Heat-activated proteolysis in lizardfish (Saurida tumbil) muscle

Autolysis of lizardfish mince and washed mince during heating at elevated temperatures was studied. Higher degradation of myosin heavy chain (MHC was generally observed in mince, compared to washed mince. The highest autolysis was observed at 65 and 60 degreesC for mince and washed mince, respectively. Autolysis was extended as the incubation time increased by the result of the decrease in MHC band intensity on SDS-PAGE and the increase in TCA-soluble peptides. Autolysis of washed mince was markedly inhibited by E-64 and soybean trypsin inhibitor, suggesting that myofibril-associated proteinases were both cysteine and serine proteinases. Sareoplasmic proteinase was characterized to be heat-activated alkaline proteinase, which had the optimal pH and temperature of 8.0 and 65 degreesC, respectively. The preteinase was inhibited by E-64 and activated by reducing agents, which was one of the characteristics of cysteine proteinase. Therefore, endogenous sarcoplasmic and myofibril-associated protemases play an important role in degradation of myofibrillar proteins of lizardfish during heat-induced gelation, which results in gel weakening. (C) 2003 Elsevier Ltd. All rights reserved.