The meat of matured chum salmon caught by the coastal set-net fishery tends to soften to a great extend when the fish is frozen-thawed, during ice-storage or in the course of processing. Recently, it was clarified that the softening phenomenon of the meat is due to the enhanced cathepsin activity in the muscle tissue. This study was undertaken to increase the use of salmons in such condition by processing them into frozen-surimi. However, there is a possibility that the gel of the surimi undergoes marked deterioration in the course of the heating (cooking) process by protease action. Therefore, first of all, the relationship between the gel forming ability and the degree of protease activity in the minced meat prepared from matured salmon was examined. A close relation was observed between them, i.e. the stronger the protease activity, the lower the gel-strength of the final product. SDS-PAGE analysis revealed the occurrence of degradation in myofibrillar proteins during the heating process. Next, the use of a protease inhibitor was examined to prevent gel-degradation. A crude inhibitor (cystatin and/or cystatin-like inhibitor) preparation from salmon testis which so far almost useless, and similar preparations from bovine serum and chicken egg white were found to be very effective in preventing gel-degradation.
