Degradation of myofibrillar proteins in the belly muscle of the threadfin bream is caused by the possible leakage of soluble serine proteinase from the viscera during storage

The present work aims to clarify the mechanism of gel weakening ( modori phenomenon) on surimi -based products and provide information on how to prevent it from happening in threadfin bream. We investigated the distribution of endogenous proteinases in the normal and belly muscles and their effects on the quality of the surimi gel. There was severe degradation of myofibrillar proteins in the belly muscle during heating at 50 °C, which was not found in the normal muscle. The surimi gel prepared from the belly muscle also showed a low gel strength as compared to that of the normal muscle. The myofibrillar proteins in the belly muscle were found to be degraded by a sarcoplasmic serine proteinase (SSP). The SSP activity was detected in the belly muscle and hepatopancreas but not in the normal muscle, while the SSP mRNA was detected only in the hepatopancreas. It is suggested that SSP in the hepatopancreas leaks to the belly muscle during post-harvest storage and is responsible for the modori phenomenon. These results imply that high-quality surimi gel of the threadfin bream can be produced by preventing protease leakage to the muscle during post-harvest storage.