Study On The Relationship Between Chemical Interactions And Structure-Function Properties Of Rabbit Myosin

In many meat processing and production process, salt-soluble protein form into a protein gel, thus affecting the water holding capacity, oil holding capacity, viscoelasticity and texture properties in meat products, and finally to produce a good taste of meat. There are many studies reported muscle myosin plays a major role in heat-induced gel. Heating leads the myosin denaturation and aggregation, eventually forming three-dimensional gel network. At present, there are already many studies on the gelation, while not so many on the relationship between the chemical interactions and structure-function properties. This study took rabbit psoas (Pasoas major, PM) and semimembranosus(Semimembranosus proprius, SMp) as material to extract the myosin, and took the temperature and pH as the factor, studied the changing of the chemical interactions during the heating and different pH value, tested the secondary structure, meanwhile, also tested water holding capacity, gel strength and Low-field NMR relaxation time, the relationship between the chemical interactions and structure-function properties and so on to provide thero for better meat products. The results of the studystated as follows:1.The changes of chemical interactions of myosin during heatingThe sulphydryl content, hydrophobicity and spectral bands of myosin at pH6.5 and 20℃～90℃(1℃/min) during linear heating were tested by traditional methods and raman spectra. The result showed that during the heating, the total sulphydryl content of PM and SMp myosin decreased and the reactive sulphydryl content first increased then decreased, while the hydrophobicity increased. Raman spectra results showed that the normalized intensity of 545 cm-1,525 cm-1 and 510 cm-1 band which reflect the disulfide bond vibration had a significant change with the temperature, inferred there was a mutual transformation between sulfhydryl and disulfide bonds in system; the normalized intensity of 760 cm-1 band which reflect hydrophobic of tryptophan residue increased with the temperature, and the ratio of conjugated double peak 850 cm-1 and 830 cm-1 band which reflect hydrophobic of tyrosine residue increased also. Correlation analysis showed that the changes of normalized intensity of specific bands from raman spectra and the chemical interactions had a strong correlation, which could be used to explain the changes of chemical interaction of myosin.2.Study on the relationship of chemical interactions and the structure of myosin during heatingThe content of secondary structure such as a-helix,β-sheet and random coil and spectral bands of myosin at pH6.5 and 20℃～90℃(1℃/min) during linear heating were tested by circular dichrosim spectra(CD) and raman spectra. The result showed that during the heating, the content of a-helix of PM and SMp myosin decreased significantly, while the content ofβ-sheet and random coil increased, which analysed with the raman spetra data using principal component analysis showed; loss of a-helical structure of myosin led to the destruction of nature-state structure at low temperature, and a large number of groups within the protein, such as sulfhydryl and hydrophobic groups exposed in the thermally induced process, and gradually participated in the formation of gel. Loss of a-helix gradually transformed intoβ-sheet and random coil, which the latter two were involved in the structure of the gel.3. Study on the relationship of chemical interactions and the function properties of myosinThe gel strength, water holding capacity, T2 relaxation time distribution and spectral bands of myosin at different pH(5.5,6.0,6.5,7.0 and 7.5) were tested by Texture analysis, centrifugation, nuclear magnetic resonance (NMR) and raman spetra. The result showed, when the pH gradually away from isoelectric point (pI), the water holding capacity and hardness of PM and SMp myosin increased significantly, while T22, T23 relaxation time, T23 peak area decreased and T22 peak area increased; the normalized intensity of 525 cm-1 and 760 cm-1 band increased; the normalized intensity of 510 cm-1 band decreased; the ratio of conjugated double peak 850 cm-1 and 830 cm-1 band first decreased then increased, which reached a minimum at pH 6.0. Principal component analysis revealed that the sample near the pI was characterized by low water holding capacity, low hardness and long T2 relaxation time, while the sample away from the pI was characterized by high water holidng capacity, high hardness and short T2 relaxation time. As the pH affected the nature state of myosin, the surface charge of protein molecular was different, thus affecting the protein functional groups of exposed and buried, ultimately affected the functional properties. In summary, with the heat induced gel formation of myosin, the changes of chemical interactions affected the structure and function properties of myosin.