Ex-vivo validation of spatial gain sonography for the quantification of echo intensity in fascicle-aligned ultrasound images in ten anatomical muscles in Bos taurus

This study aimed to validate the concept of spatial gain sonography for quantifying texture-related echo intensity in B-mode ultrasound of skeletal muscle. Fifty-one bovine muscles were scanned postmortem using B-mode ultrasonography at varying fascicle probe angles (FPA). The relationship between mean gray values (MGV) and FPA was fitted with a sinusoidal and a linear function, the slope of which was defined as tilt echo gain (TEG). Macroscopic muscle cross sections were optically analyzed for intramuscular connective tissue (IMCT) content which was plotted against MGV at 0° FPA (MGV_00). MGV peaked at FPA 0°. Sine fits were superior to linear fits (adjusted r2-values 0.647 vs. 0.613), especially for larger FPAs. In mixed models, the pennation angle was related to TEG (P < 0.001) and MGV_00 (P = 0.035). Age was relevant for MGV_00 (P < 0.001), but not TEG (P > 0.10). The correlation between the IMCT percentage and MGV_00 was significant but weak (P = 0.026; adjusted r2 = 0.103). The relationship between fascicle probe angle and echo intensity in B-mode ultrasound can be modeled more accurately with a sinusoidal but more practically for clinical use with a linear fit. The peak mean gray value MGV_00 can be used to compare echo intensity across muscles without the bias of pennation angle.

Texture maintenance and degradation mechanism of ice-stored grass carp (Ctenopharyngodon idella): A scope of intramuscular connective tissue

Although intramuscular connective tissue (IMCT) is low in fish, its impact on texture cannot be ignored due to its special location. Therefore, this study was aimed to investigate the contribution of IMCT degradation to fish softening and its mechanism induced by endogenous proteases. Results showed that IMCT honeycomb-like structure collapsed entirely on the 10th day of ice storage, along with a decrease of shear force by 36.5%. Meanwhile, IMCT and myofibrils (MF) degradation accelerated softening by 25.1% and 15.3% during 10 days of ice storage, respectively. Next, IMCT deterioration was indicated to be highly correlated with decorin degradation (0.956**), followed by elastin (0.928**) and collagen (0.904**). Ulteriorly, endogenous collagenase was shown to degrade IMCT crucial components, while endogenous cathepsins had little effect. In conclusion, this study confirmed that IMCT played an essential role in maintaining fish texture and was mainly degraded by endogenous collagenase.

Contribution of intramuscular connective tissue and its structural components on meat tenderness-revisited: a review

The tenderness of meat influences consumers' perceptions of its quality. Meat tenderness is a key quality characteristic that influences consumer satisfaction, repeat purchases, and willingness to pay higher prices for meat. Muscle fibers, connective tissues, and adipocytes are the main structural components of meat that contribute to its tenderness and texture. In the present review, we have focused on the role of connective tissue and its components in meat tenderness, specifically perimysial intramuscular connective tissue (IMCT) and its concept as an immutable "background toughness." The collagen contribution to cooked meat toughness can be altered by animal diet, compensatory growth, slaughter age, aging, and cooking. As well, progressive thickening of the perimysium leads to a progressive increase in shear force values in beef, pork, chicken, and this may occur prior to adipocyte formation as cattle finish in feedlots. Conversely, adipocyte accumulation in the perimysium can decrease cooked meat shear force, suggesting that the contribution of IMCT to meat toughness is complex and driven by both collagen structure and content. This review provides a theoretical foundation of information to modify IMCT components to improve meat tenderness.

Effects of different cooking methods on physicochemical, textural properties of yak meat and its changes with intramuscular connective tissue during in vitro digestion

The effects of vacuum cooking (VC), traditional cooking (TC), and high-pressure cooking (HPC) on the physicochemical properties and texture of yak meat and the digestibility of yak meat and intramuscular connective tissue (IMCT) were investigated. Compared with VC treatment, TC and HPC treatment significantly increased meat cooking loss and meat hardness (P < 0.05). Meanwhile, the carbonyl content of yak meat of TC and HPC was 3.73 nmol/mg protein, and the free sulfhydryl content was 7.93 nmol/mg protein, indicating that more protein was oxidized at higher temperatures. Oxidative aggregation of proteins caused by cooking reduced meat digestibility by about 25%. However, cooking reduced the undigested residue of IMCT and promoted its digestion. Principal component analysis showed that the physicochemical, texture, oxidation, and protein digestibility of TC and HPC meat were similar but significantly different from VC meat.

Physicochemical, thermal and mechanical characterization study of perimysial collagen of two bovine muscles

Chemical, thermal and mechanical collagen characteristics of intramuscular perimysial connective tissue (IMCT) from bovine Semitendinosus (ST) and Pectoralis profundus (PP) muscles were studied. Furthermore, these collagen characteristics in presence/absence of other extracellular matrix components were analyzed for both muscles. Differences between muscles were observed for collagen content; all IMCT-PP perimysial samples were higher than ST samples. In addition, for both muscles, IMCT-alkali resistant samples allowed the highest trypsin soluble collagen. The main differences between muscles were recorder for thermal and mechanical properties. The denaturation of collagen in the perimysium evidenced differences in total denaturation energy (ΔH) and peak temperatures (Tp). The ΔH resulted higher for IMCT-PP than for IMCT-ST tissues in all samples. By the tensile test it was observed that the maximum loads were constant and higher in all PP samples. In the FTIR assay, the peaks for the main amides were registered in both tissues. However, slight differences between ST and PP-IMCT were detected on hydrogen bond interactions and in secondary structure of the protein. The results reinforce the hypothesis of the presence of different IMCT-perimysial-collagen pools. In this study, chemical, thermal and mechanical characteristics were considered and quantified. However, the mechanical function and development of muscle in-vivo could be the main influence on the extracellular collagen characteristics as well as its interactions with non-collagen compounds. Its formation is essential for muscle function.

Development of myofibres and associated connective tissues in fish axial muscle: Recent insights and future perspectives

Fish axial muscle consists of a series of W-shaped muscle blocks, called myomeres, that are composed primarily of multinucleated contractile muscle cells (myofibres) gathered together by an intricate network of connective tissue that transmits forces generated by myofibre contraction to the axial skeleton. This review summarises current knowledge on the successive and overlapping myogenic waves contributing to axial musculature formation and growth in fish. Additionally, this review presents recent insights into muscle connective tissue development in fish, focusing on the early formation of collagenous myosepta separating adjacent myomeres and the late formation of intramuscular connective sheaths (i.e. endomysium and perimysium) that is completed only at the fry stage when connective fibroblasts expressing collagens arise inside myomeres. Finally, this review considers the possibility that somites produce not only myogenic, chondrogenic and myoseptal progenitor cells as previously reported, but also mesenchymal cells giving rise to muscle resident fibroblasts.

The thermal shrinkage force in perimysium from different beef muscles is not affected by post-mortem ageing

Differences in the thermal shrinkage and collagen solubility between bovine Semitendinosus (ST) and Pectoralis profundus (PP) muscles and their interactions with ageing were evaluated by studying collagen solubility, hydrothermal isometric tension and thermal denaturation properties of intramuscular connective tissue after 5-20days post-mortem storage at 4°C. Collagen solubility was higher in ST than in PP muscle at 5-13days, but the differences between the two muscles decreased at longer ageing times. A small decrease in the peak denaturation temperature of perimysium occurred with increasing ageing times in both muscles. Maximum force in isometrically-heated perimysium was broadly equivalent in both muscles. Although the amount and solubility of collagen varies between muscles and ageing decreases the stability of some of the collagen, thermal shrinkage forces in heated perimysium are not significantly diminished by ageing. These findings support the idea of one collagen fraction easily degraded by ageing and heat, and another more resistant fraction that determines the physical properties of the tissue after ageing and cooking.

A homogenization model of the Voigt type for skeletal muscle

A three-dimensional constitutive model for skeletal muscle incorporating microstructural characteristics is developed and numerically implemented in a general purpose finite element program. The proposed model takes into account explicitly the volume fractions of muscle fibers and connective tissue by using the Voigt homogenization approach to bridge the different length scales of the muscle structure. The model is used to estimate the active and passive homogenized muscle response. Next, the model is validated by experimental data and periodic three-dimensional unit cell calculations comprising various fiber volume fractions and mechanical properties of the constituents. The model is found to be in very good agreement with both the experimental data and the finite element results for all the examined cases. The influence of fiber volume fraction and material properties of constituents on effective muscle response under several loading conditions is examined.

Role of extracellular matrix in development of skeletal muscle and postmortem aging of meat

The integrity of skeletal muscle is maintained by the intramuscular connective tissues (IMCTs) that are composed of extracellular matrix (ECM) molecules such as collagens, proteoglycans, and glycoproteins. The ECM plays an important role not only in providing biomechanical strength of the IMCT, but also in regulating muscle cell behavior. Some ECM molecules, such as decorin and laminin, modulate the activity of myostatin that regulates skeletal muscle mass. Furthermore, it has been shown that decorin activates Akt downstream of insulin-like growth factor-I receptor (IGF-IR) and enhances the differentiation of myogenic cells, suggesting that decorin acts as a signaling molecule to myogenic cells. With animal growth, the structural integrity of IMCT increases; collagen fibrils within the endomysium associate more closely with each other, and the collagen fibers in the perimysium become increasingly thick and their wavy pattern grows more regular. These changes increase the mechanical strength of IMCT, contributing to the toughening of meat. However, in highly marbled beef cattle like Wagyu, intramuscular fat deposits mainly in the perimysium between muscle fiber bundles during the fattening period. The development of adipose tissues appears to disorganize the structure of IMCT and contributes to the tenderness of Wagyu beef. The IMCT was considered to be rather immutable compared to myofibrils during postmortem aging of meat. However, several studies have shown that collagen networks in the IMCT are disintegrated and proteoglycan components are degraded during postmortem aging. These changes in ECM appear to reduce the mechanical strength of IMCT and contribute to the tenderness of uncooked meat or cooked meat at low temperature. Thus, the ECM plays a multifunctional role in skeletal muscle development and postmortem aging of meat.