| Lamb possesses the features of tender meat, good taste, the low content of cholesterol,the high content of trace elements of calcium,iron,phosphorus,less fiber,the low degree of fat and easy absorption by human body. Therefore, the meat can considered as one the best meat. Tenderness is an important indicator to assess its quality. Objective and accurate assessment of postmortem mutton tenderness is very complicated, because it is influenced by many internal and external factors. Combining the actual production situation of Xinjiang, this dissertation took Bashibai lamb as study object and aimed at some controversial scientific questions in mutton tenderness mechanisms. The purpose of article was to study the effects of different storage methods on the mutton tenderness through the determination of pH value, water holding capacity, collagen content and its solubility,connective tissue residue, shear force, fiber diameter,perimysial thickness,the observation on the ultrastructure of muscle fibers and the analysis of myofibrillar protein electrophoresis and western blot. The results can evaluate the correlations between meat quality characteristics and tenderness objectively and provide a theoretical basis for playing lamb potential and improving sheep breeding, feeding management, slaughter and mature technology as well. The specific research contents and results are as follows:1. Study on changes of tenderness characteristics of fresh meat during 15? storageThis study selected the longissimus dorsi of Bashibai lamb as experimental material.The related indicators of tenderness were measured and ultra structure were observed after storing them at 15? for 45min, 2h, 6h, 12h and 24h. Results revealed that pH value, water retention, connective tissue residue, perimysial thickness, fiber diameter, sarcomere length,crude fat content and shear force significantly changed (P<0.05), while the changes of collagen content and its solubility, and connective tissue denaturation temperature changed very little (P>0.05). Correlation analysis showed that pH value, water retention, connective tissue characteristics, the content of crude fat, perimysial thickness, fiber diameter, and sarcomere length were all significantly correlated with shear force (P<0.05). Histological examination showed that connective tissue perimysium structure was integral from 45min to 12h. Primary and secondary perimysium kept stable while a small part of primary perimysium and secondary perimysium of the 24h were damaged. The gap increased between endomysial and muscle fibers. Ultrastructural observation found that myofibrils had no obvious change within 6h postmortem. Myofibrils were neatly arranged and Z line and M line were clearly visible. Some gaps appeared between 12h samples of myofibrils.However, the gaps became larger and M lines,the boundary of A band and I band were no longer clear at 24h.2. Study on changes of tenderness characteristics of chilled meat during 4? storageThis study selected the longissimus dorsi of Bashibai lamb as experimental material.The related indicators of tenderness were measured and ultrastructure were observed after aging for Id, 2d, 3d, 5d, 7d, and 14d at 4?. Results revealed that pH value, moisture content,water holding capacity, connective tissue residue, the thermal denaturation temperature of endomysium, perimysial thickness, fiber diameter, sarcomere length and shear force took place significant changes (P<0.05), while the cooking loss, thermal denaturation temperature of the perimysium and crude fat content had no significant changes (P>0.05). Histological observation revealed that the connective tissue structure had undergone significant changes in the mature period. The integrity of endomysium and perimysium was damaged, while perimysial thickness decreased and muscle fiber gap became larger. The temperature of endomysial thermal denaturation dropped.Ultrastructural observation found that Z line and M line broke from clearly visible to blurred illegible with the extension of storage time.3. Study on changes of tenderness characteristics of freeze-stored meat during -18?storageThis study selected the longissimus dorsi of Bashibai lamb as experimental material,and stored at -18? for 1d, 3d, 7d, 15d, and 30d to determine the related indicators of tenderness and measure the microscopic structure. The results showed that pH value, water retention, shear force, connective tissue and muscle fiber microstructure had significant changes (P<0.05),while collagen solubility and perimysium thermal denaturation temperature had no obvious changes (P>0.05). Histological observation revealed that, ice crystal growed with the prolonging of frozen storage time. Bundles aggregated because of compression which resulted in the shrinkage of muscle fibers and the bigger of fiber gap.Finally, the perimysium was destroyed. Ultrastructural observation found that the boundaries between A and I bands were from being clearly visible to become unable to distinguish at last. Z line had always been clear, but not being as thick as fresh meat sample.Sarcomere length decreased significantly during frozen storage (P<0.05).4. Study on degradation properties of myofibrillar protein under different storage conditionsThis study selected the longissimus dorsi of Bashibai lamb as experimental material,and stored at 15?, 4?, and -18?. Electrophoresis and Western blot analysis were performed respectively. The results showed that there were no significant degradation of myofibrillar proteins at 15?. At 4?, the key cytoskeletal protein, such as titin, nebulin,desmin and troponin -T, had different levels of degradation significantly in the period of aging (P<0.05). During frozen storage at -18?,desmin and troponin -T bands became increasingly weak, and generated a small molecular weight band around 25KDa. |
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