deprivation during late gestation and early lactation on muscle P homeostasis and muscle function in periparturient dairy cows. Thirty-six multiparous dairy cows in late gestation were randomly assigned either to undergo dietary P depletion or to be offered a diet with adequate P content from 4 wk before to 4 wk after parturition. Phosphorus-deficient rations for dry and lactating cows contained 0.15 and 0.20% P on a dry matter basis, respectively. Blood and muscle tissue for biopsy were obtained and electromyographic examinations were conducted on biceps femoris and intercostal muscles in regular intervals throughout the study. Muscle tissue was analyzed for the total P, adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, creatine phosphate, and tissue water content. Dietary P deprivation resulted in a pronounced and sustained decline of the plasma phosphate concentration, reaching a nadir at calving with mean values below 1.5 mg/dL and remaining below 2.0 mg/dL during the first 4 wk of lactation. Hypophosphatemia was not associated with signs of clinically apparent muscle weakness or disturbed muscle function and was not associated with a decline in the content of any of the studied P-containing compounds in muscle tissue. Accordingly, no association between plasma phosphate concentration and muscle tissue P content was found. Electromyographic examination identified subclinical effects on motor unit action potentials that are indicative of disturbed neuromuscular functionality. Increasing occurrence of pathologic spontaneous activity possibly resulting from membrane instability of nerve or muscle cells and suggestive of myopathy was also recorded as P deprivation progressed. These effects were predominantly observed in intercostal and to a lesser degree biceps femoris muscles. Electromyographic parameters affected by P deprivation were found to be associated primarily with the plasma phosphate and to a lesser extent with the amounts of energy storing P-containing compounds contained in muscle tissue. These results indicate that prolonged and pronounced dietary P deprivation in transition dairy cows leads to marked sustained hypophosphatemia without altering the muscle tissue P homeostasis or causing clinically apparent muscle function disturbances.     

双酶法水解牡蛎肉工艺条件的研究

采用添加枯草杆菌中性蛋白酶和木瓜蛋白酶的双酶同时水解技术,对牡蛎肉进行水解,通过对水解条件的研究确定组合酶酶解的条件为:pH7.0、温度50℃、固液比1∶4、酶用量2%、水解时间2.5h。氨基酸分析结果表明,氨基酸总量为82.76%,其中必需氨基酸占氨基酸总量的44.9%,尤其是亮氨酸、异亮氨酸、缬氨酸、苏氨酸等支链氨基酸含量以及谷氨酸、天门冬氨酸、甘氨酸等呈味氨基酸含量丰富,占总量的46.8%。     

Revisiting the conversion of muscle into meat and the underlying mechanisms

The conversion of muscle into meat is a complex process in which all mechanisms responsible for the development of meat qualities are very likely interdependent. Colour and flavour are thus both dependent on oxidative mechanisms. Oxidation and proteolysis are probably two processes involved in the development of meat tenderness. This paper reviewed the consequences of programmed cell death or apoptosis on muscle cells structure and biochemistry and on meat qualities as well. We therefore look at different new hypothesis susceptible to highlight the meat science field and provide new supports for a more dynamic meat research. One of them which would have appeared evident for our purpose since a decade, deals with the fact that, after animal bleeding, muscle cells have no other alternative to only enter the programmed cell death procedure or apoptosis. If we introduce an early phase corresponding to apoptosis, taking place before the rigor onset and overlapping it, we will see that the known consequences of that process bring forward possible answers to still unexplained observations. After an overview of the actual state-of-the-art in meat science, we will introduce the programmed cell death and its underlying mechanisms. We then described the strong analogies between the known consequences of apoptosis and the postmortem changes affecting a set of different muscle characteristics.     

Exploring the unknowns involved in the transformation of muscle to meat

Meat quality development, or the transformation of muscle to meat, involves a myriad of biochemical pathways that are largely well-studied in living muscle tissue. However, these pathways are less predictable when homeostatic ranges are violated. In addition, there is far less known about how various management or environmental stimuli impact these pathways, either by substrate load or altered cellular environment. Likewise, it is largely accepted that oxygen plays little to no role in the conversion of muscle to meat, as anaerobic metabolism predominates in the muscle tissue. Even so, the oxygen tension within the tissues does not fall precipitously at exsanguination. Therefore, transition to an anaerobic environment may impact energy metabolism postmortem. Antemortem handling, on the other hand, clearly impacts meat quality development, yet the exact mechanisms remain a mystery. In this paper, we will attempt to review those factors known to affect postmortem energy metabolism in muscle and explore those areas where additional work may be fruitful.     

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.     

Bioavailability of selenium in the defatted dark muscle of tuna

The content and bioavailability of selenium (Se) in the dark muscle of tuna (DMT) were studied. Fluorometric analysis showed that DMT contained 2.0-4.7 µg g^-1 Se. A large part of Se of the DMT was recovered in the dry powder of the defatted fraction prepared by successive treatment with acetone and n-hexane/ethanol. On trypsin digestion of the defatted DMT, release of Se paralleled that of nitrogen and about 70% of Se was released within 4 h. Male weanling ddY mice were fed a Torula yeast-based Se-deficient diet (basal diet) for 3 weeks, and then fed the basal diet or a diet supplemented with a 0.05-0.25 µg g^-1 Se as either sodium selenite or the defatted DMT for a further 1 week. Se contents and GSHPx activities in the liver increased gradually with increases in the amount of supplemented Se. No differences were observed between selenite and defatted DMT in the effect on Se content. At low Se levels, the effect of Se in the defatted DMT on the liver GSHPx activities was inferior to that of selenite, but at a high Se level, Se in the defatted DMT showed a greater effect. The bioavailability of Se in the defatted DMT, as assessed by slope ratio analysis using selenite as the reference Se, was 87% for the liver Se content and 168% for the GSHPx activity. The results indicate that the defatted DMT contains high levels of Se in a nutritionally available form.     

Bellows textile muscle

The study of innovative textile muscles is useful for the construction of prototypes of active suits. These suits are obtained by inserting small pneumatic muscles into a vest. The muscles allow some movements of the upper limb to be made for rehabilitation or motor recuperation purposes. An innovative textile bellows muscle is presented in this paper, where its performances have been evaluated by means of both an analytic and a numerical model.     

Effect of post-rigor muscle length on the texture of meat

Pre-rigor samples of beef M. sternomandibularis were allowed to pass into rigor in both lengthened and shortened states. After ageing, half of the samples from each group were stretched, the other half acting as control. The strength of the raw and heated meats was determined by a shear test. The strength of the raw meat increased in proportion to the muscle length, irrespective of when the length was altered. The strength was due mainly to the connective tissue elements. After heating, the shortened samples were tougher than the lengthened ones; stretching the muscles post-rigor tenderised the shortened samples but not the lengthened ones. These results indicate that the texture of cooked meat was dependent on the interaction of actomyosin and connective tissue components of muscle.     

Chicken muscle homogenate gelation properties: effect of pH and muscle fiber type

Gelation properties of chicken breast and thigh muscle homogenates at a protein concentration of 4.5% under different pH conditions (5.80–6.60) and those of myofibrillar proteins at a protein concentration of 2% were compared to determine the influence of muscle fibre types on gelation. The optimal gelling pH for breast muscle homogenates (pH 6.30) was slightly higher than that for thigh muscle homogenates (pH 5.80–6.30), a similar trend was found for the isolated chicken myofibrillar proteins (pH 6.00 for breast and 5.50 for leg). Similarly, the pH values at which breast muscle homogenate gels were weaker (pH<6.20) or stronger (pH6.20) than thigh muscle homogenate gels were higher when compared with chicken breast and leg myofibrillar protein gels (pH<5.80 and pH>5.90, respectively).