Degradation of myofibrils in cultured yellowtail <Emphasis Type="Italic">Seriola quinqueradiata</Emphasis> burnt meat: effects of a myofibril-bound EDTA-sensitive protease

“Burnt meat” is a term used to describe the white (pale, grainy, exudative) muscle of yellowtail or tuna. It (with lightness parameter, L* ≥ 55) was observed after 2 h storage in the suffocate in air (SA) 29°C group and after 4 h storage in the spinal cord destruction (SCD) 29°C group. In the SA 17°C group, burnt meat was also observed after 4 h storage. In contrast, the meat in the SCD 17°C group was normal until after 12 h storage. The myosin heavy chain (MHC) was more degraded than the other myofibrillar proteins, and some protein bands increased in the burnt meat. The protease that leads to the degradation of MHC was investigated using myofibrils from the meat. EDTA completely suppressed the degradation, indicating that a myofibril-bound EDTA-sensitive protease (MBESP) may exist in yellowtail muscle and this caused the degradation of MHC. The optimum pH and temperature of MBESP in yellowtail were 5.0 and 50–60°C, respectively.