The effects of high pressure processing (HPP, at 175 and 600 MPa) on the ultrastructure andin vitroprotein digestion of bovinelongissimus dorsimuscle meat were studied.
Skeletal muscle is usually composed of four types of muscle cells (I, IIA, IIX, IIB) varying on their speed of contraction (slow: type I; fast: type II) and their metabolism pathway of glycogen (oxidative: type I and IIA; glycolytic: Type IIX and IIB). Depending on the anatomical position and muscle function, the proportion of these different muscle fiber types is variable. The different fibers types are identified longstanding by histoenzymology. ATPase activity in type I fibers is labile at alkali pH and resistant at acidic pH. In contrast, the ATPase activity of type II fibers is alkali resistant and acid labile (For review, see Pette & Staron, 1990, 2000, Schiaffino & Reggiani, 2011). The molecular basis of this typology resides in the polymorphism of myosin heavy chains (MyHC). The use of monoclonal antibodies against MyHC isoforms allows to identify precisely the type I IIA IIX and IIB fibers and hybrid fibers expressing simultaneously different isoforms of myosin (Schiaffino & Reggiani, 2011). Our goal was to characterise the fiber type of porcine masseter muscle. Materiel and methodes Ten 6 months old pigs (105‐115 Kg) were slaughtered in a commercial abattoir and masseter muscles (jaw) were extracted from the head at 30 min postmortem. Muscle sample (1X1X1.5 cm) were frozen in cooled isopentane (−160 °C). Serial cross‐sections (10 µm thick, cryostat Microm, HM 560) were collected on glass. Fiber types were identified by histoenzymology both by revealing ATPase activity after acidic incubation, and SDH activity that reflect oxidative metabolism. Fiber types were also identified by immunohistofluorescence using three monoclonal antibodies specific to MyHC isoform (BAD5 specific for type I, S58 H2 all except type IIa, and BF35 all types except type IIb and IIx) (Schiaffino & Reggiani, 2011). Histological sections were observed on a photonic microscope (Olympus BX 61) coupled to a high resolution digital camera (Olympus DP 71) and the Cell F software. The percentage of each fiber type was calculated according to Meunier et al. (2010) using the image analysis Visilog 6.7 Professional Software. Results and discussion ATPase histoenzymology (Fig.1) revealed only type I (30.6%) and IIA (69.4%) oxidative fibers according to Ström & Holm, 1997. Immunohistochemistry (Fig.2) revealed that 17% of the masseter fibers are hybrid fibers containing two MyHC isoforms IIa and IIx (Fig.3). These hybrid fibers are generally a transitional step to move from a pure type to another (Schiaffino & Reggiani, 2011). In this study, no pure type IIX is highlighted, suggesting that the transition is not completed or that the IIA‐IIX hybrids are the final stage of transition in this muscle. For a given muscle, fiber type evolves mainly with physical activity and age of the animals. In our case, pigs were reared in a building without noticeable change in their physical activity. The pigs were slaughtered at the age of 6 months, which corresponds to a period of entry into sexual maturity. It is possible that the fibers are in transition classes, however, no study has highlighted the presence of IIX fibers in pork masseter, suggesting that the hybrid could be permanent. A large proportion of IIA‐IIX fibers (74 %) were found in rat masseter but several pure glycolytic fibers were detected (Pette & Staron, 1990) and unique HCIIm isoforms were identified in primate and carnivore masseter muscles (Pette & Staron, 1990, 2000). All these data highlight the special feature of masseter compared to other skeletal muscles. Conclusion The use of monoclonal antibodies revealed the presence of a high proportion of hybrid fibers IIA‐IIX in pork masseter and did not allow the detection of any pure type IIX. These results suggest a specificity of porcine masseter muscle in which the hybrid type IIA‐IIX would not be a transitory state.
Meat is exposed to heat and acid pH during technological processing and digestion, respectively. Both treatments affect the molecular structure of meat proteins. In order to characterize separately the effects of heating and acidic treatments, infrared (IR) spectra of treated meat were analyzed. IR spectra of muscle fibers were obtained from histological sections of raw and cooked meat which were incubated in 0.9% NaCl solution adjusted to pH 2, 3.5 and 5 using a transmission IR microscope. Despite the low thickness of the sections (6 μm), the Amide I and II bands’ signal were saturated: There is the possibility of having a poor linearity in quantifying these band intensities. From this reason, the spectral region of the amide vibrational modes (1700-1500 cm–1) was excluded from the data analysis. Another fingerprint region (1500-1000 cm–1) was applied to the analysis. Results showed that the band corresponding to the protonation of Aspartic acid highlighted the effect of pH separately from the effect of cooking. However, bands which can well explain the cooking effect were not found in this spectral region.
Abstract Morphogenesis relies on the active generation of forces, and the transmission of these forces to surrounding cells and tissues. Hence measuring forces directly in developing embryos is an essential task to study the mechanics of development. Among the experimental techniques that have emerged to measure forces in epithelial tissues, force inference is particularly appealing. Indeed it only requires a snapshot of the tissue, as it relies on the topology and geometry of cell contacts, assuming that forces are balanced at each vertex. However, establishing force inference as a reliable technique requires thorough validation in multiple conditions. Here we performed systematic comparisons of force inference with laser ablation experiments in three distinct Drosophila epithelia. We show that force inference accurately predicts single junction tensions, tension patterns in stereotyped groups of cells, and tissue-scale stress patterns, in wild type and mutant conditions. We emphasize its ability to capture the distribution of forces at different scales from a single image, which gives it a critical advantage over perturbative techniques such as laser ablation. Our results demonstrate that force inference is a reliable and efficient method to quantify the mechanics of epithelial tissues during morphogenesis.
Sarcomeres are stereotyped force-producing mini-machines of striated muscles. Each sarcomere contains a pseudocrystalline order of bipolar actin and myosin filaments, which are linked by titin filaments. During muscle development, these three filament types need to assemble into long periodic chains of sarcomeres called myofibrils. Initially, myofibrils contain immature sarcomeres, which gradually mature into their pseudocrystalline order. Despite the general importance, our understanding of myofibril assembly and sarcomere maturation in vivo is limited, in large part because determining the molecular order of protein components during muscle development remains challenging. Here, we applied polarization-resolved microscopy to determine the molecular order of actin during myofibrillogenesis in vivo. This method revealed that, concomitantly with mechanical tension buildup in the myotube, molecular actin order increases, preceding the formation of immature sarcomeres. Mechanistically, both muscle and nonmuscle myosin contribute to this actin order gain during early stages of myofibril assembly. Actin order continues to increase while myofibrils and sarcomeres mature. Muscle myosin motor activity is required for the regular and coordinated assembly of long myofibrils but not for the high actin order buildup during sarcomere maturation. This suggests that, in muscle, other actin-binding proteins are sufficient to locally bundle or cross-link actin into highly regular arrays.
Smoked fish fillets are pre-salted as a food conservation and quality preservation measure. Here we investigated biochemical and sensory aspects of smoked salmon fillets. Left-side salmon fillets were dry-salted while the right-side fillets underwent a mixed salting method consisting of an injection of saturated brine followed by surface application of dry salt. After 6 hours of salting, all the fillets were smoked. At each step of the process, quality was evaluated using instrumental measurements (pH, color, texture, water content, salt content, a w ), and lipid distribution was visualized by MRI. Mixed-salted fillets had a higher salt content and more heterogeneous salt distribution than dry-salted fillets. However, these variations had no effect on pH, color or texture, which showed similar values regardless of salting method. Fatty areas had a lower salt content due to slower diffusion of aqueous salt solutions through them. Mixed salting speeds up the salting of the muscle without significantly affecting the quality traits of the salmon fillet.
Characterization of thai beef macromolecular changes under various sous-vide cooking conditions: an infrared microspectroscopy study. 64. International Congress of Meat Science and Technology (ICoMST)
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