Participation of cathepsin L in modori phenomenon in carp (Cyprinus carpio) surimi gel.

Cathepsin L (Cat L) in carp (Cyprinus carpio) dorsal muscles was purified and its molecular weight determined by SDS polyacrylamide gel electrophoresis (SDS-PAGE) was 36 kDa. Its optimal temperature and pH were 50 °C and 5.5, respectively. The results of the effects of specific substrates, activators and inhibitors on the enzymatic activity showed that Cat L belongs to the family of cysteine proteinases containing thiol. Compared to the control, the gel strength of surimi with the addition of purified Cat L decreased significantly by 24.33% while that of surimi with both purified Cat L and inhibitors increased by 13.7% and 21.6%, respectively, suggesting the participation of Cat L in the modori phenomenon occurring in carp surimi. Both the SDS-PAGE electrophoretic pattern and microstructure figure revealed that Cat L could hydrolyse the main protein in carp surimi and was one of the enzymes involved in the modori phenomenon.