Effects of Postmortem Physiological Changeson Ice Crystal Morphology in the Fish Muscle Tissue

Abstract

This study focused on chilled storage before freezing fish muscle in order to explore the relation between postmortem physiological changes and ice crystal morphology in frozen muscle tissue. Specimens of horse mackerel (Trachrus japonicus) were killed by decapitating, pan-dressed and stored at 4 °C. Subsequently, a portion of dorsal muscle tissue was dissected. The dissected tissue was used for ATP-related compounds analysis, measurements of water holding capacity (WHC), scanning electron microscopic observation of endomysial connective tissue and freezing experiment for fluorescent microscopic observation of ice crystal morphology and endomysium in the frozen tissue. Changes in the ratio of ATP-related compounds and decrease of the WHC were observed during chilled storage. The connective tissue became looser during storage. On the other hand, size or number of ice crystal in frozen tissue seems to depend on chilled storage period before freezing. There were large ice crystals enough to disrupt cells, especially in the tissue of fish frozen after chilled storage. These results suggest that postmortem physiological changes in muscle tissue should have a large effect on the ice crystal morphology in freezing process.