COMPARISON OF CATHEPSIN B, D, H AND L ACTIVITY IN FOUR SPECIES OF PACIFIC FISH

Abstract

The activities of cathepsins B, D, H and L were compared in crude muscle extracts from four species of fish: Pacific whiting (PW), (Merluccius productus); arrowtooth flounder (ATF), (Atheresthes stomias); Alaska pollock (AP), (Theragra chalcogramma); and Pacific cod (PC), (Gadus macrocephalus). Both PW and ATF are known to undergo softening during post-mortem handling and cooking while AP and PC do not. Cathepsin B and L activities were both higher in extracts of PW and ATF than in AP and PC. Cathepsins B and L activities were both much higher in PW than in ATF. Cathepsin H activity was highest in AP followed by ATF with PC and PW having the lowest activities. Cathepsin D activity was extremely low in all four species. The heat stability of the various cathepsin activities showed cathepsin B to be the most heat labile and was inactivated by 50C heating for 15 min. Cathepsin H activity was inactivated at 60C, while cathepsin L required 70C for inactivation. Cathepsins B and L are the most likely responsible for softening in PW and ATF during holding and subsequent processing. However, during cooking, cathepsin L likely causes the most damage since it requires 70C for inactivation. The difference in heat stability of cathepsins B and L can be used to differentiate between their activities.