Postmortem Changes in Myofibrillar ATPase of Sardine Ordinary and Dark Muscles

Abstract

Changes in myofibrillar ATPase activity of ordinary and dark muscle of sardine Sardinops melanosticta were examined in relation with rigor mortis progress and concomitant decline of muscle pH during 24h postmortem period, along with changes during 10 days of ice and frozen storage.
Myofibrillar Ca²⁺- and EDTA-ATPase activities, and Mg²⁺-ATPase activity in the presence of Ca²⁺ of sardine ordinary muscle clearly decreased when “rigor index”, a parameter of rigor tension, proceeded to 50% and muscle pH fell to around 6.4. Mg²⁺-ATPase activity in the absence of Ca²⁺ showed a slight decrease under the same conditions. On the other hand, the ATPase activity of the dark muscle started decreasing only at full rigor when muscle pH fell to 6.4 in almost all assay systems, except Mg²⁺-ATPase activity in the absence of Call which hardly changed during rigor mortis progress. A marked decrease in the activity was observed with both sardine muscles during extended ice storage of 10 days.
Both sardine muscles showed a large fall in myofibrillar ATPase activity, when stored frozen for 10 days. With either muscle, pH decreased down to 5.8-5.9 after one day and remained essentially unchanged thereafter.