Thermal transitions were studied by means of differential scanning calorimetry (DSC) and a spectrophotometric method. Three endothermic peaks (40,43,5o"C: ordinary muscle; 46,54, 62°C: dark muscle) were observed in DSC thermograms of both myosins. Thermograms of S-l fragments showed one peak (41°C: ordinary muscle, 43°C: dark muscle). But ordinary and dark muscle rod fragments gave two peaks (41, 62°C) and one peak (58"C), respectively. The spectrophotometric results also showed two thermal transitions for both myosins and one transition for their S-l fragments. However, the rod from ordinary muscle myosin had two transitions, whereas that from dark muscle myosin had one transition.
The changes of rheological properties of a cuttlefish and four squids by heat treatment were stud ied by the differential scanning calorimetry (DSC), the rupture test, and the stress relaxation test. The thermograms of raw "ika" mantle meat showed three major endothermic peaks at 50•Ž, 57•Ž, and 74•Ž. The first and second peaks mainly corresponded with the denaturation of myosin and collagen. The third peak was that of actin which was almost native up to 63 •Ž, while the other proteins had been completely denatured below 63•Ž. The thermograms for all samples indicated that the denaturation of mantle meat had been completed up to 80•Ž. Then, the rheological properties were measured for raw meat and heated meat at 63•Ž or 80•Ž. A positive correlation between the content of crude protein and the instantaneous elastic modulus was only found in heated meat at 63•Ž. It is considered that this relationship was associated with the amount of remaining native actin.
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