Rheological and Morphological Comparison of Thermal and Hydrostatic Pressure-Induced Filamentous Myosin Gels

The structure and rheological properties of heat- and pressure-induced myosin filament gels were investigated. The apparent elasticity of heat-induced gel peaked at 55 °C (4.35 (plus-minus) 0.57 kPa), whereas that of pressure-induced gel increased with elevating pressure, and the gel formed at 500 MPa had a value of 4.79 (plus-minus) 0.25 kPa. All pressure- and heat-induced gels showed similar internal structure, namely, the gels were composed of a fine-strand network. The detailed structures of the strands induced by pressure- and heat-treatment of myosin filaments were observed using an atomic force microscope. The structural differences among the strands were not observed, whereas the elasticity of the strands measured by atomic force microscope revealed differences among the strands formed with varying heating temperature and pressure. The elasticities of the heat-induced strands were 1.19 (plus-minus) 0.09 MPa, 10.24 (plus-minus) 1.16 MPa, and 3.09 (plus-minus) 0.25 MPa at 40 °C, 55 °C, and 70 °C, respectively. On the other hand, the elasticity of the pressure-induced strand increased with elevating pressure. The elasticity values were 1.24 (plus-minus) 0.09 MPa, 2.32 (plus-minus) 0.17 MPa, and 9.80 (plus-minus) 0.84 MPa at pressures of 150, 300, and 500 MPa, respectively. Because the changes in the elasticity of the whole gel corresponded to those of the strand, it is concluded that the rheological properties of the constituting strands determine that of myosin filamentous gel.