The ATPase assay system on pH stat apparatus was developed. For the ATPase activity measurement, hydrogen ion (H+) concentration delivered from inorganic phosphate (Pi) as a hydrolysis production of ATP was estimated by titrating with 20 mM NaOH solution instead of colorimetric measurement of Pi. Inclusion of 0.5 M KCl in the ATP stock solution and 2 mM Tris‐maleate (pH 7.0) buffer in the reaction medium reduced the extent of pH change upon addition of ATP to initiate the ATPase reaction. The amount of H+ liberated from Pi was strongly affected by the set pH for the ATPase assay with a promotion at alkaline pH. Thus, it was required to estimate the coefficient to convert H+ to a Pi concentration at a specific pH. The specified coefficient at pH 7.0 was 1.248. ATPase assay on pH stat allowed us to follow the ATP hydrolysis by myofibrils continuously showing a curvature profile at low salt medium (≤0.2 M KCl) or a linear profile at high salt (≥0.3 M KCl).

The effects of non-ionic (sorbitol, maltose, trehalose) and ionic compounds (Naglutamate, Na-acetate, Na-sulfate, ammonium sulfate) on freeze denaturation of myosin subfragment-1 (S-1) and of myofibrils were compared. Sugars, Na-glutamate and Na-acetate well suppressed the freeze denaturation of myofibrils as well as S-1 in a concentration dependent manner. Although sulfate suppressed freeze denaturation of S-1 irregularly, it accelerated myofibril denaturation. It was concluded that sulfate salts were useless as cryoprotectant for myofibrils. Stabilization extent by F-actin in frozen storage was much less than that in heating.

A study was made to clarify the temperature dependence of the gel forming ability of frozen surimi from walleye pollack. The salt-ground meat was preheated at a deˆnite temperature in the range of 5 and 75°C for varying periods (preheated gel), and followed by heating at 90°C for 30 min (two-step heated gel). Changes in breaking strength ( BS ) and breaking strain (bs) of both the preheated and two-step heated gels were measured in association with the preheating time, and their maximum values recorded. When preheating at a temperature between 5 and 35°C, the rate of change in BS was dependent on temperature, where BS reached the maximum faster at higher temperature. When the meat was preheated at 40°C and over, the rate of the change in BS was independent of temperature, and BS decreased with time. At 70°C and over, BS remained at the same level with the progress of time. It was further found that there was a good positive correlation between BS and the gel stiŠness (Gs＝BS/bs) of all the two-step heated gels formed through the preheating at a temperature between 5 and 35°C.

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