抄録
Studies have been made on the relation between the lowering of freshness and the bio-chemical changes in the fish muscle during ice storage using plaice and skipjack. The changes in total amounts of free amino acids, salt-soluble proteins, volatile bases and trimethylamine, together with bacterial count, pH and “K” value (absorption ratio in percentage at 250mμ of inosine plus hypoxanthine fraction to the perchloric-acid extract of muscle) which had been proposed for an index for fresheness of fish by SAITO et al were pursued periodically.
The results were shown in Figs. 1, 2 and Table 1. Psychlophylic bacteria were little increased during the first 10 days for plaice and throughout the storage time (9 days) for skipjack. The solubility of 0.6M KCI-soluble proteins was not changed significantly in both cases. The amount of volatile bases was fairly increased at the earlier stage and thereafter kept constant. However, trimethylamine was not increased until 14 days and 9 days for plaice and skipjack respectively. The amount of free amino acids was observed to be fairly increased during the storage for plaice, and on the other hand, the tendency of increase was rather slight unexpectedly for skipjack. The freshness was organoleptically observed to be markedly lowered at the 14th days for plaice, and at the 4th days for skipjack, earlier than bacterial count and substances such as volatile bases and trimethylamine were not so much increased. Based on these results, it may be said that in the early stage of the storage the deterioration of freshness of fish is effected by autolysis rather than bacterial action. Also in the present study, “K” value was confirmed to be useful index for freshness of fish, i.e. it amounting to 40-50% when freshness was recognized to be markedly lowered in both cases.
