Post mortem changes produced in the muscle of sea bream (Sparus aurata) during ice storage

The post mortem degradation processes that take places in fish muscle gradually modify the initial state of freshness. Tissue degradation is accompanied by drastic myofibrillar proteolysis produced as a consequence of the activation of proteolytic enzymes. In this study, structural changes were correlated with the textural properties of sea bream (Sparus aurata) muscle during 14 days of post mortem cold storage through the immunohistochemical detection of muscle filament proteins (desmin, actin and dystrophin), as well as endoproteases (µ-calpain, m-calpain) and their endogenous inhibitor (calpastatin). Actin and desmin were detected in fish muscle as late as 10 days post mortem (dpm) while dystrophin could not be detected after 4 dpm. In contrast, labelling for both calpains and calpastatin persisted during the entire storage period. Fracturability was clearly reduced after 7 dpm, while greatest changes in hardness, gumminess and chewiness were observed during the first week of storage. Our immunohistochemical observations indicate the disappearance of cytoskeleton proteins at different times post mortem. Thus, actin and desmin persist even when the muscle tissue shows a deteriorated appearance and texture, while dystrophin vanishes soon after the death of the fish. Detachment between myofibres and the myocommata was concomitant with the loss of dystrophin and also corresponded to the time when the reduction in flesh hardness observed was most significant. On the contrary, after 4 days of storage, calpain activity remained practically unaltered in refrigerated muscle specimens.