抄録
It is generally believed that quality of myosin, the major protein in fish muscle, determines the quality of the meat and meat-based products. Compared with myosin from mammalian muscle, fish myosin is unstable especially from cold-water fish species. Thus, understanding of myosin denaturation upon heating and storage of meat is essential in evaluating the quality of fish muscle. As myosin exhibits ATPase activity, its inactivation is a sensitive index of myosin denaturation. ATPase inactivation provides myosin denaturation at its head region but not tail region. To obtain the information on myosin denaturation at its tail region, chymotryptic digestion technique was employed. Upon heating of myofibrils (Mf), head and tail regions denatured differently and the pattern was fish species-specific. By using the same techniques, myosin denaturation upon freezing of Mf was also studied and it was found that the tail region remained very stable. Chymotryptic digestion revealed actin denaturation proceeded in frozen Mf. A quick myosin denaturation in frozen Mf was explained by the loss of protection by actin. The actin denaturation in Mf was explained by condensation of salt upon freezing of Mf suspension. Such actin denaturation was not found with frozen stored meat. Quality of Bluefin tuna meat was also evaluated by studying myosin denaturation. The denaturation was determined by the body temperature and pH of the meat. By assuming changes of body temperature and pH, the myosin denaturation process was simulated and it was found that cooling of fish as quickly as possible is the method to keep the quality of tuna meat high.
