Function of tilapia endogenous proteases in deterioration of vacuum-refrigerated fillet texture

【Objective】To investigate key proteases that caused deterioration of tilapia meat texture quality during refrigeration，and to provide a theoretical basis for refrigerated fish meat quality improvement.【Method】Tilapia fillets were vacuum-packed and refrigerated at 4 ℃， and texture， pH， myofibril fragmentation index（MFI）， endogenous protease activity，endogenous protease distribution in organelles and myofibril SDS-PAGE profiles were determined during 0-6 d. Key proteases that caused the deterioration of fish meat texture during refrigeration were identified through Pearson correlation analysis.【Result】 pH of tilapia fish meat decreased and then increased during refrigeration， with a final pH of 6.68； hardness decreased but MFI increased；cathepsin B+L activity increased overall as it was 1.27 times of its initial value on 6 d，and it first increased and then decreased in myofibril，myogen and mitochondria but it decreased in lysosome； cathepsin B activity and cathepsin D activity increased and then decreased，and they both reached the maximum on 4 d， which were 1.20 times and 1.48 times of their initial values，respectively. Cathepsin B activity in myofibril，myogen and mitochondria first increased and then decreased but it decreased in lysosome；cathepsin D activity increased in myofibril and myogen，but it decreased in lysosome and mitochondria；calcium ion concentration increased and calcium-activated protease activity first increased and then decreased；myofibrillar protein SDS-PAGE profile showed that bands of myosin heavy chain，actin，and myosin light chain became less and blurred；cathepsin B activity and cathepsin B+L activity had an extremely negative correlation with fish meat hardness （P<0.01， the same below），and they also had an extremely negative correlation with MFI of fish meat；cathepsin D activity and calcium-activated protease activity were not significantly correlated with fish meat hardness or MFI（P>0.05）.【Conclusion】 Cathepsin B and cathepsin L participate in myofibrillar protein degradation and mitochondria-mediated apoptosis，and such situation may be attributed to the two key target enzymes for tilapia meat deterioration during refrigeration. Available techniques can be taken to inhibit their activity to improve fish meat texture quality during storage.