Extracellular matrix (ECM) structures within skeletal muscle play an important, but under-appreciated, role in muscle development, function and adaptation. Each individual muscle is surrounded by ...epimysial connective tissue and within the muscle there are two distinct extracellular matrix (ECM) structures, the perimysium and endomysium. Together, these three ECM structures make up the intramuscular connective tissue (IMCT). There are large variations in the amount and composition of IMCT between functionally different muscles. Although IMCT acts as a scaffold for muscle fiber development and growth and acts as a carrier for blood vessels and nerves to the muscle cells, the variability in IMCT between different muscles points to a role in the variations in active and passive mechanical properties of muscles. Some traditional measures of the contribution of endomysial IMCT to passive muscle elasticity relied upon tensile measurements on single fiber preparations. These types of measurements may now be thought to be missing the important point that endomysial IMCT networks within a muscle fascicle coordinate forces and displacements between adjacent muscle cells by shear and that active contractile forces can be transmitted by this route (myofascial force transmission). The amount and geometry of the perimysial ECM network separating muscle fascicles varies more between different muscle than does the amount of endomysium. While there is some evidence for myofascial force transmission between fascicles via the perimysium, the variations in this ECM network appears to be linked to the amount of shear displacements between fascicles that must necessarily occur when the whole muscle contracts and changes shape. Fast growth of muscle by fiber hypertrophy is not always associated with a high turnover of ECM components, but slower rates of growth and muscle wasting may be associated with IMCT remodeling. A hypothesis arising from this observation is that the level of cell signaling via shear between integrin and dystroglycan linkages on the surface of the muscle cells and the overlying endomysium may be the controlling factor for IMCT turnover, although this idea is yet to be tested.
Variations in the quantity and thermal stability of collagen in intramuscular connective tissue (IMCT) play a role in variations in cooked meat tenderness. This review is focussed on sources of ...variability, especially in the perimysial IMCT, and challenges some of the accepted ideas about its denaturation behaviour, its contribution to cooking shrinkage at high temperatures and the concept of IMCT as an immutable “background toughness”. IMCT dominates the shear strength of raw and lightly cooked muscle, but at cooking temperatures of 70–80° its contribution is smaller than the myofibrillar component. The thermal denaturation temperature of IMCT collagen given by differential scanning calorimetry at fast heating rates is usually in the range of 62–67 °C, but collagen denaturation is a multistep, non-equilibrium process that is highly heating-rate dependent and can occur at 55–60 °C in slow heating regimes, such as slow roasting or sous-vide cooking. Although it is commonly assumed that collagen shrinkage drives shrinkage of meat and greater cooking losses above 65 °C, an examination of currently available information suggested that there is no evidence to support this idea. The amount and thermal stability of IMCT collagen can be varied by factors manipulating growth rate, and a recent model of these effects is discussed. The characteristics of the thermally-stable fraction of IMCT collagen as the most important component influencing the connective tissue contribution to cooked meat toughness and the need for future work investigating mechanisms to degrade or turnover this specific fraction is suggested.
An associate editor of the journal has experienced an increase in the number of received reviews where the comments to either the authors or to the editor do not align with the reviewer's ...recommendation to accept, revise or reject. In particular, some recommendations for outright rejection of a submission have been accompanied by criticisms that clearly could have been solved by revision of the manuscript. The purpose of this letter is to provide some guidance to reviewers on the specific issue of deciding between a recommendation to revise versus reject.
Following a century of major discoveries on the mechanisms determining meat colour and tenderness using traditional scientific methods, further research into complex and interactive factors ...contributing to variations in meat quality is increasingly being based on data-driven “omics” approaches such as proteomics. Using two recent meta-analyses of proteomics studies on beef colour and tenderness, this review examines how knowledge of the mechanisms and factors underlying variations in these meat qualities can be both confirmed and extended by data-driven approaches. While proteomics seems to overlook some sources of variations in beef toughness, it highlights the role of post-mortem energy metabolism in setting the conditions for development of meat colour and tenderness, and also points to the complex interplay of energy metabolism, calcium regulation and mitochondrial metabolism. In using proteomics as a future tool for explaining variations in meat quality, the need for confirmation by further hypothesis-driven experimental studies of post-hoc explanations of why certain proteins are biomarkers of beef quality in data-driven studies is emphasised.
•Insights from both conventional studies and proteomics into beef meat colour and tenderness are reviewed•Proteomics meta-analysis of variations in beef colour highlights energy metabolism pathways•Energy metabolism and proteolysis emphasised in proteomics of beef tenderness•Calcium regulation, oxidation and nitrosylation pathways also prominent in tenderness•Increasing evidence points to a strong role of post-mortem mitochondrial metabolism in meat quality•Potential mechanisms suggested by data-driven experiments must be checked by hypothesis-driven studies
Intramuscular connective tissue (IMCT) forms a series of continuous networks integrating muscle fibers and fascicles into a whole organ. The contributions of IMCT to cooked meat toughness have long ...been recognized. This review concentrates on (a) the potential to manipulate IMCT in the growing animal, (b) postmortem effects on structure and properties of IMCT, and (c) developments in techniques to quantify IMCT in meat. A new hypothesis can explain why IMCT is enzymatically degraded in postmortem aging; however, after cooking, no differences are seen in the IMCT contribution to toughness. This hypothesis proposes that heat-insoluble collagen occurs in a weak pool and a strong pool, where the weak pool is most easily degraded by both proteolysis and heat. Far from being a constant background feature, the IMCT contribution to cooked meat toughness can be varied and deserves fresh research on how to achieve this.
Muscle fascia and force transmission Purslow, Peter P., PhD
Journal of bodywork and movement therapies,
10/2010, Letnik:
14, Številka:
4
Journal Article
Recenzirano
Summary This paper reviews the major intramuscular extracellular matrix (IM-ECM) structures (endomysium, perimysium and epimysium) and their possible mechanical contributions to muscle functions. The ...endomysium appears to provide an efficient mechanism for transmission of contractile forces from adjacent muscle fibres within fascicles. This coordinates forces and deformations within the fascicle, protects damaged areas of fibres against over-extension, and provides a mechanism whereby myofibrils can be interrupted to add new sarcomeres during muscle growth without loss of contractile functionality of the whole column. Good experimental evidence shows that perimysium and epimysium are capable in some circumstances to act as pathways for myofascial force transmission. However, an alternative role for perimysium is reviewed, which involves the definition of slip planes between muscle fascicles which can slide past each other to allow large shear displacements due to shape changes in the whole muscle during contraction. As IM-ECM is continually remodelled so as to be mechanically adapted for its roles in developing and growing muscles, control of the processes governing IM-ECM turnover and repair may be an important avenue to explore in the reduction of fibrosis following muscle injury.
Over the last two decades, proteomics have been employed to decipher the underlying factors contributing to variation in the quality of muscle foods, including beef tenderness. One such approach is ...the application of high-throughput protein analytical platforms in the identification of meat quality biomarkers. To broaden our understanding about the biological mechanisms underpinning meat tenderization across a large number of studies, an integromics study was performed to review the current status of protein biomarker discovery targeting beef tenderness. This meta-analysis is the first to gather and propose a comprehensive list of 124 putative protein biomarkers derived from 28 independent proteomics-based experiments, from which 33 robust candidates were identified worthy of evaluation using targeted or untargeted data-independent acquisition proteomic methods. We further provide an overview of the interconnectedness of the main biological pathways impacting tenderness determination after multistep analyses including Gene Ontology annotations, pathway and process enrichment and literature mining, and specifically discuss the major proteins and pathways most often reported in proteomics research.
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•Beef tenderness proteomics studies published during the last decade were gathered and analyzed.•124 protein biomarkers of beef tenderness were retrieved from 28 independent proteomics experiments.•Protein biomarkers of beef tenderness belong to 6 interconnected biological pathways.•64 biomarkers were identified with a cut-off ≥2 and 33 robust biomarkers were shortlisted with a cut-off ≥4.•Muscle structure, energy metabolism and cellular responses to stress and oxidative stress are the main pathways underpinning beef tenderness determination.
The amount, spatial distribution and composition of the connective tissue within muscle vary with muscle position in the carcase and with animal age. This has long been recognised to influence the ...tenderness of cooked meat. This paper builds upon some historical perspectives with a review of some recent clarifications of the biological function of intramuscular connective tissue (IMCT) and of its contribution to meat texture, which is clearly multifactorial. The perimysial component of IMCT varies most in amount between muscles and is also the IMCT structure most involved in defining the mechanical integrity of cooked meat. The distribution of perimysium defines muscle fascicle size (muscle “grain” size), which is also still regarded as an indicator of tenderness. Postmortem conditioning of meat has consistently been shown to reduce the strength of intramuscular connective tissue in the raw state, but with equal consistency, this has been shown not to affect the toughness of cooked meat. Cooking increases IMCT strength in the range 20–50 °C and decreases its contribution at higher temperatures and longer cooking times. Crosslinking of collagen in older animals is generally considered to result in tougher meat, although definitive links between mature crosslink content and cooked meat toughness have been difficult to prove. In the last quarter-century, IMCT has been increasingly viewed as a “background” contributor to meat texture, which is difficult to change. However, the large variation in perimysial content of muscles in one animal represents an incredible range of expression. This appears to be firmly fixed to the functional properties of different muscles. In particular, it is hypothesised that definition of muscle fascicle size and shape by the bounding perimysium is related to the need for sub-sections of the whole muscle to slip past each other in the normal contractile function of the tissue. Despite this, the amounts and composition of IMCT can be manipulated by animal nutrition and exercise, and factors affecting the turnover of IMCT may especially be a future target for manipulation of meat texture.
The color of fresh pork is a crucial quality attribute that significantly influences consumer perception and purchase decisions. This review first explores consumer expectations and discrimination ...regarding pork color, as well as an overview of the underlying factors that, from farm-to-fork, contribute to its variation. Understanding the husbandry factors, peri- and post-mortem factors and consumer preferences is essential for the pork industry to meet market demands effectively. This review then delves into current knowledge of pork myoglobin chemistry, its modifications and pork discoloration. Pork myoglobin, which has certain peculiarities comparted to other meat species, plays a weak role in determining pork color, and a thorough understanding of the biochemical changes it undergoes is crucial to understand and improve color stability. Furthermore, the growing role of proteomics as a high-throughput approach and its application as a powerful research tool in meat research, mainly to decipher the biochemical mechanisms involved in pork color determination and identify protein biomarkers, are highlighted. Based on an integrative muscle biology approach, the available proteomics studies on pork color have enabled us to provide the first repertoire of pork color biomarkers, to shortlist and propose a list of proteins for evaluation, and to provide valuable insights into the interconnected biochemical processes implicated in pork color determination. By highlighting the contributions of proteomics in elucidating the biochemical mechanisms underlying pork color determination, the knowledge gained hold significant potential for the pork industry to effectively meet market demands, enhance product quality, and ensure consistent and appealing pork color.
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