Skeletal Muscle Structure

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2.2 Skeletal Muscle Structure
The skeletal muscle is the predominant system which the muscle convert to meat after death. It is important to understand the properties of skeletal muscle to give an acknowledgement of the process involved in the development of meat. There are various factors that affect tenderness of meat such as the muscle structure and muscle fibre type composition. 2.2.1 Muscle structure
Mammalian skeletal muscles are heterogeneous in nature. Each muscles has their own functions. The muscles of the motor system example the motor unit, is composed of a motor neuron and a bunch of muscle fibers. To form a muscle, many motor units are assembled together, and each brings its own specific and distinct contribution. The selective
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The contraction makes the Z discs closer to each other and increases density of filaments, therefore reduces chewing ability. After slaughter, but before the rigor mortis, it is still able for filaments to slide over each other. However, after rigor mortis, the two types of filaments become fixed. Because of some reason by which the rigor mortis comes right at the time of contractile state, the meat will be very tough. It results from not enough ATP to operate the calcium pump, so the calcium concentration in sarcoplasm begins to rise, and muscle relaxation fails to start. Additionally, the stored oxygen supply is reduced, and the anaerobic metabolism starts to maintain the homeostasis. This process needs energy from ATP. All of those start the major energy reserve through glycogen catabolism because the reaction using creatine phosphate in postmortem muscle lasts shortly. Glycogen must first be degraded by glycogen phosphorylase to form glucose-1 phosphate. The whole process produces three ATP with glycogen as starting material. Due to lack of oxygen, enzyme lactate dehydrogenase catalyzes the reduction of pyruvate to lactic acid by NADH (Scanes, 2003). This process also regenerates NAD+ for glycolysis step in ATP formation. However, the built-up lactic acid inactivates the enzymes relating to glycolysis and slows down the process of ATP regeneration. That is why there is still not enough ATP for muscle relaxation, and rigor mortis is maintained. On the other hand, lactic acid makes the pH gradually fall and the rigor mortis is rapidly developed (Aberle et al., 2001), which decreases meat tenderness. The proteolysis is also one of factors affecting meat tenderness (Hwang et al., 2003). Meat cuts from carcasses at 24 hours postmortem are less tender than cuts taken for several days although they were the same sub– primal cuts taken from the same carcasses. The reason for this phenomenon is the action

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