Postmortem Changes of ATP and Its Related Compounds and Freshness Indices in Spear Squid Doryteuthis bleekeri Muscles

The changes in contents of ATP and its related compounds were examined in the mantle, arm, and fin muscles of spear squid Doryteuthis bleekeri during storage at 5 degree C. The efficacy of the values of K, K', A.E.C., Hx ratio, Xt ratio, and Hx/AMP ratio were evaluated as freshness indices. The level of ATP at time 0 and the total content of ATP and its related compounds in the mantle muscle were higher than those in the other 2 muscles. In all muscles, ATP decreased rapidly 1 day after the beginning of storage and Hx increased markedly during storage. The degradation of AMP was considered to proceed through 2 pathways, IMP and AdR pathways, in all 3 muscles. In the mantle and fin muscles, K and K' values increased markedly within 4 days of storage and may be used as freshness indicators in earlier periods of storage. The Hx, Xt, and Hx/AMP ratios increased continuously during storage; the changes in the Xt and Hx/AMP ratios were larger than those in K or K' values. It was suggested that the ratios of Hx, Xt, and Hx/AMP are more useful as freshness indices for spear squid than the K value.