Abstract
In order to improve the preserving freshness of fish on board, freshness lowering and denaturation of myofibrillar protein of amberjack, black-tipped silver-bidding, striped jack, frigate mackerel, and tiger puffer were pursued during ice storage and partially frozen (PF) storage at -3°C. The fish used were caught by set-net or cultured. The extractability of crude actomyosin (AM) at the ionic strength, I=0.85 was expressed as the ratio of AM denaturation. The results obtained in this paper were as follows;
1) The durations of preserving the freshness under ice storage were 2-11 days, while they were prolonged 2.5 8 folds or 9.5-20 days under PF storage except for frigate mackerel (Fig. 1 and Table 3).
2) As the body temperature of frigate mackerel was reported to raise as ca 10°C owing to hard exercising after being caught, it would be particularly important to chill them as soon as possible on board immediately after catching.
3) It was confirmed that PF storage was more useful than ice storage in preventing putrefaction also (Fig. 2).
4) The ratio of AM denaturation of muscle of the fish did not remarkably change during 21 days under either of ice storage and PF storage (Fig. 2).
5) The ratio of AM denaturation of the muscle of fish did not remarkably change even after putrefaction (Fig. 2 and Table 2).
6) A little denaturation of muscle protein of the fish may be attributed to the fact that pH in the muscle post mortem not so lowered, remaining above 6 during either storage (Fig. 3).
7) No simple relation was observed between the amount of lactic acid and pH in the muscle (Figs. 3 and 4).
8) The results described above indicate that PF is a useful means of improving the preservation of freshness of fish on board.
