The rheological properties of fish muscles of five species were characterized in terms of the creep compliance. A slight increase of the strain with time was observed in all species even without any load applied. The size of the linear region, where the stress increases in proportion to the strain, decreased when the loading time was prolonged. After 300s loading, the largest strain value of the linear region for each fish was, 9.5% in channel rock fish, 9.0% in plaice, 8.6% in flying fish, 8.5% in common horse mackerel, and lower than 2% in skipjack, respectively.
On analysis of the creep compliance curves, a six-element model was found to represent each fish muscle, while three more elements, two ratchets and a spring, were needed to fit the creep recovery curves. The instantaneous modulus values of the creep compliance of flying fish and skipjack were larger than those of plaice and channel rock fish. Common horse mackerel gave an intermediate value. With the permanent viscosity modulus, plaice gave the largest value followed by flying fish, channel rock fish, common horse mackerel and then skipjack in a decreasing order.
These results appeared to differ from the series obtained on our eating experience. It was suggested that our mouthfeel about “firmness” is not based on the difference in the elastic modulus of the muscles but on the ease of biting which is related to the collagen content as proved in our previous report.
