Meat blocks (3×3×3cm) were prepared from a very fresh specimen of the bigeye tuan Thunnus obesus, and stored at -20°C, -40°C, -60°C, and -80°C, for one year. At one to three month intervals, the meat blocks were analyzed for the change in color, taking the metmyoglobin (metMb) to total Mb ratio as a parameter, and for the change in water holding capacity, taking the exprssible, cooking, and free drips as parameters.
The MetMb to total Mb ratio increased from 3.9% at the start to 5-15% after one year storage at -40°C to -80°C. At -20°C, the metMb formation was clearly faster: 25% after 9 months and 56% after one year.
The pH of the meat remained at a relatively constant value near 6.5 throughout the whole period, irrespective of the storage temperatures. The amounts of exprssible, cooking, and free drips from the meat showed some changes during the storage, which did not depend upon the storage temperatures.