| The ratios of different muscle fiber types have an immediate impact on meat tenderness. According energy metabolism metabolic characteristic in muscle fibers, muscle fiber types could be classified as Oxidative type(I) and Oxidation- glycolytic type(IIa/IIx) and Glycolytic type(IIb). As the muscle fiber energy metabolism, the preference on Oxidative type or Glycolytic type will have impact on the postmortem metabolic level. Any factor which can affect the postmortem muscle fiber energy metabolic will also probably influence the calpain activity and then affects postmortem proteolysis and tenderization. Besides, as the major enzymes in the process of proteolysis, calpain is also influenced by postmortem muscle fiber energy metabolism. So this shows the muscle fiber types have a potentially regulating mechanism of proteolysis and tenderization. In this regulation mechanism, whether the difference in related enzyme activity causes the change of postmortem muscle fiber energy metabolic could lead to the change of calpain activity, there are no clear answers yet. Therefore, the research taking yak Supraspinatus, Latissimus dorsi, Semitendinosus(Gannan, Gansu province, China) as raw materials, the objectives of this work were to analyze how the fiber types and the typical property of metabolic enzymes influences the postmortem muscle fiber metabolism, calpain activity, muscle fiber proteolysis and tenderization, the muscle fiber types and the difference of metabolic enzymes of the different part of yak meat. And the muscle fiber energy metabolism releases regulation of calpain activity pathway, the differences in tenderization mechanism among different muscles of yak to illuminate the muscle fiber types and the characteristic of metabolic enzyme effect postmortem tenderization. It could help explain the difference mature mechanism among different part of yak carcasses. In order to provides evidence for tenderization of yak meat according to different muscles.The major testing results as follows:1. Yak meat muscle fiber types can be divided into IIa/IIx type, IIb type and I type according to the composition of Myosin heavy chain. The proportions of IIa/IIx type, IIb type and I type of Supraspinatus, Latissimus dorsi and Semitendinosus have significant difference. And the proportion of IIa/IIx type among three muscles doesn’t have significant difference. IIb type in Supraspinatus(21.6%) is in high proportion. I type fiber in Latissimus dorsi(20.4%) is also in a high number. It is found by analysis different muscle fiber types and the PCA of metabolic enzyme, that different muscles’ metabolic enzyme and fiber types are almost the same. The proportion of IIb type in Supraspinatus is large. The activity of Ca2+-ATPase、LDH and CK is high. So Supraspinatus is tending to Oxidative type. The I type has a high proportion in Latissimus dorsi, the activity of SDH and MDH is high, so the Latissimus dorsi is thending to oxidative. And the metabolic level of Semitendinosus is between these two muscles.2. The yak meat muscle fiber types related metabolic enzyme, such as Ca2+-ATPase, LHD, SDH and MDH and CK, their activity has significant effect on the speed of proteolysis of muscle fiber energy metabolism. The Ca2+-ATPase, LHD and CK activity has positive correlation related to the falling speed of proteolysis glycogen and growth rate of lactic acid among these three muscles. And negative correlation exists between the activity of SDH and MDH and the changing rate of three indexes above. The higher the muscle fiber metabolic enzyme activity is, the bigger the r value is, and the significance will be much greater. Muscle fiber energy metabolism has effect on endogenous enzyme activity.3. μ-calpain plays a major role of the calpain during aging. When the yak meat ages for 14 d, its activity is complete regression. The falling rate of μ-calpain activity in Latissimus dorsi is fastest. The content of glycogen is the key factor to regulate and control μ-calpain. Latissimus dorsi has greater sensitivity to μ-calpain.4. The myofibrils was already degraded in the 1d. The degrading products of Desmin 38 kDa, 36 kDa and Troponin-T 28 kDa of Latissimus dorsi generated 1d earlier than Supraspinatus and Semitendinosus. And its shear stress in 3d(12.94 g.s) is equal to the value of other two muscles 14d(12.89 g.s of Supraspinatus and 12.36 g.s of Semitendinosus). The speed of tenderization is significant higher than other two muscles. Then the paper makes a analysis and screening out that shear stress and MFI is the representative index of tenderness evaluation through PCA. And μ-calpain, shear stress is in extremely significant linear relationship with MFI. And it shows a high fitting degree with the index of tenderness evaluation of Latissimus dorsi.5. The higher the proportion of IIb type in yak meat, the worse of beginning tenderness, and thus the worse of improvement of meat tenderness postmortem. The higher the proportion of I type fiber, the better of beginning tenderness, and the better of improvement of meat tenderness postmortem. The proportion of IIa/IIx fibers has affected beginning tenderness and improvement of meat tenderness postmortem tenderization degree less. The proportion of different muscle fiber types is a good predictor of the beginning tenderness postmortem and tenderization degree. The difference of tenderness in different yak meat is determined by the differences of the proportions of different muscle fiber types.In conclusion, there is difference in the proportions of different muscle fiber types and the metabolic enzyme activity, which affects muscle fiber energy metabolism postmortem. Muscle fiber energy metabolism postmortem is the key regulation factor of releasing μ-calpain activity, μ-calpain affects and ultimately influences the forming of tenderness. This indicates the proportions of different muscle fiber types are quite good at predicting the beginning tenderness postmortem and tenderization degree. The composition of muscle fiber types differs the tenderization of different yak meat essentially. |
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