血合肉中におけるイノシン酸の分解とその酵素活性

Abstract

In order to elucidate the degradation of inosinic acid (IMP) in the dark muscle of fish, the levels of adenine nucleotides and their related compounds were compared in the white and dark muscles of yellowtail Seriola quinqueradiata and in common mackerel Scomber japonicas during iced storage. The struggling of 30 minutes before death affected the degradation rate of IMP in the dark muscle of yellowtail, while it did not affect in the white muscle. During iced storage, the degrada-tion of IMP proceeded very rapidly in the dark muscle of common mackerel. IMP was degraded optimally at pH6 and pH8 in muscle homogenates of common mackerel. The activity in the dark muscle homogenate at pH6 was 5 times higher than that of the white muscle homogenate, whereas the activity at pH8 was nearly the same in both muscle homogenates. The fact that the high activity at pH6 was present in the supernatant of the dark muscle homo-genate indicated that this enzyme is easily soluble in water. In view of these findings, the fact that the pH of red meat fish such as mackerel falls quickly to around 6 after death suggests that the enzyme activity is mainly responsible for the rapid IMP degradation in the dark muscle.