Autoxidation of Bluefin Tuna Myoglobin Associated with Freezing and Thawing

Abstract
Bluefin tuna oxymyoglobin (oxyMb) solutions were frozen either quickly at −80°C or slowly at −2O°C, thawed, and the metmyoglobin (metMb) to total myoglobin (Mb) ratio (metMb%) determined. When quick freezing was applied, autoxidation was clearly pH‐dependent, with a minimum (metMb%, 15–40) at around pH 5.9–6.3. When slowly frozen and thawed, on the other hand, tuna Mb generally showed an extremely high metMb%. Freezing and thawing partially insolubilized tuna Mb, depending upon pH. The Mb showed the minimum ratio of insolubilization at pH 6–6.3 again. Insolubilization of tuna Mb was markedly accelerated by NaCl.