Effect of various protease inhibitors on heat-induced myofibrillar protein degradation and gel-forming ability of red tilefish (Branchiostegus japonicus) meat

• Red tilefish meat had extremely low heat-induced gel-forming ability.
• Proteolysis in red tilefish meat markedly occurred at 40–70 °C.
• Chelators and serine protease inhibitors suppressed intense proteolysis.
• The gel-forming ability was improved in the presence of chelators.
• Red tilefish meat can be used as fish gel material by inhibiting endogenous protease.

Red tilefish is a popularly consumed saltwater fish in East Asian countries. However, the commercial value of undersized or damaged fish is very low. Moreover, because of its softness, red tilefish meat is not readily utilized in seafood products. Its utilization as a raw material for gel products such as unwashed fish mince represents an attractive way to increase the commercial value of red tilefish. Thus, the effect of endogenous proteases on the heat-induced gel-forming ability of red tilefish meat was investigated. Heat-induced gels could not be obtained at between 30 and 80 °C. Proteolysis including myosin heavy chain (MHC) degradation markedly occurred at between 40 and 70 °C. Proteolysis was inhibited and gel-forming ability was improved in the presence of EDTA, 1,10-phenanthroline, benzamidine or SBTI. The inhibitor mix (1,10-phenanthroline, benzamidine and SBTI) significantly enhanced the gel-forming ability more than using single inhibitors. These results indicated that one of the dominant proteases contributing to MHC degradation was a trypsin-like serine protease. Metal ion-activated proteases likely played an important role in myofibrillar protein degradation. From the above, it was concluded that red tilefish meat can be utilized as a raw material of gel products by suppressing endogenous protease activities.