Abstract
Frozen southern bluefin tuna meat discolors easily and sometimes contracts when thawed caused by thaw rigor. These phenomenon often become problematic in the transaction or handling of this kind of frozen tuna.
Frozen meat blocks of southern Bluefin tuna were thawed separately by air thawing, running water thawing and microwave thawing. Changes occurring during thawing were checked for meat color by met-myoglobin ratio determination and for contract by microscopic observation.
Results are as follows :
(1) Discoloration scarcely occurred in the process of running water thawing (at 10°C for 50 min, or at 0°C for 6 hr).
(2) No contraction was observed during thawing with running water described above and air thawing (at 18-20°C for 6 hr).
(3) Discoloration and contraction seemed to be minimized, as to latently contractile blocks, when meat temperature passed through rapidly between -10°C and -5°C, and slowly (for 5-6 hr) between -5°C and -1°C. When the block was originally not contractile, discloration was minimized by rising meat temperature rapidly from -10°C to -l°C.
