Levels of Glutathione and Related Enzymes in Yellowtail Fish Muscle Subjected to Ice Storage in a Modified Atmosphere

We investigated the effects of ice storage in a modified atmosphere on levels of glutathione (GSH) and its related enzyme activities, the metmyoglobin to total myoglobin ratio (metMb%), and the K value (a freshness index) of yellowtail fish muscle. GSH in ordinary muscle (fast skeletal muscle) as well as in dark muscle (slow skeletal muscle) stored in air decreased. GSH in those muscles was almost unchanged during storage when packaged with an oxygen absorber or with an oxygen absorber-CO(2) generator. Glutathione disulfide in each type of packaging remained at low concentrations during storage. The GSH peroxidase activities of ordinary muscle and of dark muscle after 7 d of storage in air were lower than when packaged with the oxygen absorber or with the oxygen absorber-CO2 generator. The GSH reductase (GR) activities of ordinary muscle at the 4th and 7th day of storage when packaged with the oxygen absorber showed a tendency to be lower than when stored in air. The GR activity of dark muscle in each type of packaging method was unchanged during storage. The packaging method did not influence the K values of either the ordinary muscle or the dark muscle during storage. The metMb% of dark muscle when packaged with the oxygen absorber was lower than in the other types of packaging during storage. Therefore, packaging with the oxygen absorber is an effective method to prevent the loss of GSH in fish meat as well as to reduce the discoloration during storage.